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Thus the aether model, initially so very different from action at a distance, slowly changed to
resemble simple empty space.
In 1905, Poincaré proposed gravitational waves, emanating from a body and propagating at the speed of light, as being required by the Lorentz transformations and suggested that, in analogy to an accelerating electrical charge producing electromagnetic waves, accelerated masses in a relativistic field theory of gravity should produce gravitational waves. However, until 1915 gravity stood apart as a force still described by action-at-a-distance. In that year, Einstein showed that a field theory of spacetime, general relativity, consistent with relativity can explain gravity. New effects resulting from this theory were dramatic for cosmology but minor for planetary motion and physics on Earth.
Einstein himself noted Newton's "enormous practical success".
Modern action at a distance
In the early decades of the 20th century, Karl Schwarzschild, Hugo Tetrode, and Adriaan Fokker independently developed non-instantaneous models for action at a distance consistent with special relativity. In 1949 John Archibald Wheeler and Richard Feynman built on these models to develop a new field-free theory of electromagnetism.
While Maxwell's field equations are generally successful, the Lorentz model of a moving electron interacting with the field encounters mathematical difficulties: the self-energy of the moving point charge within the field is infinite. The Wheeler–Feynman absorber theory of electromagnetism avoids the self-energy issue. They interpret Abraham–Lorentz force, the apparent force resisting electron acceleration, as a real force returning from all the other existing charges in the universe.
The Wheeler–Feynman theory has inspired new thinking about the arrow of time and about the nature of quantum non-locality. The theory has implications for cosmology; it has been extended to quantum mechanics. A similar approach has been applied to develop an alternative theory of gravity consistent with general relativity. John G. Cramer has extended the Wheeler–Feynman ideas to create the transactional interpretation of quantum mechanics.
"Spooky action at a distance" | Action at a distance | Wikipedia | 431 | 570922 | https://en.wikipedia.org/wiki/Action%20at%20a%20distance | Physical sciences | Physics basics: General | Physics |
Albert Einstein wrote to Max Born about issues in quantum mechanics in 1947 and used a phrase translated as "spooky action at a distance", and in 1964, John Stewart Bell proved that quantum mechanics predicted stronger statistical correlations in the outcomes of certain far-apart measurements than any local theory possibly could. The phrase has been picked up and used as a description for the cause of small non-classical correlations between physically separated measurement of entangled quantum states. The correlations are predicted by quantum mechanics (the Bell theorem) and verified by experiments (the Bell test). Rather than a postulate like Newton's gravitational force, this use of "action-at-a-distance" concerns observed correlations which cannot be explained with localized particle-based models. Describing these correlations as "action-at-a-distance" requires assuming that particles became entangled and then traveled to distant locations, an assumption that is not required by quantum mechanics.
Force in quantum field theory
Quantum field theory does not need action at a distance. At the most fundamental level, only four forces are needed. Each force is described as resulting from the exchange of specific bosons. Two are short range: the strong interaction mediated by mesons and the weak interaction mediated by the weak boson; two are long range: electromagnetism mediated by the photon and gravity hypothesized to be mediated by the graviton. However, the entire concept of force is of secondary concern in advanced modern particle physics. Energy forms the basis of physical models and the word action has shifted away from implying a force to a specific technical meaning, an integral over the difference between potential energy and kinetic energy. | Action at a distance | Wikipedia | 339 | 570922 | https://en.wikipedia.org/wiki/Action%20at%20a%20distance | Physical sciences | Physics basics: General | Physics |
Kale (), also called leaf cabbage, belongs to a group of cabbage (Brassica oleracea) cultivars primarily grown for their edible leaves; it has also been used as an ornamental plant.
Description
Kale plants have green or purple leaves, and the central leaves do not form a head (as with headed cabbage). The stems can be white or red, and can be tough even when cooked.
Etymology
The name kale originates from Northern Middle English cale (compare Scots kail and German Kohl) for various cabbages. The ultimate origin is Latin caulis 'cabbage'.
Cultivation
Derived from wild mustard, kale is considered to be closer to wild cabbage than most domesticated forms of B. oleracea.
Kale is usually a biennial plant grown from seed with a wide range of germination temperatures. It is hardy and thrives in wintertime, and can survive in temperatures as low as . Kale can become sweeter after a heavy frost.
History
Kale originated in the eastern Mediterranean and Anatolia, where it was cultivated for food beginning by 2000 BCE at the latest. Curly-leaved varieties of cabbage already existed along with flat-leaved varieties in Greece in the 4th century BC. These forms, which were referred to by the Romans as Sabellian kale, are considered to be the ancestors of modern kales.
The earliest record of cabbages in western Europe is of hard-heading cabbage in the 13th century. Records in 14th-century England distinguish between hard-heading cabbage and loose-leaf kale.
Russian traders introduced Russian kale into Canada and then into the United States in the 19th century. USDA botanist David Fairchild is credited with introducing kale (and many other crops) to Americans, having brought it back from Croatia, although Fairchild himself disliked cabbages, including kale. At the time, kale was widely grown in Croatia mostly because it was easy to grow and inexpensive, and could desalinate soil.
Cultivars
One may differentiate between kale varieties according to the low, intermediate, or high length of the stem, along with the variety of leaf types. The leaf colours range from light green to green, dark green, violet-green, and violet-brown. | Kale | Wikipedia | 456 | 571106 | https://en.wikipedia.org/wiki/Kale | Biology and health sciences | Brassicales | null |
Classification by leaf type:
Curly-leaf (Scots kale, blue curled kale)
Bumpy-leaf (black cabbage, better known by its Italian translation 'cavolo nero', and also known as Tuscan Cabbage, Tuscan Kale, lacinato and dinosaur kale)
Sparkly-leaf (shiny and glossy)
Plain-leaf (flat-leaf types like red Russian and white Russian kale)
Leaf and spear, or feathery-type leaf (a cross between curly- and plain-leaf)
Ornamental (less palatable and tougher leaves)
Because kale can grow well into winter, one variety of rape kale is called "hungry gap" after the period in winter in traditional agriculture when little else could be harvested. An extra-tall variety is known as Jersey kale or cow cabbage. Kai-lan or Chinese kale is a cultivar often used in Chinese cuisine. In Portugal, the bumpy-leaved kale is mostly called "couve galega" (Galician kale or Portuguese Cabbage).
Ornamental kale
Many varieties of kale and cabbage are grown mainly for ornamental leaves that are brilliant white, red, pink, lavender, blue, or violet in the interior of the rosette. The different types of ornamental kale are peacock kale, coral prince, kamone coral queen, color up kale, and chidori kale. Ornamental kale is as edible as any other variety, but potentially not as palatable. Kale leaves are increasingly used as an ingredient for vegetable bouquets and wedding bouquets.
Uses
Nutrition
Raw kale is composed of 84% water, 9% carbohydrates, 4% protein, and 1% fat (table). In a serving, raw kale provides of food energy and a large amount of vitamin K at 3.7 times the Daily Value (DV). It is a rich source (20% or more of the DV) of vitamin A, vitamin C, vitamin B6, folate, and manganese (see table "Kale, raw"). Kale is a good source (10–19% DV) of thiamin, riboflavin, pantothenic acid, vitamin E, and several dietary minerals, including iron, calcium, magnesium, potassium, and phosphorus. Boiling raw kale diminishes most of these nutrients, while values for vitamins A, C, and K and manganese remain substantial. | Kale | Wikipedia | 507 | 571106 | https://en.wikipedia.org/wiki/Kale | Biology and health sciences | Brassicales | null |
Phytochemicals
Kale is a source of the carotenoids, lutein and zeaxanthin. As with broccoli and other cruciferous vegetables, kale contains glucosinolate compounds, such as glucoraphanin, which contributes to the formation of sulforaphane, a compound under preliminary research for its potential to affect human health beneficially.
Boiling kale decreases the level of glucosinate compounds, whereas steaming, microwaving, or stir frying does not cause significant loss. Kale is high in oxalic acid, the levels of which can be reduced by cooking.
Kale contains high levels of polyphenols, such as ferulic acid, with levels varying due to environmental and genetic factors.
Culinary
Snack product
Kale chips have been produced as a potato chip substitute.
Regional uses
Europe
In the Netherlands, a traditional winter dish called "boerenkoolstamppot" is a mix of curly kale and mashed potatoes, sometimes with fried bacon, and served with rookworst ("smoked sausage").
In Northern Germany, there is a winter tradition known as "Kohlfahrt" ("kale trip"), where a group of people will go on a hike through the woods during the day before gathering at an inn or private residence where kale is served, usually with bacon and Kohlwurst ("kale sausage"). Kale is considered a Northern German staple and comfort food.
In Italy, cavolo nero kale is an ingredient of the Tuscan soup ribollita.
A traditional Portuguese soup, caldo verde, combines pureed potatoes, very finely sliced kale, olive oil and salt. Additional ingredients can include broth and sliced, cooked spicy sausage.
In Scotland, kale provided such a base for a traditional diet that the word in some Scots dialects is synonymous with food. To be "off one's kail" is to feel too ill to eat.
In Ireland, kale is mixed with mashed potatoes to make the traditional dish colcannon. It is popular on Halloween, when it may be served with sausages.
In the United Kingdom, the cultivation of kale (and other vegetables) was encouraged during World War II via the Dig for Victory campaign. The vegetable was easy to grow and provided important nutrients missing from a diet because of rationing. | Kale | Wikipedia | 492 | 571106 | https://en.wikipedia.org/wiki/Kale | Biology and health sciences | Brassicales | null |
Asia
In Sri Lanka, it is known as kola gova or ela gova. It is cultivated for edible use. A dish called 'kale mallung' is served almost everywhere on the island, along with rice.
United States
For most of the 20th century, kale was primarily used in the U.S. for decorative purposes; it became more popular as an edible vegetable in the 1990s due to its nutritional value.
In culture
The Kailyard school of Scottish writers, which included J. M. Barrie (creator of Peter Pan), consisted of authors who wrote about traditional rural Scottish life (kailyard = 'kale field'). In Cuthbertson's book Autumn in Kyle and the charm of Cunninghame, he states that Kilmaurs in East Ayrshire was famous for its kale, which was an important foodstuff. A story is told in which a neighbouring village offered to pay a generous price for some kale seeds, an offer too good to turn down. The locals agreed, but a gentle roasting on a shovel over a coal fire ensured the seeds never germinated.
Gallery | Kale | Wikipedia | 231 | 571106 | https://en.wikipedia.org/wiki/Kale | Biology and health sciences | Brassicales | null |
In mathematics, a Dirichlet problem asks for a function which solves a specified partial differential equation (PDE) in the interior of a given region that takes prescribed values on the boundary of the region.
The Dirichlet problem can be solved for many PDEs, although originally it was posed for Laplace's equation. In that case the problem can be stated as follows:
Given a function f that has values everywhere on the boundary of a region in , is there a unique continuous function twice continuously differentiable in the interior and continuous on the boundary, such that is harmonic in the interior and on the boundary?
This requirement is called the Dirichlet boundary condition. The main issue is to prove the existence of a solution; uniqueness can be proven using the maximum principle.
History | Dirichlet problem | Wikipedia | 159 | 571109 | https://en.wikipedia.org/wiki/Dirichlet%20problem | Mathematics | Differential equations | null |
The Dirichlet problem goes back to George Green, who studied the problem on general domains with general boundary conditions in his Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism, published in 1828. He reduced the problem into a problem of constructing what we now call Green's functions, and argued that Green's function exists for any domain. His methods were not rigorous by today's standards, but the ideas were highly influential in the subsequent developments. The next steps in the study of the Dirichlet's problem were taken by Karl Friedrich Gauss, William Thomson (Lord Kelvin) and Peter Gustav Lejeune Dirichlet, after whom the problem was named, and the solution to the problem (at least for the ball) using the Poisson kernel was known to Dirichlet (judging by his 1850 paper submitted to the Prussian academy). Lord Kelvin and Dirichlet suggested a solution to the problem by a variational method based on the minimization of "Dirichlet's energy". According to Hans Freudenthal (in the Dictionary of Scientific Biography, vol. 11), Bernhard Riemann was the first mathematician who solved this variational problem based on a method which he called Dirichlet's principle. The existence of a unique solution is very plausible by the "physical argument": any charge distribution on the boundary should, by the laws of electrostatics, determine an electrical potential as solution. However, Karl Weierstrass found a flaw in Riemann's argument, and a rigorous proof of existence was found only in 1900 by David Hilbert, using his direct method in the calculus of variations. It turns out that the existence of a solution depends delicately on the smoothness of the boundary and the prescribed data.
General solution
For a domain having a sufficiently smooth boundary , the general solution to the Dirichlet problem is given by
where is the Green's function for the partial differential equation, and
is the derivative of the Green's function along the inward-pointing unit normal vector . The integration is performed on the boundary, with measure . The function is given by the unique solution to the Fredholm integral equation of the second kind,
The Green's function to be used in the above integral is one which vanishes on the boundary:
for and . Such a Green's function is usually a sum of the free-field Green's function and a harmonic solution to the differential equation. | Dirichlet problem | Wikipedia | 498 | 571109 | https://en.wikipedia.org/wiki/Dirichlet%20problem | Mathematics | Differential equations | null |
Existence
The Dirichlet problem for harmonic functions always has a solution, and that solution is unique, when the boundary is sufficiently smooth and is continuous. More precisely, it has a solution when
for some , where denotes the Hölder condition.
Example: the unit disk in two dimensions
In some simple cases the Dirichlet problem can be solved explicitly. For example, the solution to the Dirichlet problem for the unit disk in R2 is given by the Poisson integral formula.
If is a continuous function on the boundary of the open unit disk , then the solution to the Dirichlet problem is given by
The solution is continuous on the closed unit disk and harmonic on
The integrand is known as the Poisson kernel; this solution follows from the Green's function in two dimensions:
where is harmonic () and chosen such that for .
Methods of solution
For bounded domains, the Dirichlet problem can be solved using the Perron method, which relies on the maximum principle for subharmonic functions. This approach is described in many text books. It is not well-suited to describing smoothness of solutions when the boundary is smooth. Another classical Hilbert space approach through Sobolev spaces does yield such information. The solution of the Dirichlet problem using Sobolev spaces for planar domains can be used to prove the smooth version of the Riemann mapping theorem. has outlined a different approach for establishing the smooth Riemann mapping theorem, based on the reproducing kernels of Szegő and Bergman, and in turn used it to solve the Dirichlet problem. The classical methods of potential theory allow the Dirichlet problem to be solved directly in terms of integral operators, for which the standard theory of compact and Fredholm operators is applicable. The same methods work equally for the Neumann problem.
Generalizations
Dirichlet problems are typical of elliptic partial differential equations, and potential theory, and the Laplace equation in particular. Other examples include the biharmonic equation and related equations in elasticity theory.
They are one of several types of classes of PDE problems defined by the information given at the boundary, including Neumann problems and Cauchy problems.
Example: equation of a finite string attached to one moving wall
Consider the Dirichlet problem for the wave equation describing a string attached between walls with one end attached permanently and the other moving with the constant velocity i.e. the d'Alembert equation on the triangular region of the Cartesian product of the space and the time: | Dirichlet problem | Wikipedia | 507 | 571109 | https://en.wikipedia.org/wiki/Dirichlet%20problem | Mathematics | Differential equations | null |
As one can easily check by substitution, the solution fulfilling the first condition is
Additionally we want
Substituting
we get the condition of self-similarity
where
It is fulfilled, for example, by the composite function
with
thus in general
where is a periodic function with a period :
and we get the general solution | Dirichlet problem | Wikipedia | 59 | 571109 | https://en.wikipedia.org/wiki/Dirichlet%20problem | Mathematics | Differential equations | null |
Serenoa repens, commonly known as saw palmetto, is a small palm, growing to a maximum height around .
Taxonomy
It is the sole species in the genus Serenoa. The genus name honors American botanist Sereno Watson.
Distribution and habitat
It is endemic to the subtropical and tropical Southeastern United States as well as Mexico, most commonly along the south Atlantic and Gulf Coastal plains and sand hills. It grows in clumps or dense thickets in sandy coastal areas, and as undergrowth in pine woods or hardwood hammocks.
Description
Erect stems or trunks are rarely produced, but are found in some populations. It is a hardy plant; extremely slow-growing, and long-lived, with some plants (especially in Florida) possibly being as old as 500–700 years.
Saw palmetto is a fan palm, with the leaves that have a bare petiole terminating in a rounded fan of about 20 leaflets. The petiole is armed with fine, sharp teeth or spines that give the species its common name. The teeth or spines are easily capable of breaking the skin, and protection should be worn when working around a saw palmetto. The leaves are light green inland, and silvery-white in coastal regions. The leaves are 1–2 m in length, the leaflets 50–100 cm long. They are similar to the leaves of the palmettos of genus Sabal. The flowers are yellowish-white, about 5 mm across, produced in dense compound panicles up to 60 cm long.
Ecology
The fruit is a large reddish-black drupe and is an important food source for wildlife and historically for humans. The plant is used as a food plant by the larvae of some Lepidoptera species such as Batrachedra decoctor, which feeds exclusively on the plant.
Medical research
Saw palmetto extract has been studied as a possible treatment for people with prostate cancer and for men with lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH). As of 2023, there is insufficient scientific evidence that saw palmetto extract is effective for treating cancer or BPH and its symptoms.
One 2016 review of clinical studies with a standardized extract of saw palmetto (called Permixon) found that the extract was safe and may be effective for relieving BPH-induced urinary symptoms compared against a placebo. | Serenoa | Wikipedia | 480 | 571215 | https://en.wikipedia.org/wiki/Serenoa | Biology and health sciences | Arecales (inc. Palms) | Plants |
Ethnobotany
Indigenous names are reported to include: or ("palmetto's uncle") in Choctaw; (Timucua); (Koasati); ("big palm", Alabama); ("big palm", Creek); ("big palm", Mikasuki); and (Taíno, possibly). Saw palmetto fibers have been found among materials from indigenous people as far north as Wisconsin and New York, strongly suggesting this material was widely traded prior to European contact. The leaves are used for thatching by several indigenous groups, so commonly that a location in Alachua County, Florida, is named Kanapaha ("palm house"). The fruit may have been used to treat an unclear form of fish poisoning by the Seminoles and Lucayans. | Serenoa | Wikipedia | 168 | 571215 | https://en.wikipedia.org/wiki/Serenoa | Biology and health sciences | Arecales (inc. Palms) | Plants |
In the fields of medicine, biotechnology, and pharmacology, drug discovery is the process by which new candidate medications are discovered.
Historically, drugs were discovered by identifying the active ingredient from traditional remedies or by serendipitous discovery, as with penicillin. More recently, chemical libraries of synthetic small molecules, natural products, or extracts were screened in intact cells or whole organisms to identify substances that had a desirable therapeutic effect in a process known as classical pharmacology. After sequencing of the human genome allowed rapid cloning and synthesis of large quantities of purified proteins, it has become common practice to use high throughput screening of large compounds libraries against isolated biological targets which are hypothesized to be disease-modifying in a process known as reverse pharmacology. Hits from these screens are then tested in cells and then in animals for efficacy.
Modern drug discovery involves the identification of screening hits, medicinal chemistry, and optimization of those hits to increase the affinity, selectivity (to reduce the potential of side effects), efficacy/potency, metabolic stability (to increase the half-life), and oral bioavailability. Once a compound that fulfills all of these requirements has been identified, the process of drug development can continue. If successful, clinical trials are developed.
Modern drug discovery is thus usually a capital-intensive process that involves large investments by pharmaceutical industry corporations as well as national governments (who provide grants and loan guarantees). Despite advances in technology and understanding of biological systems, drug discovery is still a lengthy, "expensive, difficult, and inefficient process" with low rate of new therapeutic discovery. In 2010, the research and development cost of each new molecular entity was about US$1.8 billion. In the 21st century, basic discovery research is funded primarily by governments and by philanthropic organizations, while late-stage development is funded primarily by pharmaceutical companies or venture capitalists. To be allowed to come to market, drugs must undergo several successful phases of clinical trials, and pass through a new drug approval process, called the New Drug Application in the United States. | Drug discovery | Wikipedia | 430 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Discovering drugs that may be a commercial success, or a public health success, involves a complex interaction between investors, industry, academia, patent laws, regulatory exclusivity, marketing, and the need to balance secrecy with communication. Meanwhile, for disorders whose rarity means that no large commercial success or public health effect can be expected, the orphan drug funding process ensures that people who experience those disorders can have some hope of pharmacotherapeutic advances.
History
The idea that the effect of a drug in the human body is mediated by specific interactions of the drug molecule with biological macromolecules, (proteins or nucleic acids in most cases) led scientists to the conclusion that individual chemicals are required for the biological activity of the drug. This made for the beginning of the modern era in pharmacology, as pure chemicals, instead of crude extracts of medicinal plants, became the standard drugs. Examples of drug compounds isolated from crude preparations are morphine, the active agent in opium, and digoxin, a heart stimulant originating from Digitalis lanata. Organic chemistry also led to the synthesis of many of the natural products isolated from biological sources.
Historically, substances, whether crude extracts or purified chemicals, were screened for biological activity without knowledge of the biological target. Only after an active substance was identified was an effort made to identify the target. This approach is known as classical pharmacology, forward pharmacology, or phenotypic drug discovery.
Later, small molecules were synthesized to specifically target a known physiological/pathological pathway, avoiding the mass screening of banks of stored compounds. This led to great success, such as the work of Gertrude Elion and George H. Hitchings on purine metabolism, the work of James Black on beta blockers and cimetidine, and the discovery of statins by Akira Endo. Another champion of the approach of developing chemical analogues of known active substances was Sir David Jack at Allen and Hanbury's, later Glaxo, who pioneered the first inhaled selective beta2-adrenergic agonist for asthma, the first inhaled steroid for asthma, ranitidine as a successor to cimetidine, and supported the development of the triptans. | Drug discovery | Wikipedia | 459 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Gertrude Elion, working mostly with a group of fewer than 50 people on purine analogues, contributed to the discovery of the first anti-viral; the first immunosuppressant (azathioprine) that allowed human organ transplantation; the first drug to induce remission of childhood leukemia; pivotal anti-cancer treatments; an anti-malarial; an anti-bacterial; and a treatment for gout.
Cloning of human proteins made possible the screening of large libraries of compounds against specific targets thought to be linked to specific diseases. This approach is known as reverse pharmacology and is the most frequently used approach today.
In the 2020s, qubit and quantum computing started to be used to reduce the time needed to drug discovery.
Targets
A "target" is produced within the pharmaceutical industry. Generally, the "target" is the naturally existing cellular or molecular structure involved in the pathology of interest where the drug-in-development is meant to act. However, the distinction between a "new" and "established" target can be made without a full understanding of just what a "target" is. This distinction is typically made by pharmaceutical companies engaged in the discovery and development of therapeutics. In an estimate from 2011, 435 human genome products were identified as therapeutic drug targets of FDA-approved drugs.
"Established targets" are those for which there is a good scientific understanding, supported by a lengthy publication history, of both how the target functions in normal physiology and how it is involved in human pathology. This does not imply that the mechanism of action of drugs that are thought to act through a particular established target is fully understood. Rather, "established" relates directly to the amount of background information available on a target, in particular functional information. In general, "new targets" are all those targets that are not "established targets" but which have been or are the subject of drug discovery efforts. The majority of targets selected for drug discovery efforts are proteins, such as G-protein-coupled receptors (GPCRs) and protein kinases.
Screening and design | Drug discovery | Wikipedia | 420 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
The process of finding a new drug against a chosen target for a particular disease usually involves high-throughput screening (HTS), wherein large libraries of chemicals are tested for their ability to modify the target. For example, if the target is a novel GPCR, compounds will be screened for their ability to inhibit or stimulate that receptor (see antagonist and agonist): if the target is a protein kinase, the chemicals will be tested for their ability to inhibit that kinase.
Another function of HTS is to show how selective the compounds are for the chosen target, as one wants to find a molecule which will interfere with only the chosen target, but not other, related targets. To this end, other screening runs will be made to see whether the "hits" against the chosen target will interfere with other related targets – this is the process of cross-screening. Cross-screening is useful because the more unrelated targets a compound hits, the more likely that off-target toxicity will occur with that compound once it reaches the clinic.
It is unlikely that a perfect drug candidate will emerge from these early screening runs. One of the first steps is to screen for compounds that are unlikely to be developed into drugs; for example compounds that are hits in almost every assay, classified by medicinal chemists as "pan-assay interference compounds", are removed at this stage, if they were not already removed from the chemical library. It is often observed that several compounds are found to have some degree of activity, and if these compounds share common chemical features, one or more pharmacophores can then be developed. At this point, medicinal chemists will attempt to use structure–activity relationships (SAR) to improve certain features of the lead compound:
increase activity against the chosen target
reduce activity against unrelated targets
improve the druglikeness or ADME properties of the molecule.
This process will require several iterative screening runs, during which, it is hoped, the properties of the new molecular entities will improve, and allow the favoured compounds to go forward to in vitro and in vivo testing for activity in the disease model of choice. | Drug discovery | Wikipedia | 426 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Amongst the physicochemical properties associated with drug absorption include ionization (pKa), and solubility; permeability can be determined by PAMPA and Caco-2. PAMPA is attractive as an early screen due to the low consumption of drug and the low cost compared to tests such as Caco-2, gastrointestinal tract (GIT) and Blood–brain barrier (BBB) with which there is a high correlation.
A range of parameters can be used to assess the quality of a compound, or a series of compounds, as proposed in the Lipinski's Rule of Five. Such parameters include calculated properties such as cLogP to estimate lipophilicity, molecular weight, polar surface area and measured properties, such as potency, in-vitro measurement of enzymatic clearance etc. Some descriptors such as ligand efficiency (LE) and lipophilic efficiency (LiPE) combine such parameters to assess druglikeness.
While HTS is a commonly used method for novel drug discovery, it is not the only method. It is often possible to start from a molecule which already has some of the desired properties. Such a molecule might be extracted from a natural product or even be a drug on the market which could be improved upon (so-called "me too" drugs). Other methods, such as virtual high throughput screening, where screening is done using computer-generated models and attempting to "dock" virtual libraries to a target, are also often used.
Another method for drug discovery is de novo drug design, in which a prediction is made of the sorts of chemicals that might (e.g.) fit into an active site of the target enzyme. For example, virtual screening and computer-aided drug design are often used to identify new chemical moieties that may interact with a target protein. Molecular modelling and molecular dynamics simulations can be used as a guide to improve the potency and properties of new drug leads. | Drug discovery | Wikipedia | 403 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
There is also a paradigm shift in the drug discovery community to shift away from HTS, which is expensive and may only cover limited chemical space, to the screening of smaller libraries (maximum a few thousand compounds). These include fragment-based lead discovery (FBDD) and protein-directed dynamic combinatorial chemistry. The ligands in these approaches are usually much smaller, and they bind to the target protein with weaker binding affinity than hits that are identified from HTS. Further modifications through organic synthesis into lead compounds are often required. Such modifications are often guided by protein X-ray crystallography of the protein-fragment complex. The advantages of these approaches are that they allow more efficient screening and the compound library, although small, typically covers a large chemical space when compared to HTS.
Phenotypic screens have also provided new chemical starting points in drug discovery. A variety of models have been used including yeast, zebrafish, worms, immortalized cell lines, primary cell lines, patient-derived cell lines and whole animal models. These screens are designed to find compounds which reverse a disease phenotype such as death, protein aggregation, mutant protein expression, or cell proliferation as examples in a more holistic cell model or organism. Smaller screening sets are often used for these screens, especially when the models are expensive or time-consuming to run. In many cases, the exact mechanism of action of hits from these screens is unknown and may require extensive target deconvolution experiments to ascertain. The growth of the field of chemoproteomics has provided numerous strategies to identify drug targets in these cases.
Once a lead compound series has been established with sufficient target potency and selectivity and favourable drug-like properties, one or two compounds will then be proposed for drug development. The best of these is generally called the lead compound, while the other will be designated as the "backup". These decisions are generally supported by computational modelling innovations.
Nature as source
Traditionally, many drugs and other chemicals with biological activity have been discovered by studying chemicals that organisms create to affect the activity of other organisms for survival. | Drug discovery | Wikipedia | 427 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Despite the rise of combinatorial chemistry as an integral part of lead discovery process, natural products still play a major role as starting material for drug discovery. A 2007 report found that of the 974 small molecule new chemical entities developed between 1981 and 2006, 63% were natural derived or semisynthetic derivatives of natural products. For certain therapy areas, such as antimicrobials, antineoplastics, antihypertensive and anti-inflammatory drugs, the numbers were higher.
Natural products may be useful as a source of novel chemical structures for modern techniques of development of antibacterial therapies.
Plant-derived
Many secondary metabolites produced by plants have potential therapeutic medicinal properties. These secondary metabolites contain, bind to, and modify the function of proteins (receptors, enzymes, etc.). Consequently, plant derived natural products have often been used as the starting point for drug discovery.
History
Until the Renaissance, the vast majority of drugs in Western medicine were plant-derived extracts. This has resulted in a pool of information about the potential of plant species as important sources of starting materials for drug discovery. Botanical knowledge about different metabolites and hormones that are produced in different anatomical parts of the plant (e.g. roots, leaves, and flowers) are crucial for correctly identifying bioactive and pharmacological plant properties. Identifying new drugs and getting them approved for market has proved to be a stringent process due to regulations set by national drug regulatory agencies.
Jasmonates
Jasmonates are important in responses to injury and intracellular signals. They induce apoptosis and protein cascade via proteinase inhibitor, have defense functions, and regulate plant responses to different biotic and abiotic stresses. Jasmonates also have the ability to directly act on mitochondrial membranes by inducing membrane depolarization via release of metabolites.
Jasmonate derivatives (JAD) are also important in wound response and tissue regeneration in plant cells. They have also been identified to have anti-aging effects on human epidermal layer. It is suspected that they interact with proteoglycans (PG) and glycosaminoglycan (GAG) polysaccharides, which are essential extracellular matrix (ECM) components to help remodel the ECM. The discovery of JADs on skin repair has introduced newfound interest in the effects of these plant hormones in therapeutic medicinal application.
Salicylates | Drug discovery | Wikipedia | 500 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Salicylic acid (SA), a phytohormone, was initially derived from willow bark and has since been identified in many species. It is an important player in plant immunity, although its role is still not fully understood by scientists. They are involved in disease and immunity responses in plant and animal tissues. They have salicylic acid binding proteins (SABPs) that have shown to affect multiple animal tissues. The first discovered medicinal properties of the isolated compound was involved in pain and fever management. They also play an active role in the suppression of cell proliferation. They have the ability to induce death in lymphoblastic leukemia and other human cancer cells. One of the most common drugs derived from salicylates is aspirin, also known as acetylsalicylic acid, with anti-inflammatory and anti-pyretic properties.
Animal-derived
Some drugs used in modern medicine have been discovered in animals or are based on compounds found in animals. For example, the anticoagulant drugs, hirudin and its synthetic congener, bivalirudin, are based on saliva chemistry of the leech, Hirudo medicinalis. Used to treat type 2 diabetes, exenatide was developed from saliva compounds of the Gila monster, a venomous lizard.
Microbial metabolites
Microbes compete for living space and nutrients. To survive in these conditions, many microbes have developed abilities to prevent competing species from proliferating. Microbes are the main source of antimicrobial drugs. Streptomyces isolates have been such a valuable source of antibiotics, that they have been called medicinal molds. The classic example of an antibiotic discovered as a defense mechanism against another microbe is penicillin in bacterial cultures contaminated by Penicillium fungi in 1928.
Marine invertebrates | Drug discovery | Wikipedia | 379 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Marine environments are potential sources for new bioactive agents. Arabinose nucleosides discovered from marine invertebrates in 1950s, demonstrated for the first time that sugar moieties other than ribose and deoxyribose can yield bioactive nucleoside structures. It took until 2004 when the first marine-derived drug was approved. For example, the cone snail toxin ziconotide, also known as Prialt treats severe neuropathic pain. Several other marine-derived agents are now in clinical trials for indications such as cancer, anti-inflammatory use and pain. One class of these agents are bryostatin-like compounds, under investigation as anti-cancer therapy.
Chemical diversity
As above mentioned, combinatorial chemistry was a key technology enabling the efficient generation of large screening libraries for the needs of high-throughput screening. However, now, after two decades of combinatorial chemistry, it has been pointed out that despite the increased efficiency in chemical synthesis, no increase in lead or drug candidates has been reached. This has led to analysis of chemical characteristics of combinatorial chemistry products, compared to existing drugs or natural products. The chemoinformatics concept chemical diversity, depicted as distribution of compounds in the chemical space based on their physicochemical characteristics, is often used to describe the difference between the combinatorial chemistry libraries and natural products. The synthetic, combinatorial library compounds seem to cover only a limited and quite uniform chemical space, whereas existing drugs and particularly natural products, exhibit much greater chemical diversity, distributing more evenly to the chemical space. The most prominent differences between natural products and compounds in combinatorial chemistry libraries is the number of chiral centers (much higher in natural compounds), structure rigidity (higher in natural compounds) and number of aromatic moieties (higher in combinatorial chemistry libraries). Other chemical differences between these two groups include the nature of heteroatoms (O and N enriched in natural products, and S and halogen atoms more often present in synthetic compounds), as well as level of non-aromatic unsaturation (higher in natural products). As both structure rigidity and chirality are well-established factors in medicinal chemistry known to enhance compounds specificity and efficacy as a drug, it has been suggested that natural products compare favourably to today's combinatorial chemistry libraries as potential lead molecules.
Screening
Two main approaches exist for the finding of new bioactive chemical entities from natural sources. | Drug discovery | Wikipedia | 503 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
The first is sometimes referred to as random collection and screening of material, but the collection is far from random. Biological (often botanical) knowledge is often used to identify families that show promise. This approach is effective because only a small part of the earth's biodiversity has ever been tested for pharmaceutical activity. Also, organisms living in a species-rich environment need to evolve defensive and competitive mechanisms to survive. Those mechanisms might be exploited in the development of beneficial drugs.
A collection of plant, animal and microbial samples from rich ecosystems can potentially give rise to novel biological activities worth exploiting in the drug development process. One example of successful use of this strategy is the screening for antitumor agents by the National Cancer Institute, which started in the 1960s. Paclitaxel was identified from Pacific yew tree Taxus brevifolia. Paclitaxel showed anti-tumour activity by a previously undescribed mechanism (stabilization of microtubules) and is now approved for clinical use for the treatment of lung, breast, and ovarian cancer, as well as for Kaposi's sarcoma. Early in the 21st century, Cabazitaxel (made by Sanofi, a French firm), another relative of taxol has been shown effective against prostate cancer, also because it works by preventing the formation of microtubules, which pull the chromosomes apart in dividing cells (such as cancer cells). Other examples are: 1. Camptotheca (Camptothecin · Topotecan · Irinotecan · Rubitecan · Belotecan); 2. Podophyllum (Etoposide · Teniposide); 3a. Anthracyclines (Aclarubicin · Daunorubicin · Doxorubicin · Epirubicin · Idarubicin · Amrubicin · Pirarubicin · Valrubicin · Zorubicin); 3b. Anthracenediones (Mitoxantrone · Pixantrone).
The second main approach involves ethnobotany, the study of the general use of plants in society, and ethnopharmacology, an area inside ethnobotany, which is focused specifically on medicinal uses. | Drug discovery | Wikipedia | 471 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Artemisinin, an antimalarial agent from sweet wormtree Artemisia annua, used in Chinese medicine since 200BC is one drug used as part of combination therapy for multiresistant Plasmodium falciparum.
Additionally, since machine learning has become more advanced, virtual screening is now an option for drug developers. AI algorithms are being used to perform virtual screening of chemical compounds, which involves predicting the activity of a compound against a specific target. By using machine learning algorithms to analyse large amounts of chemical data, researchers can identify potential new drug candidates that are more likely to be effective against a specific disease. Algorithms, such as Nearest-Neighbour classifiers, RF, extreme learning machines, SVMs, and deep neural networks (DNNs), are used for VS based on synthesis feasibility and can also predict in vivo activity and toxicity.
Structural elucidation
The elucidation of the chemical structure is critical to avoid the re-discovery of a chemical agent that is already known for its structure and chemical activity. Mass spectrometry is a method in which individual compounds are identified based on their mass/charge ratio, after ionization. Chemical compounds exist in nature as mixtures, so the combination of liquid chromatography and mass spectrometry (LC-MS) is often used to separate the individual chemicals. Databases of mass spectra for known compounds are available and can be used to assign a structure to an unknown mass spectrum. Nuclear magnetic resonance spectroscopy is the primary technique for determining chemical structures of natural products. NMR yields information about individual hydrogen and carbon atoms in the structure, allowing detailed reconstruction of the molecule's architecture.
New Drug Application
When a drug is developed with evidence throughout its history of research to show it is safe and effective for the intended use in the United States, the company can file an application – the New Drug Application (NDA) – to have the drug commercialized and available for clinical application. NDA status enables the FDA to examine all submitted data on the drug to reach a decision on whether to approve or not approve the drug candidate based on its safety, specificity of effect, and efficacy of doses. | Drug discovery | Wikipedia | 442 | 571274 | https://en.wikipedia.org/wiki/Drug%20discovery | Biology and health sciences | General concepts_2 | Health |
Cordyceps is a genus of ascomycete fungi (sac fungi) that includes over 260 species worldwide, many of which are parasitic. Diverse variants of cordyceps have had more than 1,500 years of use in Chinese medicine. Most Cordyceps species are endoparasitoids, parasitic mainly on insects and other arthropods (they are thus entomopathogenic fungi); a few are parasitic on other fungi.
The generic name Cordyceps is derived from the ancient Greek κορδύλη kordýlē, meaning "club", and the Latin -ceps, meaning "-headed". The genus has a worldwide distribution, with most of the known species being from Asia.
Taxonomy
There are two recognized subgenera:
Cordyceps subgen. Cordyceps Fr. 1818
Cordyceps subgen. Cordylia Tul. & C. Tul. 1865
Cordyceps sensu stricto are the teleomorphs of several genera of anamorphic, entomopathogenic fungi such as Beauveria (Cordyceps bassiana), Septofusidium, and Lecanicillium.
Splits
Cordyceps subgen. Epichloe was at one time a subgenus, but is now regarded as a separate genus, Epichloë.
Cordyceps subgen. Ophiocordyceps was at one time a subgenus defined by morphology. Nuclear DNA sampling done in 2007 shows that members, including "C. sinensis" and "C. unilateralis", as well as some others not placed in the subgenus, were distantly related to most of the remainder of species then placed in Cordyceps (e.g. the type species C. militaris). As a result, it became its own genus, absorbing new members.
The 2007 study also peeled off Metacordyceps (anamorph Metarhizium, Pochonia) and Elaphocordyceps. A number of species remain unclearly assigned and provisionally retained in Cordyceps sensu lato.
Selected species
There are over 260 species recognised in the genus Cordyceps including the following species:
Cordyceps caespitosa
Cordyceps militaris
Cordyceps sinclairii | Cordyceps | Wikipedia | 469 | 571490 | https://en.wikipedia.org/wiki/Cordyceps | Biology and health sciences | Edible fungi | Plants |
Biology
When Cordyceps attacks a host, the mycelium invades and eventually replaces the host tissue, while the elongated fruit body (ascocarp) may be cylindrical, branched, or of complex shape. The ascocarp bears many small, flask-shaped perithecia containing asci. These, in turn, contain thread-like ascospores, which usually break into fragments and are presumably infective.
Research
Polysaccharide components and the nucleoside cordycepin isolated from C. militaris are under basic research, but more advanced clinical research has been limited and too low in quality to identify any therapeutic potential of cordyceps components.
Uses
Along with Ophiocordyceps, Cordyceps has long been used in traditional Chinese medicine in the belief it can be used to treat diseases. There is no strong scientific evidence for such uses.
Cultural representations
The video game series The Last of Us (2013–present) and its television adaptation present Cordyceps as a deadly threat to the human race, its parasitism powerful enough to result in global calamity. The result is a zombie apocalypse and the collapse of human civilization. Scientific American notes that some species in the genus "are indeed body snatchers–they have been making real zombies for millions of years", though of ants or tarantulas, not of humans. The Last of Us proceeds from the premise that a new species of Cordyceps manages to jump between species of host, just as diseases like influenza have done. Its human hosts initially become violent "infected" beings, before turning into blind zombie "clickers", complete with fungal "fruiting bodies sprouting from their faces". In an additional detail that reflects Cordyceps biology, "clickers" then seek out a dark place in which to die and release the fungal spores, enabling the parasite to complete its life cycle. Scientific American comments that by combining a plausible mechanism with effective artistic design, the series gains "both scientific rigor and beauty". | Cordyceps | Wikipedia | 419 | 571490 | https://en.wikipedia.org/wiki/Cordyceps | Biology and health sciences | Edible fungi | Plants |
In similar vein, Cordyceps causes a pandemic that wipes out most of humanity in Mike Carey's 2014 postapocalyptic novel The Girl with All the Gifts and its 2016 film adaptation. In this case, an infected person becomes a "hungry", a zombie thirsting for blood. In the fiction, Dr. Caldwell explains that the human-infecting fungus is a mutated form of Ophiocordyceps unilateralis (a group of species now split off from Cordyceps) which alters the behaviour of infected insects. The children of infected mothers, however, become "hybrids" with antibodies protecting them against the fungus.
Gallery | Cordyceps | Wikipedia | 138 | 571490 | https://en.wikipedia.org/wiki/Cordyceps | Biology and health sciences | Edible fungi | Plants |
A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadlike with many nuclei and is called a muscle fiber. Muscle cells develop from embryonic precursor cells called myoblasts.
Skeletal muscle cells form by fusion of myoblasts to produce multinucleated cells (syncytia) in a process known as myogenesis. Skeletal muscle cells and cardiac muscle cells both contain myofibrils and sarcomeres and form a striated muscle tissue.
Cardiac muscle cells form the cardiac muscle in the walls of the heart chambers, and have a single central nucleus. Cardiac muscle cells are joined to neighboring cells by intercalated discs, and when joined in a visible unit they are described as a cardiac muscle fiber.
Smooth muscle cells control involuntary movements such as the peristalsis contractions in the esophagus and stomach. Smooth muscle has no myofibrils or sarcomeres and is therefore non-striated. Smooth muscle cells have a single nucleus.
Structure
The unusual microscopic anatomy of a muscle cell gave rise to its terminology. The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma. The sarcolemma receives and conducts stimuli.
Skeletal muscle cells
Skeletal muscle cells are the individual contractile cells within a muscle and are more usually known as muscle fibers because of their longer threadlike appearance. Broadly there are two types of muscle fiber performing in muscle contraction, either as slow twitch (type I) or fast twitch (type II).
A single muscle such as the biceps brachii in a young adult human male contains around 253,000 muscle fibers. Skeletal muscle fibers are the only muscle cells that are multinucleated with the nuclei usually referred to as myonuclei. This occurs during myogenesis with the fusion of myoblasts each contributing a nucleus to the newly formed muscle cell or myotube. Fusion depends on muscle-specific proteins known as fusogens called myomaker and myomerger. | Muscle cell | Wikipedia | 491 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
A striated muscle fiber contains myofibrils consisting of long protein chains of myofilaments. There are three types of myofilaments: thin, thick, and elastic that work together to produce a muscle contraction. The thin myofilaments are filaments of mostly actin and the thick filaments are of mostly myosin and they slide over each other to shorten the fiber length in a muscle contraction. The third type of myofilament is an elastic filament composed of titin, a very large protein.
In striations of muscle bands, myosin forms the dark filaments that make up the A band. Thin filaments of actin are the light filaments that make up the I band. The smallest contractile unit in the fiber is called the sarcomere which is a repeating unit within two Z bands. The sarcoplasm also contains glycogen which provides energy to the cell during heightened exercise, and myoglobin, the red pigment that stores oxygen until needed for muscular activity.
The sarcoplasmic reticulum, a specialized type of smooth endoplasmic reticulum, forms a network around each myofibril of the muscle fiber. This network is composed of groupings of two dilated end-sacs called terminal cisternae, and a single T-tubule (transverse tubule), which bores through the cell and emerge on the other side; together these three components form the triads that exist within the network of the sarcoplasmic reticulum, in which each T-tubule has two terminal cisternae on each side of it. The sarcoplasmic reticulum serves as a reservoir for calcium ions, so when an action potential spreads over the T-tubule, it signals the sarcoplasmic reticulum to release calcium ions from the gated membrane channels to stimulate muscle contraction.
In skeletal muscle, at the end of each muscle fiber, the outer layer of the sarcolemma combines with tendon fibers at the myotendinous junction. Within the muscle fiber pressed against the sarcolemma are multiply flattened nuclei; embryologically, this multinucleate condition results from multiple myoblasts fusing to produce each muscle fiber, where each myoblast contributes one nucleus.
Cardiac muscle cells | Muscle cell | Wikipedia | 494 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
The cell membrane of a cardiac muscle cell has several specialized regions, which may include the intercalated disc, and transverse tubules. The cell membrane is covered by a lamina coat which is approximately 50 nm wide. The laminar coat is separable into two layers; the lamina densa and lamina lucida. In between these two layers can be several different types of ions, including calcium.
Cardiac muscle like the skeletal muscle is also striated and the cells contain myofibrils, myofilaments, and sarcomeres as the skeletal muscle cell.
The cell membrane is anchored to the cell's cytoskeleton by anchor fibers that are approximately 10 nm wide. These are generally located at the Z lines so that they form grooves and transverse tubules emanate. In cardiac myocytes, this forms a scalloped surface.
The cytoskeleton is what the rest of the cell builds off of and has two primary purposes; the first is to stabilize the topography of the intracellular components and the second is to help control the size and shape of the cell. While the first function is important for biochemical processes, the latter is crucial in defining the surface-to-volume ratio of the cell. This heavily influences the potential electrical properties of excitable cells. Additionally, deviation from the standard shape and size of the cell can have a negative prognostic impact.
Smooth muscle cells
Smooth muscle cells are so-called because they have neither myofibrils nor sarcomeres and therefore no striations. They are found in the walls of hollow organs, including the stomach, intestines, bladder and uterus, in the walls of blood vessels, and in the tracts of the respiratory, urinary, and reproductive systems. In the eyes, the ciliary muscles dilate and contract the iris and alter the shape of the lens. In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature or fear. | Muscle cell | Wikipedia | 417 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
Smooth muscle cells are spindle-shaped with wide middles, and tapering ends. They have a single nucleus and range from 30 to 200 micrometers in length. This is thousands of times shorter than skeletal muscle fibers. The diameter of their cells is also much smaller which removes the need for T-tubules found in striated muscle cells. Although smooth muscle cells lack sarcomeres and myofibrils they do contain large amounts of the contractile proteins actin and myosin. Actin filaments are anchored by dense bodies (similar to the Z discs in sarcomeres) to the sarcolemma.
Development
A myoblast is an embryonic precursor cell that differentiates to give rise to the different muscle cell types. Differentiation is regulated by myogenic regulatory factors, including MyoD, Myf5, myogenin, and MRF4. GATA4 and GATA6 also play a role in myocyte differentiation.
Skeletal muscle fibers are made when myoblasts fuse together; muscle fibers therefore are cells with multiple nuclei, known as myonuclei, with each cell nucleus originating from a single myoblast. The fusion of myoblasts is specific to skeletal muscle, and not cardiac muscle or smooth muscle.
Myoblasts in skeletal muscle that do not form muscle fibers dedifferentiate back into myosatellite cells. These satellite cells remain adjacent to a skeletal muscle fiber, situated between the sarcolemma and the basement membrane of the endomysium (the connective tissue investment that divides the muscle fascicles into individual fibers). To re-activate myogenesis, the satellite cells must be stimulated to differentiate into new fibers.
Myoblasts and their derivatives, including satellite cells, can now be generated in vitro through directed differentiation of pluripotent stem cells.
Kindlin-2 plays a role in developmental elongation during myogenesis.
Function
Muscle contraction in striated muscle | Muscle cell | Wikipedia | 406 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
Skeletal muscle contraction
When contracting, thin and thick filaments slide concerning each other by using adenosine triphosphate. This pulls the Z discs closer together in a process called the sliding filament mechanism. The contraction of all the sarcomeres results in the contraction of the whole muscle fiber. This contraction of the myocyte is triggered by the action potential over the cell membrane of the myocyte. The action potential uses transverse tubules to get from the surface to the interior of the myocyte, which is continuous within the cell membrane.
Sarcoplasmic reticula are membranous bags that transverse tubules touch but remain separate from. These wrap themselves around each sarcomere and are filled with Ca2+.
Excitation of a myocyte causes depolarization at its synapses, the neuromuscular junctions, which triggers an action potential. With a singular neuromuscular junction, each muscle fiber receives input from just one somatic efferent neuron. Action potential in a somatic efferent neuron causes the release of the neurotransmitter acetylcholine.
When the acetylcholine is released it diffuses across the synapse and binds to a receptor on the sarcolemma, a term unique to muscle cells that refers to the cell membrane. This initiates an impulse that travels across the sarcolemma.
When the action potential reaches the sarcoplasmic reticulum it triggers the release of Ca2+ from the Ca2+ channels. The Ca2+ flows from the sarcoplasmic reticulum into the sarcomere with both of its filaments. This causes the filaments to start sliding and the sarcomeres to become shorter. This requires a large amount of ATP, as it is used in both the attachment and release of every myosin head. Very quickly Ca2+ is actively transported back into the sarcoplasmic reticulum, which blocks the interaction between the thin and thick filament. This in turn causes the muscle cell to relax. | Muscle cell | Wikipedia | 437 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
There are four main types of muscle contraction: isometric, isotonic, eccentric and concentric. Isometric contractions are skeletal muscle contractions that do not cause movement of the muscle. and isotonic contractions are skeletal muscle contractions that do cause movement. Eccentric contraction is when a muscle moves under a load. Concentric contraction is when a muscle shortens and generates force.
Cardiac muscle contraction
Specialized cardiomyocytes in the sinoatrial node generate electrical impulses that control the heart rate. These electrical impulses coordinate contraction throughout the remaining heart muscle via the electrical conduction system of the heart. Sinoatrial node activity is modulated, in turn, by nerve fibers of both the sympathetic and parasympathetic nervous systems. These systems act to increase and decrease, respectively, the rate of production of electrical impulses by the sinoatrial node.
Evolution
The evolutionary origin of muscle cells in animals is highly debated: One view is that muscle cells evolved once, and thus all muscle cells have a single common ancestor. Another view is that muscles cells evolved more than once, and any morphological or structural similarities are due to convergent evolution, and the development of shared genes that predate the evolution of muscle – even the mesoderm (the mesoderm is the germ layer that gives rise to muscle cells in vertebrates). | Muscle cell | Wikipedia | 275 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
Schmid & Seipel (2005) argue that the origin of muscle cells is a monophyletic trait that occurred concurrently with the development of the digestive and nervous systems of all animals, and that this origin can be traced to a single metazoan ancestor in which muscle cells are present. They argue that molecular and morphological similarities between the muscles cells in Cnidaria and Ctenophora are similar enough to those of bilaterians that there would be one ancestor in metazoans from which muscle cells derive. In this case, Schmid & Seipel argue that the last common ancestor of Bilateria, Ctenophora and Cnidaria, was a triploblast (an organism having three germ layers), and that diploblasty, meaning an organism with two germ layers, evolved secondarily, because of their observation of the lack of mesoderm or muscle found in most cnidarians and ctenophores. By comparing the morphology of cnidarians and ctenophores to bilaterians, Schmid & Seipel were able to conclude that there were myoblast-like structures in the tentacles and gut of some species of cnidarians and the tentacles of ctenophores. Since this is a structure unique to muscle cells, these scientists determined based on the data collected by their peers that this is a marker for striated muscles similar to that observed in bilaterians. The authors also remark that the muscle cells found in cnidarians and ctenophores are often contested due to the origin of these muscle cells being the ectoderm rather than the mesoderm or mesendoderm. | Muscle cell | Wikipedia | 349 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
The origin of true muscle cells is argued by other authors to be the endoderm portion of the mesoderm and the endoderm. However, Schmid & Seipel (2005) counter skepticism – about whether the muscle cells found in ctenophores and cnidarians are "true" muscle cells – by considering that cnidarians develop through a medusa stage and polyp stage. They note that in the hydrozoans' medusa stage, there is a layer of cells that separate from the distal side of the ectoderm, which forms the striated muscle cells in a way similar to that of the mesoderm; they call this third separated layer of cells the ectocodon. Schmid & Seipel argue that, even in bilaterians, not all muscle cells are derived from the mesendoderm: Their key examples are that in both the eye muscles of vertebrates and the muscles of spiralians, these cells derive from the ectodermal mesoderm, rather than the endodermal mesoderm. Furthermore, they argue that since myogenesis does occur in cnidarians with the help of the same molecular regulatory elements found in the specification of muscle cells in bilaterians, that there is evidence for a single origin for striated muscle. | Muscle cell | Wikipedia | 275 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
In contrast to this argument for a single origin of muscle cells, Steinmetz, Kraus, et al. (2012) argue that molecular markers such as the myosin II protein used to determine this single origin of striated muscle predate the formation of muscle cells. They use an example of the contractile elements present in the Porifera, or sponges, that do truly lack this striated muscle containing this protein. Furthermore, Steinmetz, Kraus, et al. present evidence for a polyphyletic origin of striated muscle cell development through their analysis of morphological and molecular markers that are present in bilaterians and absent in cnidarians, ctenophores, and bilaterians. Steinmetz, Kraus, et al. showed that the traditional morphological and regulatory markers such as actin, the ability to couple myosin side chains phosphorylation to higher concentrations of the positive concentrations of calcium, and other MyHC elements are present in all metazoans not just the organisms that have been shown to have muscle cells. Thus, the usage of any of these structural or regulatory elements in determining whether or not the muscle cells of the cnidarians and ctenophores are similar enough to the muscle cells of the bilaterians to confirm a single lineage is questionable according to Steinmetz, Kraus, et al. Furthermore, they explain that the orthologues of the Myc genes that have been used to hypothesize the origin of striated muscle occurred through a gene duplication event that predates the first true muscle cells (meaning striated muscle), and they show that the Myc genes are present in the sponges that have contractile elements but no true muscle cells. Steinmetz, Kraus, et al. also showed that the localization of this duplicated set of genes that serve both the function of facilitating the formation of striated muscle genes, and cell regulation and movement genes, were already separated into striated much and non-muscle MHC. This separation of the duplicated set of genes is shown through the localization of the striated much to the contractile vacuole in sponges, while the non-muscle much was more diffusely expressed during developmental cell shape and change. Steinmetz, Kraus, et al. found a similar pattern of localization in cnidarians except with the cnidarian N | Muscle cell | Wikipedia | 494 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
vectensis having this striated muscle marker present in the smooth muscle of the digestive tract. Thus, they argue that the pleisiomorphic trait of the separated orthologues of much cannot be used to determine the monophylogeny of muscle, and additionally argue that the presence of a striated muscle marker in the smooth muscle of this cnidarian shows a fundamental different mechanism of muscle cell development and structure in cnidarians | Muscle cell | Wikipedia | 91 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
Steinmetz, Kraus, et al. (2012) further argue for multiple origins of striated muscle in the metazoans by explaining that a key set of genes used to form the troponin complex for muscle regulation and formation in bilaterians is missing from the cnidarians and ctenophores, and 47 structural and regulatory proteins observed, Steinmetz, Kraus, et al. were not able to find even on unique striated muscle cell protein that was expressed in both cnidarians and bilaterians. Furthermore, the Z-disc seemed to have evolved differently even within bilaterians and there is a great deal of diversity of proteins developed even between this clade, showing a large degree of radiation for muscle cells. Through this divergence of the Z-disc, Steinmetz, Kraus, et al. argue that there are only four common protein components that were present in all bilaterians muscle ancestors and that of these for necessary Z-disc components only an actin protein that they have already argued is an uninformative marker through its pleisiomorphic state is present in cnidarians. Through further molecular marker testing, Steinmetz et al. observe that non-bilaterians lack many regulatory and structural components necessary for bilaterians muscle formation and do not find any unique set of proteins to both bilaterians and cnidarians and ctenophores that are not present in earlier, more primitive animals such as the sponges and amoebozoans. Through this analysis, the authors conclude that due to the lack of elements that bilaterian muscles are dependent on for structure and usage, nonbilaterian muscles must be of a different origin with a different set of regulatory and structural proteins.
In another take on the argument, Andrikou & Arnone (2015) use the newly available data on gene regulatory networks to look at how the hierarchy of genes and morphogens and another mechanism of tissue specification diverge and are similar among early deuterostomes and protostomes. By understanding not only what genes are present in all bilaterians but also the time and place of deployment of these genes, Andrikou & Arnone discuss a deeper understanding of the evolution of myogenesis. | Muscle cell | Wikipedia | 464 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
In their paper, Andrikou & Arnone (2015) argue that to truly understand the evolution of muscle cells the function of transcriptional regulators must be understood in the context of other external and internal interactions. Through their analysis, Andrikou & Arnone found that there were conserved orthologues of the gene regulatory network in both invertebrate bilaterians and cnidarians. They argue that having this common, general regulatory circuit allowed for a high degree of divergence from a single well-functioning network. Andrikou & Arnone found that the orthologues of genes found in vertebrates had been changed through different types of structural mutations in the invertebrate deuterostomes and protostomes, and they argue that these structural changes in the genes allowed for a large divergence of muscle function and muscle formation in these species. Andrikou & Arnone were able to recognize not only any difference due to mutation in the genes found in vertebrates and invertebrates but also the integration of species-specific genes that could also cause divergence from the original gene regulatory network function. Thus, although a common muscle patterning system has been determined, they argue that this could be due to a more ancestral gene regulatory network being coopted several times across lineages with additional genes and mutations causing very divergent development of muscles. Thus it seems that the myogenic patterning framework may be an ancestral trait. However, Andrikou & Arnone explain that the basic muscle patterning structure must also be considered in combination with the cis regulatory elements present at different times during development. In contrast with the high level of gene family apparatuses structure, Andrikou and Arnone found that the cis-regulatory elements were not well conserved both in time and place in the network which could show a large degree of divergence in the formation of muscle cells. Through this analysis, it seems that the myogenic GRN is an ancestral GRN with actual changes in myogenic function and structure possibly being linked to later coopts of genes at different times and places.
Evolutionarily, specialized forms of skeletal and cardiac muscles predated the divergence of the vertebrate / arthropod evolutionary line. This indicates that these types of muscle developed in a common ancestor sometime before 700 million years ago (mya). Vertebrate smooth muscle was found to have evolved independently from the skeletal and cardiac muscle types. | Muscle cell | Wikipedia | 498 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
Invertebrate muscle cell types
The properties used for distinguishing fast, intermediate, and slow muscle fibers can be different for invertebrate flight and jump muscle. To further complicate this classification scheme, the mitochondrial content, and other morphological properties within a muscle fiber, can change in a tsetse fly with exercise and age. | Muscle cell | Wikipedia | 68 | 571549 | https://en.wikipedia.org/wiki/Muscle%20cell | Biology and health sciences | Muscular system | null |
The muskrat or common muskrat (Ondatra zibethicus) is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America.
The muskrat is found in wetlands over various climates and habitats. It has crucial effects on the ecology of wetlands, and is a resource of food and fur for humans.
Adult muskrats weigh , with a body length (excluding the tail) of . They are covered with short, thick fur of medium to dark brown color. Their long tails, covered with scales rather than hair, are laterally compressed and generate a small amount of thrust, with their webbed hind feet being the main means of propulsion, and the unique tail mainly important in directional stability. Muskrats spend most of their time in the water and can swim underwater for 12 to 17 minutes. They live in families of a male and female pair and their young. They build nests to protect themselves from the cold and predators, often burrowed into the bank with an underwater entrance. Muskrats feed mostly on cattail and other aquatic vegetation but also eat small animals.
Ondatra zibethicus is the only extant species in the genus Ondatra; its closest relative is the round-tailed muskrat (Neofiber alleni). It is the largest species in the subfamily Arvicolinae, which includes 142 other species of rodents, mostly voles and lemmings. Muskrats are referred to as "rats" in a general sense because they are medium-sized rodents with an adaptable lifestyle and an omnivorous diet. They are not, however, members of the genus Rattus. They are not closely related to beavers, with which they share habitat and general appearance.
Etymology
The muskrat's name probably comes from a word of Algonquian (possibly Powhatan) origin, muscascus (literally "it is red", so called for its colorings), or from the Abenaki native word mòskwas, as seen in the archaic English name for the animal, musquash. Because of the association with the "musky" odor, which the muskrat uses to mark its territory, and its flattened tail, the name became altered to musk-beaver; later it became "muskrat" due to its resemblance to rats. | Muskrat | Wikipedia | 498 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Similarly, its specific name zibethicus means "musky", being the adjective of zibethus "civet musk; civet". The genus name comes from the Huron word for the animal, ondathra, and entered Neo-Latin as Ondatra via French.
Description
An adult muskrat is about long, half of that length being the tail, and weighs . That is about four times the weight of the brown rat (Rattus norvegicus), though an adult muskrat is only slightly longer. It is almost certainly the most prominent and heaviest member of the diverse family Cricetidae, which includes all voles, lemmings, and most mice native to the Americas, and hamsters in Eurasia. The muskrat is much smaller than a beaver (Castor canadensis), with which they often share a habitat.
Muskrats are covered with short, thick fur, which is medium to dark brown or black, with the belly a bit lighter (countershaded); as the animal ages, it turns partly gray. The fur has two layers, which protect it from cold water. They have long tails covered with scales rather than hair. To aid in swimming, their tails are slightly flattened vertically, a shape that is unique to them. When they walk on land, their tails drag on the ground, which makes their tracks easy to recognize.
Muskrats spend most of their time in water and are well suited to their semiaquatic life. They can swim underwater for 12 to 17 minutes. Their bodies, like those of seals and whales, are less sensitive to the buildup of carbon dioxide than those of most other mammals. They can close off their ears to keep water out. Their hind feet are partially webbed and are their primary means of propulsion. Their tail functions as a rudder, controlling the direction they swim.
Distribution and ecology
Muskrats are found in most of Canada, the United States, and a small part of northern Mexico. They were introduced to Europe at the beginning of the 20th century and have become an invasive species in northwestern Europe. They primarily inhabit wetlands, areas in or near saline and freshwater wetlands, rivers, lakes, or ponds. They are not found in Florida, where the round-tailed muskrat, or Florida water rat (Neofiber alleni), fills their ecological niche. | Muskrat | Wikipedia | 491 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Their populations naturally cycle; in areas where they become abundant, they can remove much of the vegetation in wetlands. They are thought to play a major role in determining the vegetation of prairie wetlands in particular. They also selectively remove preferred plant species, thereby changing the abundance of plant species in many kinds of wetlands. Species commonly eaten include cattail and yellow water lily. Alligators are thought to be an important natural predator, and the absence of muskrats from Florida may, in part, be the result of alligator predation.
While much wetland habitat has been eliminated due to human activity, new muskrat habitat has been created by the construction of canals or irrigation channels (e.g., acequias), and the muskrat remains widespread. They can live alongside streams that contain the sulfurous water that drains away from coal mines. Fish and frogs perish in such streams, yet muskrats may thrive and occupy the wetlands. Muskrats also benefit from human persecution of some of their predators.
The muskrat is classed as a "prohibited new organism" under New Zealand's Hazardous Substances and New Organisms Act 1996, preventing it from being imported into the country.
The trematode Metorchis conjunctus can also infect muskrats.
Decline in the United States
According to an article in Hakai Magazine, from April 2024, the muskrat populations have declined by at least one-half in 34 US states. The collapse was near-total, between 90 and 99 percent in a handful of states. Rhode Island's muskrat populations are estimated to be roughly 15 percent of what they were several decades ago.
The decline in muskrat populations began in the 1990s and early 2000s.
Subspecies
Ondatra zibethicus has 16 subspecies: O.z. albus, O.z. aquihnis, O.z. bemardi, O.z. cinnamominus, O.z. macrodom, O.z. mergens, O.z. obscurus, O.z. occipitalis, O.z. osoyoosensis, O.z. pallidus, O.z.ripensis, O.z. rivalicus, O.z. roidmani, O.z. spatulatus, O.z. zalaphus and O.z. zibethicus. | Muskrat | Wikipedia | 498 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Invasiveness status
In Europe, the muskrat has been included in the list of invasive alien species of Union concern (the Union list) since August 2, 2017. This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union. Muskrats were introduced to Europe in the early 20th century for fur farming. In many European countries, muskrats have become problematic, damaging flood control systems, crops, and river banks with burrowing activities. Their presence is particularly concerning in areas with delicate ecosystems, where they can outcompete or displace native species. Several European countries have implemented control measures and eradication programs to manage muskrat populations and mitigate their impact.
Behavior
Muskrats normally live in families consisting of a male and female and their young. During the spring, they often fight with other muskrats over territory and potential mates. Many are injured or killed in these fights. Muskrat families build nests to protect themselves and their young from cold and predators. Muskrats burrow into the bank with an underwater entrance in streams, ponds, or lakes. These entrances are wide. In marshes, push-ups are constructed from vegetation and mud. These push-ups are up to in height. In snowy areas, they keep the openings to their push-ups closed by plugging them with vegetation, which they replace daily. Some muskrat push-ups are swept away in spring floods and must be replaced yearly. Muskrats also build feeding platforms constructed in the water from cut pieces of vegetation supported by a branch structure. They help maintain open areas in marshes, which helps to provide habitat for aquatic birds.
Muskrats are most active at night or near dawn and dusk. They feed on cattails and other aquatic vegetation. They do not store food for the winter, but sometimes eat the insides of their push-ups. While they may appear to steal food beavers have stored, more seemingly cooperative partnerships with beavers exist, as featured in the BBC David Attenborough wildlife documentary The Life of Mammals. Plant materials compose about 95% of their diets, but they also eat small animals, such as freshwater mussels, frogs, crayfish, fish, and small turtles. Muskrats follow trails they make in swamps and ponds. They continue to follow their trails under the ice when the water freezes. | Muskrat | Wikipedia | 502 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Muskrats provide an important food resource for many other animals, including mink, red and gray foxes, cougars, coyotes, wolves, boreal lynxe, Canada lynx bobcats, raccoons, brown and black bears, wolverines, eagles, hawks, large owls, snakes, alligators, and bull sharks. Otters, snapping turtles, heron,s bullfrogs, large fish such as pike and largemouth bass, and predatory land reptiles such as monitor lizards prey on baby muskrats. Caribou, moose, and elk sometimes feed on the vegetation which makes up muskrat push-ups during the winter when other food is scarce for them. In their introduced range in the former Soviet Union, the muskrat's greatest predator is the golden jackal. They can be completely eradicated in shallow water bodies. During the winter of 1948–49 in the Amu Darya (river in central Asia), muskrats constituted 12.3% of jackal feces contents, and 71% of muskrat houses were destroyed by jackals, 16% of which froze and became unsuitable for muskrat occupation. Jackals also harm the muskrat industry by eating muskrats caught in traps or taking skins left out to dry.
Muskrats, like most rodents, are prolific breeders. Females can have two or three litters a year of six to eight young each. The babies are born small and hairless and weigh only about . In southern environments, young muskrats mature in six months, while in colder northern environments, it takes about a year. Muskrat populations appear to go through a regular pattern of rise and dramatic decline spread over a six- to 10-year period. Some other rodents, including famously the muskrat's close relatives, such as the lemmings, go through the same type of population changes.
In human history
Native Americans have long considered the muskrat to be an important animal. Some predict winter snowfall levels by observing the size and timing of muskrat lodge construction.
In several Native American creation myths, the muskrat dives to the bottom of the primordial sea to bring up the mud from which the earth is created after other animals have failed in the task. | Muskrat | Wikipedia | 470 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Muskrats have sometimes been a food resource for North Americans. In the southeastern portion of Michigan, a longstanding dispensation allows Catholics to consume muskrat as their Friday penance, on Ash Wednesday, and on Lenten Fridays (when the eating of flesh, except for fish, is prohibited); this tradition dates back to at least the early 19th century. In 2019, it was reported that a series of muskrat dinners were held during Lent in the areas along the Detroit River, with up to 900 muskrats being consumed at a single dinner. The preparation involved the removal of the musk glands and the gutting and cleaning of the carcass before the meat was parboiled for four hours with onion and garlic and finally fried.
Muskrat fur is warm, becoming prime in northern North America at the beginning of December. In the early 20th century, the trapping of the animal for its fur became an important industry there. During that era, the fur was specially trimmed and dyed to be sold widely in the US as "Hudson seal" fur. Muskrats were introduced at that time to Europe as a fur resource and spread throughout northern Europe and Asia.
In some European countries, such as Belgium, France, and the Netherlands, the muskrat is considered an invasive pest, as its burrowing damages the dikes and levees on which these low-lying countries depend for protection from flooding. In those countries, it is trapped, poisoned, and hunted to attempt to keep the population down. Muskrats also eat corn and other farm and garden crops growing near water bodies.
Royal Canadian Mounted Police winter hats are made from muskrat fur. | Muskrat | Wikipedia | 345 | 571662 | https://en.wikipedia.org/wiki/Muskrat | Biology and health sciences | Rodents | null |
Sabal is a genus of New World palms (or fan-palms). Currently, there are 17 recognized species of Sabal, including one hybrid species.
Distribution
The species are native to the subtropical and tropical regions of the Americas, from the Gulf Coast/South Atlantic states in the Southeastern United States, south through the Caribbean, Mexico, and Central America to Colombia and Venezuela.
Description
Members of this genus are typically identified by the leaves which originate from a bare, unarmed petiole in a fan-like structure. All members of this genus have a costa (or midrib) that extends into the leaf blade. This midrib can vary in length; and it is due to this variation that leaf blades of certain species of Sabal are strongly curved or strongly costapalmate (as in Sabal palmetto and Sabal etonia) or weakly curved (almost flattened), weakly costapalmate, (as in Sabal minor). Like many other palms, the fruit of Sabal are drupe, that typically change from green to black when mature.
Taxonomy
The name Sabal was first applied to members of the group by Michel Adanson in the 18th century. Previous names that this genus was associated with include Corypha, Chamaerops, Rhapis. This section highlights important phylogenetic work done within the genus Sabal. | Sabal | Wikipedia | 273 | 571727 | https://en.wikipedia.org/wiki/Sabal | Biology and health sciences | Arecales (inc. Palms) | Plants |
In 1990, Scott Zona outlined key morphological and anatomical characters that he used to analyze species relationships of Sabal. Through this analysis of characters, Zona produced a cladogram that portrays evolutionary relationships amongst 15 species of Sabal. Based on the distribution of species within his cladogram, Zona recognized four distinct clades. The clades within his study include (Clade 1) Sabal minor; (Clade 2) Sabal bermudana, Sabal palmetto, Sabal miamiensis, and Sabal etonia; (Clade 3) Sabal maritima, Sabal domingensis, Sabal causiarum, Sabal maurittiformis, Sabal yapa, Sabal mexicana, and Sabal guatemalensis; (Clade 4) Sabal uresana, Sabal rosei, and Sabal pumos. These clades associate closely with geographic distributions. Most of the species within Clade 3 occur in the Greater Antilles and southern Mexico, where species that occur in the Greater Antilles are more closely related to each other than those that occur in southern Mexico. Although Clade 4 also occurs in Mexico, these species occur on the west coast where they are geographically separated from the Mexican species within the southern part of the country. The remaining two clades, Clade 1 and Clade 2 predominantly occur in the southeastern United States although S. palmetto and S. minor are also known from Cuba and the Bahamas (S. palmetto) and northern Mexico (S. minor). Sabal bermudana is only known from Bermuda. | Sabal | Wikipedia | 316 | 571727 | https://en.wikipedia.org/wiki/Sabal | Biology and health sciences | Arecales (inc. Palms) | Plants |
In 2016 Heyduk, Trapnell, Barrett, and Leebens-Mack conducted a new study on Sabal that analyzed molecular (e.g. nuclear, plastid) data from 15 species of the group. This study incorporated plastid and nuclear sequence data that together were used to estimate the relatedness between the species of Sabal. The results of the study show species relationships to be different from the distribution of Zona's cladogram. Within the framework of this study, a major difference between the results of Zona and this study is the placement of "Clade 4" (Sabal uresana, Sabal rosei, and Sabal pumos) which split and integrate these species throughout the phylogeny of Sabal. The largest of the clades identified by Zona, "Clade 3" is disrupted significantly as it is split into multiple clades. Although Sabal causiarum and S. domingensis retain their relationship as sister species, they are included in a clade that also includes S. maritima and S. rosei. Despite these disruptions in placement between these two studies, the overall integrity of "Clade 1" and "Clade 2" is in congruence with the clades established from the molecular data.
Species
Prehistoric taxa
Extinct species within this genus include:
†Sabal bigbendense Manchester et al. 2010
†Sabal bracknellense (Chandler) Mai
†Sabal grayana Brown 1962
†Sabal imperialis Brown 1962
†Sabal jenkinsii (Reid & Chandler) Manchester 1994
†Sabal lamanonis
†Sabal raphipholia
Plants of the genus lived from the late Cretaceous to the Quaternary period (from 66 million to 12 thousand years ago). Fossils have been found in the United States, as well as in Europe (Italy, Switzerland, Germany, Greece, Slovakia, the United Kingdom, France) and Japan. Leaf fossils of Sabal lamanonis have been recovered from rhyodacite tuff of Lower Miocene age in southern Slovakia near the town of Lučenec. 27 million year old Sabal lamanonis and Sabal raphipholia leaf fossils in volcanic rocks have been described from the Evros region in Western Thrace, Greece.
Formerly placed in Sabal
Serenoa repens (W.Bartram) Small (as S. serrulata (Michx.) Nutt. ex Schult. & Schult.f.) | Sabal | Wikipedia | 508 | 571727 | https://en.wikipedia.org/wiki/Sabal | Biology and health sciences | Arecales (inc. Palms) | Plants |
Ecology
Sabal species are used as food sources by several species of birds (including Mimus polyglottos, Turdus migratorius, Dendroica coronata, Corvus ossifragus, and Drycopus pileatus) as well as insects, such as Caryobruchus and various species of Hymenoptera. American black bears (Ursus americanus) and raccoons (Procyon lotor) are also known to feed on fruit of various species of Sabal. Sabal palmetto is recorded to have its own lichen, Arthonia rubrocincta, that only occurs on its leaf bases. In Europe, the introduced Lepidopteran species Paysandisia archon has become a prominent pest whose larvae are known to feed on some of the cultivated species of Sabal.
Uses
Arborescent species are often transplanted from natural stands into urban landscapes and are rarely grown in nurseries due to slow growth. Several species are cultivated as ornamental plants and because several species are relatively cold-hardy, can be grown farther north than most other palms. The central bud of Sabal palmetto is edible and, when cooked, is known as 'swamp cabbage'. Mature fronds are used as thatch, to make straw hats, and for weaving mats. | Sabal | Wikipedia | 269 | 571727 | https://en.wikipedia.org/wiki/Sabal | Biology and health sciences | Arecales (inc. Palms) | Plants |
Campylobacter jejuni is a species of pathogenic bacteria that is commonly associated with poultry, and is also often found in animal feces. This species of microbe is one of the most common causes of food poisoning in Europe and in the US, with the vast majority of cases occurring as isolated events rather than mass outbreaks. Active surveillance through the Foodborne Diseases Active Surveillance Network (FoodNet) indicates that about 20 cases are diagnosed each year for each 100,000 people in the US, while many more cases are undiagnosed or unreported; the CDC estimates a total of 1.5 million infections every year. The European Food Safety Authority reported 246,571 cases in 2018, and estimated approximately nine million cases of human campylobacteriosis per year in the European Union. In Africa, Asia, and the Middle East, data indicates that C. jejuni infections are endemic.
Campylobacter is a genus of bacteria that is among the most common causes of bacterial infections in humans worldwide. Campylobacter means "curved rod", deriving from the Greek kampylos (curved) and baktron (rod). Of its many species, C. jejuni is considered one of the most important from both a microbiological and public health perspective. | Campylobacter jejuni | Wikipedia | 271 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
C. jejuni is commonly associated with poultry, and is also commonly found in animal feces. Campylobacter is a helical-shaped, non-spore-forming, Gram-negative, microaerophilic, nonfermenting motile bacterium with a single flagellum at one or both poles, which are also oxidase-positive and grow optimally at 37 to 42 °C. When exposed to atmospheric oxygen, C. jejuni is able to change into a coccal form. This species of pathogenic bacteria is one of the most common causes of human gastroenteritis in the world. Food poisoning caused by Campylobacter species can be severely debilitating, but is rarely life-threatening. It has been linked with subsequent development of Guillain–Barré syndrome, which usually develops two to three weeks after the initial illness. Individuals with recent C. jejuni infections develop Guillain-Barré syndrome at a rate of 0.3 per 1000 infections, about 100 times more often than the general population. Another chronic condition that may be associated with campylobacter infection is reactive arthritis. Reactive arthritis is a complication strongly associated with a particular genetic make-up. That is, persons who have the human leukocyte antigen B27 (HLA-B27) are most susceptible. Most often, the symptoms of reactive arthritis will occur up to several weeks after infection.
History
Campylobacter jejuni was originally named Vibrio jejuni due to its likeness to Vibrio spp. until 1963. Seabald and Vernon proposed the genus Campylobacter due to its low levels of guanine and cytosine, non-fermentative metabolism, and microaerophilic growth requirements. The first well recorded incident of Campylobacter infection occurred in 1938. Campylobacter found in milk caused diarrhea among 355 inmates in two state institutions in Illinois. C. jejuni was first discovered in the small intestines of humans in the 1970s, however, symptoms have been noted since the early 20th century. The CDC, USDA and FDA collectively identified C. jejuni as responsible for over 40% of bacterial gastroenteritis found in laboratories as of 1996. | Campylobacter jejuni | Wikipedia | 476 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Metabolism
C. jejuni is unable to use sugars as a carbon source, primarily using amino acids for growth instead. The main reason C. jejuni lacks glycolytic capabilities is a lack of glucokinase and a lack of the 6-phosphofructokinase enzyme to employ the EMP pathway. The four main amino acids C. jejuni takes in are serine, aspartate, asparagine, and glutamate, which are listed in order of preference. If all of these are depleted, some strains can use proline as well. Either the host or metabolic activity of other gut microbes can supply these amino acids.
The metabolic pathways C. jejuni is capable of include the TCA cycle, a non-oxidative pentose phosphate pathway, gluconeogenesis, and fatty acid synthesis. Serine is the most important amino acid used for growth, brought into the cell by SdaC transport proteins and further broken down into pyruvate by the SdaA dehydratase. Though this pyruvate cannot directly be converted into phosphoenolpyruvic acid (as C. jejuni lacks this synthetase), the pyruvate can enter the TCA cycle to form oxaloacetic acid intermediates that can be converted to phosphoenolpyruvic acid for gluconeogenesis. This production of carbohydrates is important for the virulence factors of C. jejuni. The pyruvate created from serine can also be converted to acetyl CoA and be applied to fatty acid synthesis or continue into the TCA cycle to create precursors for other biosynthetic pathways. Aspartate and glutamate are both brought into the cell via Peb1A transport proteins. Glutamate can be transaminated into aspartate, and aspartate can be deaminated to make fumerate that feeds into the TCA cycle as well. Asparagine is also able to be deaminated into aspartate (which follows the process into the TCA cycle mentioned above). While the amino acids listed above are able to be metabolized, C. jejuni is capable of taking in many of the other amino acids which helps to lower the anabolic cost of de novo synthesis. | Campylobacter jejuni | Wikipedia | 497 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
If other sources of carbon are exhausted, C. jejuni can also use acetate and lactate as carbon sources. Acetate is a normal secreted byproduct of C. jejuni metabolism stemming from the recycling of CoA, and the absence of other carbon sources can cause C. jejuni to "switch" this reaction to take in acetate for the conversion to acetyl-CoA (catalyzed by phosphate acetyltransferase and acetate kinase enzymes). Lactate is a normal byproduct of many fermentative bacteria in the gut, and C. jejuni can take in and oxidize this lactate to supply pyruvate through the activity of dehydrogenase iron-sulfur enzyme complexes.
The energetic needs of these anabolic pathways are met in multiple ways. The cytochrome c and quinol terminal oxidases allow for C. jejuni to use oxygen as a terminal electron acceptor for the reduced carriers produced through the TCA cycle (hence why C. jejuni is considered an obligate microaerophile). The conversion of acetyl-CoA to acetate mentioned above has substrate-level phosphorylation take place, giving another form of energy production without the use of microaerophilic respiration.
C. jejuni can use many different electron donors for its metabolic processes, using NADH and FADH most commonly – though C. jejuni uses NADH poorly compared to FADH due to a replacement of genes encoding subunits for NADH dehydrogenases for genes contributing to processes relating to FADH electron donation. Aside from these donors, C. jejuni can turn to products from the host gut microbiota including hydrogen, lactate, succinate, and formate to contribute electrons; formate, for example, is generated through intestinal mixed-acid fermentation. Unlike almost all other Campylobacter or Helicobacter species, C. jejuni can also accept electrons from sulfite and metabisulfite through its cytochrome c oxidoreductase system. | Campylobacter jejuni | Wikipedia | 449 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
While oxygen is mainly used as a terminal electron acceptor, C. jejuni can use nitrate, nitrite, sulfur oxides (such as dimethyl sulfoxide or trimethylamine N-oxide), or fumarate as terminal electron acceptors as well to survive as a microaerophilic bacterium. Due to oxygen-limited conditions in the common areas of colonization, C. jejuni possesses two separate terminal oxidases with different affinities for oxygen, where the low affinity oxidase can directly retrieve electrons from menaquinones. The adaptations allowing for multiple electron acceptors help to combat the problem with reactive oxygen species arising from the sole use of oxygen as well; C. jejuni cannot grow under strictly aerobic conditions. Enzymes C. jejuni carries to impede the effects of reactive oxygen species include: superoxide dismutase SodB, alkyl hydroxide reductase AhpC, catalase KatA, and thiol peroxidases Tpx and Bcp.
Disease
Campylobacteriosis is an infectious disease caused by bacteria of the genus Campylobacter. In most patients presenting with campylobacteriosis, symptoms develop within two to five days of exposure to the organism and illness typically lasts seven days following onset. Infection with C. jejuni typically results in enteritis, or inflammation of the small intestine, which is characterized by abdominal pain, voluminous diarrhea (often bloody), fever, and malaise. Individuals infected with this bacteria can experience a prodromal phase of symptoms for the first 1 to 3 days, in which the more severe portion of the disease occurs. The prodromal phase presents with symptoms including rigors, high fever, body aches, and dizziness. Other than the prodromal phase, the acute diarrheal phase of enteritis usually lasts around 7 days, however abdominal pain can persist for weeks afterward. The disease is usually self-limiting; however, it does respond to antibiotics. Severe (accompanying fevers, blood in stools) or prolonged cases may require erythromycin, azithromycin, ciprofloxacin, or norfloxacin. Fluid replacement via oral rehydration salts may be needed and intravenous fluid may be required for serious cases. Possible complications of campylobacteriosis include Guillain–Barré syndrome and reactive arthritis. | Campylobacter jejuni | Wikipedia | 509 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Transmission
C. jejuni is a zoonotic disease meaning it is more commonly spread from animals to people than in between humans. People most often contract it by touching something that has been in contact with raw or undercooked chicken in addition to eating or touching poultry that is raw or undercooked. Additionally, it can also be obtained from being in contact with animals or eating undercooked seafood. The fecal oral route is the most common way it spreads as the bacterium is excreted in animal feces. C. jejuni seldomly causes disease in animals and infections are more common in lower income countries. Deadly infections are not often seen in young adults but rather among the young and elderly. Due to poor sanitation practices in some areas, the bacteria can also be found in ice and water. It is difficult to know the science behind its transmission due to its sporadic nature. The use of antibiotics and other treatments help in slowing and preventing the transmission of C. jejuni. C. jejuni is a fastidious microaerophiles meaning it does need some oxygen to grown, spread, and transmit. However, it is highly adaptable and has adapted to grow in higher concentrations of oxygen.
Pathogenesis
C. jejuni employs unique strategies to breach the intestinal epithelial layer of its host cells. It uses proteases, particularly HtrA, to cleverly disrupt cell junctions and temporarily traverse the cells. The membrane-bound protein Fibronectin is a critical binding site for C. jejuni on the basolateral side of the polarized epithelial cell, facilitating this process. Once inside the cell, C. jejuni leverages dynein to access the perinuclear space within the Clathrin-Coated Vesicle, avoiding lysosomal digestion for up to 72 hours. | Campylobacter jejuni | Wikipedia | 380 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
To initiate infection, C. jejuni must penetrate the gut enterocytes. C. jejuni releases several different toxins, mainly enterotoxin and cytotoxins, which vary from strain to strain and correlate with the severity of the enteritis (inflammation of the small intestine). During infection, levels of all immunoglobulin classes rise. Of these, IgA is the most important because it can cross the gut wall. IgA immobilises organisms, causing them to aggregate and activate complement, and also gives short-term immunity against the infecting strain of organism. The bacteria colonize the small and large intestines, causing inflammatory diarrhea with fever. Stools contain leukocytes and blood. The role of toxins in pathogenesis is unclear. C jejuni antigens that cross-react with one or more neural structures may be responsible for triggering the Guillain–Barré syndrome.
Hypoacylated lipopolysaccharide (LPS) from C. jejuni induces moderate TLR4-mediated inflammatory response in macrophages and such LPS bioactivity may eventually result in the failure of local and systemic bacterial clearance in patients. At the same time, moderation of anti-bacterial responses may be advantageous for infected patients in clinical practice, since such an attenuated LPS may not be able to induce severe sepsis in susceptible individuals. | Campylobacter jejuni | Wikipedia | 300 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
One of the most important virulence factors of C. jejuni are flagella. The flagellar protein FlaA has been proven to be one of the abundant proteins in the cell. Flagella are required for motility, biofilm formation, host cell interactions and host colonization. The flagella in C. jejuni can also aid in the secretion intracellular proteins. The production of flagella is energetically costly so the production must be regulated from metabolic standpoint. CsrA is a post-transcriptional regulator that regulates the expression of FlaA by binding to flaA mRNA and is able to repress its translation. CsrA mutant strains have been studied and the mutant strains exhibit dysregulation of 120–150 proteins that are included in motility, host cell adherence, host cell invasion, chemotaxis, oxidative stress resistance, respiration and amino acid and acetate metabolism. Transcriptional and post-transcriptional regulation of flagellar synthesis in C. jejuni enables proper biosynthesis of flagella and it is important for pathogenesis of this bacteria.
C. jejuni employs a highly sophisticated navigation system called chemotaxis. This system is crucial when the bacterium requires guidance through chemical signals. The chemotaxis system uses specific chemoattractants that direct the bacterium toward areas with a higher concentration of the attractants. The exact nature of chemoattractants is dependent on the surrounding environmental conditions. Additionally, when the bacterium needs to move away, it uses negative chemotaxis to move in the opposite direction.
Other important virulence factors of C. jejuni include the pgl locus, which confers the ability to produce N-linked glycosylation of at least 22 bacterial proteins, at least some of which appear to be important for competence, host adherence and invasion. C. jejuni secretes Campylobacter invasive antigens (Cia), which facilitate invasion. The bacteria also produce cytolethal distending toxins that participate in cell cycle control and induction of host cell apoptosis. C. jejuni also exploits different adaptation strategies in which the host factors seem to play a role for pathogenesis of this bacteria. | Campylobacter jejuni | Wikipedia | 463 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
DNA repair
In the intestines, bile functions as a defensive barrier against colonization by C. jejuni. When C. jejuni is grown in a medium containing the bile acid deoxycholic acid, a component of bile, the DNA of C. jejuni is damaged by a process involving oxidative stress. To survive, C. jejuni cells repair this DNA damage by a system employing proteins AddA and AddB that are needed for repair of DNA double-strand breaks.
C. jejuni uses homologous recombination to repair its DNA, facilitated by the AddA and AddB proteins. These proteins replace RecBCD, which is used in other bacteria like Escherichia coli. AddA and AddB are crucial for nuclease, helicase, and Chi recognition, which allow for successful homologous recombination.
When AddA and AddB are introduced into a wild C. jejuni variant, an added deletion mutant gene addAB gene is formed, which repairs DNA damaged by oxidative stress. This inclusion protects C. jejuni from deoxycholate found in bile, allowing for survival. However, the added gene is absent during growth in deoxycholate from 10 to 16 hours and may be up-regulated in response to environmental conditions. Additionally, AddAB proteins enhance C. jejuni colonization of chicken intestines.
Immune response
Campylobacter jejuni infection and eventual destruction of host cell cause the release of chemokines that cause inflammation and activate immune response cells. Inflammatory chemokines such as CXCL1, CCL3/CCL4, CCL2, and CXCL10 are upregulated, further triggering the immune response. The immune response activation is primarily driven by the use of ADP-heptoses to activate ALPK1, by a C. jejuni infection | Campylobacter jejuni | Wikipedia | 401 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Neutrophil granulocytes use phagocytosis to combat C. jejuni infection, releasing antimicrobial proteins and proinflammatory substances. However, C. jejuni can influence the differentiation process of specific types of neutrophil granulocytes, triggering hypersegmentation and increased reactivity, which leads to delayed apoptosis and higher production of reactive oxygen species. In experimental processes, T cells from an immune response only start to grow in number at the inflammation site from the seventh day after infection.
After 11 days of having a Campylobacter jejuni infection, the B lymphocytes in the body increase the production of antibodies that specifically fight against C. jejuni flagellin. The persistence of these antibodies in the body can last up to one-year post-infection. In this case, the development of Guillain-Barré syndrome (GBS) is associated with autoimmune IgG1 antibodies.
Campylobacter infections often precede GBS, indicating that molecular mimicry between the bacteria and host nervous tissues may be the underlying cause. C. jejuni , the most common causative agent of human campylobacteriosis, can survive in the gut for several days but does not establish a long-term infection due to its low replication rate, which is incompatible with a persistent bacterial presence. The bacteria-induced apoptosis of infected gut cells results in the rapid clearance of the pathogen, which likely contributes to the self-limiting nature of the disease. | Campylobacter jejuni | Wikipedia | 321 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Sources
Campylobacter jejuni is commonly associated with poultry, and it naturally colonises the digestive tract of many bird species. All types of poultry and wild birds can become colonized with campylobacter. One study found that 30% of European starlings in farm settings in Oxfordshire, United Kingdom, were carriers of C. jejuni. It is also common in cattle, and although it is normally a harmless commensal of the gastrointestinal tract in these animals, it can cause campylobacteriosis in calves. It has also been isolated from wombat and kangaroo feces, being a cause of bushwalkers' diarrhea. Contaminated drinking water and unpasteurized milk provide an efficient means for distribution. Contaminated food is a major source of isolated infections, with incorrectly prepared meat and poultry as the primary source of the bacteria. Moreover, surveys show that 20 to 100% of retail chickens are contaminated. This is not overly surprising, since many healthy chickens carry these bacteria in their intestinal tracts and often in high concentrations, up to 108 cfu/g. The bacteria contaminate the carcasses due to poor hygiene during the slaughter process. Several studies have shown increased concentrations of campylobacter on the carcasses after the evisceration. Studies have investigated the chicken microbiome to understand how, why and when campylobacter appears within the chicken gut. The impact of industrial system production systems on the chicken gut microbiome and campylobacter prevalence has also been investigated.
Raw milk is also a source of infections. The bacteria are often carried by healthy cattle and by flies on farms. Unchlorinated water may also be a source of infections. However, properly cooking chicken, pasteurizing milk, and chlorinating drinking water kill the bacteria. While salmonella is transmitted vertically in eggs, campylobacter is not. Therefore, consumption of eggs does result in human infection from campylobacter. | Campylobacter jejuni | Wikipedia | 412 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Complications
Local complications of campylobacter infections occur as a result of direct spread from the gastrointestinal tract and can include cholecystitis, pancreatitis, peritonitis, and massive gastrointestinal hemorrhage. Extraintestinal manifestations of campylobacter infection are quite rare and may include meningitis, endocarditis, septic arthritis, osteomyelitis, and neonatal sepsis. Bacteremia is detected in <1% of patients with campylobacter enteritis and is most likely to occur in patients who are immunocompromised or among the very young or very old. Transient bacteremia in immunocompetent hosts with C. jejuni enteritis may be more common but not detected because the killing action rapidly clears most normal human serotypes, and blood cultures are not routinely performed for patients with acute gastrointestinal illness.
Serious systemic illness caused by campylobacter infection rarely occurs, but can lead to sepsis and death. The case-fatality rate for campylobacter infection is 0.05 per 1000 infections. For instance, one major possible complication that C. jejuni can cause is Guillain–Barré syndrome, which induces neuromuscular paralysis in a sizeable percentage of those who suffer from it. Over time, the paralysis is typically reversible to some extent; nonetheless, about 20% of patients with GBS are left disabled, and around 5% die. Another chronic condition that may be associated with campylobacter infection is reactive arthritis. Reactive arthritis is a complication strongly associated with a particular genetic make-up. That is, persons who have the human leukocyte antigen B27 (HLA-B27) are most susceptible. Most often, the symptoms of reactive arthritis will occur up to several weeks after infection.
Epidemiology
Frequency | Campylobacter jejuni | Wikipedia | 402 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
United States
An estimated 2 million cases of campylobacter enteritis occur annually, accounting for 5–7% of cases of gastroenteritis. Campylobacter has a large animal reservoir, with up to 100% of poultry, including chickens, turkeys, and waterfowl, having asymptomatic intestinal infections. The major reservoirs of C. fetus are cattle and sheep. More than 90% of campylobacter infections occur during the summer months due to undercooked meats from outdoor cooking. Nonetheless, the incidence of campylobacter infections has been declining. Changes in the incidence of culture-confirmed Campylobacter infections have been monitored by the Foodborne Diseases Active Surveillance Network (FoodNet) since 1996. In 2010, campylobacter incidence showed a 27% decrease compared with 1996–1998. In 2010, the incidence was 13.6 cases per 100,000 population, and this did not change significantly compared with 2006–2008.
Europe
In 2020, there were around 120,000 cases of C. jejuni infection, which showed a decline of about 25.4% compared to the previous year. However, the COVID-19 pandemic may have influenced this decrease, and its statistical significance is yet to be determined. C. jejuni infections tend to peak in July, which could be linked to the rise in temperature worldwide. This pattern is associated with an increased reflection rate of the bacteria, which needs further investigation to establish any potential correlations.
Globally
Campylbacter jejuni infections are extremely common worldwide, although exact figures are not available. New Zealand reported the highest national rate, which peaked in May 2006 at 400 per 100,000 population. C. jejuni infection is a significant global health issue, with infection rates ranging from 0.3 to 2.9%. It is a widespread infection that affects individuals of all ages but is more prevalent in developing countries. In these areas, diarrhea is the most common clinical presentation, and it has a severe impact on children.
Sex
Campylobacter is more frequently isolated in males than females, and homosexual men appear to have a higher risk of infection by atypical campylobacter-related species such as Helicobacter cinaedi and Helicobacter fennelliae. | Campylobacter jejuni | Wikipedia | 484 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Age
Campylobacter infections can occur in all age groups. Studies show a peak incidence in children younger than 1 year and in people aged 15–29 years. The age-specific attack rate is highest in young children. In the United States, the highest incidence of Campylobacter infection in 2010 was in children younger than 5 years and was 24.4 cases per 100,000 population. Community based studies done in developing countries show about 60,000 out of every 100,000 children under five years old are affected by campylobacter infections. However, the rate of fecal cultures positive for campylobacter species is greatest in adults and older children.
Diagnosis
Diagnostic tests are available to identify campylobacter infections, including those caused by C. jejuni. The stool culture is considered the gold standard for diagnosing C. jejuni, and selective culture techniques are used to distinguish it from other variants. Stool cultures are grown at 42 degrees Celsius in an atmosphere of 85% N2, 10% CO2, and 5% O2, as C. jejuni requires these conditions due to being thermophilic and microaerophilic. A final diagnosis from a stool sample requires a gram stain or phase contrast microscopy.
Aside from stool cultures, C. jejuni can be detected using enzyme immunoassay (EIA) or polymerase chain reaction (PCR). These methods are more sensitive than stool cultures, but PCR tends to be the most sensitive especially in children and developing countries.
Treatment
Campylobacter infections tend to be mild, requiring only hydration and electrolyte repletion while diarrhea lasts. Maintenance of electrolyte balance, not antibiotic treatment, is the cornerstone of treatment for campylobacter enteritis. Depending on the degree of dehydration, alternate measures may be taken including parenteral methods of hydration. Indeed, most patients with this infection have a self-limited illness and do not require antibiotics at all; however, they may be the best form of treatment in more severe cases of infection. | Campylobacter jejuni | Wikipedia | 439 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Antibiotic treatment
Antibiotic treatment for Campylobacter infections is usually not required nor recommended. Antibiotics are limited for treating high-risk patients including immunocompromised and older individuals. Severe cases exhibiting symptoms such as bloody stools, fever, severe abdominal pain, pregnancy, infection with HIV, and prolonged illness (symptoms that last > 1 week) may also require treatment by antibiotics which can help to shorten the duration of the symptoms. It is advisable to treat these infections with macrolide antibiotics, such as erythromycin or azithromycin. Erythromycin is inexpensive and limits toxic exposure to patients, however resistance rates are reportedly increasing; its use is continued however, as resistance rates remain below 5%. Azithromycin usage is increasing due to various drug characteristics, including its once-a-day dosage, tolerability by patients, decreased relation to Infantile hypertrophic pyloric stenosis (IHPS), and less negative symptoms; this is comparative to erythromycin. Fluoroquinolones are another source of treatment, however resistance rates of bacteria to this type of antibiotic is greatly increasing. | Campylobacter jejuni | Wikipedia | 244 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Antibiotic resistance
Fluoroquinolones were first approved as a treatment for campylobacter infections in 1986, and were later U.S. Food and Drug Administration (FDA) approved in 1996, so as to control infections in poultry flocks. The CDC began monitoring campylobacter in 1997 in the National Antimicrobial Resistance Monitoring System (NARMS). Data from NARMS indicated ciprofloxacin, a fluoroquinolone, had microbial resistance rates of 17% in 1997–1999, which further increased to 27% in 2015–2017. On September 12, 2005, the FDA suspended the use of all fluoroquinolones in poultry production, and the prevalence of campylobacter strains that are fluoroquinolone resistant in poultry flocks, poultry products, production facilities, and human infections became vital to monitor; this was in an effort to determine if the fluoroquinolone ban led to a reduction in the antibiotic-resistant strains. A presence of drug-resistance to ciprofloxacin has been observed in isolate studies, as well as significant drug-resistance among campylobacter to the antibiotics nalidixic acid and tetracyclines. There is a low rate of resistance to erythromycin, the preferred source of antibiotic treatment for campylobacter infections, however resistant strains have been detected in many countries among sources of the origin of food from farm animals.
Prevention
Some simple food-handling practices can help prevent campylobacter infections.
Cook all poultry products thoroughly. Make sure that the meat is cooked throughout (no longer pink) and any juices run clear. All poultry should be cooked to reach a minimum internal temperature of .
Wash hands with soap before preparing food.
Wash hands with soap after handling raw foods of animal origin and before touching anything else.
Prevent cross-contamination in the kitchen by using separate cutting boards for foods of animal origin and other foods and by thoroughly cleaning all cutting boards, countertops, and utensils with soap and hot water after preparing raw food of animal origin.
Do not drink unpasteurized milk or untreated surface water.
Make sure that people with diarrhea, especially children, wash their hands carefully and frequently with soap to reduce the risk of spreading the infection.
Wash hands with soap after contact with pet feces.
Laboratory characteristics | Campylobacter jejuni | Wikipedia | 492 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Under light microscopy, C. jejuni has a characteristic "sea-gull" shape as a consequence of its helical form. Campylobacter is grown on specially selective "CAMP" agar plates at 42 °C, the normal avian body temperature, rather than at 37 °C, the temperature at which most other pathogenic bacteria are grown. Since the colonies are oxidase positive, they usually only grow in scanty amounts on the plates. Microaerophilic conditions are required for luxurious growth. A selective blood agar medium (Skirrow's medium) can be used. Greater selectivity can be gained with an infusion of a cocktail of antibiotics: vancomycin, polymixin-B, trimethoprim, and actidione (Preston's agar), and growth under microaerophilic conditions at 42 °C.
Genome
The genome of C. jejuni strain NCTC11168 was published in 2000, revealing 1,641,481 base pairs (30.6% G+C) predicted to encode 1,654 proteins and 54 stable RNA species. The genome is unusual in that virtually no insertion sequences or phage-associated sequences and very few repeat sequences are found. One of the most striking findings in the genome was the presence of hypervariable sequences. These short homopolymeric runs of nucleotides were commonly found in genes encoding the biosynthesis or modification of surface structures, or in closely linked genes of unknown function. The apparently high rate of variation of these homopolymeric tracts may be important in the survival strategy of C. jejuni. The genome was re-annotated in 2007 updating 18.2% of product functions. Analysis also predicted the first pathogenicity island in C. jejuni among select strains, harbouring the bacteria's Type VI secretion system and putative cognate effectors.
Initial transposon mutagenesis screens revealed 195 essential genes, although this number is likely to go up with additional analysis. | Campylobacter jejuni | Wikipedia | 427 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Natural genetic transformation
C. jejuni is naturally competent for genetic transformation. Natural genetic transformation is a sexual process involving DNA transfer from one bacterium to another through the intervening medium, and the integration of the donor sequence into the recipient genome by homologous recombination. C. jejuni freely takes up foreign DNA harboring genetic information responsible for antibiotic resistance. Antibiotic resistance genes are more frequently transferred in biofilms than between planktonic cells (single cells that float in liquid media). | Campylobacter jejuni | Wikipedia | 102 | 571816 | https://en.wikipedia.org/wiki/Campylobacter%20jejuni | Biology and health sciences | Gram-negative bacteria | Plants |
Tencent QQ (), also known as QQ, is an instant messaging software service and web portal developed by the Chinese technology company Tencent. QQ offers services that provide online social games, music, shopping, microblogging, movies, and group and voice chat software. As of March 2023, there were 597 million monthly active QQ accounts.
History
Tencent QQ was first released in China in February 1999 under the name of OICQ ("Open ICQ", a reference to the early IM service ICQ).
After the threat of a trademark infringement lawsuit by the AOL-owned ICQ, the product's name was changed to QQ (with "Q" and "QQ" used to imply "cute"). The software inherited existing functions from ICQ, and additional features such as software skins, people's images, and emoticons. QQ was first released as a "network paging" real-time communications service. Other features were later added, such as chatrooms, games, personal avatars (similar to "Meego" in MSN), online storage, and Internet dating services.
The official client runs on Microsoft Windows and a beta public version was launched for Mac OS X version 10.4.9 or newer. Formerly, two web versions, WebQQ (full version) and WebQQ Mini (Lite version), which made use of Ajax, were available. Development, support, and availability of WebQQ Mini, however, has since been discontinued. On 31 July 2008, Tencent released an official client for Linux, but this has not been made compatible with the Windows version and it is not capable of voice chat.
In response to competition with other instant messengers, such as Windows Live Messenger, Tencent released Tencent Messenger, which is aimed at businesses. | Tencent QQ | Wikipedia | 381 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
Membership
In 2002, Tencent stopped its free membership registration, requiring all new members to pay a fee. In 2003, however, this decision was reversed due to pressure from other instant messaging services such as Windows Live Messenger and Sina UC.
Tencent currently offers a premium membership scheme, where premium members enjoy features such as QQ mobile, ringtone downloads, and SMS sending/receiving. In addition, Tencent offers "Diamond" level memberships. Currently, there are seven diamond schemes available:
Red for the QQ Show service which features some superficial abilities such as having a colored account name.
Yellow to obtain extra storage and decorations in Qzone—a blog service.
Blue to obtain special abilities in the game-plays of QQ games.
Purple for obtaining special abilities in games including QQ Speed, QQ Nana, and QQ Tang
Pink for having different boosts in the pet-raising game called QQ Pet.
Green for using QQ music—a service for users to stream music online.
VIP for having extra features in the chat client such as removing advertisements
Black for gaining benefits related to DNF (Dungeon & Fighter), a multiplayer PC beat 'em up video game.
QQ Coin
The QQ Coin is a virtual currency used by QQ users to "purchase" QQ related items for their avatar and blog. QQ Coins are obtained either by purchase (one coin for one RMB) or by using the mobile phone service. Due to the popularity of QQ among young people in China, QQ Coins are accepted by online vendors in exchange for "real" merchandise such as small gifts. This has raised concerns of replacing (and thus "inflating") real currency in these transactions.
The People's Bank of China, China's central bank, tried to crack down on QQ Coins due to people using QQ Coins in exchange for real world goods. However, this only caused the value of QQ coins to rise as more and more third-party vendors started to accept them. Tencent claims the QQ Coin is a mere regular commodity, and is, therefore, not a currency.
Q Zone
Qzone is a social networking website based in China which was created by Tencent in 2005. Q Zone is a personal blog for QQ users. It can be set as a public page or a private friend-only page. Users can upload diaries and share photos.
QQ International
Windows | Tencent QQ | Wikipedia | 494 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
In 2009, QQ began to expand its services internationally with its QQ International client for Windows distributed through a dedicated English-language portal.
QQ International offers non-Mandarin speakers the opportunity to use most of the features of its Chinese counterpart to get in touch with other QQ users via chat, VoIP, and video calls, and it provides a non-Mandarin interface to access Qzone, Tencent's social network. The client supports English, French, Spanish, German, Korean, Japanese and Traditional Chinese.
One of the main features of QQ International is the optional and automatic machine translation in all chats.
Android
An Android version of QQ International was released in September 2013. The client's interface is in English, French, Spanish, German, Korean, Japanese and Traditional Chinese. In addition to text messaging, users can send each other images, videos, and audio media messages. Moreover, users can share multimedia content with all contacts through the client's Qzone interface.
The live translation feature is available for all incoming messages and supports up to 18 languages.
iOS
QQ International for iPhone and iOS devices was released at the end of 2013, fully equivalent to its Android counterpart.
Partnerships
In India, Tencent has partnered with ibibo to bring services such as chat, mail and game to the developing Indian internet sphere.
In Vietnam, Tencent has struck a deal with VinaGame to bring the QQ Casual Gaming portal as well as the QQ Messenger as an addition to the already thriving Vietnamese gaming communities.
In the United States, Tencent has partnered with AOL to bring QQ Games as a contender in the US social gaming market. Launched in 2007, QQ Games came bundled with the AIM installer, and competed with AOL's own games.com to provide a gaming experience for the AIM user base.
Web QQ
Tencent launched its web-based QQ formally on 15 September 2009, the latest version of which being 3.0. Rather than solely a web-based IM, WebQQ 3.0 functions more like its own operating system, with a desktop in which web applications can be added. | Tencent QQ | Wikipedia | 436 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
Social network website
In 2009, Tencent launched Xiaoyou (校友, 'schoolmate'), its first social network website. In mid-2010, Tencent changed direction and replaced Xiaoyou with Pengyou (朋友, 'friends'), trying to establish a more widespread network, to which extant QQ users could be easily redirected, hence giving Pengyou a major advantage over its competitors. Tencent's social network Qzone is linked to in the International and native versions of QQ.
Open source and cross-platform clients
Using reverse engineering, open source communities have come to understand the QQ protocol better and have attempted to implement client core libraries compatible with more user-friendly clients, free of advertisements. Most of these clients are cross-platform, so they are usable on operating systems which the official client does not support. However, these implementations had only a subset of functions of the official client and therefore were limited in features. Furthermore, QQ's parent company, Tencent, has over successive versions modified the QQ protocol to the extent that it can no longer be supported by most, and perhaps any, of the third-party implementations that were successful in the past (some of which are listed below). As of 2009, none of the developers of third-party clients have publicized any plans to restore QQ support.
Pidgin, an open source cross-platform multiprotocol client, with third-party plugin
Adium, an open source macOS client, with third-party plugin built on top of libqq-pidgin
Kopete, an open source multiprotocol client by KDE
Note: Kopete, old versions of Pidgin, and any other client whose QQ support was based on libpurple no longer supports QQ as of May 2011
Miranda NG, an open source multiprotocol client, designed for Microsoft Windows, with MirandaQQ2 plugin.
Eva
Merchandise
Tencent has taken advantage of the popularity of the QQ brand and has set up many Q-Gen stores selling QQ branded merchandise such as bags, watches, clothing as well as toy penguins. | Tencent QQ | Wikipedia | 444 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
Related characteristics
The accounts of QQ are purely a combination of numbers. The account numbers provided for the registered users are selected randomly by the system user registration. In 1995, the registered QQ accounts had only 5 digits, while currently, the digital numbers used for QQ accounts has reached 12. The first QQ number is held by Ma Huateng and his account number is 10001.
Membership to a QQ account usually lasts one month. When this membership is overdue and not renewed, the membership of the account will be suspended.
In relation to calculating "QQ Age", being logged in for 2 full hours would be considered as one full day. Thus, being logged in to QQ for around 700 hours would make the age increase by 1 year. In the 2012 version of QQ, users can see the age on the personal information page.
In 2004, Tencent launched QQ hierarchy which shows the level of a registered member. At the very beginning, this hierarchy was solely based on the hours a member spent in QQ. Hence, the longer the member stayed, the higher level they can attain. These results, however, were criticized as people tend to waste electrical energy due to longer hours of stay on the site. Therefore, Tencent changed the basis from an hour unit to a daily unit due to the involvement of several departments.
Controversies and criticisms
Coral QQ
Coral QQ, a modification of Tencent QQ, is another add-on for the software, providing free access to some of the services and blocking Tencent's advertisements. In 2006, Tencent filed a copyright lawsuit against Chen Shoufu (aka Soft), the author of Coral QQ, after his distribution of a modified Tencent QQ was ruled illegal. Chen then published his modification as a separate add-on. On 16 August 2007, Chen was detained again for allegedly making profits off of his ad-blocking add-on. The case resulted in a three-year prison sentence for Shoufu.
Dispute with Qihoo 360 | Tencent QQ | Wikipedia | 413 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
In 2010, Chinese anti-virus company, Qihoo 360, analyzed the QQ protocol and accused QQ of automatically scanning users' computers and uploading their personal information to QQ's servers without the users' consent. In response, Tencent called 360 a malware and denied users of installing 360 access to some of the QQ's services. The Chinese Ministry of Industry and Information reprimanded both companies for "improper competition" and ordered them to come to an agreement.
Government surveillance
Some observers have criticized QQ's compliance in the Chinese government's Internet surveillance and censorship. A 2013 report by Reporters Without Borders specifically mentioned QQ as allowing authorities to monitor online conversations for keywords or phrases and track participants by their user number.
Adware controversy
The Chinese version of QQ makes use of embedded advertisements. Older versions of the client have been branded as malicious adware by some antivirus and anti-spyware vendors.
Both the Chinese and International versions of QQ had been tested in 2013. Currently it is identified as malware by DrWeb, Zillya, NANO-Antivirus, and VBA32 give positive results, most of which identify it as a trojan.
Security
On March 6, 2015, QQ scored 2 out of 7 points on the Electronic Frontier Foundation's secure messaging scorecard. It received points for having communications encrypted in transit and for having a recent independent security audit. It lost points because communications are not end-to-end encrypted, users can not verify contacts' identities, past messages are not secure if the encryption keys are stolen (i.e. the service does not provide forward secrecy), the code is not open to independent review (i.e. the code is not open-source), and the security design is not properly documented. | Tencent QQ | Wikipedia | 374 | 571903 | https://en.wikipedia.org/wiki/Tencent%20QQ | Technology | Social network and blogging | null |
Cottontail rabbits are in the Sylvilagus genus, which is in the Leporidae family. They are found in the Americas. Most Sylvilagus species have stub tails with white undersides that show when they retreat, giving them their characteristic name. However, this feature is not present in all Sylvilagus, nor is it unique to the genus.
The genus is widely distributed across North America, Central America, and northern and central South America, though most species are confined to some particular regions. Most species live in nests called forms, and all have altricial young. An adult female averages three litters per year, which can occur in any season. Occurrence and litter size depend on several factors, including time of the year, weather, and location. The average litter size is four, but can range from as few as two to as many as eight, most of whom do not go on to survive to adulthood.
Cottontail rabbits show a greater resistance to myxomatosis than European rabbits.
Evolution
Cottontails are one of several species of Sylvilagus. Their closest relative is Brachylagus, the pygmy rabbit. They are more distantly related to the European and other rabbits, and more distantly still to the hares. The cladogram is based on mitochondrial gene analysis.
Lifespan
The lifespan of a cottontail averages about two years, depending on the location. Almost every living carnivorous creature comparable to or larger in size than these lagomorphs is a potential predator, including such diverse creatures as domestic dogs, cats, humans, snakes, coyotes, mountain lions, foxes, and if the cottontail is showing signs of illness, even squirrels. The cottontail's most frequent predators are various birds of prey. Cottontails can also be parasitized by botfly species including Cuterebra fontinella. Newborn cottontails are particularly vulnerable to these attacks. Cottontails use burrows vacated by other animals, and the burrows are used for long enough periods that predators can learn where the cottontails reside and repeatedly return to prey on the lagomorphs. Though cottontails are prolific animals that can have multiple litters in a year, few of the resulting offspring survive to adulthood. Those that do survive grow very quickly and are full grown adults at three months. | Cottontail rabbit | Wikipedia | 476 | 571933 | https://en.wikipedia.org/wiki/Cottontail%20rabbit | Biology and health sciences | Lagomorphs | Animals |
Eating mechanics
In contrast to rodents (squirrels, etc.), which generally sit on their hind legs and hold food with their front paws while feeding, cottontail rabbits eat while on all fours. Cottontail rabbits typically only use their nose to move and adjust the position of the food that it places directly in front of its front paws on the ground. The cottontail will turn the food with its nose to find the cleanest part of the vegetation (free of sand and inedible parts) to begin its meal. The only time a cottontail uses its front paws while feeding is when vegetation is above its head on a living plant, at which point the cottontail will lift its paw to bend the branch to bring the food within reach.
Cottontails are rarely found foraging for food on windy days, because the wind interferes with their hearing capabilities. Hearing an incoming predator before they get close enough to attack is their primary defense mechanism.
Species
The subgenera were described in the 19th century based on limited morphological data that have been shown to not be of great use, nor to depict phylogenetic relationships. Molecular studies (limited in scope to the mitochondrial 12S gene) have shown that the currently accepted subgeneric structure, while of some heuristic value, is unlikely to withstand additional scrutiny.
Prehistoric species
Sylvilagus hibbardi (Early-Mid Pleistocene)
Sylvilagus leonensis - Dwarf cottontail (Late Pleistocene)
Sylvilagus webbi (Pleistocene) | Cottontail rabbit | Wikipedia | 301 | 571933 | https://en.wikipedia.org/wiki/Cottontail%20rabbit | Biology and health sciences | Lagomorphs | Animals |
Pointing dogs, sometimes called bird dogs, are a type of gundog typically used in finding game. Gundogs are traditionally divided into three classes: retrievers, flushing dogs, and pointing breeds. The name pointer comes from the dog's instinct to point, by stopping and aiming its muzzle towards game. This demonstrates to the hunter the location of their quarry and allows them to move into gun range. Pointers were selectively bred from dogs who had abundant pointing and backing instinct. They typically start to acquire their hunting instincts at about 2 months of age.
History
Pointing dogs may have descended from dogs from Spain, specifically of the Old Spanish Pointer (Furgus, 2002). Pointing dogs were originally used by hunters who netted the game. The dog would freeze or set (as in Setter) and allow the hunter to throw the net over the game before it flushed. Flushing dogs, on the other hand, were often used by falconers to flush game for the raptors. Most continental European pointing breeds are classified as versatile gun dog breeds or sometimes HPR breeds (for hunt, point, and retrieve). The distinction is made because versatile breeds were developed to find and point game as all pointing breeds, but were also bred to perform other hunting tasks as well. This distinction likely arose because while the British developed breeds which specialized in tasks such as pointing, flushing, and retrieving from land or water, in Continental Europe, the same dog was trained to be able to perform each of these tasks (albeit less effectively). The North American Versatile Hunting Dog Association defines versatility as "the dog that is bred and trained to dependably hunt and point game, to retrieve on both land and water, and to track wounded game on both land and water." As an example, German Shorthaired Pointers are often used to retrieve birds, i.e. duck hunting, whereas calling upon a Pointer to do the same would be less common. Unlike the pure pointing and setting breeds, many versatile dogs were bred for working in dense cover, and traditionally have docked tails.
The Westminster Kennel Club was organized in the early 1870s, and the club's early English import, "Sensation", is still used as the club logo.
Appearance
Pointing dogs come in all varieties of coats, from short-haired dogs, to wire-haired dogs, to silky-coated Setters. Most breeds tend to have some sort of spots on their body, whether the spots are small and round, or a large oval shape.
Breeds | Pointing dog | Wikipedia | 509 | 571970 | https://en.wikipedia.org/wiki/Pointing%20dog | Biology and health sciences | Dogs | Animals |
Pointers (and setters) include the following breeds:
English Setter
Gordon Setter
Irish Red and White Setter
Irish Setter
Pointer
The following breeds are also considered versatile hunting dogs:
Ariège Pointer
Bracco Italiano
Braque d'Auvergne
Braque du Bourbonnais
Braque Dupuy (extinct)
Braque Français (two sizes: larger type Gascogne and Braque Français and smaller type Pyrénées)
Braque Saint-Germain
Brittany
Burgos Pointer
Český Fousek
French Spaniel
German Longhaired Pointer
German Roughhaired Pointer
German Shorthaired Pointer
German Wirehaired Pointer
Large Münsterländer
Labrador Retriever
Old Danish Pointer
Pachón Navarro
Perdigueiro Galego
Portuguese Pointer
Pudelpointer
Slovak Rough-haired Pointer
Small Münsterländer
Spinone Italiano
Stabyhoun
Vizsla
Weimaraner
Wirehaired Pointing Griffon
Wirehaired Vizsla | Pointing dog | Wikipedia | 182 | 571970 | https://en.wikipedia.org/wiki/Pointing%20dog | Biology and health sciences | Dogs | Animals |
A hairbrush is a brush with rigid (hard or inflexible) or light and soft spokes used in hair care for smoothing, styling, and detangling human hair, or for grooming an animal's fur. It can also be used for styling in combination with a curling iron or hair dryer.
A brush is normally used for detangling hair, for example after sleep or showering. A round brush can be used for styling and curling hair, especially by a professional stylist, often with a hair dryer. A paddle brush is used to straighten hair and tame fly-aways. For babies with fine, soft hair, many bristle materials are not suitable due to the hardness; some synthetic materials and horse/goat hair bristles are used instead.
Animal use
Special brushes are made for cats, dogs and horses. Two different brushes can be made specifically for either short hairy pets, or long haired pets. For an equine's tougher hair, a curry-comb is used.
Types
Various types of brushes are used for different purposes, or have special features that are beneficial to certain hair types. For example:
Round brush: Usually used with a blow dryer to add fullness and movement to the hair. Some have a metal or ceramic base which is designed to heat up during blow drying.
Vent brush: Vents allow more air flow between the bristles but does not affect the drying time.
Cushion brush: Bristles are mounted on a rubber cushion or mat for added flexibility, to minimize hair breakage during detangling.
Paddle brush: A wide base allows more exposure while blow drying; flexible teeth are designed to minimize breakage, though some believe it does not work.
Detangler brush: Features such as widely spaced, flexible, nylon teeth are designed to be gentle on tangled or knotted hair.
Boar bristle brush: Tightly spaced boar-hair bristles are designed to increase tension while brushing, to smooth the hair.
Blow Dryer Attachment: An additional tool that can be attached to a hair blow dryer to brush and dry hair at the same time.
The effects of brushing will be different depending texture and whether the hair is wet or dry. Straight hair typically looks smoother when brushed. Curly hair tends to expand when brushed while dry. | Hairbrush | Wikipedia | 466 | 572393 | https://en.wikipedia.org/wiki/Hairbrush | Biology and health sciences | Hygiene products | Health |
Materials
Common materials used for the handle are ebony, rosewood, New Guinea rosewood, beech, ABS plastic and polyacetal. Common materials used for bristles include boar bristle, horsehair, nylon, stainless steel and goat hair.
United States history
The earliest U.S. patent for a modern hairbrush was by Hugh Rock in 1854.
A brush with elastic wire teeth along with natural bristles, was patented by Samuel Firey in 1870 as . In 1898, Lyda D. Newman invented an "Improved Hairbrush", which allowed for easy cleaning and had bristles separated wide enough to allow for easily combing. She was awarded . | Hairbrush | Wikipedia | 131 | 572393 | https://en.wikipedia.org/wiki/Hairbrush | Biology and health sciences | Hygiene products | Health |
The vicuña (Lama vicugna) or vicuna (both , very rarely spelled vicugna, its former genus name) is one of the two wild South American camelids, which live in the high alpine areas of the Andes; the other camelid is the guanaco, which lives at lower elevations. Vicuñas are relatives of the llama, and are now believed to be the wild ancestor of domesticated alpacas, which are raised for their coats. Vicuñas produce small amounts of extremely fine wool, which is very expensive because the animal can only be shorn every three years and has to be caught from the wild. When knitted together, the product of the vicuña's wool is very soft and warm. The Inca valued vicuñas highly for their wool, and it was against the law for anyone but royalty to wear vicuña garments; today, the vicuña is the national animal of Peru and appears on the Peruvian coat of arms.
Both under the rule of the Inca and today, vicuñas have been protected by law, but they were heavily hunted in the intervening period. When they were declared endangered in 1974, only about 6,000 animals were left. Today, the vicuña population has recovered to about 350,000, and although conservation organizations have reduced its level of threat classification, they still call for active conservation programs to protect populations from poaching, habitat loss, and other threats.
Previously, the vicuña was not considered domesticated, and the llama and the alpaca were regarded as descendants of the closely related guanaco. However, DNA research published in 2001 has demonstrated that the alpaca may have vicuña parentage. Today, the vicuña is mainly wild, but the local people still perform special rituals with these creatures, including a fertility rite. | Vicuña | Wikipedia | 369 | 572518 | https://en.wikipedia.org/wiki/Vicu%C3%B1a | Biology and health sciences | Artiodactyla | null |
Description
The vicuña is considered more delicate and gracile than the guanaco and smaller. A key distinguishing element of morphology is the better-developed incisor roots for the guanaco. The vicuña's long, woolly coat is tawny brown on the back, whereas the hair on the throat and chest is white and quite long. Its head is slightly shorter than guanaco's, and the ears are slightly longer. The length of the head and body ranges from 1.45 to 1.60 m (about 5 ft); shoulder height is from 75 to 85 cm (around 3 ft); its weight is from 35 to 65 kg (under 150 lb). It falls prey to the cougar and culpeo.
Taxonomy and evolution
There are two subspecies of vicuña:
Lama vicugna vicugna
Lama vicugna mensalis
While vicuñas are restricted to the more extreme elevations of the Andes in modern times, they may have also been present in the lowland regions of Patagonia as much as 3500 km south of their current range during the Late Pleistocene and Early Holocene. Fossils of these lowland camelids have been assigned to a species known as Lama gracilis, but genetic and morphological analysis between them and modern vicuña indicate the two may be the same.
Distribution and habitat
Vicuñas are native to South America's central Andes. They are found in Peru, northwestern Argentina, Bolivia, and northern Chile. A smaller, introduced population lives in central Ecuador.
Vicuñas live at altitudes of . They feed in the daytime on the grassy plains of the Andes Mountains but spend the nights on the slopes. In these areas, only nutrient-poor, tough, bunch grasses and Festuca grow. The sun's rays can penetrate the thin atmosphere, producing relatively warm temperatures during the day; however, the temperatures drop to freezing at night. The vicuña's thick but soft coat is a unique adaptation that traps layers of warm air close to its body to tolerate freezing temperatures.
Chief predators include pumas and the culpeo.
Behavior | Vicuña | Wikipedia | 426 | 572518 | https://en.wikipedia.org/wiki/Vicu%C3%B1a | Biology and health sciences | Artiodactyla | null |
The behavior of vicuñas is similar to that of the guanacos. They are timid animals and are easily aroused by intruders due, among other things, to their extraordinary hearing. Like the guanacos, they frequently lick calcareous stones and rocks, which, together with salt water, is its source of salt. Vicuñas are clean animals and always deposit their excrement in the same place. Their diets consist mainly of low grasses which grow in clumps on the ground.
Vicuñas live in family-based groups of a male, 5 to 15 females, and their young. Each group has its territory of about , which can fluctuate depending on food availability.
Mating usually occurs in March–April. After a gestation about 11 months, the female gives birth to a single fawn, which is nursed for about ten months. The fawn becomes independent at about 12 to 18 months old. Young males form bachelor groups, and the young females search for a sorority to join. This deters intraspecific competition and inbreeding.
Conservation
Until 1964, hunting of the vicuña was unrestricted, which reduced its numbers to only 6,000 in the 1960s. As a result, the species was declared endangered in 1974, and its status prohibited the trade of vicuña wool. In Peru, during 1964–1966, the Servicio Forestal y de Caza in cooperation with the US Peace Corps, Nature Conservancy, World Wildlife Fund, and the National Agrarian University of La Molina established a nature conservatory for the vicuña called the Pampa Galeras – Barbara D'Achille in Lucanas Province, Ayacucho. During that time, a game warden academy was held in Nazca, where eight men from Peru and six from Bolivia were trained to protect the vicuña from poaching. | Vicuña | Wikipedia | 379 | 572518 | https://en.wikipedia.org/wiki/Vicu%C3%B1a | Biology and health sciences | Artiodactyla | null |
To cooperate on the conservation of the vicuña, the governments of Bolivia and Peru signed the Convention for the Conservation of the Vicuña on 16 August 1969 in La Paz, explicitly leaving the treaty open to accession by Argentina and Chile. Ecuador acceded on 11 February 1976. The Convention prohibited their international trade and domestic exploitation, and ordered the parties to create reserves and breeding centres. A follow-up treaty, the Convention for the Conservation and Management of the Vicuña, was signed between Bolivia, Chile, Ecuador and Peru on 20 December 1979 in Lima. It explicitly allowed only Argentina to sign it if it also signed the 1969 La Paz Convention (Article 12; Argentina joined in 1981), and did not allow other countries to accede to the convention 'due to its specific character' (Article 13). The 1979 Convention did allow the use of the vicuña under strict circumstances if the animal population had recovered sufficiently. In combination with CITES (effective in 1975), as well as USA and EU trade legislation, the Conventions were highly successful, as the vicuña population substantially grew as a result.
The estimated population in Peru was 66,559 in 1994, 103,161 in 1997, 118,678 in 2000, and 208,899 in 2012. Currently, the community of Lucanas conducts a chaccu (herding, capturing, and shearing) on the reserve each year to harvest the wool, organized by the National Council for South American Camelids (CONACS).
In Bolivia, the Ulla Ulla National Reserve was founded 1977 partly as a sanctuary for the species. Their numbers grew to 125,000 in Peru, Chile, Argentina, and Bolivia. Since this was a ready "cash crop" for community members, the countries relaxed regulations on vicuña wool in 1993, enabling its trade once again. The wool is sold on the world market for over $300 per kg. In 2002, the US Fish and Wildlife Service reclassified most populations as threatened, but still lists Ecuador's population as endangered. While the population levels have recovered to a healthy level, poaching remains a constant threat, as do habitat loss and other threats. Consequently, the IUCN still supports active conservation programs to protect vicuñas, though they lowered their status to least concern in 2018. | Vicuña | Wikipedia | 462 | 572518 | https://en.wikipedia.org/wiki/Vicu%C3%B1a | Biology and health sciences | Artiodactyla | null |
In 2015, French luxury group LVMH said that "Loro Piana saved the species." The Italian company has been criticized for underpaying local communities collecting the wool. In 2022, the Argentine government's National Council for Scientific and Technical Investigation estimated that "Andean communities receive around 3% of the value generated by the vicuña fiber chain."
Vicuña wool
Its wool is famous for its warmth and is used for apparel, such as socks, sweaters, accessories, shawls, coats, suits, and home furnishings, such as blankets and throws. Its properties come from the tiny scales on the hollow, air-filled fibres, which causes them to interlock and trap insulating air. Vicuñas have some of the finest fibers in the world, at a diameter of 12 μm. The fiber of cashmere goats is 14 to 19 μm, while angora rabbit is 8 to 12 μm, and that of shahtoosh from the Tibetan antelope, or chiru, is from 9 to 12 μm.
Gallery | Vicuña | Wikipedia | 217 | 572518 | https://en.wikipedia.org/wiki/Vicu%C3%B1a | Biology and health sciences | Artiodactyla | null |
A physical disability is a limitation on a person's physical functioning, mobility, dexterity or stamina. Other physical disabilities include impairments which limit other facets of daily living, such as respiratory disorders, blindness, epilepsy and sleep disorders.
Causes
Prenatal disabilities are acquired before birth. These may be due to diseases or substances that the mother has been exposed to during pregnancy, embryonic or fetal developmental accidents or genetic disorders.
Perinatal disabilities are acquired between some weeks before to up to four weeks after birth in humans. These can be due to prolonged lack of oxygen or obstruction of the respiratory tract, damage to the brain during birth (due to the accidental misuse of forceps, for example) or the baby being born prematurely. These may also be caused due to genetic disorders or accidents.
Post-natal disabilities are gained after birth. They can be due to accidents, injuries, obesity, infection or other illnesses. These may also be caused due to genetic disorders.
Types
Mobility impairment includes upper or lower limb loss or impairment, poor manual dexterity, and damage to one or multiple organs of the body. Disability in mobility can be a congenital or acquired problem or a consequence of disease. People who have a broken skeletal structure also fall into this category.
Visual impairment is another type of physical impairment. There are hundreds of thousands of people with minor to various serious vision injuries or impairments. These types of injuries can also result in severe problems or diseases such as blindness and ocular trauma. Some other types of vision impairment include scratched cornea, scratches on the sclera, diabetes-related eye conditions, dry eyes and corneal graft, macular degeneration in old age and retinal detachment.
Hearing loss is a partial or total inability to hear. Deaf and hard of hearing people have a rich culture and benefit from learning sign language for communication purposes. People who are only partially deaf can sometimes make use of hearing aids to improve their hearing ability.
Speech and language disability: the person with deviations of speech and language processes which are outside the range of acceptable deviation within a given environment and which prevent full social or educational development
Physical impairment can also be attributed to disorders causing, among others, sleep deficiency, chronic fatigue, chronic pain, and seizures. | Physical disability | Wikipedia | 459 | 573313 | https://en.wikipedia.org/wiki/Physical%20disability | Biology and health sciences | Disability | null |
{{DISPLAYTITLE: C3 carbon fixation}}
carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, the other two being and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into two molecules of 3-phosphoglycerate through the following reaction:
CO2 + H2O + RuBP → (2) 3-phosphoglycerate
This reaction was first discovered by Melvin Calvin, Andrew Benson and James Bassham in 1950. C3 carbon fixation occurs in all plants as the first step of the Calvin–Benson cycle. (In and CAM plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.)
Plants that survive solely on fixation ( plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and groundwater is plentiful. The plants, originating during Mesozoic and Paleozoic eras, predate the plants and still represent approximately 95% of Earth's plant biomass, including important food crops such as rice, wheat, soybeans and barley.
plants cannot grow in very hot areas at today's atmospheric CO2 level (significantly depleted during hundreds of millions of years from above 5000 ppm) because RuBisCO incorporates more oxygen into RuBP as temperatures increase. This leads to photorespiration (also known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis), which leads to a net loss of carbon and nitrogen from the plant and can therefore limit growth.
plants lose up to 97% of the water taken up through their roots by transpiration. In dry areas, plants shut their stomata to reduce water loss, but this stops from entering the leaves and therefore reduces the concentration of in the leaves. This lowers the :O2 ratio and therefore also increases photorespiration. and CAM plants have adaptations that allow them to survive in hot and dry areas, and they can therefore out-compete plants in these areas. | C3 carbon fixation | Wikipedia | 442 | 573489 | https://en.wikipedia.org/wiki/C3%20carbon%20fixation | Biology and health sciences | Metabolic processes | Biology |
The isotopic signature of plants shows higher degree of 13C depletion than the plants, due to variation in fractionation of carbon isotopes in oxygenic photosynthesis across plant types. Specifically, plants do not have PEP carboxylase like plants, allowing them to only utilize ribulose-1,5-bisphosphate carboxylase (Rubisco) to fix through the Calvin cycle. The enzyme Rubisco largely discriminates against carbon isotopes, evolving to only bind to 12C isotope compared to 13C (the heavier isotope), contributing to more 13C depletion seen in plants compared to plants especially since the pathway uses PEP carboxylase in addition to Rubisco.
Variations
Not all C3 carbon fixation pathways operate at the same efficiency.
Refixation
Bamboos and the related rice have an improved C3 efficiency. This improvement might be due to its ability to recapture CO2 produced during photorespiration, a behavior termed "carbon refixation". These plants achieve refixation by growing chloroplast extensions called "stromules" around the stroma in mesophyll cells, so that any photorespired CO2 from the mitochondria has to pass through the RuBisCO-filled chloroplast.
Refixation is also performed by a wide variety of plants. The common approach involving growing a bigger bundle sheath leads down to C2 photosynthesis.
Synthetic glycolate pathway
C3 carbon fixation is prone to photorespiration (PR) during dehydration, accumulating toxic glycolate products. In the 2000s scientists used computer simulation combined with an optimization algorithm to figure out what parts of the metabolic pathway may be tuned to improve photosynthesis. According to simulation, improving glycolate metabolism would help significantly to reduce photorespiration. | C3 carbon fixation | Wikipedia | 386 | 573489 | https://en.wikipedia.org/wiki/C3%20carbon%20fixation | Biology and health sciences | Metabolic processes | Biology |
Instead of optimizing specific enzymes on the PR pathway for glycolate degradation, South et al. decided to bypass PR altogether. In 2019, they transferred Chlamydomonas reinhardtii glycolate dehydrogenase and Cucurbita maxima malate synthase into the chloroplast of tobacco (a model organism). These enzymes, plus the chloroplast's own, create a catabolic cycle: acetyl-CoA combines with glyoxylate to form malate, which is then split into pyruvate and CO2; the former in turn splits into acetyl-CoA and CO2. By forgoing all transport among organelles, all the CO2 released will go into increasing the CO2 concentration in the chloroplast, helping with refixation. The end result is 24% more biomass. An alternative using E. coli glycerate pathway produced a smaller improvement of 13%. They are now working on moving this optimization into other crops like wheat. | C3 carbon fixation | Wikipedia | 219 | 573489 | https://en.wikipedia.org/wiki/C3%20carbon%20fixation | Biology and health sciences | Metabolic processes | Biology |
Culling is the process of segregating organisms from a group according to desired or undesired characteristics. In animal breeding, it is removing or segregating animals from a breeding stock based on a specific trait. This is done to exaggerate desirable characteristics, or to remove undesirable characteristics by altering the genetic makeup of the population. For livestock and wildlife, culling often refers to killing removed animals based on their characteristics, such as their sex or species membership, or as a means of preventing infectious disease transmission.
In fruits and vegetables, culling is the sorting or segregation of fresh harvested produce into marketable lots, with the non-marketable lots being discarded or diverted into food processing or non-food processing activities. This usually happens at collection centres located at, or close to farms.
Etymology
The word cull comes from the Latin verb , meaning "to gather". The term can be applied broadly to mean partitioning a collection into two groups: one that will be kept and one that will be rejected. The cull is the set of items rejected during the selection process. The culling process is repeated until the selected group is of proper size and consistency desired.
Pedigreed animals
Culling is:
In the breeding of pedigreed animals, both desirable and undesirable traits are considered when choosing which animals to retain for breeding and which to place as pets. The process of culling starts with examination of the conformation standard of the animal and will often include additional qualities such as health, robustness, temperament, color preference, etc. The breeder takes all things into consideration when envisioning their ideal for the breed or goal of their breeding program. From that vision, selections are made as to which animals, when bred, have the best chance of producing the ideal for the breed.
Breeders of pedigreed animals cull based on many criteria. The first culling criterion should always be health and robustness. Secondary to health, temperament and conformation of the animal should be considered. The filtering process ends with the breeder's personal aesthetic preferences on pattern, color, etc. | Culling | Wikipedia | 433 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Tandem method
The tandem method is a form of selective breeding where a breeder addresses one characteristic of the animal at a time, thus selecting only animals that measure above a certain threshold for that particular trait while keeping other traits constant. Once that level of quality in the single trait is achieved, the breeder will focus on a second trait and cull based on that quality. With the tandem method, a minimum level of quality is set for important characteristics that the breeder wishes to remain constant. The breeder is focusing improvement in one particular trait without losing quality of the others. The breeder will raise the threshold for selection on this trait with each successive generation of progeny, thus ensuring improvement in this single characteristic of his breeding program.
For example, a breeder that is pleased with the muzzle length, muzzle shape, and eye placement in the breeding stock, but wishes to improve the eye shape of progeny produced may determine a minimum level of improvement in eye shape required for progeny to be returned into the breeding program. Progeny is first evaluated on the existing quality thresholds in place for muzzle length, muzzle shape, and eye placement with the additional criterion being improvement in eye shape. Any animal that does not meet this level of improvement in the eye shape while maintaining the other qualities is culled from the breeding program; i.e., that animal is not used for breeding, but is instead neutered and placed in a pet home.
Independent levels
Independent levels is a method where any animal who falls below a given standard in any single characteristic is not used in a breeding program. With each successive mating, the threshold culling criteria are raised thus improving the breed with each successive generation.
This method measures several characteristics at once. Should progeny fall below the desired quality in any one characteristic being measured, it will not be used in the breeding program regardless of the level of excellence of other traits. With each successive generation of progeny, the minimum quality of each characteristic is raised thus ensuring improvement of these traits.
For example, a breeder has a view of what the minimum requirements for muzzle length, muzzle shape, eye placement, and eye shape they are breeding toward. The breeder will determine what the minimum acceptable quality for each of these traits will be for progeny to be folded back into their breeding program. Any animal that fails to meet the quality threshold for any one of these criteria is culled from the breeding program. | Culling | Wikipedia | 489 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Total score method
The total score method is a selection method where the breeder evaluates and selects breeding stock based on a weighted table of characteristics. The breeder selects qualities that are most important to them and assigns them a weight. The weights of all the traits should add up to 100. When evaluating an individual for selection, the breeder measures the traits on a scale of 1 to 10, with 10 being the most desirable expression and 1 being the lowest. The scores are then multiplied by their weights and then added together to give a total score. Individuals that fail to meet a threshold are culled (or removed) from the breeding program. The total score gives a breeder a way to evaluate multiple traits on an animal at the same time.
The total score method is the most flexible of the three. it allows for weighted improvement of multiple characteristics. It allows the breeder to make major gains in one aspect while moderate or lesser gains in others.
For example, a breeder is willing to make a smaller improvement in muzzle length and muzzle shape in order to have a moderate gain in improvement of eye placement and a more dramatic improvement in eye shape. Suppose the breeder determines that she would like to see 40% improvement in eye shape, 30% improvement in eye placement, and 15% improvement in both muzzle length and shape. The breeder would evaluate these characteristics on a scale of 1 to 10 and multiply by the weights. The formula would look something like: 15 (muzzle length) + 15 (muzzle shape) + 30 (eye placement) + 40 (eye shape) = total score for that animal. The breeder determines the lowest acceptable total score for an animal to be folded back into their breeding program. Animals that do not meet this minimum total score are culled from the breeding program.
Livestock and production animals
Livestock bred for the production of meat or milk may be culled by farmers. Animals not selected to remain for breeding are sold, killed, or sent to the slaughterhouse.
Criteria for culling livestock and production animals can be based on population or production (milk or egg). In a domestic or farming situation, the culling process involves the selection and selling of surplus stock. The selection may be done to improve breeding stock—for example, for improved production of eggs or milk—or simply to control the group's population for environmental and species preservation. In order to increase the frequency of preferred phenotypes, agricultural practices typically involve using the most productive animals as breeding stock. | Culling | Wikipedia | 505 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
With dairy cattle, culling may be practised by inseminating cows—considered to be inferior—with beef breed semen and by selling the produced offspring for meat production.
Approximately half of the chicks of egg-laying chickens are males who would grow up to be roosters. These individuals have little use in an industrial egg-producing facility as they do not lay eggs, so the majority of male chicks are killed shortly after hatching.
Culling of farmed animals is considered a necessary practice to prevent the spread of damaging and fatal diseases such as foot-and-mouth disease, avian flu, Influenza A virus subtype H5N1 and bovine spongiform encephalopathy ("mad cow disease").
Wildlife
In the United States, hunting licenses and hunting seasons are a means by which the population of game animals is maintained. Each season, a hunter is allowed to kill a certain amount of wild animals, determined both by species and sex. If the population seems to have surplus females, hunters are allowed to take more females during that hunting season. If the population is below what is desired, hunters may not be permitted to hunt that particular species, or only hunt a restricted number of males.
Populations of game animals such as elk may be informally culled if they begin to excessively eat winter food set out for domestic cattle herds. In such instances the rancher will inform hunters that they may hunt on their property in order to thin the wild herd to controllable levels. These efforts are aimed to counter excessive depletion of the winter feed supplies. Other managed culling instances involve extended issuance of extra hunting licenses, or the inclusion of additional "special hunting seasons" during harsh winters or overpopulation periods, governed by state fish and game agencies.
Culling for population control is common in wildlife management, particularly on African game farms and Australian national parks. In the case of very large animals such as elephants, adults are often targeted. Their orphaned young, easily captured and transported, are then relocated to other reserves. Culling is controversial in many African countries, but reintroduction of the practice has been recommended in recent years for use at the Kruger National Park in South Africa, which has experienced a swell in its elephant population since culling was banned in 1995. | Culling | Wikipedia | 464 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Arguments against wildlife culling
Culling acts as a strong selection force and can therefore impact the population genetics of a species. For example, culling based on specific traits, such as size, can enforce directional selection and remove those traits from the population. This can have long-term effects on the genetic diversity of a population.
However, culling can act as a selection force intentionally implemented by humans to counteract the selection force of trophy hunting. Hunting typically enforces selection towards unfavorable phenotypic traits because of the strong hunting bias for specific traits, such as large antler size. Culling "low-quality" traits can counteract this force.
Animal rights activists argue that killing animals for any reason (including hunting) is cruel and unethical.
Birds
Some bird species are culled when their populations impact upon human property, business or recreational activity, disturb or modify habitats or otherwise impact species of conservation concern. Cormorants are culled in many countries due to their impact on commercial and recreational fisheries and habitat modification for nesting and guano deposition. They are culled by shooting and the smothering of eggs with oil. Another example is the culling of silver gulls in order to protect the chicks of the vulnerable banded stilt at ephemeral inland salt lake breeding sites in South Australia. The gulls were culled using bread laced with a narcotic substance. In the Australian states of Tasmania and South Australia, Cape Barren geese are culled to limit damage to crops and the fouling of waterholes. Cape Barren Geese remain one of the rarest geese in the world, though much of their habitat is now regarded as secure.
Seals
In South Australia, the recovery of the state's native population of New Zealand fur seals (Arctocephalus forsteri) after severe depletion by sealers in the 1800s has brought them into conflict with the fishing industry. This has prompted members of Parliament to call for seal culling in South Australia. The State Government continues to resist the pressure and as of July 2015, the animals remain protected as listed Marine Mammals under the state's National Parks and Wildlife Act 1972.
Sharks | Culling | Wikipedia | 437 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Shark culling occurs in four locations : New South Wales, Queensland, KwaZulu-Natal and Réunion. Between 1950 and 2008, 352 tiger sharks and 577 great white sharks were killed in the nets in New South Wales—also during this period, a total of 15,135 marine animals were caught and killed in the nets, including whales, turtles, rays, dolphins, and dugongs. From 2001 to 2018, a total of 10,480 sharks were killed on lethal drum lines in Queensland. In a 30-year period up to early 2017, more than 33,000 sharks were killed in KwaZulu-Natal's shark-killing program—during the same 30-year period, 2,211 turtles, 8,448 rays, and 2,310 dolphins were killed. Authorities on Réunion kill about 100 sharks per year. All of these culls have been criticized by environmentalists, who say killing sharks harms the marine ecosystem.
In 2014, a controversial policy was introduced by the Western Australian state government which became known as the Western Australian shark cull. Baited hooks known as drum lines were to be set over several consecutive summers to catch and kill otherwise protected great white sharks. The policy's objective was to protect users of the marine environment from fatal shark attack. Thousands of people protested against its implementation, claiming that it was indiscriminate, inhumane and worked against scientific advice the government had previously received. Seasonal setting of drum lines was abandoned in September 2014 after the program failed to catch any great white sharks, instead catching 172 other elasmobranchii, mostly tiger sharks.
Deer
White-tailed deer (Odocoileus virginianus) have been becoming an issue in suburbs across the United States due to large population increases. This is thought to be caused mainly by the extirpation of most of their major predators in these areas. In response to these population booms, different management approaches have been taken to decrease their numbers mainly in the form of culls. Culls of deer are often partnered with exclusions with fencing and also administering contraceptives. | Culling | Wikipedia | 427 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
The effectiveness of these deer culls has been debated and often criticized as only a temporary fix to the larger problem of deer overpopulation and argue that the use of culling will increase fertility of remaining deer by reducing competition. Those in favor of the culls argue that they can be used to combat the selection pressure that is imposed by hunting that creates smaller antler and body sizes in deer. People in favor of the culls recommend that they not be random and actively select for smaller individuals and bucks with smaller antlers, specifically "button bucks" or bucks with only spiked antler in their first year as opposed to forked antlers.
Culling of deer can also have benefits in the form of disease prevention and in places that the white-tailed deer is an invasive species such as New Zealand culling of deer has added benefits for native species. Diseases are density dependent factors and decreases in the density of the deer populations through culling causes diseases, such as chronic wasting disease and Lyme disease, to spread less quickly and effectively.
Zoos
Many zoos participate in an international breeding program to maintain a genetically viable population and prevent inbreeding. Animals that can no longer contribute to the breeding program are considered less desirable and are often replaced by more desirable individuals. If an animal is surplus to a zoo's requirements and a place in another zoo can not be found, the animal may be killed. In 2014, the culling of a young, healthy giraffe Marius raised an international public controversy.
Zoos sometimes consider female animals to be more desirable than males. One reason for this is that while individual males can contribute to the birth of many young in a short period of time, females give birth to only a few young and are pregnant for a relatively long period of time. This makes it possible to keep many females with just one or two males, but not the reverse. Another reason is that the birth of some animal species increases public interest in the zoo.
Germany's Animal Welfare Act 1972 orders that zoo animals cannot be culled without verification by official veterinary institutes of the Landkreis or federated state.
In the UK, there is no general prohibition on animal euthanasia, which is allowed when overcrowding compromises the well-being of the animals.
Ethics
Jaak Panksepp, an American neuroscientist, concludes that both animals and humans have brains wired to feel emotions, and that animals have the capacity to experience pleasure and happiness from their lives. | Culling | Wikipedia | 503 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Culling has been criticized on animal rights grounds as speciesist—it has been argued that killing animals for any reason is cruel and unethical, and that animals have a right to live.
Some argue that culling is necessary when biodiversity is threatened. However, the protection of biodiversity argument has been questioned by some animal rights advocates who point out that the animal which most greatly threatens and damages biodiversity is humanity, so if we are not willing to cull our own species we cannot morally justify culling another.
Non-lethal alternatives
There are non-lethal alternatives which may still be considered culling, and serve the same purpose of reducing population numbers and selecting for desired traits without killing existing members of the population. These methods include the use of wildlife contraceptives and reproductive inhibitors. By using such methods population numbers might be reduced more gradually and in a potentially more humane fashion than by directly lethal culling actions.
Currently, wildlife contraceptives are largely in the experimental phase and include such products as Gonacon, an adjuvant vaccine which delivers a high dosage of a competitor ligand of the hormone GnRH to female mammals (e.g. whitetail deer). The complex formed of GnRH and the Gonacon molecule promotes production of antibodies against the animal's own GnRH, which themselves complex with GnRH. This encourages an extended duration of the drug's effects (namely, reduction of active/unbound GnRH in the animal's system). Though the endocrinology behind Gonacon is sound, the need for multiple lifetime doses for full efficacy make it a less-guaranteed and less-permanent solution for wildlife than lethal culls. Even among domestic animals in controlled conditions, Gonacon cannot ensure 100% reduction in the occurrence of pregnancies.
Reproductive inhibitors need not act on the parental individuals directly, instead damaging reproductive processes and/or developing offspring to reduce the number of viable offspring per mating pair. One such compound called Nicarbazin has been formulated into bait for consumption by Canada Geese, and damages egg yolk formation to reduce the viability of clutches without harming the adult geese. | Culling | Wikipedia | 437 | 2980973 | https://en.wikipedia.org/wiki/Culling | Technology | Animal husbandry | null |
Sea apple is the common name for the colorful and somewhat round sea cucumbers of the genus Pseudocolochirus, found in Indo-Pacific waters. Sea apples are filter feeders with tentacles, ovate bodies, and tube-like feet. As with many other holothurians, they can release their internal organs or a toxin into the water when stressed.
Physiology
Sea apples are holothuroids, and as such share many of the same physical characteristics. A few notable characteristics are discussed below.
Anatomy and feeding
The ovate body of an adult sea apple can grow up to long. A central mouth-like cavity is surrounded by feathery tentacles, which add additional length. Sea apples, like many echinoderms, have rows of tube feet which help them move over and adhere to structures.
The bodies and tentacles of sea apples come in many different colorings. The Australian species has a primarily purple body, red feet, and purple and white tentacles.
The sea apple feeds primarily on plankton, which it filters from the water with its tentacles. It alternately brings each tentacle to its mouth, scraping off the captured plankton.
Sea apples usually feed at night, a time when their delicate tentacles are less at risk from predators.
Defense
When disturbed, sea apples, like other holothuroids, can violently extrude their entrails from their posterior in a process called evisceration (autotomy). In addition, sea apples can release a toxic saponin called holothurin into the water as a defense mechanism.
In addition, if threatened or in an unsuitable environment, sea apples can consume large amounts of surrounding seawater to swell to nearly double their original size, this allows them to be moved to a new area by water currents, and much more quickly than they could walk.
Problems in captivity
Because of their interesting appearance and behaviour, sea apples are often widely desired as specimen for display marine aquarium. They are considered reef safe as far as their compatibility with other species. However, they can be considered unsafe for reef aquaria for multiple reasons: | Sea apple | Wikipedia | 422 | 2981932 | https://en.wikipedia.org/wiki/Sea%20apple | Biology and health sciences | Echinoderms | Animals |
Starvation
Sea apples often starve to death in display aquaria. Levels of plankton in aquaria are often lower than optimal, and sea apples are often seen attempting to feed not only at night, as in their natural habitat, but also in the daytime. With only low levels of food available, these sea apples often starve, becoming progressively smaller as this happens. To try to circumvent these problems, hobbyists attempt to give the sea apple specimens supplemental feedings of plankton and liquid food.
Harassment and predation
Sea apples are often harassed by many aquarium inhabitants. Crustaceans, such as hermit crabs, and fish often peck or pick at sea apple's feathery tentacles. This may be for predatory purposes, or simply to steal trapped particles and plankton from the tentacles.
Occasionally, sea apples use their defense mechanisms in response to harassment. The release of their toxin can poison other aquarium inhabitants, and is one of the reasons they are not commonly seen in aquariums. | Sea apple | Wikipedia | 200 | 2981932 | https://en.wikipedia.org/wiki/Sea%20apple | Biology and health sciences | Echinoderms | Animals |
Transform, clipping, and lighting (T&L or TCL) is a term used in computer graphics.
Overview
Transformation is the task of producing a two-dimensional view of a three-dimensional scene. Clipping means only drawing the parts of the scene that will be present in the picture after rendering is completed. Lighting is the task of altering the colour of the various surfaces of the scene on the basis of lighting information.
Hardware
Hardware T&L had been used by arcade game system boards since 1993, and by home video game consoles since the Sega Genesis's Virtua Processor (SVP), Sega Saturn's SCU-DSP and Sony PlayStation's GTE in 1994 and the Nintendo 64's RSP in 1996, though it wasn't traditional hardware T&L, but still software T&L running on a coprocessor instead of the main CPU, and could be used for rudimentary programmable pixel and vertex shaders as well. More traditional hardware T&L would appear on consoles with the GameCube and Xbox in 2001 (the PS2 still using a vector coprocessor for T&L). Personal computers implemented T&L in software until 1999, as it was believed faster CPUs would be able to keep pace with demands for ever more realistic rendering. However, 3D computer games of the time were producing increasingly complex scenes and detailed lighting effects much faster than the increase of CPU processing power.
Nvidia's GeForce 256 was released in late 1999 and introduced hardware support for T&L to the consumer PC graphics card market. It had faster vertex processing not only due to the T&L hardware, but also because of a cache that avoided having to process the same vertex twice in certain situations. While DirectX 7.0 (particularly Direct3D 7) was the first release of that API to support hardware T&L, OpenGL had supported it much longer and was typically the purview of older professionally oriented 3D accelerators which were designed for computer-aided design (CAD) instead of games.
Aladdin's ArtX integrated graphics chipset also featured T&L hardware, being released in November 1999 as part of the Aladdin VII motherboards for socket 7 platform.
S3 Graphics launched the Savage 2000 accelerator in late 1999, shortly after GeForce 256, but S3 never developed working Direct3D 7.0 drivers that would have enabled hardware T&L support. | Transform, clipping, and lighting | Wikipedia | 497 | 6961053 | https://en.wikipedia.org/wiki/Transform%2C%20clipping%2C%20and%20lighting | Technology | Computer science | null |
Usefulness
Hardware T&L did not have broad application support in games at the time (mainly due to Direct3D games transforming their geometry on the CPU and not being allowed to use indexed geometries), so critics contended that it had little real-world value. Initially, it was only somewhat beneficial in a few OpenGL-based 3D first-person shooter titles of the time, most notably Quake III Arena. 3dfx and other competing graphics card companies contended that a fast CPU would make up for the lack of a T&L unit.
ATI's initial response to GeForce 256 was the dual-chip Rage Fury MAXX. By using two Rage 128 chips, each rendering an alternate frame, the card was able to somewhat approach the performance of SDR memory GeForce 256 cards, but the GeForce 256 DDR still retained the top speed. ATI was developing their own GPU at the time known as the Radeon which also implemented hardware T&L.
3dfx's Voodoo5 5500 did not have a T&L unit but it was able to match the performance of the GeForce 256, although the Voodoo5 was late to market and by its release it could not match the succeeding GeForce 2 GTS.
STMicroelectronics' PowerVR Kyro II, released in 2001, was able to rival the costlier ATI Radeon DDR and NVIDIA GeForce 2 GTS in benchmarks of the time, despite not having hardware transform and lighting. As more and more games were optimised for hardware transform and lighting, the KYRO II lost its performance advantage and is not supported by most modern games.
Futuremark's 3DMark 2000 heavily utilized hardware T&L, which resulted in the Voodoo 5 and Kyro II both scoring poorly in the benchmark tests, behind budget T&L video cards such as the GeForce 2 MX and Radeon SDR.
Industry standardization
By 2000, only ATI with their comparable Radeon 7xxx series, would remain in direct competition with Nvidia's GeForce 256 and GeForce 2. By the end of 2001, all discrete graphics chips would have hardware T&L. | Transform, clipping, and lighting | Wikipedia | 454 | 6961053 | https://en.wikipedia.org/wiki/Transform%2C%20clipping%2C%20and%20lighting | Technology | Computer science | null |
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