The name thyroid-stimulating hormone ( TSH ) has been given to a substance found in the anterior pituitary gland of all species of animal so tested for its presence.

With their often complex reproductive needs and permeable skins, amphibians are often ecological indicators and in recent decades there has been a dramatic decline in amphibian populations of many species around the globe.

A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales.

The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied.

A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, climate change, endocrine-disrupting pollutants, destruction of the ozone layer ( ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians ), and diseases like chytridiomycosis.

By its inclusion the order has grown enormously in number of species.

The group has more than 23, 000 currently accepted species, spread across 1620 genera and 12 subfamilies.

Each abalone species has a typical number of holes in the selenizone which remain open.

Although the family ( Amaranthaceae ) is distinctive, the genus has few distinguishing characters among the 70 species included.

The species Amaranthus palmeri ( Palmer amaranth ) causes the greatest reduction in soybean yields and has the potential to reduce yields by 17-68 % in field experiments.

It has the capacity to get to large heights and can outcompete native plant species around it.

Ailanthus are capable of forming thick blankets of roots and heavy shade to the extent that native species are prevented from being able to reclaim an area that has been logged or deforested, as well as areas that have been heavily developed.

Widespread usage of antibacterial drugs in hospitals has also been associated with increases in bacterial strains and species that no longer respond to treatment with the most common antibacterials.

Although there were low levels of preexisting antibiotic-resistant bacteria before the widespread use of antibiotics, evolutionary pressure from their use has played a role in the development of muiltidrug resistance varieties and the spread of resistance between bacterial species.

Lastly, abiotic stress has enabled species to grow, develop, and evolve, furthering natural selection as it picks out the weakest of a group of organisms.

It has been observed through a variety of environments that as the level of abiotic stress increases, the number of species decreases.

Australia has several indigenous plants which are popular among modern ayahuasqueros there, such as various DMT-rich species of Acacia.

Moreover they argued that some species have been created for the purpose of being sacrificed and eaten by humans, that it is normal for animals to kill and eat other animals, that agriculture, too, inevitably leads to the death of many animals, that plants are living beings as well and must still be destroyed, that we unintentionally and unknowingly destroy life forms all the time, and that a hunted animal has a fair chance to survive by killing the hunter.

Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.

It has not been definitively established whether the existence of these brainless species indicates that the earliest bilaterians lacked a brain, or whether their ancestors evolved in a way that led to the disappearance of a previously existing brain structure.

No modern species should be described as more " primitive " than others, strictly speaking, since each has an equally long evolutionary history — but the brains of modern hagfishes, lampreys, sharks, amphibians, reptiles, and mammals show a gradient of size and complexity that roughly follows the evolutionary sequence.

The relationship between brain size, body size and other variables has been studied across a wide range of vertebrate species.

The brain of a shark shows the basic components in a straightforward way, but in teleost fishes ( the great majority of existing fish species ), the forebrain has become " everted ", like a sock turned inside out.

* Bisexual species, in biology, one that has members of two different distinct sexes ( e. g. humans ), opposed to unisexual ( only one sex present, always females )

As a result of its relief and geographic situation, the Ubaye Valley has an " abundance of plant and animal species ".

On chemical grounds it seems most likely that iodide is first converted to Af and then to Af as the active iodinating species.

Of these, 1, 356 ( 33. 6 %) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1, 427 species for which there was insufficient data to assess their status.

This means that species are more likely to become population threatened, endangered, and even extinct, when and where abiotic stress is especially harsh.

Fewer than 5000 animals of each species likely remain.

Another likely explanation for the loss of its eyes is that of selective neutrality and genetic drift: in the dark environment of the cave, the eyes are neither advantageous nor disadvantageous and thus any genetic factors that might impair the eyes ( or their development ) can take hold with no consequence on the individual or species.

The turnover in this group is clearly marked at the species level .< ref > Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in speciation .< ref > The K – T boundary record of dinoflagellates is not as well-understood, mainly because only microbial cysts provide a fossil record, and not all dinoflagellate species have cyst-forming stages, thereby likely causing diversity to be underestimated.

This is currently the only member of this family but it seems likely that other species will be allocated to this family in the near future.

Its distribution within the Americas, however, is most likely restricted to the United States and Mexico, where the highest species diversity occurs.

Many other species of Entamoeba have been described and it is likely that many others remain to be found.

While some other, extinct Homo species might have been ancestors of Homo sapiens, many were likely our " cousins ", having speciated away from our ancestral line.

It was considered to be the first species of the genus Homo until May 2010, when a new species, Homo gautengensis was discovered in South Africa, that most likely arose earlier than Homo habilis.

The first ancestral hyenas were likely similar to the modern banded palm civet ; one of the earliest hyena species exhumed, Plioviverrops, was a lithe, civet-like animal that inhabited Eurasia 20-22 millions years ago, and is identifiable as a hyaenid by the structure of the middle ear and dentition.

As fossil striped hyenas are absent from the Mediterranean region, it is likely that the species is a relatively late invader to Eurasia, having likely spread outside Africa only after the extinction of spotted hyenas in Asia at the end of the Ice Age.

While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites.

He then proceeded to roughly map out a likely course for evolution using examples of gradually more complex eyes of various species.

The IUCN reported in 2008, " The taxonomy of this genus is clearly in need of review, and it is likely that O. orca will be split into a number of different species or at least subspecies over the next few years.

Animal forms vary accordingly with cultures and local species ( including bears and wolves ), for example, a coyote is more likely to be found as a skinwalker's alternate form in the Great Plains region.

For example, if a species of grass grows on both sides of a highway, pollen is likely to be transported from one side to the other and vice versa.

In fact, it includes weakly bound species that would not traditionally be considered molecules, such as the helium dimer, He < sub > 2 </ sub >, which has one vibrational bound state and is so loosely bound that it is only likely to be observed at very low temperatures.

One study on genetic variations between different species of Drosophila suggests that if a mutation changes a protein produced by a gene, the result is likely to be harmful, with an estimated 70 percent of amino acid polymorphisms having damaging effects, and the remainder being either neutral or weakly beneficial.

In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less likely to interbreed, and thereby preserving genetic differences between these populations.

This suggests a single dispersion event of just one species, most likely a relative to South America's monito del monte ( a microbiothere, the only New World australidelphian ).