Green Frog, blue coloured, Fletcher Wildlife Garden

Axanthism is a mutation that interferes with an animal's ability to produce yellow pigment. The mutation affects the amount of xanthophores and

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, cor ...

vesicles, sometimes causing them to be completely absent. Erythrophores and iridophores, which are responsible for red coloration and light reflecting pigments respectively, may also be affected. Axanthism is most obvious in green animals, specifically amphibians, making them appear blue. Green coloration in animals is caused by iridiphores reflecting blue wavelengths of light back through the

s in the xanthophores. In the absence of xanthophores and carotenoids, the blue light is unaltered and reflected back normally. Animals that are normally yellow will appear white if affected with axanthism. While axanthism commonly makes green animals blue, it can also make the animal gray or even black, making it appear as if the animal has

melanism The term melanism refers to black pigment and is derived from the gr, μελανός. Melanism is the increased development of the dark-colored pigment melanin in the skin or hair. Pseudomelanism, also called abundism, is another variant of pi ...

; though they can be distinguished by how axanthic animals are slightly lighter and how melanistic animals produce more melanophores. When iridophores are affected by axanthism, the animal typically becomes duller or darker in coloration due to a lesser amount of light reflected. Typically it is only the skin that is affected, and the eyes still have iridophores. The opposite of axanthism is

xanthochromism Xanthochromism (also called xanthochroism or xanthism) is an unusually yellow pigmentation in an animal. It is often associated with the lack of usual red pigmentation and its replacement with yellow. The cause is usually genetic but may also be ...

, which is an excess of yellow coloration.

In Amphibians

There are three basic types of axanthism in amphibians: complete to partial blue coloration, complete or partial gray or dark coloration, and normal coloration with black eyes. These are not distinct categories, and there can be amphibians that have a combination of these. The first one is most common in the family Ranidae, which is also the family that happens to be most commonly affected by axanthism. It is not yet known exactly why axanthism occurs in amphibians and whether it is genetic or environmental. Axanthism seems to be most common in North America, and is more common in Northern regions; there have been over one hundred reports of blue green frogs ('' Lithobates clamitans''), but only one is from the southeastern United States. Axanthism is also most common in frogs, with salamanders and newts having almost no cases. Axanthic individuals are usually at higher risk at predation by sight predators compared to normal amphibians. Axanthism can affect the

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

and

aposematic Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste o ...

patterns of amphibians, making these individual stand out more or render their defenses useless. However, individuals that are darker than normal may have an advantage in

thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...

, which is especially important in

ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...

ic vertebrates.

References

{{Reflist Genetic disorders with no OMIM Disturbances of pigmentation