Axanthism

An axanthic green frog (Lithobates clamitans). Axanthism is most common in species of Ranidae.
Yellow-collared lovebirds (Agapornis personatus) are a good example of the effects of axanthism. The feathers that would be normally green are blue, and the feathers that would be yellow are white.

Axanthism is a mutation that interferes with an animal's ability to produce yellow pigment. The mutation affects the amount of xanthophores and carotenoid vesicles, sometimes causing them to be completely absent.[1] Erythrophores and iridophores, which are responsible for red coloration and light reflecting pigments respectively, may also be affected.[2] 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 carotenoids in the xanthophores.[3] In the absence of xanthophores and carotenoids, the blue light is unaltered and reflected back normally.[4] 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; though they can be distinguished by how axanthic animals are slightly lighter and how melanistic animals produce more melanophores.[5] When iridophores are affected by axanthism, the animal typically becomes duller or darker in coloration due to a lesser amount of light reflected.[2] Typically it is only the skin that is affected, and the eyes still have iridophores.

The opposite of axanthism is xanthochromism, which is an excess of yellow coloration.

  1. ^ Henle, Dubois, Klaus, Alain (15 August 2017). Studies on Anomalies in Natural Populations of Amphibians. Chimaira. p. 12. ISBN 978-3-89973-570-3.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ a b Jablonski, Alena, Vlček, Jandzik, Daniel, Andrej, Petr, David (July 2014). "Axanthism in amphibians: A review and the first record in the widespread toad of the Bufotes viridis complex (Anura: Bufonidae)". Belgian Journal of Zoology. 144: 93–101 – via ResearchGate.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ Taylor, Bagnara, John D., Joseph T. (February 1972). "Dermal Chromatophores". American Zoologist. 12 (1): 43–62. doi:10.1093/icb/12.1.43. JSTOR 3881731.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ Berns, Narayan, Michael W., K. Shankar (October 1970). "An histochemical and ultrastructural analysis of the dermal chromatophores of the variant ranid blue frog". Journal of Morphology. 132 (2): 169–179. doi:10.1002/jmor.1051320205. hdl:2027.42/50255. S2CID 42830540.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Frost-Mason, Mason (August 1996). "What insights into vertebrate pigmentation has the axolotl model system provided?". The International Journal of Developmental Biology. 40 (4): 685–693. PMID 8877441.