By Eduardo Venegas Castro, Naturalist Guide
Albinism results in whitish pink fur or feathers, and eyes with reddish pupils, because the blood vessels are visible through the tissues. The gene responsible for albinism is recessive, so it is only expressed if both parents transfer it to their offspring. It may not appear in all generations, so it is possible that an animal or plant can transmit albinism to its offspring without expressing the gene itself or realizing that it is a carrier.
Leucism, also genetic, is the condition of partial or total loss of pigmentation. More common in birds, leucines – unlike albino animals – have normal-colored eyes, and may or may not have normally colored legs and beaks. This Hoffman’s Woodpecker (Melanerpes hoffmannii; above right) is an example of leucism.
On the other hand, melanism, which is also hereditary and is produced by the mutation of different genes, results in an excess of dark pigmentation in an animal. Melanism is found in many different species, including amphibians, reptiles, and mammals. The “black jaguar” was once thought to be a separate species but is now known to be a melanistic version of the same species, Panthera onca. The variegated squirrel (Sciurus variegatoides) shown above is an example of melanism.
There are also other cases of altered pigmentation. Erythrism is abundance of red or orange coloration. The leaf insect (Phoebolampta caeruleotergum) shown above is an example of erythrism. Xanthism (or xanthochromism) is the abundance of yellow pigment and lack of other pigments. And axanthism is the opposite: the absence of yellow pigment. Axanthism is what causes some species of tree frogs to show a striking blue coloration, rather than being green.
Translated and edited by Lindsay Stallcup