Melanism

Pseudomelanism, also called abundism, is another variant of pigmentation, identifiable by dark spots or enlarged stripes, which cover a large part of the body of the animal, making it appear melanistic.

[4] Typically, adaptive melanism is heritable: A dominant allele, which is entirely or nearly entirely expressed in the phenotype, is responsible for the excessive amount of melanin.

By contrast, adaptive melanism associated with Batesian mimicry in Zelandoperla fenestrata stoneflies is controlled by a recessive allele at the ebony locus.

[5][6] Adaptive melanism has been shown to occur in a variety of animals, including mammals such as squirrels, many cats and canids, and coral snakes.

Adaptive melanism can lead to the creation of morphs, a notable example being the peppered moth, whose evolutionary history in the United Kingdom is offered as a classic instructional tool for teaching the principles of natural selection.

[8][9][10][11][12][13] Other explanations have been proposed, such as that the melanin pigment enhances function of immune defences,[14] or a thermal advantage from the darker coloration.

[15][16][17] Melanistic coat coloration occurs as a common polymorphism in 11 of 37 felid species and reaches high population frequency in some cases but never achieves complete fixation.

Melanistic animals were found to carry at least one copy of a mutant MC1R sequence allele, bearing a 15-base pair inframe deletion.

[23] Other theories are that genes for melanism in felines may provide resistance to viral infections, or a high-altitude adaptation, since black fur absorbs more light for warmth.

They have a dominant gene that causes hyperpigmentation (Fibromelanosis), making the chicken entirely black; including feathers, beak, and internal organs.

This rare genetic disorder is characterized by the development of macules with hyperpigmentation on the lips and oral mucosa (melanosis), as well as benign polyps in the gastrointestinal tract.