IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Caimi, B. | |
| Melanism in felids: _Panthera pardus'_ and _Panthera onca'_s case | |
| 2021 Full Book | |
Skin is composed by a basal tissue, the dermis, and a more superficial one, the epidermis. In mammals dermis there are hair follicles which are responsible for hair formation, a typical skin appendage of this class of Vertebrates, while in epidermis there is a cell class, the melanocytes, fundamental for individual's pigmentation. Melanocytes synthesize and accumulate in specialized organelles called melanosomes, the melanin, a pigment which protects skin from ultraviolet radiation. In addition, its accumulation determines skin and hair coloration: in particular, mammals' mantle pigmentation is linked to the production of two variants of melanin, namely eumelanin, a darker pigment tending to black, and feomelanin, a lighter pigment tending to red. Production of pigment type is controlled by Melanocortin 1 receptor (MC1R), regulated by melanocortins, peptide hormones produced by the pituitary gland. The only endogenous antagonist known, which acts on this receptor for pigmentation control, is Agouti Signaling protein (ASIP), which leads to an interruption in eumelanin production by melanocytes and subsequent synthesis of feomelanin. Mutations in genes encoding for MC1R or ASIP are at the basis of melanism, because they determine an increase in receptor activity or loss of functionality of its antagonist, respectively. In both cases MC1R is constitutively activated, causing eumelanin synthesis. Therefore, melanism, a very common polymorphism in the animal kingdom, gives rise to specimens with coloration tending to dark brown or black. It is believed that this polymorphism is associated to biological factors such as protection from UV rays, but also to phenomena such as aposematism and reduction of susceptibility to parasites. In addition, such condition seems to be advantageous for thermoregulation, especially in animals that live in humid environments such as tropical forests, where a dark color also favors camouflage. These advantages would allow the maintenance of this polymorphism during evolution. There are many examples of melanistic animals, both among vertebrates and invertebrates. In particular, one of the taxa in which melanism is very common is the felids family. In these animals melanism is a polymorphic character from species to species and the best known example is the one of "black panthers", i.e. melanism in _Panthera pardus_, the leopard, and _Panthera onca_, the jaguar. In _P. pardus_' case, melanism is determined by a recessive mutation of ASIP gene, on the contrary in _P. onca _is caused by a dominant mutation affecting MC1R gene. In this thesis, the molecular mechanisms underlying melanism phenomenon were taken into consideration, with particular attention to the felid family. |
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