Animals with black skin or fur are not black by chance, suggests new research, but because the dark coloration helps them live longer.
The finding adds to the growing body of evidence that black coloration isn’t just a product of genetic drift — happenstance in the course of evolution.
The coloration stems from melanism, or development of the dark-colored pigment melanin in the skin and its appendages (fur, hair, eyelashes, etc.). How melanism directly ties to better health, however, remains a mystery.
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“We don’t know for certain,” said Gregory Barsh of the HudsonAlpha Institute for Biotechnology, co-author of the study “Recurrent Evolution of Melanism in South American Felids,” which was published Feb. 19, 2015, in PLOS Genetics. “Factors such as foliage, humidity, temperature, and/or infectious agents are all possibilities, and could affect camouflage, resistance to heat or thermoregulation, or resistance to infections.”
He added that one of the most famous examples of melanism working to a species’ advantage is the dark peppered moth, which blends in more easily in dark surroundings — offering better camouflage from prey.
Lead author Alexsandra Schneider, senior author Eduardo Eizirik and their colleagues have studied melanism before in other animals, but focused their work this time on three closely related South American wild cats: the pampas cat, the kodkod, and Geoffroy’s cat. They identified the mutations responsible for melanism in the cats, and found that there was strong evidence for natural selection of black coloration, particularly for pampas cats.
Linking domestic cats and their wild counterparts, the researchers found that the same gene that causes melanism in the pampas cat and the kodkod also causes the rich black fur of certain leopards, panthers and jaguars, as well as house kitties that sport such a coat, Eizirik told Discovery News. He is a researcher at the Pontifícia Universidade Católica do Rio Grande do Sul and the Instituto Pró-Carnívoros, both of which are in Brazil.
Barsh mentioned that, in an earlier study, he and his colleagues also found that “black wolves may have increased fitness in some environments due to a melanism mutation in a different gene from the ones studied here.” Certain domesticated dogs may also benefit from darker fur colors, although breeding by humans now influences the process.
Research on baby owls conducted by another team found that melanism in these birds, via gene expression, may be tied to sleep patterns and even brain development.
Dark spots in owls corresponds to a range of behavioral traits which have been tied to immune system function and energy regulation in the animals, explained co-author Alexander Roulin from the University of Lausanne.
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It could be that melanism’s perks are compromised when a species moves to a place with a different climate and habitat.
“For example,” Eizirik said, “a small black cat may have increased fitness in a dark forest, but decreased fitness in an open field.”
In this case, even if the dark fur and skin help with immunity and other things, those would be lost if the animal is highly visible to predators.
As for humans, it appears that predation was not the greatest factor affecting gene expression for skin and hair coloration, at least during the more recent stages of human evolution.