Colors of Primate Pelage: The Independent Evolution of Sexual Dichromatism in the Primate Order

Abstract

There is a large body of research describing the evolutionary importance of plumage coloration among avian species. However, similar datasets are lacking for mammalian pelage. Furthermore, very little research has examined the variations of nonhuman primate (NHP) pelage coloration and patterning. Primatologists have noted conspicuous differences in coloration and patterning among NHPs, including neo-natal coats and sexual dichromatism. Sexual dichromatism refers to the differences in pelage coloration between the sexes of a single species. Sexual dichromatism is rare, but found among some species of lemurs, New World monkeys, and lesser apes. To illuminate the genetic mechanism of NHP sexual dichromatism, I examined published amino acid sequences for the MC1R and OCA2 genes of nine NHP species across multiple genera. This dataset incorporated sexually dichromatic NHPs including white-cheeked gibbons (Nomascus leucogenys), lar gibbons (Hylobates lar), and black howler monkeys (Alouatta caraya). I also examined closely allied monochromatic NHPs including brown lemurs (Eulemur fulvus), long-tailed macaques (Macaca fascicularis), black snub-nosed monkeys (Rhinopithecus bieti), Mueller’s gibbon (Hylobates muelleri), mantled howler monkeys (Alouatta palliata), and chimpanzees (Pan troglodytes). Comparisons across these species suggest the MC1R gene does not play an important role in pelage coloration. In contrast, the OCA2 sequence of N. leucogenys differed, on average, ~16% from the three monochromatic species. Furthermore, the OCA2 sequences exhibit a low phylogenetic signal, suggesting that this gene may regulate dichromatic pelage. To expand these genetic datasets, I analyzed socioecological variables among these species and found that smaller home-range sizes and dispersal of both sexes may have played a role in the evolution of dichromatic pelage in NHPs.