Interspecific variation in primate coat colour supports Gloger’s rule

Aim In 1833, C.L. Gloger observed that bird populations living in warm and wet habitats were darker than those found in dry, cool areas. However, this hypothesis has seldom been evaluated, particularly for mammals. Here, we test Gloger’s rule using a dataset consisting of more than 100 primate species representing all major primate clades. Location  Africa, Madagascar, Asia and the Neotropics. Methods We used museum skins, digital photography, and colour correction software to quantify the brightness of the dorsal and ventral pelage surface of each species. We utilized the mean actual evapotranspiration (AET) within the geographic range of each species as a proxy for habitat conditions and accounted for additional variables that may influence coloration. To analyse the data, we used a generalized linear model that simultaneously accounts for the effects of phylogenetic and spatial autocorrelation. Results We found that increasing levels of AET were significantly related to increasing pelage darkness on the dorsal surface of species, while accounting for other effects. Main conclusions Our finding provides further support for the applicability of Gloger’s rule to mammals, and is the first broad‐scale evaluation for primates. The mechanism driving Gloger’s rule is not easy to discern, but may include increased background matching for species living in relatively light or dark habitats, increased resistance to keratin‐degrading micro‐organisms in hair with large amounts of eumelanin, and/or thermoregulation.