The evolutionary ecology of primate hair coloration: a phylogenetic approach

Understanding trait evolution is essential for explaining modern biological diversity, and this is particularly exemplified by studies of coloration. Recent studies have applied evolutionary models to understand animal coloration, yet we have limited knowledge of how this trait evolves in mammals in a comparative context. Here we use phylogenetic methods to examine how different traits are associated with the evolutionary diversity of primate hair color. We hypothesize that hair color evolves independently across body regions, and that variation in biological and ecological traits influence patterns of hair color evolution. To test this, we quantify the phylogenetic signal of coloration for each body region, then compare the fit of three evolutionary models and a null, non-phylogenetic model to explain color variation across 94 primate species. We then test how trait optima and rate of color evolution covary with biological traits, clade membership, and habitat. Phylogenetic signal varies across regions, with head and forelimb coloration exhibiting the highest values. Head and forelimb coloration is best explained by an Ornstein-Uhlenbeck model, which could suggest stabilizing selection, whereas a null model best fits other body regions. Rates of hair color evolution and optimal color values vary across species with different visual systems, activity patterns, habitat types, and clade memberships. These results suggest that selective pressures are acting independently across body regions and across different primate taxa. Our results emphasize the importance of investigating patterns of trait evolution across regions of the body, as well as incorporating relevant biological and ecological traits into evolutionary models.