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.