Reevaluating cases of trait-dependent diversification in primates

Previous investigations have identified several ecological traits that may have shaped differences in species richness among primate clades by influencing speciation and extinction probabilities. In this study, I reevaluate these cases in light of concerns about high false-positive rates of the methods used to detect trait-dependent diversification.

Data for six traits were taken from the literature: activity pattern, sociality, mating system, terrestriality, frugivory, and mutualistic interactions with angiosperms (i.e., seed dispersal and pollination). These traits were treated as binary variables and analyzed in a phylogenetic framework using likelihood-based and nonparametric methods for estimating trait-specific diversification rates.

Of the traits analyzed here, only activity pattern was found by all methods to be correlated with diversification: diurnal primates diversify at higher rates than nocturnal primates. Solitary foragers have a lower rate of diversification than group-living primates, but this link is driven by the association between solitariness and nocturnality.

These results indicate that ecological traits have had a more limited influence on primate diversification than suggested by previous studies. The false positives detected here can be linked with heterogeneity in diversification caused by sources other than the focal traits. One of these sources is the very high rate of diversification in Cercopithecoidea found in previous investigations. Another is the correlation between activity patterns and diversification. The underlying causal mechanism for the contrast in diversification dynamics between diurnal and nocturnal primates is unclear, but this correlation highlights the important role of activity pattern in shaping primate evolutionary history.