Correlated evolution of multivariate traits: detecting co-divergence across multiple dimensions

Abstract

Tests of correlated evolution typically treat phenotypic characters as univariate variables, even though different trait attributes may contribute to its association with other traits. In this study, patterns of character covariation among species are analyzed in a multivariate framework to test for both correlated rates and directions of evolutionary change in traits forming the genitalic complex of male grasshoppers. While the covariation structure differs among traits, and among the constituent species of two grasshopper clades, significant co-divergence was detected among the most closely interacting genitalic traits (i.e., intromittent characters) in both clades. Co-divergence across shape space is not accompanied by similar rates of evolution among species, although the intromittent characters tend to show accelerated evolution (relative to non-intromittent characters). Differences in the evolutionary trajectories among traits may relate to their varied roles during mating. The study emphasizes the importance of a multivariate framework for detecting macroevolutionary patterns of correlated change.