Correlated divergence in functionally coupled and rapidly evolving traits

     In collaboration with L. Lacey Knowles, we studied the dimensionality of correlated divergence between functionally coupled traits. Specifically, we asked how functional integration affects the trajectory of divergence of rapidly-evolving traits when both the intraspecific variation and the phylogenetic disparity of these traits span a large number of dimensions. For this work, we compared patterns of disparity of genitalic traits from male grasshoppers of the genus Melanoplus, a set of rapidly diverging structures whose evolutionary dynamics is most likely driven by sexual selection. Results from two clades of this genus suggest that co-divergence of most tightly coupled mating traits has a remarkably low dimensionality (i.e. multiple traits seem to diverge along nearly linear and highly correlated trajectories), despite the enormous disparity shown by these phenotypes in both clades.
     Our study suggests that the dimensionality of individual traits does not necessarily predict the dimensionality of the direction in which they diverge. Evolutionary associations among multivariate traits do not necessarily span the full set of dimensions of any of these traits, making it valuable to distinguish among the dimensions of a trait that do co-diverge with other traits from those that evolve independently.

Coevolutionary trajectory in multivariate shape space of genitalic traits in a clade of grasshoppers.