Genetic constraint, non-independence of traits and consequences of adaptive evolution in acridid grasshoppers

Abstract

Evolutionary trajectories of quantitative traits are influenced by the underlying genetic architecture of such traits. But traits do not occur in isolation, and the genetic covariation between traits can be statistically summarized by the additive genetic variance covariance matrix, G. I studied the evolution of G for five morphological traits which are conserved, and five song traits which are presumably under sexual selection, using a half-sib breeding design in grasshoppers. I also studied male indirect genetic effects (IGEs) under a potential sexual conflict scenario in a grasshopper, as IGEs can manipulate female reproductive traits to maximize fitness because of conflicting evolutionary interests over trade-offs between current and future reproduction. I found that G matrices have diverged in shape and orientation for both conserved morphological traits and variable song traits. The differentiation in morphology has been along wing length, and the G matrix of the most distant species is the most different. Evolutionary trajectories of both the song and morphology seem to be directly influenced by selection. I also found IGEs were high initially after mating, but they tapered with time. Hence, the phenotypic evolution of female reproductive traits will be influenced mostly by direct selection on female additive genetic variance rather than indirectly on male IGEs.