Asymmetry in cross-sex cross-trait genetic covariances and the evolvability of sexual dimorphism

The evolution of sexual dimorphism is predicted to resolve conflict that can arise from divergent evolutionary interests between sexes, enabling each sex to reach its fitness optimum. However, most of the genome is shared between sexes, which can lead to a genetic constraint for dimorphism evolution. Most studies of intersexual genetic constraints have focused on the effect of genetic correlations, rmf, for single traits. However, multivariate studies of the B-matrix of intersexual genetic covariances suggest that sexual dimorphism may be more evolvable than inferred from rmf because of the potential for indirect responses to selection from correlated traits. To comprehensively address this question, we collected and re-analyzed published estimates of B using a recently developed approach to quantify the evolvability of sexual monomorphism and dimorphism. We find that across the traits and species we study, the evolvability of dimorphism is lower than that of monomorphism, but also that sexually concordant and antagonistic selection are almost equally capable of producing dimorphism. We also find that asymmetry in B would affect the response to selection more in females than in males. Our results show that sexual dimorphism is more evolvable than studies of rmf suggest and underscore that sexually antagonistic selection is not required for the evolution of sexual dimorphism.