Sexually concoradant and antagonistic genetic variation predicts the evolution of sexual dimorophism over millions of years
Author: Jacqueline Sztepanacz
Affiliation: Department of Ecology and Evolutionary Biology, University of Toronto
Keywords: Other (Quantitative Genetics)
Sexual dimorphism is widely viewed as adaptive, reflecting the evolution of males and females towards divergent fitness optima. Its evolution, however, may often be constrained by the shared genetic architecture of the sexes. Cross-sex genetic covariances determine the extent and timescales on which sexual dimorphism can evolve. Here we start to disentangle the role of multivariate cross-sex covariances in the evolution of sexual dimorphism of wing shape in Drosophila. Drosophila wing-shape has emerged as a model high-dimensional complex trait; it is highly evolvable in contemporary populations, and yet perplexingly stable across phylogenetic timescales. We show that when we transform the space of genetic variance and cross-sex covariance in wing shape into a space of sexually concordant and antagonistic genetic variation, we tend to find more genetic variation that would allow a response to sexually concordant selection. Using a phylogenetic analysis of sexual shape dimorphism for 82 taxa that have been diverging for at least 33 million years we show that shape dimorphism is qualitatively conserved among species, but that with males characterized by longer thinner wings than females. However, we did find quantitative variation among, with evidence that shape dimorphism has adapted to different evolutionary optima in different clades on timescales of about 10 million years. We also found that allometry constrained the evolution of shape dimorphism for the two most variable multivariate trait combinations we studied, but that shape dimorphism was evolutionary labile in other multivariate trait combinations. Our results highlight that the keys for disentangling alternative explanations for dimorphism evolution are a deeper understanding of how microevolutionary parameters of genetic variation relate to macroevolutionary patterns of divergence, together with studies of natural and sexual selection.