Polygenic outcomes of sexually antagonistic selection

Sexual antagonism occurs when males and females have different fitness optima for a phenotype, but are constrained from evolving to these optima because of their shared genome. We study the response of a polygenic phenotype to the onset of sexually antagonistic selection, modeling a phenotype initially under stabilizing selection around an optimum, followed by a sudden divergence of the male and female optima. We observe rapid phenotypic evolution to these new optima via small changes in allele frequencies genome-wide. We study the role of sex chromosomes in this divergence and find that, in the absence of dosage compensation, the X chromosome favors evolution toward the female optimum, inducing co-evolutionary male-biased responses on the autosomes. However, dosage compensation obscures the female-biased interests of the X, causing it to contribute equally to male and female phenotypic change. In both scenarios, we see little effect of dominance in the genetic variation utilized by the X chromosome vs. the autosomes. We go on to examine the dynamics of stabilizing selection once the male and female optima have been reached, exploring a subtle mechanism through which the X chromosome, via the Bulmer effect, can cause higher equilibrium phenotypic variance in males than females. Finally, we consider how sexual antagonistic selection might persist across longer time scales, demonstrating that random fluctuations in an adaptive landscape can generate prolonged intragenomic conflict. Overall, our results provide insight into the response of complex phenotypes to sexually antagonistic selection and the evolution of sexual dimorphism.