Sex-specific dominance maintains multilocus polymorphism and can resolve sexual conflict

Abstract

Sexually antagonistic selection arises when females and males favour different phenotypes but share their genetic basis. Beneficial sex-specific dominance can alleviate this conflict by allowing each allele to be more dominant in the sex in which it is beneficial. Whether the coevolution of dominance and allelic diversity can generate and maintain polymorphism across a polygenic trait remains unclear. We investigate a quantitative trait encoded by multiple diploid loci, with allelic effects shared between the sexes and evolving sex-specific promoter affinities determining dominance. We show that sex-specific dominance can generate polymorphism across many loci, including under weak or asymmetric selection. Whereas additive allelic effects lead to the concentration of polymorphism at a single major locus, evolving dominance allows polymorphism to become distributed across loci. This distributed polygenic architecture generates sexual dimorphism while reducing within-sex phenotypic variance: increasing the number of polymorphic loci, as well as allelic diversity within loci, allows female and male phenotypes to approach their respective optima with lower segregation load. Sufficiently strong selection can instead cause polymorphism to collapse toward a single major locus, but the selection strength required for this transition increases sharply with the number of contributing loci. Thus, evolving sex-specific dominance can make widespread genetic polymorphism part of the resolution of sexual conflict.