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

Sexually antagonistic selection occurs when females and males prefer different traits, yet share the same genetic foundation. Under these conditions, beneficial sex-specific dominance can help resolve this conflict by favoring each allele more in the sex where it provides an advantage. The coevolution of dominance and allelic diversity may create and sustain polymorphism across a polygenic trait, although this remains uncertain.

The study examines a quantitative trait controlled by multiple diploid loci, with effects that are both shared between the sexes and sex-specific promoter affinities determining dominance. The research demonstrates that sex-specific dominance can produce polymorphism across numerous loci, even when selection is weak or uneven. While typical additive allelic effects tend to concentrate polymorphism in a single major locus, evolving dominance allows polymorphism to spread out across various loci.

This polygenic architecture, with its distributed nature, results in sexual dimorphism and lowers within-sex phenotypic variance. Consequently, a larger number of polymorphic loci and allelic diversity within these loci enable female and male phenotypes to reach their respective optima with less segregation load. In contrast, if the selection is strong enough, polymorphism may collapse towards a single major locus.

However, the required selection strength to achieve this transition grows rapidly with the number of contributing loci. In essence, the evolution of sex-specific dominance can make extensive genetic polymorphism an integral part of resolving sexual conflict.