Fig 2. Alternative scenarios for genetic architecture and sexual dimorphism. In each panel, small circles outlined in black represent all autosomal or X-linked genes in a developmental pathway underlying a phenotype. Solid lines represent loci that contribute to variation in phenotype (genetic architecture) and the width represents effect sizes. Inner circles represent phenotype distribution in females (red) and males (blue) as well as phenotypic optima (dashed lines). Panel (a): representation of the traditional conceptualization of sexual conflict, where phenotypic optima differ substantially but genetic architectures are largely overlapping. Panel (b): male and female phenotypes can diverge towards phenotypic optima as more of the shared architecture affects only females (red circles and lines) or males (blue circles and lines). Panel (c): non-overlapping phenotypic distributions occur with complete decoupling of male and female architecture of a phenotype. Panel (d): recent work suggests that many monomorphic traits have sex differences in genetic architecture. Panel (e): loci on the Y chromosome (or W in ZW systems) can lead to sex-specific phenotypic distributions even when the remainder of the genetic architecture is shared.
Abstract
Anisogamy, different-sized male and female gametes, sits at the heart of sexual selection and conflict between the sexes. Sperm producers (males) and egg producers (females) of the same species generally share most, if not all, of the same genome, but selection frequently favours different trait values in each sex for traits common to both. The extent to which this conflict might be resolved, and the potential mechanisms by which this can occur, have been widely debated. Here, we summarize recent findings and emphasize that once the sexes evolve, sexual selection is ongoing, and therefore new conflict is always possible. In addition, sexual conflict is largely a multivariate problem, involving trait combinations underpinned by networks of interconnected genes. Although these complexities can hinder conflict resolution, they also provide multiple possible routes to decouple male and female phenotypes and permit sex-specific evolution. Finally, we highlight difficulty in the study of sexual conflict over shared traits and promising directions for future research.