Pruvot, C. | bioRxiv Science

bioRxiv2026

Sexual conflict, directional sexual selection and phenotypic plasticity jointly drive the evolution of extreme phenotypic variation

How broad phenotypic variation is maintained in natural populations in the face of selection is a central question in evolutionary biology. We address this question in the water strider Microvelia longipes, where males exhibit striking variation in rear leg length used in male-male contests for dominance. Using reaction norm experiments on inbred lines, we demonstrate that phenotypic plasticity contributes to expanding phenotypic variation, but requires high genetic variation to generate the broad range of trait expression observed in natural populations. Experimental evolution favouring trait exaggeration revealed that directional sexual selection not only fails to erode variation of male rear leg length, but rather amplifies it beyond the natural distribution. Additionally, male-limited selection in favour of dominance generated substantial fecundity costs in females, underscoring the role of sexual conflict driven by females in constraining exaggerated secondary sexual traits in males. Our findings show that sexually antagonistic selection and directional sexual selection jointly generate high genetic variation, which phenotypic plasticity inflates into broad phenotypic distribution of male weapon size. This provides an empirical explanation for the high variability of male exaggerated weapons in nature.

evolutionary biology↗

bioRxiv2024

A shared genetic basis for sexually antagonistic male and female adaptations in the toothed water strider

Sexual conflict can drive the divergence of male and female phenotypes and several cross-species comparative analyses have documented patterns of correlated evolution of sex-specific traits that promote the evolutionary interests of the sexes. However, male-female coevolution can be highly dynamic. Moreover, if male and female traits do not have an entirely distinct genetic basis, this can have profound effects on their coevolutionary dynamics. Here, we use water striders, a well-studied model system for sexually antagonistic coevolution, and ask whether sex-specific phenotypic adaptations covary across populations and whether they share a common developmental genetic basis. Using comparative analyses both at the population and species levels, we document an association between a derived male mate-grasping trait and a likely female anti-grasping counteradaptation in the toothed water strider Gerris odontogaster. Interestingly, in one population where males did not express their derived grasping trait, females had also regained the ancestral morphology. We then used experimental manipulation of gene expression, and show that these male and female traits are both linked to a common developmental genetic program containing Hox and sex determination genes, despite the fact that they are different structures on different segments. Our work thus suggests that the pleiotropic nature of developmental genetic programs can blur the distinction between inter- and intralocus genetic conflict.

evolutionary biology↗