Female-driven intersexual coevolution in beetle genitalia

Genital coevolution is a pervasive phenomenon as changes in one sex tend
to impose fitness consequences on the other generating sexual conflict.
Sexual conflict is often thought to cause stronger selection on males due
to the Darwin-Bateman’s anisogamy paradigm. However, recent studies have
demonstrated that female genitalia may be equally elaborated and perform
diverse extra-copulatory functions. These characteristics suggest that
female genitals can also be primary targets of selection, especially where
natural selection acts on female-exclusive functions such as oviposition.
Here, we test this hypothesis in a statistical phylogenetic framework
across the whole beetle (Coleoptera) phylogeny, investigating whether
coevolution of specific genital traits may be triggered by changes in
females. We focus on traits of the proctiger, which composes part of the
male terminalia and the female ovipositor. Our results present a
comprehensive case of male-female genital coevolution, and provide solid
statistical evidence for a female-initiated coevolutionary process where
the vast majority of evolutionary transitions in males have occurred only
after changes in females. We corroborate the hypothesis that female traits
may change independently and elicit counter-adaptations in males.
Furthermore, by showing a consistent pattern across the phylogeny of the
most diverse group of animals, our results suggest that this female-driven
dynamics may persist through long time scales.