Females drive postmating reproductive trait evolution across Drosophila species, but not via remating rate

While traits that contribute to premating sexual interactions are known to be wildly diverse, much less is known about the diversity of postmating (especially female) reproductive traits and the mechanisms shaping this diversity. To assess the rate, pattern, and potential drivers of postmating reproductive trait evolution, we analyzed male and female traits across up to 30 Drosophila species within a phylogenetic comparative framework. In addition to postmating reproductive morphology (e.g., sperm length, reproductive tract length and mass), we also quantified mating behaviors including female remating rate—a common proxy for the strength of postmating sexual selection. We found evidence for strong coevolution between male and female postmating traits (specifically sperm length and sperm storage organ size). However, remating rate was not associated with the rate of evolution or exaggeration of either male or female postmating reproductive morphology, once phylogenetic relatedness was accounted for. We infer that female-mediated and intersexual selection predominantly drive the evolution of our postmating morphological traits, including via divergent male and female interests in controlling paternity. In comparison, remating rate has a complex and likely secondary role in shaping this evolution, in part because this trait can be both a driver and a product of postmating selection.