Data from: Correlated evolution of male and female reproductive traits drive a cascading effect of reinforcement in Drosophila yakuba

Selection against maladaptive hybridization can drive the evolution of
reproductive isolation in a process called reinforcement. While the
importance of reinforcement in evolution has been historically debated,
many examples now exist. Despite these examples, we typically lack a
detailed understanding of the mechanisms limiting the spread of reinforced
phenotypes throughout a species' range. Here we address this issue in
the fruit fly Drosophila yakuba, a species that hybridizes with its sister
species D. santomea and is undergoing reinforcement in a well-defined
hybrid zone on the island of São Tomé. Within this region, female D.
yakuba show increased postmating-prezygotic (gametic) isolation towards D.
santomea when compared with females from allopatric populations. We use a
combination of natural collections, fertility assays, and experimental
evolution to understand why reinforced gametic isolation in D. yakuba is
confined to this hybrid zone. We show that, among other traits, D. yakuba
males from sympatric populations sire fewer progeny than allopatric males
when mated to allopatric D. yakuba females. Our results provide a novel
example of reinforcement acting on a postmating-prezygotic trait in males,
resulting in a cascade of reproductive isolation among conspecific
populations.