Postcopulatory sexual selection generates speciation phenotypes in Drosophila

Background: Identifying traits that reproductively isolate species, and the selective forces underlying their divergence, is a central goal of evolutionary biology and speciation research. There is growing recognition that postcopulatory sexual selection, which can drive rapid diversification of interacting ejaculate and female reproductive tract traits that mediate sperm competition, may be an engine of speciation. Conspecific sperm precedence (CSP) is a taxonomically widespread form of reproductive isolation, but the selective causes and divergent traits responsible for CSP are poorly understood.
Results: To test the hypothesis that postcopulatory sexual selection can generate reproductive isolation, we expressed green (GFP) or red fluorescent protein (RFP) in sperm heads of recently diverged sister species, Drosophila simulans and D. mauritiana, to enable detailed resolution of species-specific sperm precedence mechanisms. Between-species divergence in sperm competition traits and m...