Who’s zooming who? seminal fluids and cryptic female choice in diptera

Abstract

Dipteran females have many opportunities to influence the reproductive success of their mates. After each mating, females may influence their mates’ postcopulatory reproductive success by choosing whether and where to store sperm, whether and when to remate and lay eggs, and how much to invest in eggs fertilized by different males. Female neural, endocrine, and muscular mechanisms are necessary for these processes to occur. We review physiological experiments that have borne this out. Further evidence from many Diptera shows that seminal fluid proteins (Sfps) also influence female post-copulatory processes including ones that affect sperm use. The most comprehensive evidence comes from Drosophila melanogaster, whose seminal proteome is well characterized. In this species, studies of sequence variation, including in natural populations, and of gene-specific knockdown in the laboratory, have identified male and female genes whose actions influence and/or correlate with post-copulatory processes in the female. Furthermore, co-evolution between Sfps and female reproductive proteins suggests their involvement in common functional pathways. We review the evidence for the interaction of Sfp-mediated effects and cryptic female choice (CFC), with a focus on D. Melanogaster and evidence from other Diptera as available. Finally, we conclude by assessing what is known and as yet unknown about the interface between CFC and Sfps and by suggesting avenues for further research in this fascinating area.