Investigating the mechanisms by which two Drosophila melanogaster seminal fluid proteins, sex peptide and ovulin, elicit post-mating responses in the female

The actions of seminal fluid proteins (SFPs), which are part of the ejaculate that males transfer to females upon mating, are important for reproductive success in both sexes in a wide range of taxa. Research that has focused on identifying these proteins and studying their functions in the female has provided invaluable insight into understanding reproduction across species. For the first part of my thesis, I investigated the role of the SFP, sex peptide (SP), in the post-mating change in female nutrition and digestion. Previous work has shown that SP increases female food intake after mating and slows the rate of intestinal transit, thereby causing her to produce more concentrated excreta. SP can have both transient and long-term effects on mated females; the latter occur because of the peptide's binding to, and slow release from, sperm in the female. I used timed measures of excretion by female flies that had mated to males mutant in SP or in its regulators, to test the duration of SP's effect on excretion. I found that SP's effect on excretion persists for at least ~1 week after mating, and that this persistence requires that SP bind to and be released from sperm.;Interactions between the sexes continue at the molecular level in the female beyond the conclusion of mating. Thus, SFPs need to interact with female proteins. Although the suite of Drosophila SFPs are known, a female receptor for only one Drosophila SFP has been identified (the sex peptide receptor). For the second part of my thesis, I focused on identifying a female receptor for the SFP, ovulin, which increases ovulation within the first 24 hours after mating by stimulating octopaminergic signaling in the female nervous system. By screening for Drosophila receptors that exhibit a correlated rate of evolution with ovulin, we identified 19 ovulin receptor candidates and upon further phenotypic analysis, I was able to narrow it down to one candidate, CG15744. Several assays have been initiated to confirm the ovulin-CG15744 interaction, including a cell culture-based calcium assay, split-ubiquitin yeast two hybrid, and a Tango reporter assay.