31 Oral - Evolution I
Thursday April 07, 6:15 PM - 6:30 PM

Authors:
Nora Brown ¹; Benjamin Gordon ¹; Snigdha Misra ¹; Caitlin McDonough-Goldstein ²; Andrew Clark ¹; Geoffrey Findlay ³; Mariana Wolfner ¹

Affiliations:
1) Cornell University, Ithaca, NY; 2) University of Vienna, Vienna, Austria; 3) College of the Holy Cross, Worcester, MA

Keywords:
u. other (Reproduction/sexual conflict); h. sex-specific traits and molecules

In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology and behavior. Genes encoding SFPs include some of the fastest evolving in the genome and display remarkable levels of turnover between species, likely the consequence of sperm competition and/or sexual conflict. The SFP suite in D. melanogaster includes several members of large gene families, including the odorant binding protein (Obp) family. Previous work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility in the ejaculate. Interestingly, Obps are found in the seminal fluid of several arthropod species, though the reproductive functions of these proteins in any species remains uncharacterized. By analyzing comparative RNAseq data from the male reproductive tract of multiple Drosophila species, we found that one seminal Obp, Obp56g, shows high male reproductive tract expression only in a subset of species in the melanogaster and obscura groups, suggesting co-option of this protein for reproductive function over evolutionary time. We used RNAi and CRISPR/Cas9 generated mutants to test the role of Obp56g, as well as the other six seminal Obps, in D. melanogaster fertility. Whereas male flies lacking six of the seven seminal Obp genes tested so far were fully fertile, males lacking Obp56g failed to induce post-mating responses in their mates. We found that Obp56g is expressed in the male’s ejaculatory bulb, an important tissue in the reproductive tract that synthesizes components of the mating plug. Indeed, we found males lacking Obp56g fail to form a mating plug in the mated female’s reproductive tract, which is needed to induce post-mating responses and sperm storage. We then used tissue specific RNAi experiments to show that ejaculatory bulb/duct expression of Obp56g is necessary for both mating plug formation and male fertility. Together, this work uncovers a novel role for Obp56g in reproduction and enhances our understanding of seminal fluid evolution.