Investigating the Female's Role in Sperm Competition in Drosophila Melanogaster

Abstract

The process of fertilization involves many interactions between males, females, and their gametes. This is even more complex in cases of multiple mating, such as in Drosophila melanogaster, as the presence of ejaculates from multiple males and the female’s ability to store sperm presents the opportunity for sperm competition to occur. In D. melanogaster, male- derived seminal fluid proteins are known to influence various post-mating responses in the female including sperm competition outcomes. While studies have shown that female genotype is also important for sperm competition outcome, the mechanisms underlying the female’s contribution to the success of a particular male’s sperm are less understood. To begin to examine the female’s role in sperm competition, we took two approaches in D. melanogaster: First, we used RNAi knockdown of candidate genes to assess the impact of decreased expression of these genes on sperm competition outcomes. We found that of 29 candidate genes tested, 10 affect sperm competition outcomes when knocked down in females. Second, we used fly lines mutant for neuromodulators to assess sperm storage outcomes from two different types of males mated sequentially. We found that the neuromodulators octopamine and tyramine may influence relative sperm storage of sperm from competing males. Collectively, results from these experiments provide a clearer picture of the genes and mechanisms involved in the female control of sperm competition outcomes and sperm dynamics.