The second sex: Functions and mechanisms of sperm manipulation in female Drosophila melanogaster

Offspring production commences with mate-choice and culminates in the generation of genetically similar individuals. Males and females play distinct roles in this process: males compete to gain access to females, and females exhibit choice. When a female mates more than once, these pre-copulatory interactions extend to the female reproductive tract as sperm from multiple males compete to fertilize her eggs. To investigate the possibility that females bias sperm use after copulation, I employed the fruit fly, Drosophila melanogaster. By reviewing the literature, I found that our understanding of female post-copulatory behaviours is relatively limited and set out to investigate the mechanisms and functions of two female post-copulatory behaviours: sperm storage (movement of sperm into storage organs) and sperm ejection (removal of ejaculate). I found that females alter their attractiveness and chances of remating via ejection of sperm and anti-aphrodisiac pheromones. I also found that females who remate in quick succession produce different patterns of paternity compared to females with slower remating rates indicating an influence of the female on whose sperm is used to fertilize her eggs. To explore how this choice occurs, I artificially modified the activity of various populations of neurons and determined that sperm storage and ejection are regulated by neuronal circuits in the female central nervous system. Overall, I conclude that females’ active control over reproduction extends past pre-copulatory mate choice to include an influence on whose sperm fertilizes her eggs to produce offspring.