The ’battle for life’ can act on different levels, causing individuals of distinct species, as well as individuals of the same species, to compete over a variety of limiting resources such as food, breeding sites and mates. An important form of competition is driven by sexual conflict and often occurs when reproductive strategies between males and female diverge. This has led to the evolution of different strategies to overcome manipulations by the other sex, while maintaining a level of cooperation sufficient to ensure successful reproduction. The manipulation of one sex by the other through molecular interactions has been illuminated by studies of Drosophila melanogaster. Males tend to maximize their chances at fatherhood by releasing sperm and semen proteins into the females. The semen proteins can benefit both sperm and eggs, however they can also sometimes favour the interests of males whilst generating costs in females. One enigmatic semen protein that falls into this category is the ‘Sex Peptide’, which generates strikingly diverse changes in behavior, reproductive and immune system of females.
In most studies of the effects of Sex peptide, genetic variation has been minimized to delineate its’ function. However, to understand the evolutionary processes and dynamics that characterise Sex Peptide-mediated interactions between both sexes, it is important to study this genetic variation. In this thesis, I trace the impact of Sex Peptide on the consequences of sexual conflict in the Drosophila melanogaster genome. An in-depth investigation was performed to measure female post-mating phenotypic traits (immunity, egg laying, receptivity to re-mating and starvation lifespan) in response to receipt of Sex Peptide, using 32 Drosophila Genome Reference Panel (DGRP) lines. I also developed a novel quantification technique to measure variation in the amount of Sex Peptide transferred among males. A genome wide association (GWAS) and functional annotation study of the tested phenotypic traits revealed significant genetic variation involved in the transfer of, and the post-mating responses to, Sex Peptide. This investigation of natural variation allowed me to map phenotypes onto underpinning genomic variation, and to determine the likely impact of sexual conflict on genome evolution
