Sexual conflict in Drosophila melanogaster

Conflicts between the sexes over mating and reproduction are common in many taxa. In Drosophila melanogaster sexual conflict over mating frequency occurs because male fitness is maximised by a higher mating frequency than that which maximises female fitness. In addition, females incur survival and reproductive costs from mating frequently. The female cost of mating is mediated by male accessory gland proteins (Acps), which are transferred to females in the seminal fluid of males during mating. Theory predicts that sexual conflict can lead to antagonistic coevolution between the sexes in which males evolve traits that benefit males but harm females and females evolve traits to minimise the extent of male-induced harm. This coevolution may be rapid and has the potential to promote speciation. In this thesis I used Drosophila melanogaster as a model organism to investigate the evolution and genetics of sexual conflict. In Chapters 3 and 4 I used selection lines in which the level of sexual conflict had been experimentally manipulated. Chapter 3 describes how females in the selection lines adapted to the level of sexual conflict by evolving different levels of resistance to male-induced harm. Chapter 4 shows that the selected females did not differ in pre-mating resistance to males, suggesting instead that the resistance to male harm had evolved via post-mating changes. Chapter 5 describes how a single Acp, the sex peptide (SP), which reduces female receptivity and increases egg production after first matings, also causes female mating costs. Chapter 6 confirms that SP benefits males by increasing their post-mating reproductive success. Thus, SP benefits males but harms females suggesting that the SP gene underlies sexual conflict in D. melanogaster. Finally, Chapter 7 summarises the thesis and discusses future directions for investigating sexual conflict in Drosophila.