Mechanisms underlying sexual selection and sexual conflict in Drosophila melanogaster.

The revelation that females of many taxa mate with multiple males has broadened perspectives in sexual selection to encompass the study of conflicts of interest between males and females over mating and reproduction. Conflict often exists between the sexes over reproductive decisions such as how often to mate, because the optimum mating rate may often be higher for males than for females. Selection is expected to favour traits in males that manipulate female mating frequency and that confer an advantage over competing males, particularly in relation to post- copulatory competition. A significant fraction of male post-copulatory success in Drosophila melanogaster is determined by the action of accessory gland proteins (Acps) that are transferred by males to females during mating. Acps have significant effects on female behaviour and physiology and have been shown to play a role in mediating sexual conflict. Exploring the role of the male accessory glands and of Acps in moulding evolutionary interactions between the sexes and in determining overall fitness remains an important task and one that will illuminate the mechanisms underlying sexual selection and sexual conflict. In this thesis I use Drosophila melanogaster as a model system to ask how reproductive traits, strategies and morphologies have been shaped by sexual selection and sexual conflict. I show that traits related to ejaculate investment and depletion have evolved in lines of D. melanogaster with an evolutionary history of exposure to high or low levels of sperm competition and mating opportunities. I then describe how I initiated, propagated and analysed lines selected for increased and decreased male accessory gland size. I describe the direct and correlated responses to selection and show that accessory gland size is associated with male post- copulatory success but not with the magnitude of female mating costs. I further probe the nature of female mating costs by analysing the contribution to them of a single Acp, Acp62F. Finally, I summarise my thesis and discuss future directions for investigating the mechanisms of sexual selection and sexual conflict in Drosophila