The Effects of Sexual Selection and Ecology on Adaptation and Diversification in Drosophila Melanogaster

Sexual selection is pervasive in nature and plays an important role in the evolution of biological diversity both within and among sexual species. However, while we have a good understanding of how competition for reproductive opportunities and mate choice can drive the evolution of exaggerated secondary sexual traits, much less is known about how sexual selection interacts with other forms of natural selection and the consequences such interactions may have for adaptation to novel environments, the purging of deleterious mutations, and population divergence/speciation. In my thesis, I carried out a series of experiments with the fruit fly Drosophila melanogaster to test hypotheses regarding the operation of sexual selection and to broaden our understanding of how sexual selection may influence adaptation and diversification. Theory suggests that natural and sexual selection may align to promote adaptation and the purging of deleterious mutations, although the harm imposed by sexual conflict may counter this. In two separate experiments, I find no evidence that sexual selection promotes adaptation to a novel environment and, rather than aligning with natural selection, I find that the effects of sexual conflict may cause sexual selection to hamper the purging of deleterious mutations. With respect to diversification, sexual conflict has been suggested to be an important, non-ecological driver of population divergence. However, the traits involved in sexual conflict may also affect nonsexual fitness and natural selection may therefore act to constrain diversification. Using an evolution experiment, I demonstrate ecologically-dependent parallel evolution of traits involved in sexual conflict, providing evidence for ecology’s importance in divergence via sexual conflict. Overall, my work has shed light on the interaction of natural and sexual selection and the consequences this may have beyond the evolution of exaggerated sexual displays and armaments