Hesketh, J; (2013) Sex-specific selection and sexual antagonism in the fruit fly, Drosophila melanogaster. Doctoral thesis , UCL (University College London).

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Abstract

Males and females differ in their reproductive roles, and as a consequence each sex is subject to divergent selection pressures to optimise its own reproductive success. Due to the shared genome between males and females these selection pressures frequently act on shared phenotypic traits. Divergent selection can favour the invasion of sexually antagonistic alleles which increase the fitness of one sex at the detriment of the other. Sexual antagonism can be subsequently resolved through the evolution of sex-specific gene expression, allowing the sexes to diverge phenotypically. While sexual dimorphism is common, recent evidence shows that antagonistic genetic variation continues to segregate in populations of many organisms. The basis of sexual antagonism remains poorly understood. I first present empirical data on the interaction between sexual antagonism and genetic drift in small populations that had independently evolved under standardised conditions. I demonstrated that these experimental populations of Drosophila melanogaster had diverged in male and female fitness, with some populations showing increased male but decreased female fitness, while other populations showed the reverse pattern. I also exploited a sample of nine genomes that belonged to three fitness classes (low male/high female, high male/low female, intermediate in both sexes) to test the association between the sexually dimorphic trait wing morphology (size and shape) and fitness in both sexes. I found that wing morphology significantly affected the fitness of both males and females, but to a differing degree in each sex. In males wing shape rather than wing size was especially important. I found evidence that there was appropriate genetic architecture for the existence of sexual antagonism, and for divergent selection on aspects of wing morphology. I place all of my findings in the context of variation in sexually dimorphic traits and sex-specific fitness.

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