Evolution of gene expression in response to sexual selection

We are fascinated with morphological differences between the sexes. Darwin explained the observation that males and females can differ dramatically in morphology with his theory of sexual selection, or the competition for mates. Subsequent interest in sexually dimorphic traits showed that males who bear exaggerated features enjoyed greater mating success. Thus, increased intensity of sexual selection is predicted to increase trait exaggeration and therefore sexual selection is considered to be a major force responsible for biodiversity. For these trait changes to occur, however, the genes that control them must also change. This fact gave rise to the idea that sexual selection is also a strong force responsible for molecular evolution. However, evidence that sexual selection also causes changes in the genome is indirect, largely based on correlations between differences in genes associated with reproduction (e.g., sexually dimorphic expression or expression in reproductive tissues) and the presence of sexual selection. Recent technological advances allow us to move beyond correlative studies and directly examine genomic changes in response to sexual selection. Here we propose to test the role of sexual selection in molecular evolution by a combined approach of experimental evolution of fruit flies, in which sexual selection is manipulated to be either present or absent, and next generation sequencing, in which genetic changes due to variation in sexual selection are identified directly. We already have found that populations in which sexual selection is present have evolved greater sex differences in morphology and behaviour compared to populations in which sexual selection is absent. We can thus connect these phenotypic biodiversity changes that were predicted as a consequence of sexual selection with the underlying genetic changes associated with these traits. This work will provide decisive evidence for how sexual selection causes genetic divergence, and in turn how it may generate the spectacular diversity of phenotypic traits associated with variation in mating systems. Thus, we will improve our understanding of one of the major drivers of biological diversity.