Evolutionary causes and consequences of sexual conflict and phenotypic divergence under the constraint of a shared genome

Abstract

Sexual dimorphism is common in nature. Whether it is sexual size dimorphism, or exaggerated trait dimorphism, males and females often look quite different. This sexual dimorphism arises despite a largely shared genome. To explore the evolution of sexual dimorphism, we use artificial selection, experimental evolution, and RNA-seq. We explore sex-biased gene expression in the sexually dimorphic Drosophila prolongata using RNA-seq analysis. We show that in D. prolongata, there are changes in sex-biased gene expression in developmental genes and transcription factors and changes in the magnitude and number of differentially expressed genes potentially leading to exaggerated trait development. Using artificial selection lineages with reversed sexual size dimorphism in D. melanogaster we identify a polygenic response to discordant selection, and a region differentially segregating between the sexes where selection pulls the sexes against their original sexual dimorphism. Using experimental evolution, we show that current hypotheses for the ecological precursors for sexually dimorphic evolution may be incomplete. Previous work has hypothesized that an ecological setting that creates potential for male monopolization of females and differential success for males who win duels would be sufficient to initiate the evolution of sexually dimorphic weapons. Here, we show that these ecological structures were insufficient to initiate sexually dimorphic evolution in D. melanogaster and propose that low density and opportunity for male-male signalling may be additional ecological ingredients critical for weapon evolution. Using these diverse methodologies, we expect to be able to add to our understanding of how sexual dimorphism evolves, and how a shared genome contributes to divergent phenotypes within a species.