Dancing in the Dark: The evolution of visually mediated courtship behaviors and sexual dimorphisms in spotted winged Drosophila

Abstract

I employed a multidisciplinary approach to examine the function and evolution of sexual dimorphisms, male wing spots and male wing displays, across four species subgroups of Drosophila. In chapter one, I explored the function of wing spots in three species of the D. suzukii group using female choice tests by placing mating pairs in darkness. I found that females do not show a statistical preference for spotted males in choice experiments, but that vision is either required for or facilitates mating success. The wing spot may not be as important for mating decisions as previously hypothesized but could enhance courtship displays in more complex environments. In chapter two, I used whole genome sequence data to build a phylogeny of the spotted winged Drosophila in the D. melanogaster group, identified the likelihood of ancestral states of the wing spot character, and tested for conservation of the morphology. The rate of evolution is too rapid to determine if wing spots are ancestral and subsequently gained or lost throughout the subgroups, but multiple convergent events were identified. The wing spot did not have a phylogenetic signal and was correlated with frontal courtship display behaviors, suggesting that wing spots are likely a rapidly fluctuating sexually selected character. In chapter three, I measured visually mediated behaviors of 13 species of spotted and non-spotted Drosophila and mapped behavior to the phylogeny to identify associations between behavior and wing spot morphology that could explain the observed evolutionary patterns. Courtship behavior is labile, and visually mediated long-term copulation acceptance is associated with wing spot morphology. The results in total suggest that species delimitation could be driven by female choice sexual selection on male dimorphisms. In chapter four, I detailed potential functions of the wing spot. This study lays the groundwork for further study on the function of various male displays observed in species where males have sexual dimorphisms.