Reproductive Biology and Speciation in Drosophila pseudoobscura

Sexual selection is an important force driving the evolution of reproductive traits, including sperm morphology and mating behaviour. Divergent sexual selection among populations can eventually lead to errors in spermatogenesis in inter-population hybrids, and subsequently speciation. In Chapter 2, I identify a novel sperm class and how its proportion in the ejaculate is adjusted when Drosophila pseudoobscura males are exposed to competition. In Chapter 3, I assess how competition causes both males and females to adjust their mating behaviour. In Chapter 4, I characterize interspecific hybrid spermatogenic breakdown from two closely-related sub-species. While the genetics of hybrid sterility has been widely studied, the defective spermatogenic phenotypes have largely been ignored. I found that spermatogenic errors are exclusively postmeiotic and partially caused by divergence at the ‘speciation gene’ overdrive. The results of this thesis expand our understanding of the evolution of novel reproductive traits and the evolution of hybrid male sterility