It has been almost 150 years since Darwin’s “The Origin of Species” was published, yet the mechanisms that lead to the creation of new species are still a topic of fervent research in Evolutionary Biology. In the last several decades, there has been considerable interest in how genetic drift and adaptive processes internal to populations may lead to population divergence. It has been recognized that intersexual co-evolution may drive the rapid evolution of reproductive traits, leading to reproductive isolation between populations in allopatry. To explore the nature of this process, I conducted a series of interpopulation interaction experiments using a set of laboratory-evolved Drosophila melanogaster populations. These “B” (for baseline) populations share a common ancestor and had evolved in identical habitats in allopatry for 650-700 generations prior to my experiments. When different populations were combined in competitive fitness assays, I found that foreign males usually suffer depressed fitness when competing with males who share a common evolutionary history with the focal females. I selected a subset of B populations to investigate potential sources of variation that could explain this result. I examined; 1) characters involved in post-copulatory interactions between mates and 2) traits involved in mating behaviour. I found that sperm precedence patterns varied significantly depending on female population of origin and suggestive evidence that males between populations vary in ability to compete in sperm offence. Males also varied in mating behaviour between populations, however we found no evidence that divergence of these traits was correlated to that of traits involved in post-copulatory interactions, suggesting that understanding how intersexual co-evolution drives population divergence requires considering independent components of the reproductive phenotype and their contributions to overall fitness differences. / Thesis (Master, Biology) -- Queen's University, 2008-08-13 12:29:52.602