Genetic Mechanisms for the Maintenance of Behavioral Mating Barriers in Drosophila

One of the most successful and diverse systems involved in the maintenance of behavioral barriers between closely related animal species is pheromonal communication. In the fruit fly, contact chemosensation input is especially important during sexual decision-making as it allows for the sensing of sex and species-specific non-volatile cuticular hydrocarbons (CHCs), which function as insect pheromones. However, how pheromonal systems support the maintenance of mating barriers is puzzling since any change in either pheromone ligands or their cognate receptors would carry a fitness cost, which should be eliminated by stabilizing selection. To resolve this evolutionary conundrum I hypothesized that pleiotropic genes play a role in both the perception and synthesis of mating-related pheromones. In support of my hypothesis, I found that the gene Gr8a, a sexually dimorphic member of the gustatory receptor (Gr) family, is expressed in both chemosensory neurons and pheromone-producing oenocytes. Mutations in Gr8a lead to courtship related phenotypes that are consistent with a role in sensing inhibitory mating pheromone in males and females and the synthesis of inhibitory pheromones in males. Thus, my findings indicate that a single chemosensory receptor affects not only the perception, but also the production of pheromones in Drosophila. My thesis provides a simple solution to an important unresolved evolutionary question by suggesting that a single major genetic locus can drive the evolution of both pheromones and their receptors and thus the maintenance of behavioral mating barriers between closely related species