Speciation is responsible for the diversity of life on earth. The process of speciation requires the evolution of reproductive isolation. One type of reproductive isolation is sexual isolation derived from differences in mating behaviors. The fruit fly species to be studied, Drosophila simulans and D. sechellia, differ in two elements of courtship. The first element, courtship song, is produced by the male to stimulate the female. Females prefer the song of their own species and only reluctantly mate in the presence of a different species' song. The second element is a contact pheromone. D. sechellia females have a different major pheromone than D. simulans females. D. simulans males discriminate against D. sechellia females because of this pheromone difference. The project uses two genetic analyses of these traits. First, quantitative genetics will be used to estimate the number of genes involved, their location in the genome and their individual effects. These will be studied for both courtship elements (song and pheromones) and for the preferences exhibited by the opposite sex for these traits. Second, regions of the genome genetically implicated in the courtship traits will be introduced from one species to the other, in isolation of all other gene regions. These genetic analyses will be performed to identify the genes that have had a regulatory change between the species. Teaching activities will focus on improving existing courses on evolution and genetics and developing new courses on speciation and behavioral genetics. The intellectual merit of this project is to elucidate the genetics of species differences that can contribute to speciation, a topic that is not well understood. The broader impacts of this project include educational opportunities for students who will receive interdisciplinary training in behavioral and genetic methods. In addition, understanding behavior in Drosophila, a model system, provides insights into the behavioral analysis of both more complex species and pest species.