Biological diversity in any given community is maintained by reproductive barriers, or factors that prevent interbreeding between species. Multiple, distinct reproductive barriers may prevent interbreeding between species and a central question concerns the chronological order in which these different barriers evolve. Theory predicts that behavioral isolation, or the absence of interbreeding due to differences in courtship behavior, will be the first reproductive barrier to evolve among populations characterized by the strong action of sexual selection. Through the co-evolution of male courtship traits and female preferences, females are predicted to recognize only the courtship traits of males of their own species. Few studies test this prediction directly and evidence that sexual selection plays a primary role in the origin of species remains largely indirect. Darters are a colorful group of North American freshwater fish with diverse and highly exaggerated male courtship signals and this project quantifies the relative rates of evolution of different reproductive barriers and tests, in particular, whether behavioral isolation evolves earliest. Results will provide one of the few direct tests of the fundamental hypothesis that sexual selection drives the origin of species through the co-evolution of male signals and female preferences. Training of undergraduate and graduate students from groups underrepresented in advanced biology is integral to the project. Results will also be presented to area secondary schools, specifically targeting schools with a high representation of minorities and underprivileged students.
