Differences in reproductive behaviors can prevent interbreeding between populations, thereby promoting the formation of new species (speciation). How do differences in the brain contribute to behavioral divergence and speciation? This project combines functional neuroanatomy, genetics, and behavioral experiments to study differences in the brain that may lead to different mating decisions between populations in a single species. The researcher will focus on variation within a species of a frog, Physalaemus petersi. The experiments will test which sensory cues the females in the two populations of P. petersi are using to make their divergent mating decisions, and identify which brain regions function differently to cause these behavioral differences. The proposal is a novel attempt to understand fundamental questions about the neural mechanisms of natural decisions. The proposed work will take significant steps in linking evolution of the brain to the behavioral differences that, by promoting reproductive isolation between populations, may contribute to speciation. The proposed work will include numerous opportunities for training. Four US undergraduates and four Ecuadorian undergraduates will participate in the project and receive training in neuroscience, behavior, and field experiments. One of the Ecuadorian students will spend a semester in the US working with the researcher and the US undergraduates to experience the laboratory side of research in neuroethology.