How can we explain the enormous diversity of life on our planet? For example, there are over 7,000 species of frogs and toads alone. What is the origin of this diversity? Biologists tend to agree that species differ in their basic biology, but how species differences arise is often difficult to study unless one can see catch species just as they form. Social communication in frogs, where individuals produce sounds heard by others, is a key aspect of what makes a species. This project will explore the idea that processes in the brain that influence the choice of mates play a pivotal role in promoting formation of new species (speciation). The work will investigate how neuronal circuits in the brain change in Upland chorus frogs when they encounter other frogs that also produce sounds that are needed for females to choose mates. A primary objective is to better understand what aspects of brain function are particularly prone to change among frog populations and how this divergence promotes the formation of new species. The populations of Upland chorus frogs to be studied are presently undergoing speciation and, therefore, are ideal for this investigation. This project will also train postdoctoral researchers and graduate students to understand brain physiology, animal behavior, and evolution. This project will investigate how ultimate evolutionary forces drive diversification of proximate neural mechanisms of speciation, and how neural divergence, in turn, feeds back to acc