Acoustic Communication by Temporal Codes: Evolution and Neurobiology

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The goal of Dr. Gerhardt's research is to gain knowledge about mechanisms and evolution of acoustic communication in vertebrate animals. In particular, the research will focus on temporal codes, that is, information encoded in the timing of repeated elements in natural communication sounds. Dr. Gerhardt will carry out behavioral studies of signal (sound) structure and the discrimination of these sounds, with both wild-type and hybrid animals, and he will also perform neurophysiological studies of the responses of auditory neurons to time patterns in sounds of biological relevance. Two species of North American gray treefrogs (Hyla chrysoscelis and H. versicolor) will be studied. These frogs are particularly suitable as a model system for vertebrate sound communication because males of each species produce a small set of very stereotyped communication signals. Females reliably respond to natural and synthetic (computer-generated) signals by approaching a loudspeaker, just as they approach a calling male in nature. The timing properties of the male's sounds are not learned, but develop normally when the frogs are raised in acoustic isolation. The two species will be cross-mated artificially to produce viable hybrids, thus affording the opportunity to study genetic mechanisms of both calling and selective approach to sounds. There are extensive areas where just one species occurs, and other areas where both species breed in the same ponds at the same time, at the risk of producing sterile hybrids if they make an error of identification. Thus, the selectivity of females from areas of overlap will be compared with that of frogs from areas where only one species occurs. The auditory system of treefrogs has been well studied, so that a great deal of basic information is already available as a foundation for the neurophysiological studies of time coding that will be done in these two species. In this research the results of the behavioral experiments will guide and complement the neurophysiological work. The results of this research should provide insights into fundamental properties of all acoustic communication systems in vertebrates. The treefrog system is especially powerful in that a combination of genetic and neurophysiological techniques can be used in ways that would be impossible in higher animals.