During the past decade a number of model systems have been studied in attempts to understand the cellular correlates of sexual dimorphisms in the behavior of vertebrates. Much of this work has focused on neurons and muscles controlling the production of social communication signals that play a major role in reproductive behavior during breeding seasons. The principal advantages in studying sexual dimorphisms in all of these systems is that the communication signal--a song, a call, or an electric organ discharge--is stereotyped in appearance, easily quantifiable and controlled by a discrete set of muscles and central neurons. Dr. Andrew Bass is interested in structure- function studies of physiologically identified cells which are sexually dimorphic. This research project concerns studies of a motor system controlling the production of sound communication signals in fishes. The system chosen is the swimbladder or sonic motor system of marine teleosts. The acoustic signal is produced by a single set of muscles which are controlled by a central motor nucleus that may be comparable to the hypoglossal motor nucleus of tetrapods. Dr. Bass has discovered a dramatic sex difference in the gross and ultrastructural features of the muscles controlling sound production in one group of marine teleosts, the midshipmen, Porichthys notatus. There is also a behavioral sex difference in that only males are known to be sonic. Although a major goal of this research project is characterization of structure-function organization in the sonic motor system of male midshipmen, the same studies will be carried out with females to elucidate sexual dimorphisms in the system. Such studies will lead to more well delineated experiments for understanding the cellular mechanisms underlying the development of sexual dimorphisms in the brain behavior of vertebrates.
