EVOLUTION OF SENSORY SYSTEMS

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The long range goals of this project are to determine the ecological and neurological correlates of the variation in auditory abilities in mammals and to examine the role of vision in the evolution of hearing. It embarks on a comparative survey of hearing and passive sound localization in bats. Bats present an opportunity to examine the effects that elaborations of hearing for the active use of sonar have had on the more basic auditory and visual abilities that are part of the common mammalian plan. We propose to examine the auditory abilities of a variety of bat species selected to help answer the questions of why mammals hear as they do (evolution of hearing) and how different hearing abilities are achieved (anatomical and physiological substrates of hearing). There are three specific aims; 1. To determine the hearing capacities of a variety of species selected on the basis of their foraging strategy (type of sonar and reliance on passive sound localization and vision). Behavioral tests will include:complete audiograms with special emphasis given to the frequencies of the echo pulse and prey-generated noises, frequency difference limens, passive sound localization acuity, and the use of binaural time and intensity cues. 2. To determine whether the relation between vision and sound-localization acuity found in other mammals also applies to bats. Bats have altered the relative roles of vision and audition and provide an opportunity to explore further the relation between hearing and vision in mammalian evaluation. Retinae will be examined histologically to determine the field of best vision and limit of visual acuity; these features will be examined for their relation to sound-localization. 3. To examine and quantify the auditory brainstem nuclei of the bats tested in this project in order to determine the relation between auditory anatomy and behavioral hearing abilities. These nuclei are some of the most variable in the auditory nervous system and they vary widely among bats of differing lifestyles and echolocation calls. The ultimate goal of this research is to gain perspective on the atypical auditory functioning and neural systems of humans. We will gain insight into how the interaction of the senses in different lifestyles has influenced the evolution of perceptual adaptations and the neural substrates underlying those adaptations.