Doctoral Dissertation Improvement: Structure, Performance and Evolution of the Primate Auditory System

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The auditory system is the most mechanically complex sense in mammals, comprised of numerous bones, muscles, and other soft tissues. Consequently, this region provides many opportunities to study acoustical function and structural differences between various groups of animals have also been used to help infer their relationships to each other. Despite substantial investigation of the function of the auditory system in other groups of mammals (e.g., rodents), primates have received only limited attention in this regard even though considerable variation in the auditory structures both within and between different primate groups has been documented. To help understand the functional and evolutionary implications of primate auditory diversity, this dissertation will measure a set of functionally relevant auditory structures in ten species of primates and one species of tree shrew. The structures that will be examined include the eardrum, middle ear bones and cavities, and the cochlea and will be analyzed using state-of-the-art techniques including micro-computed tomography, impression molding, and digital imaging and measurement. In addition to examining a large comparative data set of extant specimens, a 30 million year old fossil primate specimen from Africa will also be evaluated. Lastly, the hearing sensitivity of a relatively large-bodied prosimian (a "primitive" group of primates), weighing approximately 3.5 kg, will be determined. This final step is necessary since hearing sensitivity data are available for only 18 species of primates and only four of these are prosimians, all four of which weigh 2 kg or less. These data will be used to test hypotheses relating ear structure and function and will be useful for studying the evolution of hearing in primates and other closely related groups. In turn, this type of fundamental data can be applied to further test and generalize broader ideas utilizing acoustic theory in comparative analyses of other mammalian groups. This line of research may eventually be used to investigate the evolution of hearing in humans and its relationship to the unique aspects of human communication.One of the broader impacts of this project relates to its integration of multiple scientific disciplines, bringing together research, researchers, and educators from various fields such as functional morphology, paleontology, behavioral ecology, anatomy, geology, and acoustics. This will help foster partnerships between research facilities such as the Duke Primate Research Center, Duke Medical Center Hearing Research Laboratories, and the Computed Tomography Facility at the University of Texas at Austin. Beyond providing heuristic value in acoustical and evolutionary studies, the information gleaned from this study will expand our understanding of the implications of invasive surgical techniques that require damaging certain auditory structures in order to repair others. The multifarious nature of this investigation will permit the data and results to reach a wide professional audience through publications in acoustical, evolutionary, behavioral, and medical journals.