| Hearing is vital to the survival and reproductive success of primates, yet >70 years of attempting to identify relationships between ecology and audition have been obscured by vicissitudes within a data set of behaviorally-derived audiograms. Primates rely on acoustic information to avoid predators, locate food, and find mates; however, few studies have addressed how well primates hear such stimuli. The auditory thresholds of most primate species are unknown. To address this deficit, I explored the efficacy of the auditory brainstem response (ABR) method---an evoked potential technique that can be used to safely and efficiently construct audiograms for virtually any animal. I constructed ABR audiograms for fourteen primate taxa, and found that same-species ABR- and behaviorally-derived audiograms were similar in shape; the thresholds were significantly correlated, and parameters such as frequency of best sensitivity and high-frequency limit were comparable.;For decades, the prevailing neutral model has held that primate audition is generalized---a function of size. However, I found that, among 11 strepsirrhine taxa, auditory sensitivity was not significantly correlated with interaural distance---smaller species were not more sensitive to high frequencies. In platyrrhine monkeys, the high-frequency limit was negatively related to interaural distance, but other audiometric parameters were not. Moreover, the relatively large mantled howler was insensitive to low frequencies; instead, its audiogram had an enhanced region of sensitivity corresponding to the high-frequency and ultrasonic harmonics of an infant call.;These findings exemplify that primate audition does not always follow a purely allometric trend. In fact, I found that enhanced auditory sensitivity is strongly correlated with sociality---indicating that an enhanced ability to communicate complex information may have driven the evolution of hearing in primates. Using these data, I explored a previously identified relationship between cochlear labyrinth volume and high-frequency sensitivity. In doing so, I identified a corresponding relationship between cochlear labyrinth volume and group size, indicating potential for reconstructing behavior in the fossil record. A uniform, primate-wide data set on auditory sensitivity, such as that which can be constructed via the ABR method, is an essential step in identifying form-function-ecology relationships such as these. |
