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1 December 2017 Do Body Wall Vibrations Over the Lungs Aid Aerial Hearing in Salamanders? An Investigation into Extratympanic Hearing Mechanisms
Jeffrey N. Zeyl, Carol E. Johnston
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Tympanic middle ears are key innovations in the evolution of terrestrial hearing. These structures facilitate sound transmission between air and the inner ear, across an impedance mismatch boundary. Nontympanic taxa present an opportunity to explore extratympanic hearing mechanisms, which could inform our understanding of terrestrial hearing evolution. Salamanders are useful models in this regard because they lack tympanic middle ears. Lung-based extratympanic auditory mechanisms have been demonstrated in earless anurans and are hypothesized to apply to salamanders, based on observations that the body walls overlying the lungs vibrate in response to airborne sound. We tested the hypothesis that body wall vibrations over the lungs aid aerial hearing in salamanders. We immersed the body walls and pectoral girdle below a water surface in two lunged species, Notophthalmus viridescens and Ambystoma talpoideum, predicting that this would elevate auditory thresholds (measured using evoked potentials) by inhibiting body wall motion. This submersion treatment did not significantly affect auditory sensitivities in either species. We conclude that lung-based aerial auditory pathways through the body walls are negligible or absent in the tested salamanders. Whereas lungs can potentially contribute to extratympanic hearing in small tetrapods, the extent to which these peripheral vibrations are transmitted to and detected in the ear varies across taxa. Over the course of experimentation, we discovered that modifying the positioning of both the speaker and salamander shifted thresholds (expressed relative to sound pressure) by up to 15 dB, indicating that vibration, rather than pressure, might be the appropriate acoustic measurement for aerial hearing. We discuss implications of a vibration-based auditory system for evaluating the terrestrial auditory capacities of salamanders.

© 2017 by The Herpetologists' League, Inc.
Jeffrey N. Zeyl and Carol E. Johnston "Do Body Wall Vibrations Over the Lungs Aid Aerial Hearing in Salamanders? An Investigation into Extratympanic Hearing Mechanisms," Herpetologica 73(4), 283-290, (1 December 2017).
Accepted: 1 June 2017; Published: 1 December 2017
Cavity resonance
Hearing evolution
Lung-based hearing
Vibration detection
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