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Seismic sensitivity and bone conduction mechanisms enable extratympanic hearing in salamanders
G Capshaw1, D Soares2, J Christensen-Dalsgaard3
1Department of Biology, University of Maryland, College Park, MD 20742, USA gcapshaw@umd.edu.
The Journal of Experimental Biology
|November 8, 2020
Summary
Many tetrapods lack tympanic ears but can still hear airborne sounds. This study reveals that sound-induced head vibrations, not seismic sensitivity, enable low-frequency hearing in atympanic salamanders.
Area of Science:
- * Comparative bioacoustics and evolutionary biology.
- * Auditory system evolution and sensory mechanisms.
Background:
- * Tympanic middle ears evolved in terrestrial tetrapods to hear airborne sound but have been lost in many species.
- * Extratympanic hearing in atympanic species may involve seismic vibration, bone conduction, or resonant body cavities.
Purpose of the Study:
- * To investigate extratympanic hearing mechanisms for airborne sound in atympanic salamanders.
- * To assess the roles of body cavity resonance, seismic sensitivity, and bone conduction in sound detection.
Main Methods:
- * Auditory brainstem response recording to measure auditory sensitivity thresholds.
- * Laser vibrometry to assess vibrational responses of body cavities and head movements.
- * Testing eight different salamander species.
Main Results:
- * Salamanders showed sensitivity to low-frequency airborne sound (0.05–1.2 kHz) and vibration (0.02–1.2 kHz).
- * Vibrational responsiveness of lungs and mouth cavity did not facilitate airborne sound sensitivity.
- * Airborne sound stimuli caused head vibrations detectable by the inner ear, indicating a direct mechanism.
Conclusions:
- * Extratympanic hearing in atympanic salamanders relies on detecting sound-induced head vibrations.
- * This mechanism is effective for low-frequency airborne sound detection in vertebrates lacking specialized aerial ears.
- * Head vibration detection may be a common terrestrial hearing strategy for atympanic tetrapods.
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