Auditory mechanics in a bush-cricket: direct evidence of dual sound inputs in the pressure difference receiver

Jonsson, Thorin and Montealegre-Z, Fernando and Soulsbury, Carl (2016) Auditory mechanics in a bush-cricket: direct evidence of dual sound inputs in the pressure difference receiver. Journal of the Royal Society Interface, 13 (22). p. 20160560. ISSN 1742-5689

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The ear of the bush-cricket Copiphora gorgonensis consists of a system of paired eardrums (tympana) on each foreleg. In these insects, the ear is backed by an air-filled tube, the acoustic trachea (AT), which transfers sound from the prothoracic acoustic spiracle to the internal side of the eardrums. Both surfaces of the eardrums of this auditory system are exposed to sound, making it a directionally sensitive pressure-difference receiver. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces at the tympanum. The mechanism responsible for reduction in sound velocity in the AT remains elusive, yet it is deemed to depend on adiabatic or isothermal conditions. To investigate the biophysics of such multiple input ears, we used micro-scanning laser Doppler vibrometry and micro-computed X-ray tomography. We measured the velocity of sound propagation in the acoustic trachea, the transmission gains across auditory frequencies, and the time-resolved mechanical dynamics of the tympanal membranes in Copiphora gorgonensis. Tracheal sound transmission generates a gain of ~15 dB SPL, and a propagation velocity of ca. 255 m/s, a ~25% reduction from free field propagation. Modelling tracheal acoustic behaviour that accounts for thermal and viscous effects, we conclude that reduction in sound velocity within the acoustic trachea can be explained, amongst 34 others, by heat exchange between the sound wave and the tracheal walls.

Keywords:Tympanum, Sound processing, Katydid, Bushcricket, Sound propagation, Acoustic trachea, JCNotOpen
Subjects:H Engineering > H341 Acoustics
B Subjects allied to Medicine > B610 Audiology
F Physical Sciences > F361 Laser Physics
B Subjects allied to Medicine > B120 Physiology
F Physical Sciences > F380 Acoustics
Divisions:College of Science > School of Life Sciences
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ID Code:24116
Deposited On:16 Sep 2016 08:01

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