Auditory mechanics in a bush-cricket: direct evidence of dual sound inputs in the pressure difference receiver.
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 AT, the transmission gains across auditory frequencies and the time-resolved mechanical dynamics of the tympanal membranes in C. gorgonensis Tracheal sound transmission generates a gain of approximately 15 dB SPL, and a propagation velocity of ca 255 m s-1, an approximately 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 AT can be explained, among others, by heat exchange between the sound wave and the tracheal walls.
School of Life Sciences, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Thorin
http://orcid.org/0000-0002-5049-7612
T
Jonsson
School of Life Sciences, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK fmontealegrez@lincoln.ac.uk.
Fernando
F
Montealegre-Z
School of Life Sciences, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK.
Carl D
CD
Soulsbury
Imaging Lab, Archaeology and Anthropology, University of Bristol, 43 Woodland Road, Bristol BS8 1UG, UK.
Kate A
KA
Robson Brown
School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
Daniel
D
Robert
acoustic trachea; bush-cricket; katydid; sound processing; sound propagation; tympanum
J Exp Biol. 2005 Jan;208(Pt 1):157-68
15601886
Hear Res. 1998 Jan;115(1-2):27-38
9472733
Bioinspir Biomim. 2008 Mar;3:011001
18364558
J Exp Biol. 2013 Mar 1;216(Pt 5):777-87
23125342
J Comp Physiol A. 1994 Aug;175(2):145-51
8071893
J Exp Biol. 2002 Sep;205(Pt 18):2935-42
12177158
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2015 Jan;201(1):5-18
25515594
News Physiol Sci. 1998 Feb;13:32-38
11390756
J Exp Biol. 1974 Jun;60(3):821-37
4847283
Science. 2012 Nov 16;338(6109):968-71
23162003
Science. 1978 Aug 18;201(4356):633-4
17794126