Mechanical response of the tympanal membranes of the tree cricket Oecanthus henryi
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Crickets have two tympanal membranes on the tibiae of each foreleg. Among several field cricket species of the genus Gryllus (Gryllinae), the posterior tympanal membrane (PTM) is significantly larger than the anterior membrane (ATM). Laser Doppler vibrometric measurements have shown that the smaller ATM does not respond as much as the PTM to sound. Hence the PTM has been suggested to be the principal tympanal acoustic input to the auditory organ. In tree crickets (Oecanthinae), the ATM is slightly larger than the PTM. Both membranes are structurally complex, presenting a series of transverse folds on their surface, which are more pronounced on the ATM than on the PTM. The mechanical response of both membranes to acoustic stimulation was investigated using microscanning laser Doppler vibrometry. Only a small portion of the membrane surface deflects in response to sound. Both membranes exhibit similar frequency responses, and move out of phase with each other, producing compressions and rarefactions of the tracheal volume backing the tympanum. Therefore, unlike field crickets, tree crickets may have four instead of two functional tympanal membranes. This is interesting in the context of the outstanding question of the role of spiracular inputs in the auditory system of tree crickets.
KeywordsAuditory organ Cricket Orthoptera Eardrum Tree cricket
We would like to thank the UK India Education and Research Initiative for funding this collaborative research. We would like to thank the Indian Ministry of Environment and Forests for supporting N.M. F.M-Z is sponsored by the Human Frontier Science Program (Cross Disciplinary Fellowship LT00024/2008-C). All experiments carried out in the present work comply with the “Principles of animal care” publication No. 86-23, revised 1985 of the National Institute of Health, and also with the current laws of the United Kingdom.
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