Tympanal hearing organs of insects emit distortion–product otoacoustic emissions (DPOAEs), which in mammals are used as indicator for nonlinear cochlear amplification, and which are highly vulnerable to manipulations interfering with the animal’s physiological state. Although in previous studies, evidence was provided for the involvement of auditory mechanoreceptors, the source of DPOAE generation and possible active mechanisms in tympanal organs remained unknown. Using laser Doppler vibrometry in the locust ear, we show that DPOAEs mechanically emerge at the tympanum region where the auditory mechanoreceptors are attached. Those emission-coupled vibrations differed remarkably from tympanum waves evoked by external pure tones of the same frequency, in terms of wave propagation, energy distribution, and location of amplitude maxima. Selective inactivation of the auditory receptor cells by mechanical lesions did not affect the tympanum’s response to external pure tones, but abolished the emission’s displacement amplitude peak. These findings provide evidence that tympanal auditory receptors, comparable to the situation in mammals, comprise the required nonlinear response characteristics, which during two-tone stimulation lead to additional, highly localized deflections of the tympanum.
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This project was supported by a grant from the Deutsche Forschungsgemeinschaft (No. 841/1-1), and by a “Nachwuchswissenschaftler/innen im Fokus” grant from the Goethe-Universität, Frankfurt, Germany. All experiments performed in this study comply with the “Principle of Animal Care”, Pub. no. 86–23, revised 1985, of the NIH, and with the current laws in Germany.
Conflict of interest
The authors declare that they have no conflict of interest.
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