, Volume 176, Issue 4, pp 563-573

How respiration affects auditory sensitivity in the grasshopper Chorthippus biguttulus (L.)

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Abstract

  1. Up to 9 kHz, the tympanal membrane of the grasshopper Chorthippus biguttulus responds with equal sensitivity at the attachment sites of the low and the high-frequency receptors; at the latter site it is also particularly sensitive between 10 and 20 kHz.

  2. The frequency spectra of the songs of both sexes exhibit maxima at 7–8 kHz, to which the membrane is well matched. In the high-frequency region, where the male songs have a peak at 30 kHz, there is no corresponding maximum in the membrane oscillation.

  3. Because the tympanal membrane is immediately adjacent to air sacs in the tracheal system, it is deflected inward and outward by as much as 80 μm during the respiratory cycle.

  4. Measurements by laser vibrometry show that acoustically induced membrane oscillations are attenuated severely due to the respiratory displacement of the membrane for frequencies up to 10–12 kHz. By contrast, at higher frequencies the membrane sensitivity is doubled or tripled.

  5. As a result of these membrane effects, the discharge in the tympanal nerve was profoundly reduced in the low-frequency range, whereas above 11 kHz there was a marked increase. This modulation of auditory sensitivity affects the animals' ability to detect conspecific songs.