Evolution of directional hearing in moths via conversion of bat detection devices to asymmetric pressure gradient receivers

Andrew Reid, Thibaut Marin-Cudraz, James F. C. Windmill, Michael D. Greenfield

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Abstract

Small animals typically localize sound sources by means of complex internal connections and baffles that effectively increase time or intensity differences between the 2 ears. But some miniature acoustic species achieve directional hearing without such devices, indicating that other mechanisms have evolved. Using 3D laser vibrometry to measure tympanum deflection, we show that female lesser waxmoths (Achroia grisella) can orient toward the 100-kHz male song because each ear functions independently as an asymmetric pressure gradient receiver that responds sharply to high-frequency sound arriving from an azimuth angle 30° contralateral to the animal's midline. We found that females presented with a song stimulus while running on a locomotion compensation sphere follow a trajectory 20° - 40° to the left or right of the stimulus heading but not directly toward it, movement consistent with the tympanum deflections and suggestive of a monaural mechanism of auditory tracking. Moreover, females losing their track typically regain it by auditory scanning – sudden, wide deviations in their heading – and females initially facing away from the stimulus quickly change their general heading toward it, orientation indicating superior ability to resolve the front-rear ambiguity in source location. X-ray CT scans of the moths did not reveal any internal coupling between the 2 ears, confirming for the first time that an acoustic insect can localize a sound source based solely on the distinct features of each ear.
Original languageEnglish
Pages (from-to)E7740-E7748
Number of pages9
JournalProceedings of the National Academy of Sciences
Volume113
Issue number48
Early online date14 Nov 2016
DOIs
Publication statusPublished - 29 Nov 2016

Keywords

  • acoustic communication
  • Lepidoptera
  • sound localization
  • ultrasound
  • directional hearing
  • tympanum deflection
  • auditory tracking

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    Sensor of the Week: The mighty moth

    James Windmill (Interviewee)

    3 Apr 2018

    Activity: Other activity typesTypes of Public engagement and outreach - Media article or participation

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