A narrow ear canal reduces sound velocity to create additional acoustic inputs in a microscale insect ear

Daniel Veitch, Emine Celiker, Sarah Aldridge, Christian Pulver, Carl D. Soulsbury, Thorin Jonsson, Charlie Woodrow, Fernando Montealegre-Z

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Located in the forelegs, katydid ears are unique among arthropods in having outer, middle, and inner components, analogous to the mammalian ear. Unlike mammals, sound is received externally via two tympanic membranes in each ear and internally via a narrow ear canal (EC) derived from the respiratory tracheal system. Inside the EC, sound travels slower than in free air, causing temporal and pressure differences between external and internal inputs. The delay was suspected to arise as a consequence of the narrowing EC geometry. If true, a reduction in sound velocity should persist independently of the gas composition in the EC (e.g., air, CO2). Integrating laser Doppler vibrometry, microcomputed tomography, and numerical analysis on precise three-dimensional geometries of each experimental animal EC, we demonstrate that the narrowing radius of the EC is the main factor reducing sound velocity. Both experimental and numerical data also show that sound velocity is reduced further when excess CO2 fills the EC. Likewise, the EC bifurcates at the tympanal level (one branch for each tympanic membrane), creating two additional narrow internal sound paths and imposing different sound velocities for each tympanic membrane. Therefore, external and internal inputs total to four sound paths for each ear (only one for the human ear). Research paths and implication of findings in avian directional hearing are discussed.
Original languageEnglish
Article numbere2017281118
Number of pages8
JournalProceedings of the National Academy of Sciences
Volume118
Issue number10
Early online date3 Mar 2021
DOIs
Publication statusPublished - 9 Mar 2021

Keywords

  • Bioacoustics
  • Katyid Hearing
  • Sound Propagation
  • Finite Element Analysis

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