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An Eocene insect could hear conspecific ultrasounds and bat echolocation

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journal contribution
posted on 2024-02-08, 16:15 authored by C Woodrow, E Celiker, F Montealegre-Z
Hearing has evolved independently many times in the animal kingdom and is prominent in various insects and vertebrates for conspecific communication and predator detection. Among insects, katydid (Orthoptera: Tettigoniidae) ears are unique, as they have evolved outer, middle, and inner ear components, analogous in their biophysical principles to the mammalian ear. The katydid ear consists of two paired tympana located in each foreleg. These tympana receive sound externally on the tympanum surface (usually via pinnae) or internally via an ear canal (EC). The EC functions to capture conspecific calls and low frequencies, while the pinnae passively amplify higher-frequency ultrasounds including bat echolocation. Together, these outer ear components provide enhanced hearing sensitivity across a dynamic range of over 100 kHz. However, despite a growing understanding of the biophysics and function of the katydid ear, its precise emergence and evolutionary history remains elusive. Here, using microcomputed tomography (μCT) scanning, we recovered geometries of the outer ear components and wings of an exceptionally well-preserved katydid fossilized in Baltic amber (∼44 million years [Ma]). Using numerical and theoretical modeling of the wings, we show that this species was communicating at a peak frequency of 31.62 (± 2.27) kHz, and we demonstrate that the ear was biophysically tuned to this signal and to providing hearing at higher-frequency ultrasounds (>80 kHz), likely for enhanced predator detection. The results indicate that the evolution of the unique ear of the katydid, with its broadband ultrasonic sensitivity and analogous biophysical properties to the ears of mammals, emerged in the Eocene.

Funding

This study was funded by a European Research Council grant ERCCoG-2017-773067 (to F.M.-Z. for the project “The Insect Cochlea”) and an NSF-NERC grant NSF DEB-1937815-NE/T014806/1 (to F.M.-Z.).

History

Author affiliation

School of Engineering, University of Leicester

Version

  • VoR (Version of Record)

Published in

Current Biology

Volume

33

Issue

24

Pagination

5304 - 5315.e3

Publisher

Elsevier BV

issn

0960-9822

eissn

1879-0445

Copyright date

2023

Available date

2024-02-08

Spatial coverage

England

Language

eng