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| Eomortoniellus handlirschi Zeuner, 1936 in Woodrow, Celiker & Montealegre-Z, 2023. Illustration by C. Woodrow. |
Highlights:
• A 44-million-year-old amber fossil katydid reveals exquisite ear preservation
• Biophysics of wings reveals this species utilized ultrasounds for communication
• Modeling of auditory range demonstrates tuning to male sexual signal, as well as to bat cries
• Ultrasound discrimination in insects was established by the Eocene
Summary:
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.
Keywords: palaeoentomology, fossil, bioacoustics, predation, arms race, hearing, finite element analysis, bats, eavesdropping, echolocation
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| Remarkable preservation of the ears and wings of Eomortoniellus handlirschi provides insights into the evolution of katydid communication (A) E. handlirschi male habitus μCT reconstruction showing ECs. (B) View of the anterior tympanum and external ear structures through amber, with dotted line indicating cross-section in (C). (C) μCT cross-section of the foretibial ear. (D) Forewings and associated sound-production regions through amber. (E) Illustrated diagram of (C). (F) Illustrated diagram of (D). (G) Reconstruction of E. handlirschi moments before encapsulation in tree resins. Abbreviations are as follows: ap, anterior pinna; at, anterior tracheal branch; atm, anterior tympanum; c, cuticle; ca, crista acustica; dw, dorsal wall; h1–3, harp regions; m, mirror; pp, posterior pinna; pt, posterior tracheal branch; ptm, posterior tympanum; s, septum; v, volume. Illustration in (F) modified from Gorochov (2010) Illustrations in (E) and (G) by C Woodrow. |
Eomortoniellus handlirschi Zeuner, 1936
Charlie Woodrow, Emine Celiker and Fernando Montealegre-Z. 2023. An Eocene Insect could hear conspecific ultrasounds and bat echolocation. Current Biology. In Press. DOI: 10.1016/j.cub.2023.10.040
