Revisiting convergence: katydid hearing (Introduction)

by David Turell , Tuesday, November 14, 2023, 17:07 (165 days ago) @ David Turell

Mimics ours:

https://www.cell.com/current-biology/fulltext/S0960-9822(23)01441-0?dgcid=raven_jbs_aip...

"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.

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"In light of recent evidence supporting a theory of an arms race between the ancestral katydid lineage and mammalian acoustics, it seems increasingly likely that there have been unique long acoustic interactions between orthopteran and mammalian lineages through time. This arms race may have started through katydids increasing their acoustic signal frequencies beyond the predator upper hearing limit and the predators evolving ears that are more capable of higher-frequency eavesdropping.

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"This fossil supports these predictions of bat echolocation frequency, as E. handlirschi shows no acoustic pinnae adaptations to bat detection above 80 kHz, but it could certainly detect this modern bat common ancestor through its ECs [ear canals]. Importantly, this early bat predator could also hear E. handlirschi for predation. The sophisticated katydid ear with its cochlea-like anatomy was established at this time (as evidenced in this report, indicating that discrimination between conspecific and predator ultrasounds occurred through tonotopically organized auditory sensilla and traveling waves for frequency mapping."

Comment: more evidence that evolution always reaches the same solutions in design, in this case ultrasounds and echolocation. again, evidence for a designing mind.