Sounds from the past: from fossil to song in Ensifera

Publication Type:Conference Paper
Year of Publication:2016
Authors:T. Jonsson, Montealegre-Z, F., Robson-Brown, K.
Conference Name:The 7th International Conference on Fossil Insects, Arthropods and Amber
Date Published:26/04/2016
Publisher:Siri Scientific Press
Conference Location:National Museum of Scotland, Edinburgh

Ensifera (Orthoptera) were amongst the earliest terrestrial arthropods to develop acoustic communication; probably as early as the mid-Triassic. Extant male bush-crickets (Ensifera: Tettigoniidae) are known to produce loud courtship songs by tegminal stridulation, i.e. the rubbing together of specialised structures on the forewings, namely the file (a serrated vein) and the scraper (a plectrum-like, hardened region). The songs are further amplified by modified and specifically resonating wing cells and detected by other bush-crickets via pressure-sensitive tympanal organs located in the front tibiae. The general biomechanics and bioacoustics of this system are well understood in modern bush-crickets, where it was found that most species communicate with signals in the ultrasonic frequency range (20–150 kHz). However, earlier research provided evidence to suggest that the origins of tettigoniid courtship songs lie in audible, much lower frequency signals (<7 kHz). Here, we describe how detailed understanding of the anatomy and biophysical function of the auditory communication system in living bush-crickets and the use of modern imaging techniques, comparative methods and multiphysics modelling of the signal producing and receiving structures in fossils can help to gain insight into the evolution of singing in Ensifera. By incorporating results from experiments using laser Doppler vibrometry on ears and wings of extant species with 3D models, we can build finite element models recreating the bioacoustic properties of these structures. By applying the same models to 3D resonstructions of fossilised wings and ears, we will then be able to infer the resonances of these systems and thereby the likely frequency ranges used in acoustic communication by the extinct taxa. A more detailed understanding of the evolution of singing in ensiferans will enable us to shed light on changes in the sensory physiology and the palaeoecology of these insects and their predators through time.

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