Auditory system biophysics in a new species of false-leaf katydid (Tettigoniidae: Pseudophyllinae) supports a hypothesis of broadband ultrasound reception

Abstract

The auditory system of the katydid is an established model system for studies of hearing, predator-prey interactions, and cochlea dynamics. The components peripheral to the ear substantially influence the hearing threshold, with an internal auditory trachea tuned to the calling song of conspecifics, and external pinnae capable of enhancing ultrasounds for predator detection. The trade-off between such auditory pathways has been subject to multiple discussions, but received little experimental validation. In the most ultrasonic katydids (Pseudophyllinae and Meconematinae), it has been suggested that the external auditory pathway is of greater importance than the internal one, but the biophysical properties of the pinnae and tracheae in such groups have not been compared. Here, we describe the bioacoustics of a new species of pseudophylline katydid, Eubliastes viridicorpus. This species is found to produce a pure tone two-syllable song at 23.4 kHz, similar to other members of the genus. Using micro-CT scanning and finite element modelling, we describe the biophysical tuning of the internal auditory tracheae, and use 3D printed model experiments to investigate external auditory pinnae resonances. By modelling the natural resonant frequencies of the ear, we provide evidence that the acoustic trachea of E. viridicorpus female is tuned to the male song frequency. Experiments on 3D printed models of the pinnae demonstrate that E. viridicorpus has an external auditory pathway capable of broadband ultrasound amplification, providing pressure gains across an effective frequency range of 20–200 kHz, which could also provide enhanced reception of the male song. The importance of pinnae in ultrasonic rainforest katydids is discussed.