Reviving the sound of a 150-year-old insect: The bioacoustics of Prophalangopsis obscura (Ensifera: Hagloidea)

Abstract

Determining the acoustic ecology of extinct or rare species is challenging due to the inability to record their acoustic signals or hearing thresholds. Katydids and their relatives (Orthoptera: Ensifera) offer a model for inferring acoustic ecology of extinct and rare species, due to allometric parameters of their sound production organs. Here, the bioacoustics of the orthopteran Prophalangopsis obscura are investigated. This species is one of only eight remaining members of an ancient family with over 90 extinct species that dominated the acoustic landscape of the Jurassic. The species is known from only a single confirmed specimen-the 150-year-old holotype material housed at the London Natural History Museum. Using Laser-Doppler Vibrometry, 3D surface scanning microscopy, and known scaling relationships, it is shown that P. obscura produces a pure-tone song at a frequency of ~4.7 kHz. This frequency range is distinct but comparable to the calls of Jurassic relatives, suggesting a limitation of early acoustic signals in insects to sonic frequencies (<20 kHz). The acoustic ecology and importance of this species in understanding ensiferan evolution, is discussed.

Fig 1. The holotype of Prophalangopsis obscura (collected in India, Walker 1869).

A, dorsal habitus; B, lateral habitus; C, tympanal organ.

Fig 2. Stridulatory file anatomy and inter-tooth distances in Prophalangopsis obscura.

Orientation of both files is along the anal (left) to basal (right) axis.

Fig 3. Forewing resonance in Prophalangopsis obscura.

(A) Displacement map of the LW; (B) Deflection pattern of the white profile line in A; (C) Frequency spectrum of the left mirror; (D) Displacement map of the RW; (E) Deflection pattern of the profile line in D; (F) Frequency spectrum of the right mirror; (G) Angled view of the left forewing displacement pattern at 4.8 kHz.

Fig 4. Reconstruction and spectral analysis of a diplo-syllable containing two pulses of the sound of Prophalangopsis obscura.

Waveform of two chirps (top), with spectrogram below and frequency spectrum on the left marginal axis. The 2^nd chirp is an artificial reversal of the 1^st chirp, to demonstrate that frequency modulation (FM) will differ depending on whether sound is produced during the opening or closing wing stroke.