Matching sender and receiver: poikilothermy and frequency tuning in a tree cricket

Abstract

SUMMARYAnimals communicate in non-ideal and noisy conditions. The primary method they use to improve communication efficiency is sender-receiver matching: the receiver's sensory mechanism filters the impinging signal based on the expected signal. In the context of acoustic communication in crickets, such a match is made in the frequency domain. The males broadcast a mate attraction signal, the calling song, in a narrow frequency band centred on the carrier frequency (CF), and the females are most sensitive to sound close to this frequency. In tree crickets, however, the CF changes with temperature. The mechanisms used by female tree crickets to accommodate this change in CF were investigated at the behavioural and biomechanical level. At the behavioural level, female tree crickets were broadly tuned and responded equally to CFs produced within the naturally occurring range of temperatures (18 to 27°C). To allow such a broad response, however, the transduction mechanisms that convert sound into mechanical and then neural signals must also have a broad response. The tympana of the female tree crickets exhibited a frequency response that was even broader than suggested by the behaviour. Their tympana vibrate with equal amplitude to frequencies spanning nearly an order of magnitude. Such a flat frequency response is unusual in biological systems and cannot be modelled as a simple mechanical system. This feature of the tree cricket auditory system not only has interesting implications for mate choice and species isolation but may also prove exciting for bio-mimetic applications such as the design of miniature low frequency microphones.

Active auditory mechanics in female black-horned tree crickets (Oecanthus nigricornis)

“…However, whether corresponding changes in the mechanics and neurophysiology of the ear maintain signal-receiver matching has yet to be established in Oecanthus. At amplitudes of 66 dB SPL the O. henryi membrane mechanics show no modification in response to a temperature range between 18 -27 o C (Mhatre et al 2011). At this amplitude, however, the ear is pushed into its passive regime without active contributions driving tuning or generating gain that can be detected from external measurements of membrane mechanics.…”

A statistical approach to understanding reproductive isolation in two sympatric species of tree crickets

“…The animals are found on bushes of the aromatic weed Hyptis suaveolens (Deb et al, 2012;Mhatre et al, 2011). The animals were collected from Hyptis suaveolens bushes in fields near the village of Ullodu, situated near Bangalore, India (13°38′27″N, 77°42′0″E).…”

“…Two loudspeakers (X-mini Capsule Speaker V1.1, Xmi Pte Ltd, Singapore) were placed at the horizontal ends of the T (120 cm apart). The vertical branch of the T was placed so that it bisected the horizontal branch at its midpoint, thus the junction was 60 cm from the ends of the horizontal branch of the T [see (Mhatre et al, 2011) for details].…”

“…The two species thus provide an ideal system to study precopulatory reproductive isolation through acoustic communication. The response of O. henryi females to male calling song based on the carrier frequency was found to be broadly tuned for the entire natural range of carrier frequencies (Mhatre et al, 2011). Such a broad tuning to a range of carrier frequencies that encompasses the heterospecific values (O. indicus calling song) implies that O. henryi females are unable to distinguish between the signals of O. henryi and O. indicus using spectral features.…”

Low pass filters and differential tympanal tuning in a paleotropical bushcricket with an unusually low frequency call

“…This stringent criterion is not applicable to the study of intensity dependence. Responses were fitted with a simple harmonic oscillator model where the transfer function varied with angular frequency (ω) as described in Mhatre et al (Mhatre et al, 2011):…”