H. C. Bennet-Clark

Wing resonances in the Australian field cricket Teleogryllus oceanicus

SUMMARY The anatomy and mechanics of the fore-wings of the Australian cricket Teleogryllus oceanicus were examined to study how resonances of the wings were excited, to model the interactions between the two wings during sound production, to account for the frequency changes that occur within the pulses and to determine the variation in sound amplitude during the pulses. Sound is produced after raising the wings by closing the right wing over the left; the plectrum of the left wing engages and releases teeth on the file on the underside of the right wing. The mean number of teeth on the right file is 252; the teeth are more closely spaced in the posterior part of the file, which is engaged at the start of the song pulses. The anterior part of the file is separated from the base of the harp by a short flexible region. The dorsal field of the wing, in which the harp is situated, is largely mechanically isolated from the driving veins of the lateral field, except for a cross vein at the apex of the harp. The harps of the two wings did not differ significantly in area but the plectrum of the left wing was significantly longer and wider than that of the right wing. The posterior edge of the plectrum has a radius of approximately 0.5 μm, which allows it to engage the 20 μm-tall teeth of the file. The plectrum is separated from the wing by a 0.5 μm-thick crescent that allows it to twist lengthways and thus disengage the file teeth. The sigmoid shape of the file allows the plectrum to engage teeth over most of the length of the file. The calling song of T. oceanicus consists of a chirp of four similar pulses followed by a trill of pairs of pulses. The dominant frequency of all pulses is approximately 4.8 kHz but cycle-by-cycle analysis suggests that the different types of pulse are produced by wing-closing movements through different arcs. Free resonances of the left wing occurred at 4.56 kHz [quality factor (Q)=25.1] and of the right wing at 4.21 kHz (Q=23.9). Driven by loud sound, maximum vibration of the harp was seen at approximately 4.5 kHz; at lower sound levels, the vibration was confined to the cross-veins of the harp that extend distally from the file. Resonances of the left wing driven by vibration of the same wing, either at the plectrum or on the anal area, occurred at similar frequencies to those of the songs and had similar Qs but were approximately anti-phase, demonstrating that movement of the plectrum (e.g. by the file teeth) causes an opposite movement of the harp. When the right wing was driven directly on the file, the resonant frequency was 5.88 kHz but, when driven on the file via a length of the left file and the left plectrum, it was 4.83 kHz. The amplitude of the vibration increased from the posterior end of the file to the middle then fell towards the anterior end of the file. Pushing a left plectrum across the middle of the right file produced trains of damped sound pulses at 4.82 kHz (Q=23.4). Clicks excited from the anterior end of the file had lower frequencies. The resonances excited from both the left wing via its plectrum and from the right wing when driven via the left plectrum were similar in frequency to that of the song. The resonance of the dorsal field persisted after ablation of the harp but the mean resonant frequency increased 1.12-fold with a similar Q to the intact wing. Droplets of water on the distal end of the harp or proximal part of the dorsal field raised the resonant frequency. The resonant frequency was lowered by the addition of weights to the harp or the file; the factor of the decrease suggested that the mass of the resonant system was approximately 1.4 mg, which accords with the mass of the harp plus file plus anal area of the wing (left wing, 1.27 mg; right wing, 1.15 mg) but is far heavier than the harp (0.22 mg). An earlier suggestion that the harp is the resonator is not supported; instead, it is proposed that the major elastic component of the resonant system is the file plus 1st anal vein and that the mass component is the combined mass of the file, anal area and harp.

THE MECHANISM OF TUNING OF THE MOLE CRICKET SINGING BURROW

ABSTRACT 1. Experimental and theoretical studies on the acoustics of the singing burrow of the mole cricket Gryllotalpa australis are reported. 2. The burrow typically consists of a bulb about 26 mm long and 20 mm in diameter, connected through a constriction of diameter about 10 mm to a flaring horn with length about 40 mm and equivalent mouth diameter about 34 mm. The mouth geometry of the burrow differs from one species to another, and the aperture may be either single, double or even multiple. The end of the bulb opposite the horn connects to a narrow exit tunnei of diameter about 8 mm and length up to 1 m. The singing cricket positions itself close to the constriction between the bulb and the horn and produces a song with a frequency around 2.5 kHz. 3. Measurements of sound pressure within the burrow when it is excited by an external sound source at the song frequency show a pressure minimum at the constriction and an amplitude and phase distribution that is consistent with resonance of the burrow at...

THE FIRST DESCRIPTION OF RESILIN

![Figure][1] It was at one of the weekly seminars in the Department of Zoology at the University of Cambridge in the late 1950s that I heard, with great excitement, Torkel Weis-Fogh describing resilin. In his masterly first written description, Weis-Fogh explained its roles in the thorax of

WHICH QS TO CHOOSE: QUESTIONS OF QUALITY IN BIOACOUSTICS?

ABSTRACT Two Q factors are in common use in bioacoustics: Q, the Quality Factor and Q10 dB. The usage, definitions and separate application of these two terms can be traced back for more than 30 years. The two terms provide different measurements of the sharpness of tuning of e.g. acoustic systems. The two terms have been used in separate contexts and they measure different things. In view of the confusion that arises from the shared use of the letter Q, it is important that whichever Q is used is defined clearly in all publications.

Impedance Matching in Sound Production and Hearing: a Comparative Study

Sound production involves stages of impedance matching between the higher-density body of the animal and lower-density air. Hearing involves further impedance matching, from air to the higher-density sensory cells. Initial stages of sound production may include a frequency multiplier that converts slow muscle contractions into higher frequency mechanical vibrations. The frequency multiplier may also determine the sound frequency. Larger sound sources allow better impedance amtching with the air so sound radiation often exploits acoustic transformers to increase the effective size of the sound source. In many cases the conversion efficiency of muscle power to sound power is high, giving a large effective range for the signal. Sound detection often uses acoustic transformers to concentrate the sound onto relatively dense vibrating sturctures that are coupled to the sensory cells, providing the inverse of the impedance matching that occurs in sound production. These transformers may be associated with directional mechanisms and may drive arrays of receptors that allow frequency analysis. Sound production and hearing are special cases of the general phenomenon of impedance matching that occurs throughout biomechanics.

How Creatures Work

654 September 2010 / Vol. 60 No. 8 www.biosciencemag.org rat race of the research grants system, and instead has been able to pursue his interests in such areas as the flowinduced ventilation of sponges and prairie-dog burrows, or the responses of leaves and trees to wind. Vogel is part of the school of physiology and biomechanics, fostered by the legendary Knut Schmidt-Nielsen, at Duke University, and his eclecticism and inventiveness are remarkable. He has a good knowledge of both the animal and plant kingdoms, plus a knowledge of physics, engineering, and physical chemistry, and thus is able to apply principles used in, for example, commercial chemical engineering to the problems of gaseous exchange or water loss by leaves. He also has the ability to sense a problem and an enviable knack for explaining what is happening.

How to get one jump ahead

Humans and fleas have a common ability: they can jump from a standing start by stretching a pair of legs. However, when it comes to jumping performance, humans are puny. Bush-babies – particularly charming small relatives of monkeys – can leap to heights of over 1.5 m, about eight times their body length; locusts, with bodies about 50 mm long, can leap to heights of more than 700 mm. Fleas are even more spectacular, attaining about 100 body lengths. These differences are partly a result of their various jumping techniques, but does each animal necessarily use the best method for its size and body design? If humans jumped like fleas, would they jump any higher?