Neuromuscular mechanism of sound production in Australian cicadas
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- Young, D. J. Comp. Physiol. (1972) 79: 343. doi:10.1007/BF00696251
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Cystosoma saundersii Westw., a most unusual cicada, has neurogenic tymbal muscles, which contract simultaneously (Figs. 2, 3a, 4a), giving a pulse repetition frequency (p.r.f.) of only 40/sec. The greatly enlarged abdomen (Kg. 9) acts as a resonant chamber at the low sound frequency (850 Hz) of the natural song.
Arunta perulata (Guérin) has neurogenic muscles, contracting simultaneously (Figs. 3b, 4b), giving a low p.r.f. of 65/sec. The powerful song is rendered highly directional by greatly enlarged tymbal covers (Fig. 11) which probably act also as resonant chambers.
Psaltoda harrisii (Leach) has neurogenic tymbal muscles, contracting simultaneously (Figs. 3c, 4c) and a high p.r.f., varying from 225–500/sec. Both the IN and the OUT clicks of the tymbal contribute to the p.r.f. but supplementary mechanisms may be required to account for the highest p.r.f. Abdominal movements contribute to the marked amplitude modulation of the natural song.
Abricta curvicosta (Germar) has neurogenic tymbal muscles contracting alternately (Figs. 3d, 4d). The tymbal is strongly ribbed so that during the IN movement of the tymbal each rib buckles separately to produce a pulse of sound, thus giving 7–9 sound pulses for each muscle contraction (Figs. 5d, 6d). The p.r.f. of the natural song is 1050/sec.
The mechanism described for the first three of these species has not been described before. The mechanism described forAbricta is similar to that of the AmericanMagicicada. There is no correlation between mechanism of sound production and taxonomic classification in cicadas.
It is suggested that tymbals with parallel ribs give sound pulses of regular waveform (i.e. with few harmonics) and that tymbals with ribs not parallel give sound pulses of irregular waveform (i.e. with a high harmonic content).