Underwater stridulation by corixids: Stridulatory signals and sound producing mechanism in Corixa dentipes and Corixa punctata

Abstract

1. (1) The species-specific songs of Corixa dentipes and Corixa punctata males are composed of pulse trains, each of which contains about eleven sound pulses. C. dentipes has a repertoire of four different songs (Song A-D). These songs differ in overall duration, pulse-train repetition rate, and amount of variability in pulse-train rate, pulse rate and sound intensity during the song or individual verces. C. punctata produces only one song. Its sound pattern is considerably more variable, even for an individual animal, than the very precisely performed C. dentipes songs. 2. (2) In the case of C. dentipes, the highest measured peak sound pressure level (SPL) of single pulses was 133 dB re 1 μPa at a distance of 0.1 m from the animal, and the mean of the largest pulses per pulse train over the entire Song A was 115 dB. The song of C. punctata is less loud, with a SPL ca. 10–20 dB lower than that of the C. dentipes songs. The measurements permit estimation of the alternating pressures at the thoracic tympanal organs during acoustic communication. 3. (3) The stridulatory apparatus consists of two specialized structures. The file (pars stridens) is a field of ca. 20 parallel rows of thickened bristles (pegs) on the femur of each foreleg. There are distinct species- and sex-specific differences in the spacing of the rows and the thickness of the pegs. The counterpart of the file, the maxillary plate or scraper (plectrum), is a specially thickened cuticular projection on the side of the head. 4. (4) A single downstroke of the file over the scraper produces a train of acoustic pulses. Each pulse is associated with the contact between one row of pegs in the file and the scraper. Structure and movement of the stridulatory apparatus indicate that at most three adjacent pegs in a row contact the scraper to generate a single pulse. 5. (5) The foreleg movements during various songs can be unilateral, alternating or synchronous. Results indicate that even when the two forelegs move in synchrony the sounds are produced by only one leg, so that in general superposition of stridulatory pulses is avoided. The speed of the downstroke, the repetition rate of consecutive leg movements and the duration of stridulation are temperature-dependent. The Q 10 for the pulse-train rate is between 2.7 and 2.0 for water temperatures between 4°C and 25°C.