The Tymbal Mechanism and Song Patterns of the Bladder Cicada, Cystosoma Saundersii

In Cystosoma saundersii sound is generated by collapse of a pair of tymbals and radiated by a large, resonant, air-filled abdomen. Each tymbal comprises a flexible, biconvex membrane bearing seven long ribs. Tymbal collapse is caused by contraction of a large tymbal muscle, which acts on the tymbal plate. Each tymbal muscle is innervated by one motor neurone. A single collapse of a tymbal produces two distinct pulses of sound, one when rib 1 buckles and one when ribs 2–4 buckle. A quieter sound is produced when the ribs click outwards. A slowly contracting tensor muscle increases the convexity and stiffness of the tymbal, resulting in a reduction in the delay between the first and second sound pulse and in louder pulses. Protest songs contain features of other songs. There is a delay between the spike in one tymbal motor neurone and its partner, and hence between sound produced by one tymbal and the other, of one-quarter of the interval between spikes in one motor neurone alone. Calling songs are produced by males at dusk. Sound pulses have a smooth envelope and are very loud as a result of contraction of the tensor muscles and extension of the abdomen. Courtship songs are triggered in a calling male by the presence of a female. Song is quite quiet, and broken into short chirps.