Structure and function of the auditory system of the cicada,Cystosoma saundersii

Summary

Cystosoma saundersii is a cicada in which the male is specialised for the production of low frequency (800 Hz) sound. The basic anatomical and physiological features of its auditory system are examined in males and females.

• 1. Paired auditory (chordotonal) organs are located in auditory capsules on the second abdominal segment (Figs. 6, 9 A). Each auditory organ is suspended between a distal attachment horn and a proximal apodeme (Figs 5B, 7A, B) connected to a complex tympanum (Figs. 4, 10). Male and female tympana are approximately equal in area. Male tympana are loaded (Figs. 5A, 7C) with masses of amorphous material.

• 2. Both tympana are coupled into a single abdominal air chamber which, in males, almost fills the enlarged abdomen, but in females occupies a restricted volue within the abdomen (Fig. 8).

• 3. Male and female auditory organs are both sharply tuned to the frequency of the species' song at 800 Hz (Figs. 11, 12).

• 4. Each female auditory organ exhibits a directional sensitivity which is limited to frequencies near 800 Hz but males lack directional hearing (Figs. 13, 14).

• 5. The enlarged male abdomen acts as an omnidirectional receiver of sound at frequencies near 800 Hz, which results in an augmented sound pressure at the inside surfaces of the tympana (Figs. 15, 16). However, male and female absolute sensitivities at the hearing optima are similar (Figs. 11, 12) which indicates reduced sensitivity of the male tympana.

• 6. We conclude that the auditory system ofC. saundersii is finely adapted to the requirements of intraspecific acoustic communication with low frequency sound.