Journal of Neuroscience, Vol 7, 3191-3197, Copyright © 1987 by Society for Neuroscience
Vocalizations by a sexually dimorphic isolated larynx: peripheral constraints on behavioral expression
ML Tobias and DB Kelley
Department of Biological Sciences, Columbia University, New York, New York 10027.
The clawed frog Xenopus laevis uses sexually dimorphic vocalizations, mate
calling and ticking, to advertise reproductive state. The basic unit of
vocalization is a brief click, produced by the movement of cartilagenous
disks located within the larynx. The rate of click production in the
male-specific mate call (71 Hz) is an order of magnitude faster than the
rate of click production in female typical ticking (6 Hz). To determine if
vocalization rate is constrained by the periphery, male and female larynges
were isolated and response of the muscles to nerve stimulation was studied.
Laryngeal muscle response is markedly dimorphic in the 2 sexes, both in the
amplitude potentiation of electromyograms and in the rate at which discrete
tension transients can be produced. At 6 Hz (ticking), both sexes generate
discrete tension transients in response to each stimulus pulse. In response
to nerve stimulation at 71 Hz (mate calling), male laryngeal muscle
generates discrete tension transients while female laryngeal muscle does
not. Since expression of sex-specific vocalizations is regulated by
androgenic hormones, responses of laryngeal muscle to nerve stimulation in
androgen-treated adult females and castrated adult males were also
examined. The responses of laryngeal muscle from castrated and intact males
are similar. Androgen-treated female larynx is partially masculinized but
does not produce tension transients at the mate call rate. These
physiological results are in close agreement with behavioral observations.
Sounds produced by the isolated larynx were nearly identical in spectral
properties to those produced by an intact male. We determined that the
production of a discrete tension transient is prerequisite to click
production. Thus, one reason females do not mate call, even when treated
with androgens, is that female laryngeal muscle cannot produce discrete
tension transients at a rapid rate.
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