Androgen and gonadotropin effects on male mate calls in South African clawed frogs, Xenopus laevis.

Mate calling is a prominent reproductive behavior of male South African clawed frogs. Calls consist of alternating slow- and fast-amplitude-modulated trills. Each trill is made up of a series of clicks. The effects of administration of exogenous gonadotropin and androgen on mate calling were studied in male Xenopus laevis. Males were paired with unreceptive female frogs to elicit maximal calling. The amount of time each animal spent calling during the testing period, the peak fundamental frequency of the calls, the rate of calling, and the interclick interval (ICI, a measure of the temporal patterning of the calls) were measured in intact, castrated, and hormone-replaced frogs. Injection of human chorionic gonadotropin (HCG) into intact frogs increased the amount of time spent calling and the ICI relative to measures taken after water injection. Castrated males did not call even when given HCG. Testosterone and dihydrotestosterone treatment reinstated calling in castrates and increased circulating levels of androgens. When androgen-replaced castrated males were injected with HCG, the amount of time spent calling increased and approached levels of intact, HCG-injected males. The above results suggest that androgens are necessary for the production of calls. Gonadotropins appear to play an important role in mate calling, a role at least partly independent of effects on testicular androgen synthesis.