BURMEISTER, S.: Social Context Influences Androgenic Effects on Calling in the Green Treefrog

Courtship behavior in frogs is an ideal model for investigating the relationships among social experience, gonadal steroids and behavior. Communication is mediated primarily by acoustic signals, and the auditory system projects to the hypothalamus. Listening to mating calls causes an increase in androgens in the receiving male. Reception of mating calls also evokes calling, and the vocal production pathway receives projections from the auditory system. In addition, researchers have shown that both the auditory system and the vocal production pathway concentrate sex steroids. We examined the influence of androgens on calling behavior of treefrogs (Hyla cinerea) in the presence and absence of social signals. We exposed castrated, intact, or castrated/testosterone (T)-implanted males to tones or a mating chorus for 7 nights. We categorized calling during a stimulus (chorus or tones) as evoked and calling in the absence of a stimulus as spontaneous. Intact males call in response to a mating chorus, but not tones. We found that castration abolished and testosterone replacement maintained calling, indicating that calling is androgen-dependent. However, among intact and T-implanted males, the influence of testosterone on calling was complex. T-implants promoted spontaneous calling but inhibited the chorus-specific increase in calling that is evident in intact males. These data indicate that androgens influence the motivation to call, but that, when socially stimulated, androgens are necessary but insufficient for calling. The influence of androgen level on spontaneous calling suggests that inhibition of response calling was not caused by inhibition of the vocal production pathway. Rather, inhibition of response calling by high androgens suggests inhibition of other systems that are critical to acoustically-evoked calling.