Mating vocalizations of female frogs: control and evolutionary mechanisms

Abstract

Vocalization behaviors of anuran amphibians are universally sexually dimorphic. Usually, only male frogs give an advertisement call, while female frog calls are limited to a soft and simple release call which is specifically suppressed at mating. In a very few species, however, female frogs also give mating vocalizations. We examined possible mechanisms for control of this rare heterotypical behavior. At the peripheral level, most differences in temporal and spectral characteristics between female mating calls and the calls of conspecific males related directly to sexual dimorphisms in laryngeal and oblique muscle morphology. At the neural and hormonal level, we first developed an integrated model for control of vocalizations, based primarily on male frog data. When this model is applied to females, female mating vocalizations were most similar to male advertisement calls, rather than being modified release calls. Females may have conscripted preexisting androgen-sensitive neural pathways typically used only by males but present in both sexes. Female mating calls have been heard only during courtship and amplexus. Androgen levels in females at this time are significantly higher than even those levels in males. Because this situation is common in frogs, female mating vocalizations likely evolved independently multiple times. Character optimization suggests that mate location is the most common biological role for female mate calling, but the particular aspects of reproductive biology vary widely across species.