Social Influences on Androgen Levels in the Southern Leopard Frog, Rana sphenocephala

Abstract

Social cues play an important role in modulating neuroendocrine and hormonal states in many vertebrates. Social cues in the form of conspecific advertisement calls have been demonstrated to modulate plasma androgen levels in male Rana sphenocephala, the Southern leopard frog. Male R. sphenocephala were captured and brought to the laboratory for testing. Animals were exposed to one of two acoustical environments: a recording of an active conspecific breeding chorus or a recording of the same chorus in which all the spectral frequencies had been digitally shifted 500 Hz higher. Following 12 nights of exposure to either stimulus, plasma androgen levels were assessed by radioimmunoassay and gonadal morphology was examined to compare group differences. Plasma levels of dihydrotestosterone were significantly higher in males exposed to the conspecific chorus, compared with males exposed to the altered version of the chorus. Gonadal morphology did not differ between the two groups. These results suggest that in addition to environmental cues such as rainfall and other seasonal changes, social cues may also serve as environmental synchronizers among anurans to coordinate reproductive effort.