Sharon Emerson, at the University of Utah, proposes a multifaceted study of voiceless frogs in the genus Rana that occur in southeast Asia. Emerson's goal is to gain an understanding of the evolution of a suite of secondary sexual characters, associated with the frogs reproductive ecology and breeding behavior (voicelessness), that appears to have evolved on two separate occasions among four species in Borneo. To gain this understanding, Emerson proposes a systematic study of the southeast Asian Ranids based on morphological characters independent of the functional complex of secondary sexual features. Field studies will be conducted in Borneo to determine the details of the breeding biology of the four species and to determine the functional significance of the secondary sexual characters. Assays of blood hormone levels will be made in these species and in other species of Rana to determine the relationship between testosterone levels and the lack of vocal development. Emerson hypothesizes that the evolution of voicelessness may be mediated by the evolution of reduced testosterone levels.
