Sexual monomorphism in the advertisement calls of a Neotropical frog

Abstract

In anurans, production of advertisement calls in sexual contexts is predominantly an attribute of males. Female calls occur in a small proportion of species, and these signals typically differ from those of males. The occurrence of such vocalizations has been suggested to be related to sexual recognition before courtship. In the present study, we compared acoustic variables of male and female advertisement calls of two populations of the Neotropical frog Eleutherodactylus cystignathoides (Cope, 1877). To assess the potential for sexual recognition of these signals, their distinctiveness and variability were measured. Calls have a potential for distinctiveness in the dominant frequency and call duration, but such variation depends mostly on size differences between the sexes. Also divergence in call characteristics is larger between populations than between sexes. The restricted sexual differentiation in the advertisement calls of E. cystignathoides suggests that female advertisement calls are deceptive signals promoting male agonistic responses.