The Nuptial Pads of Melanophryniscus (Anura: Bufonidae), with the Unexpected Occurrence of Nuptial-Pad–Like Structures in Females of Two Species

Nuptial pads are patches of thickened skin, associated with sexually dimorphic skin glands, present only in the thumbs and fingers of male anurans, and hence considered dimorphic sexual characters. Despite the morphological description for many species, the evolution and function of nuptial pads are still unclear. In this study, we describe the presence of nuptial-pad–like structures in females of two species of Melanophryniscus and compare their morphology and histology to males' nuptial pads. The epidermal modifications found in females are conical papillary epidermal projections, similar to the structures found in males; however, the density of these projections in males is twice the average found in females. Also, the nuptial-pad–like structure found in females cannot be considered an actual nuptial pad, because there are no specialized skin glands associated with the structure. This study brings the first records of epidermal modification in females of Melanophryniscus and provides the description of male nuptial pads for the genus.