Nuptial pads of rock frogs (Thoropa, Cycloramphidae, Anura): How papillary epidermal projections are related to sexual maturity and taxonomy

Abstract

The rock frog species of the genus Thoropa possess nuptial pads composed of papillary epidermal projections (PEPs) on the hands of males. The morphology, number, and distribution of PEPs are employed to distinguish between species of Thoropa. Here we describe the morphology and distribution of the spine-shaped PEPs on the hands of five species of Thoropa: T. megatympanum, T. miliaris, T. petropolitana, T. saxatilis, and T. taophora. We test if PEP color is related to collection month or years in preservative. We also investigate if there is a relationship between the occurrence of spermatozoa and the appearance of PEPs, which would be a criterion to define adult males. Additionally, we test whether the number of PEPs differs among the five species, and also whether it is related to body size (snout–vent length, SVL). There is no temporal pattern in the color of PEPs. The occurrence of spermatozoa and PEPs is unrelated, with mature spermatozoa being present in males that lack PEPs. The number of PEPs is positively related to SVL. Statistically, the number of PEPs differs among species, but the ranges of intraspecific variation in this trait overlaps among species, hindering their use in diagnosing species of Thoropa.