A scanning electron microscopic study of the surface morphology of nuptial pads in male amphibians (Genus: Bombina , Pelophylax , Rana )

Abstract

The fine structure of nuptial pad surface of the anuran amphibians Bombina variegata , Pelophylax epeiroticus , Pelophylax ridibundus and Rana dalmatina , was examined by scanning electron microscopy. Nuptial pads are cutaneous secondary sexual characters of males that appear during the breeding season and disappear afterwards following an annual cycle. In males of P. epeiroticus , P. ridibundus and R. dalmatina , nuptial pads were observed on the ventrolateral aspect of the first digit (the thumb) as darkish and remarkably keratinized papillae. In males of B. variegata nuptial pads were almost black and very visible on the thumb, the second and the third digit of the front legs. They also extended on the ventral surface of the forearms. Under scanning electron microscope numerous small papillae were observed rising above pad’s surface. In P. epeiroticus , P. ridibundus and R. dalmatina , these papillae were almost rounded at the base while at the dome shaped top they had many microprocesses organised in groups, thus assuming the shape of a “flower” which differed slightly among these three ranid species. In B. variegata the protuberances were conical with heavily keratinized hooks without microprocesses. Our results show that surface morphology of nuptial pads is unique for each species and could be considered as a species-specific character.