Structure and Functional Significance of the Nuptial Thumb Pads in Rana esculenta and R. perezi

Abstract

The nuptial thumb pads of Rana esculenta and R. perezi are cutaneous specialisations including rows of glands, defined nuptial glands, embedded in the pad dermis. The pads are covered by a black, strongly keratinised epidermis, where high papillae alternate with gland pores. The mucous nature of the above glands is confirmed both under light and transmission electron microscopes. The nuptial pads function in promoting male’s ability to retain the female during amplexus. The nuptial glands release their product onto the keratinised pads, which indicates an adhesive function of the secretion. Such performance is synergic with the complex ridge apparatus of the pad surface, capable of working like a multi-lamellar sucker. Secretions of these glands may also prevent sexual interference by rival males.