Morphological characterization of the glandular system in the salamander Plethodon shermani (Caudata, Plethodontidae)
Amphibians have evolved a wide variety of mechanisms that provide a certain degree of protection against predators, including camouflage, tail autonomy, encounter behavior and noxious or toxic skin secretions. In addition to these strategies, some amphibians release a glue-like secretion onto the surface of their skin when threatened. While some information regarding the origin and production of these adhesive secretions is available for frogs such as Notaden bennetti, these aspects are only partially understood in salamanders. We contribute to an earlier study and provide additional information regarding the origin, production, and characterization of the adhesive secretion in the red-legged salamander (Plethodon shermani) at a microanatomical level. When stressed, this salamander secretes a milky, viscous liquid from its dorsal and ventral skin. This secretion is extremely adhesive and hardens within seconds upon exposure to air. This study describes two cutaneous gland types (mucous and granular) in the dorsal and ventral epithelial tissue that differ considerably in their secretory content. While the smaller mucous glands contains flocculent to granular material, mostly acidic glycoproteins, the granular glands synthesize various granules of differing size and density that consist of basic proteinaceous material. The results strongly indicate that the secretions of both gland types from the dorsal as well as the ventral side form the adhesive mucus in Plethodon shermani, consisting of basic and acidic glycoproteins, glycoconjugates with mannose and alpha-L-fucose residues as well as lipid components.