A new scent organ for Gymnodactylus lizards (Squamata: Phyllodactylidae) and an updated evolutionary scenario for the origin of squamate epidermal glands

Semiochemical dispersion-based communication is a determinant in squamate behaviour and reproduction. This communication mode is driven by different scent glands and is distributed widely among squamate lineages. However, most studies of such communication have focused on femoral glands, and there is little literature about semiochemical-based communication among clades that lack this structure. In this study, we describe a cloacal scent gland in Gymnodactylus lizards and discuss its evolutionary significance. This sexually dimorphic holocrine gland is located in the posterior cloacal lip, promoting the dispersion of its chemical compounds. Morphological analysis shows that this gland is derived from the inner epidermal generation and shares numerous characteristics with the femoral and pre-cloacal glands. Histochemical analysis confirms a lipid composition. Our study is the first report of this organ and provides the first autapomorphy for Gymnodactylus. Our histological and comparative approach provides a model for the evolution of this organ together with a reinterpretation of the evolutionary hypothesis proposed for the origin of generation glands and follicular glands. Finally, we also propose a terminology scheme to standardize the nomenclature of these different structures based on their origin and morphology.