A biologia, morfologia craniana e as glândulas de veneno das pererecas-de-capacete: uma integração bem-sucedida

Abstract

With the great biodiversity existing on our planet, different organisms have developed defensive strategies based on the use of toxins. Among tetrapods, the Amphibia class are highlighted in this sense, since all its representatives have poison glands in their skin. A very interesting group from the toxinological point of view are the frogs, especially the casque-headed tree frogs. They form a group belonging to the Lophiohylini tribe, in which many species have a skull with high bone coverage, bone projections in the form of spines, dermal coossification and phragmotic behavior, using the head to seal the entrance of their shelters. Aspects of the natural history of representative species of Lophiohylini (Nyctimantis spp, Trachycephalus spp, Corythomantis greeningi and Itapotihyla langsdorffii) were elucidated through fieldwork. These data were associated with cranial anatomical and histological analyzes of the head of each species. The present work verified a correlation between the increase of the cranial bone coverage and its spinous projections related to venom glands with the execution of the phragmosis. It was also evidenced in the skin secretions of these species, significant differences in chemical composition, with the presence of molecules with enzymatic activities widely found in animal venoms, such as hyaluronidases. Furthermore, except for N. galeata and I. langsdorffii, the other species showed evident cytotoxic potential. Through the information gathered, it was possible to list different species of casque-headed tree frogs endowed with a “Toxin Inoculating System” (SIT), defined by the presence of spines related to cutaneous glands containing toxic secretions, which can, therefore, be considered venomous (instead of poisonous) species.