Comparative skin histology of neotropical odontophrynid frogs

Amphibian skin is a complex organ with dermal glands which, according to their morphology, are classified as acinar and alveolar (both usually known as mucous glands) and syncytial (usually known as serous, granular or poison glands). The latter may be scattered or grouped forming protuberances known as warts or macroglands, which are histologically distinguished. Particularly, skin protuberances in the family Odontophrynidae have been used as diagnostic characters; however, scarce works describe them in detail. For this reason, we studied the histomorphology and histochemical properties of the skin in the postorbital-supratympanic and dorsal regions in species of the three genera composing this family. Our results showed that Odontophrynidae has peculiar characteristics such as the presence of neutral glycoconjugates in the secretion of the syncytial glands. Similarities were mostly observed between the sister taxa Odontophrynus and Macrogenioglottus with respect to the presence of blunt spine-like projections, large syncytial glands with stoma-like pores, and the morphology and histochemistry of the secretion in the large syncytial glands. The described histomorphological characteristics do not support the recognition of phenetic groups; however, they contribute to the identification at the species level, particularly differentiating cryptic species. Regarding differences between the three genera, the protuberances of the postorbital-supratympanic region in species of Odontophrynus, excepting Odontophrynus reigi, can be recognized as macroglands, while in Proceratophrys they are observed as warts. In Macrogenioglottus alipioi protuberances show intermediate traits between warts and macroglands.