Parotoid, radial, and tibial macroglands of the frog Odontophrynus cultripes: Differences and similarities with toads

Abstract

Anuran integument is characterized by the presence of glands, some of which are responsible for toxin production. In some species these glands accumulate in parts of the body strategically located against predators, forming structures known as macroglands. This is the case for parotoid macroglands, on the dorsum of the head, tibial macroglands, on the rear limbs, and radial macroglands, on the forelimbs of toads and some other anurans. The toad Rhinella jimi, for example, simultaneously displays all three types of macroglands, which is unusual even among bufonids. Interestingly, considering the phylogenetic distance, the frog Odontophrynus cultripes (Odontophrynidae) also presents these three macroglandular types. In this study we analyze the morphology of O. cultripes macroglands and the chemical composition of their poison using an interdisciplinary approach. In this species, the parotoid, tibial, and radial macroglands consist of aggregates of elongated and juxtaposed poison glands, arranged in a honeycomb style, very similar to that of toads. Comparative analysis of these three macrogland types shows significant differences in both the morphology of secretory granules and biochemical composition. The present work on O. cultripes contributes to the evidence that amphibians, or at least anurans, share a basic design for all cutaneous glandular accumulations. The determinant factor for macroglandular formation may be the selective pressure for defense against predators.

Keywords: Amphibia; Frog; Odontophrynidae; Poison; Rhinella; Skin gland.