Head co-ossification, phragmosis and defence in the casque-headed tree frog Corythomantis greeningi

Some anurans have a peculiar casqued head with the skin co-ossified with the underlying bones. This type of skull usually is associated with phragmosis, a protective behaviour in which the animal enters a hole and closes it with the head. Although co-ossification of the head in lissamphibians frequently has been associated with water economy, recent studies of Corythomantis greeningi, a casque-headed tree frog from semi-arid areas in north-eastern Brazil, suggest that cranial co-ossification contributes little to conservation of water in the frog. Instead, during phragmotic behaviour, the co-ossified head protects the animal against predators and indirectly enhances water balance. Thus, the primary role of co-ossification is defence, a hypothesis that is the focus of this study, which describes the morphology of the head of C. greeningi with an emphasis on the co-ossification and the venom glands. We report on behavioural features and on the toxicity of the cutaneous secretion produced by the abundant venom glands that are associated with large spicules on the skull.

The inguinal macroglands of the frog Physalaemus nattereri (Leptodactylidae) Structure, toxic secretion and relationship with deimatic behaviour

Amphibian skin is characterized by the presence of mucous glands, related to cutaneous breathing, reproduction and water balance, and granular glands, related to the production of toxins used in defence. In some species the granular glands can form accumulations in certain regions of the body. This is the case for inguinal macroglands of the leptodactylid frog Physalaemus nattereri, where these structures form a pair of black discs associated with deimatic behaviour. The morphology of the inguinal macroglands and their secretion were studied in this species and correlated to deimatic behaviour. The inguinal macroglands are formed from elongated granular glands that, in contrast with the granular glands of the rest of the skin, have small spherical granules with a proteinic content. In the dermis of the whole body, except for the inguinal macroglands and the inguinal region, a well-developed calcified dermal layer is observed. During deimatic behaviour these macroglands discourage a potential predator from attacking, but if visual cues are insufficient and the predator persists in the attack, a toxic secretion is eliminated in its mouth. This elimination is favoured by the absence of a calcified dermal layer in the macroglands, which makes the dermal region softer than the rest of the dorsal skin.