Alternative reproductive and developmental mechanisms in marsupial frogs

摘要

The aquatic larval period has been reduced or totally eliminated in the egg-brooding hylid frogs from South America. In Cryptobatrachus, Stefania, and in Hemiphractus, embryos are exposed on the mother's back during incubation. In contrast, the female of the marsupial frogs (Gastrotheca, and Flectonotus) has a dorsal pouch, and embryos are kept inside the pouch during incubation. In Gastrotheca riobambae, the male moves the eggs into the pouch at amplexus, which occurs on land. The incubation of embryos lasts for about four months. At the time of birth, the female aids in the emergence of about 120 tadpoles by removing them from the pouch with her toes. However, in the majority of egg-brooding hylid frogs, juvenile frogs are born, eliminating in this way the aquatic tadpole stage. The protection provided by the mother frog is associated with the production of fewer eggs (from 2 to 220) of large size (from 2.2 to 10 mm in diameter, according to species). Development is slow, like in the mammals. In contrast, frogs with aquatic reproduction, like Xenopus, produce large quantities of small eggs, that develop rapidly in the water (see del Pino, 1989 Development 107: 169 for a review).