The gastric-brooding frog, Rheobatrachus silus, was a species native to Southeast Queensland belonging to the class Anura. The species has been extinct since the mid-1980s years. They are medium in size, measuring an average of 55mm in body length.

What is interesting about this frog is its unique method of reproduction. The Rheobatrachus silus is the only species known in the animal kingdom to reproduce through gastric-brooding, in which the young develop in the mothers’ stomach cavity. The mothers swallow the eggs during the early stages of germination and the young develop within its stomach cavity. During this period, the stomach functions as a uterus, and feeding and digestion cease.  The mother’s lungs also retain minimal function and it relies on gas exchange through the skin. The presence of the developing young within the stomach cavity produces an increasing sense of satiation to the mother, and after they have developed past the tadpole stage, they are eventually expelled through the mouth as small frogs.

This behaviour contributes to the wide range of parental care behaviour exhibited by animals. Many models of animal parental care have been developed, and they centre around the common concept of an all or none strategic choice of either desertion, guarding, or no care, care (Winkler, 1987).  In the case of the gastric-brooding frogs, they exhibit one of the more unique forms of parental care ever known in the amphibian world (Corben et al., 1974).

Similar forms of parental care have been observed, in which development occurs within a parent, yet the gastric-brooding method of the Rheobatrachus silus is the only example known of its kind. In animals exhibiting such similar reproduction methods, most commonly in several species of fish, the eggs are usually taken into and transported via the oral cavity of the parent and they undergo oral incubation, but never are the eggs digested (Corben et al., 1974).

Perhaps an additional consideration in the case of the gastric-brooding frog, could relate its reproductive method to its current status of being extinct. While Winkler (1987:527) developed his General Model for Parental Care on the basis that”natural selection has favoured parents that respond to their broods….in such ways as to maximise their reproductive value”, in this case ensuring the eggs make it through development, perhaps the method of reproduction resulted in a certain trade-off with other aspects vital for survival, such as adaptability to changes. The exact cause(s) of its extinction, however, remain to be established.

References

Corben, C. J., Ingram, G. J., Tyler, M. J., 1974. Gastric brooding: Unique form of parental care in an Australian frog. Science, New Series, 186(4167): 946-947.

 Tyler, M. J. & Carter, D. B., 1981. Oral birth of the young of the gastric brooding frog Rheobatrachus silus. Animal Behaviour, 29(1): 280-282. (Main Article)

Winkler, D. W., 1987. A general model for parental care. The American Naturalist, 130 (4): 526-543.