I was recently doing some research on species that have gone extinct in my lifetime. And I discovered the coolest frog: the gastric brooding frog. There are actually two species of these frogs, Rheobatrachus vitellinus and Rheobatrachus silus, both native to the Australian rainforest.
As their common names suggest, the frogs have a highly unusual reproductive strategy: after the females lay their eggs and the males fertilize them, the mothers swallow the whole clutch of frogs-to-be. Over the next six to seven weeks, the eggs develop into tadpoles, and then little froglets, inside the mother’s stomach. When this transformation is complete, the female regurgitates her offspring–as many as two dozen of them–out into the world. (There are a couple great photos of this, but alas, I do not have permission to repost them here. But I urge you to take a look.)
This brooding behavior is made all the more remarkable by the fact that a female frog’s stomach is awash in hydrochloric acid–not exactly a hospitable place for a youngster to develop. But the gastric brooding frogs have that covered, too. It turns out that the young frogs themselves secrete a compound known as prostaglandin E2, which inhibits the production of stomach acid. (Unfortunately, before scientists could unravel exactly how this process worked, the gastric brooding frogs went extinct, so the precise details will forever remain a mystery.) In other words, the little froglets keep themselves safe during development by producing a substance that shuts down their mothers’ digestive systems. It’s a beautiful bit of evolution.
During the brooding period the female’s digestive process would shut down and her stomach would become so bloated that her lungs would collapse under the pressure, forcing her to rely solely on gas exchange through her skin for respiration. It was observed that during pregnancy females remained completely active even though their buoyancy and centre of gravity were affected to the point that when resting they floated vertically, rather than horizontally, in the stream.
The females don’t eat anything during the entire time their young are incubating in their stomachs, but their digestive systems return to normal after the froglets are born.
One interesting twist to the story is that scientists thought the gastric brooding frogs–with their ability to suppress stomach acid production–might have possessed a key to treating gastric ulcers. Sadly, the frogs died out before that was possible.
Michael J. Tyler, & David B. Carter (1981). Oral birth of the young of the gastric brooding frog Rheobatrachus silus Animal Behaviour, 29 (2) DOI: 10.1016/S0003-3472
Fanning JC, Tyler MJ, & Shearman DJ (1982). Converting a stomach to a uterus: the microscopic structure of the stomach of the gastric brooding frog Rheobatrachus silus. Gastroenterology, 82 (1), 62-70 PMID: 7053337
MJ Tyler, DJ Shearman, R Franco, P O’Brien, RF Seamark, & R Kelly (1983). Inhibition of gastric acid secretion in the gastric brooding frog, Rheobatrachus silus Science, 220 (4597) DOI: 10.1126/science.6573024
de la Lande IS, O’Brien PE, Shearman DJ, Taylor P, & Tyler MJ (1984). On the possible role of prostaglandin E2 in intestinal stasis in the gastric brooding frog Rheobatrachus silus. The Australian journal of experimental biology and medical science, 62 ( Pt 3), 317-23 PMID: 6437385
Ed Meyer, David Newell, Harry Hines, Sarah May, Jean-Marc Hero, John Clarke, Frank Lemckert 2004. Rheobatrachus silus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1.