Thanks for Merike for suggesting the gastric brooding frog and to Hally for suggesting newly-discovered frogs!!

The Gastric brooding frog:

Darwin's frog, round boi:

The Surinam toad carries her eggs and tadpoles in the skin of her back:

Kermit the frog and a newly discovered glass frog:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we have another fantastic listener suggestion, about frogs! Merike is a herpetologist from Estonia, who suggested the gastric brooding frog, and another listener, Hally, also wanted to learn about some of the new frog species discovered recently.

The gastric brooding frog is native to eastern Australia, specifically Queensland. There are two species, and both of them live in creeks in separate rainforests. The habitat is specific and small, and unfortunately both species went extinct less than forty years ago. Researchers aren’t sure why they went extinct, but it was probably due to pollution and habitat loss.

The gastric brooding frog was a slender frog, with the northern gastric brooding frog being about three inches long, or about 8 cm, while the southern gastric brooding frog was about half that size. Females were larger than males. It was grey or brown-gray in color with some darker and lighter patches on the back with a lighter belly. During the day it spent most of its time at the water’s edge, hidden in leaf litter or among rocks, although it generally only fully came out of the water when it was raining. It ate insects and may have hibernated in winter.

As you may have guessed from its name, the gastric brooding frog had a unique way of taking care of its eggs. After the eggs were fertilized, the female would actually swallow the eggs and keep them in her stomach while they developed. Even after the eggs hatched into tadpoles, they stayed in the mother’s stomach. As they grew larger, the stomach also grew larger, until it pretty much filled up the mother’s insides, to the point where she couldn’t even use her lungs to breathe. Fortunately many frogs, including the gastric brooding frog, can absorb a certain amount of oxygen through the skin. Finally the tadpoles metamorphosed into little frogs, at which point the mother regurgitated one or a few of them at a time, or sometimes all of them at once if she felt threatened.

So how did the mother keep from digesting her own eggs or tadpoles? How did she eat when her stomach was full of babies? How did the babies eat?

The jelly around the gastric brooding frog’s eggs contained prostaglandin E2, also called PGE2, which causes the stomach to stop producing hydrochloric acid. That’s a digestive acid, so once the eggs were inside the stomach, the stomach basically stopped stomaching. There is some speculation that the first eggs the mother frog swallowed actually got digested, but then the acid production stopped and the rest of the eggs remained. Once the eggs hatched, the tadpoles also produced PGE2 in the mucus in their gills.

The tadpoles continued to live off the yolk sac from their eggs as they developed, and in fact their mouths weren’t even connected to their gut yet. As for the mother, she just didn’t eat until the babies were developed and released into the water on their own, which took about six weeks.

The gastric brooding frog is the only frog known to raise its babies this way, but other frog species have interesting variations of the usual way frogs reproduce. Most female frogs lay their eggs, and then the male fertilizes them. But about a dozen species of frog have developed internal fertilization, where the female retains the eggs in her body until the male fertilizes them. The tailed frog from California in the United States, in North America, gets its name from a structure that looks like a tail, but is actually an extension of the cloaca. That’s the opening used for both excretion and reproduction. Only males have the tail,