the gastric-brooding frog – not quite back from the dead

I first found out about gastric-brooding frogs (Rheobatrachus silus) when reading Stephen Jay Gould’s essay "Here Goes Nothing" (as published in the 1991 book Bully for Brontosaurus). As he said, these frogs really do live up to their name: the frog

swallows its fertilised eggs, broods tadpoles in its stomach, and gives birth to young frogs through its mouth.

Gould’s tale first introduces another example of the ability of natural selection to shape truly strange behaviour: male Rhinoderma darwini frogs swallow the eggs they’ve fertilised and brood them, not in their stomachs, but in their throat pouches. These are the same pouches that male frogs inflate with air & use in croaking (& whistling, & chirping, depending on species) during courtship, which means that a brooding male is rendered voiceless for the duration. However, it doesn’t stop them feeding normally, something that was first demonstrated way back in 1888 by biologist G.B.Howes (Gould, 1991). I was interested to find out, while researching this post, that the eggs aren’t ingested immediately after fertilisation: they’re laid in damp leaf litter and the male remains close by, but waits until the embryonic tadpoles are wriggling around inside the egg membrane before taking them up in his mouth. (I’m guessing that the behaviour’s triggered by the sight of the wriggling tadpoles.)

As for the gastric-brooding species: Gould provides an engaging description of how this habit was uncovered. Until 1979

[n]atural birth had not yet been observed in Rheobatrachus. All young had either emerged unobserved or been vomited forth as a violent reaction after hatching.

However, scientists finally managed to get a gravid (I hope that’s the right word in these circumstances!) female in an aquarium with their cameras all at the ready:

The mother "partially emerged from the water, shook her head, opened her mouth, and two babies actively struggled out."

It’s no small feat to incubate froglets in this way:

This… female, about two inches long, weighed 11.62 grams after birth. Her twenty-six children weighted 7.66 grams, or 66 percent of her weight without them.

And of course, the incubating female must stop eating and switch off production of gastric juices for the duration!

Sadly, confirmation of this highly unusual method of parental care was rapidly followed by news that the species appeared to be extinct in the wild. Which is why I was so intrigued by my student’s news of its resurrection. However, it seems that reports of that resurrection may have been somewhat exaggerated. A quick search turned up several articles (this one’s a good example) that describe what’s been achieved so far: R.silus tissues that had been in the freezer were thawed, and cell nuclei from those tissues were implanted in enucleate eggs from another, distantly-related, species of frog (an example of somatic cell nuclear transfer). Some of those went on to an early (but unspecified) stage of embryonic development before being frozen in their turn, to await possible reanimation in the future.

In other words, R.silus froglets won’t be hopping around just yet. (And I’m moved to wonder how achievable the aim of the Lazarus project actually is, as it relates to this species. After all, if the gastric brooding part is an essential part of development, where’s the stomach going to come from?)

S.J.Gould (1991) Bully for Brontosaurus. Penguin Books.

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