Newly Discovered Fanged Frog Shocks Science: Births Live Tadpoles

Most frogs lay eggs and some birth froglets; the rare Limnonectes larvaepartus is the only one known to actually release tadpoles into the world.

Ruth Schuster
Will Dunham
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Limnonectes larvaepartus, a small frog from Indonesia that not only has fangs - but uniquely, gives birth to live tadpoles.
Limnonectes larvaepartus, a small frog from Indonesia that not only has fangs - but uniquely, gives birth to live tadpoles.Credit: Reuters
Ruth Schuster
Will Dunham

A recently discovered species of Indonesian frogs not only sports fangs in its jaws – uniquely on the planet, it gives birth to live tadpoles.

Most frogs lay eggs, from which tadpoles hatch and you know the rest. Limnonectes larvaepartus, a little amphibian from the rain forests of Sulawesi Island, is the only one of the world's 6,455 frog species to give direct birth to tadpoles, scientists said on Wednesday.

"Reproduction in most frogs could not be more different from human reproduction. In this case, what is most interesting, ironically, is that the reproductive mode is more similar to our own," said herpetologist Jimmy McGuire of the University of California, Berkeley, whose research appears in the scientific journal PLOS ONE.

This frog, usually gray or brown, are small, measuring about 4 centimeters in length. They weigh less than 5 grams and belongs to the rare Asian group of fanged frogs.

By the way, don't start having nightmares about getting savaged by rampaging frogs. The "fangs" are projections from the lower jaw that the males used in fighting each other.

The frog lives along small streams and puddles in rainforest habitats, doing its best to avoid being eaten by larger fanged frog species as well as snakes and frog-munching birds.

Its mode of reproduction sets this frog apart."The vast, vast majority of frogs have external fertilization. For mating, the male grips the female around the waist and releases sperm as she releases her eggs," McGuire said.

Those eggs mature through stages including the aquatic tadpole larval phase, typically limbless with a tail that propels it through the water.

About a dozen frog species rely on internal fertilization, McGuire said. All but the newly identified one either deposit fertilized eggs or give birth to froglets, essentially miniature versions of an adult that already passed through a modified tadpole stage while still in an egg capsule inside the female.

Where do scientists get those names

The female Limnonectes larvaepartus (meaning "marsh swimmer that gives birth to larvae") instead gives birth to tadpoles.

"It's totally unclear why this mode of reproduction has not evolved more frequently," McGuire said.

"My favorite topic when it comes to frog evolution and diversification is the bewildering variation in reproductive modes that occur. Frogs exhibit all sorts of interesting twists."

There have been frogs that swallowed their eggs and brooded them in the stomach, a species in which the male broods the eggs in his vocal sac, and many species that carry eggs and tadpoles in pouches on their backs and sides, he said.

Here's one: The flattish pipa toad of South America not only eschews the croak for a weird clicking sound to attract the females; then during the act of procreation, the eggs the female releases get embedded into the skin on the mother's back. Blister-type bumps form in which the fertilized eggs mature into live froglets. The kids then hatch from her back.

By the way, the island of Sulawesi is quite the froggy heaven, and this diminutive amphibian isn't its only impressive denizen. According to McGuire and his team, one of the species can reach 900 grams in weight, compared with the fanged frog's 5 grams. In other words it weighs almost as much as your brain.

The following video shows pipa babies hatching.

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