Scientists have discovered the first known frog that gives birth to live tadpoles instead of laying eggs in the rainforests of Indonesia's Sulawesi Island.
University of California, Berkeley herpetologist Jim McGuire grabbed what he thought was a male frog and found himself juggling not only a frog but also dozens of slippery, newborn tadpoles.
A member of the Asian group of fanged frogs, the new species was discovered a few decades ago by Indonesian researcher Djoko Iskandar, McGuire's colleague, and was thought to give direct birth to tadpoles, though the frog's mating and an actual birth had never been observed before.
"Almost all frogs in the world - more than 6,000 species - have external fertilisation, where the male grips the female in amplexus and releases sperm as the eggs are released by the female," McGuire said.
"But there are lots of weird modifications to this standard mode of mating. This new frog is one of only 10 or 12 species that has evolved internal fertilisation, and of those, it is the only one that gives birth to tadpoles as opposed to froglets or laying fertilised eggs," said McGuire.
Iskander, McGuire and Ben Evans of McMaster University in Ontario, Canada, named the species Limnonectes larvaepartus.
Frogs have evolved an amazing variety of reproductive methods, said McGuire.
Most male frogs fertilise eggs after the female lays them. About a dozen species, including California's tailed frogs, have evolved ways to fertilise eggs inside the female's body.
However, the mechanisms of internal fertilisation are poorly understood in all but California's two species of tailed frogs.
Whereas the tailed frogs deposit their fertilised eggs under rocks in streams, the other frogs previously known to have internal fertilisation give birth to froglets - miniature replicas of the adults.
Although internal fertilisation is extremely rare among frogs, there are many other bizarre reproductive variations. Some frogs carry eggs in pouches on their back, brood tadpoles in their vocal sac or mouth, or transport tadpoles in pits on their back.
Fanged frogs - so-called because of two fang-like projections from the lower jaw that are used in fighting - may have evolved into as many as 25 species on Sulawesi, though L larvaepartus is only the fourth to be formally described.
They range in size from 2-3 grams - the weight of a couple of paper clips - to 900 grams, or two pounds. L larvaepartus is in the 5-6 gram range, McGuire said.
The new species seems to prefer to give birth to tadpoles in small pools or seeps located away from streams, possibly to avoid the heftier fanged frogs hanging out around the stream. There is some evidence the males may also guard the tadpoles.
The research was published in the journal PLOS ONE.
