Limnonectes larvaepartus: Scientists Discover Tadpole-Bearing Species of Frog in Indonesia

Limnonectes larvaepartus is unique among frogs in having both internal fertilization and birth of tadpoles. Top: male, left, and female. Bottom: an adult male observed calling while perched on the edge of a small pool 2 m away from a 2 m wide stream; several tadpoles were present in the pool including the two visible within the yellow circle. Image credit: Jimmy McGuire.

Fanged frogs are so-called because of two fang-like projections from the lower jaw that are used in fighting.

They may have evolved into as many as 25 species on Sulawesi, though Limnonectes larvaepartus is only the fourth to be formally described. They range in size from 2 to 900 grams. The newly-described species is in the 5-6 gram range.

“Almost all frogs in the world – more than 6,000 species – have external fertilization, where the male grips the female in amplexus and releases sperm as the eggs are released by the female. But there are lots of weird modifications to this standard mode of mating,” said Dr McGuire, who is the senior author of the paper published in the open-access journal PLoS ONE.

“Limnonectes larvaepartus is one of only 10-12 species that has evolved internal fertilization, and of those, it is the only one that gives birth to tadpoles as opposed to froglets or laying fertilized eggs.”

Limnonectes larvaepartus 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.

Dr McGuire first encountered this frog in 1998, the year he began studying the amazing diversity of reptiles and amphibians on Sulawesi, an island east of Borneo and south of the Philippines.

The island is a geographical hodgepodge, having formed from the merger of several islands about 8-10 million years ago.

“Sulawesi is an incredible place from the standpoint of species diversity endemic to the island as well as in situ diversification,” Dr McGuire said.

Although many vertebrate species have diversified on Sulawesi after arriving by overwater ‘sweepstakes’ dispersal, most – such as the flying lizards and black-crested macaque monkeys – have speciated in such a way that their geographic ranges are non-overlapping, with their ranges meeting like pieces in a jigsaw puzzle.

“The fanged frogs are special because they appear to represent a virtually unexplored adaptive radiation with many species occurring at the same sites but adapted to occupy distinct ecological niches.”

“We are really interested in understanding how much of Sulawesi’s in situ diversification was initiated on the paleo-islands, or if much or even all of the diversification was postmerger.”