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.”
