Having studied amphibians for many years, herpetologist Jim
McGuire is used to handling frogs and toads. But when he picked up a fanged
frog while conducting fieldwork on the Indonesian island of Sulawesi, he got
quite a shock. What he thought was a male turned out to be a pregnant female,
who proceeded to squirt live tadpoles all over his hand! The unusual amphibian
has been named Limnonectes larvaepartus,
and is the only frog species known to reproduce in this way.
There are around 6000 known species of frog, and most reproduce
through external fertilisation. In a typical frog life cycle, the female lays a
large clutch of eggs, which are fertilised by the male as they leave her body –
a mating behaviour known as amplexus. The eggs are surrounded by a jelly-like
substance, which keeps the larvae safe during their gestation. After hatching,
the tadpoles undergo metamorphosis, growing legs and turning first into
froglets and then into adult frogs.
Internal fertilisation is much less common, only found in a dozen
or so species. These include two species of frog found in California, USA,
which have evolved penis-like organs called “tails”. The male uses its tail to
release sperm into the female, who then lays the fertilised eggs in streams and
rivers. Other species are able to incubate eggs inside their bodies – for
example, female horned marsupial frogs carry their offspring inside a special
pouch, where they develop into froglets. However, only Limnonectes larvaepartus actually gives birth to tadpoles – so it’s
no wonder Dr McGuire was taken by surprise!
Watch Midwife toads to discover another amphibian
with an unusual method of reproduction.
