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Midwife Toads

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 larvaepartusactually 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.