Madagascar frog rears tadpoles in dead palm leaves

Matt Walker BBC News 10 May 10;

A new species of frog has been discovered that lays its eggs and grows its tadpoles in dead leaves that litter the forest floor.

The frog, found in the rainforest of Madagascar, is the first amphibian known to reproduce in this way.
Other species reproduce in water that collects or pools within plants, but the new frog is the first discovered to rear its young in fallen leaves.

Details are published in the journal Naturwissenschaften.

Scientists have called the new species Blommersia angolafa.

It is a small frog, measuring 17 to 21mm from rear to nose, with expanded tips on the ends of its toes and fingers.

Males tend to be yellow, while females are brown coloured. Both have pale bluish spots on their flanks and finger and toe tips.

The most striking characteristic of the new species is its reproductive behaviour.

More than 100 species of frog are known to reproduce away from free water such as ponds or rivers.

Most breed in standing pools of water, often that collect in tree holes, within bamboo or within folded leaves growing on trees or plants.

However, a team of biologists has discovered B. angolafa breeding in rainfall collecting in the dead, upturned leaves of palm trees that have fallen to the forest floor.

"Within these leaf sheaths, egg laying and complete larval development occur," says Ms Gonçalo de Sousa Miranda Rosa of the University of Lisbon, Portugal, who helped discover the new species during rainforest surveys for her MSc thesis.

After mating, female frogs lay clutches of 2-10 yellowish eggs within a brown jelly onto the insides of dead leaves of three different palm species.

The frogs lay their eggs a few millimetres above the surface of water pooling in the leaf, which then hatch into tadpoles.

During their surveys, the researchers found egg clutches, tadpoles, new metamorphosised froglets and adult males and females within the dead leaves, including males calling out for a mate.

More often than not, males were found alongside the eggs and tadpoles, suggesting that males may guard the eggs and offspring.

No B. angolafa frogs were found living among the crowns of the palm trees or anywhere outside the dead leaves on the forest floor.

Nor did any other frog species inhabit the dead leaves.

Four other frog species are known to reproduce in fallen dry plant matter: three species breed in the fruit capsules of the Brazil nut tree, while another breeds in tree holes, empty nuts and occasionally snail shells.

But B. angolafa is the first known to breed in fallen dead leaves.

Surveys have discovered the frog living in four locations in northeast Madagascar, within the protected areas of Ambatovaky, Betampona, Masoala and Zahamena.

Ms Rosa and her colleagues say that B. angolafa belongs to a group of frogs that usually breed in ponds, where oxygen levels are lower than in streams or rivers.

This tolerance to low oxygen levels may have allowed B. angolafa to adapt to its new habitat.

However, its reliance on the palm leaves also places it at risk.

B. angolafa is so far known to breed within the leaves of three palms called Dypsis lastelliana, D. tsaravoasira and D. hovomantsina.

Dypsis palms are being logged across Madagascar, and both D. tsaravoasira and D. hovomantsina are known to already be critically endangered.

If these palm trees disappear it is likely that the new species of frog may disappear with them, say the researchers.