Rare bush frog breeds inside bamboo

Critically Endangered white spotted bush frogs in South India breed inside bamboo, representing a new reproductive mode in frogs and toads

It's an extraordinary act by an extraordinary animal. A rare frog, only recently rediscovered after being presumed extinct for a century, has now been found to do something no other frog was known to do; reproduce within grass, actually inside the stems of bamboo.

The tiny amphibian, the white spotted bush frog (Raorchestes chalazodes), which is less than 25mm in length, was rediscovered in 2003 in the Western Ghats mountain range after being presumed extinct for over 100 years.

Scientists from the National University of Singapore and the Indian Institute of Science describe the bush frogs' breeding behaviour in the Biological Journal of the Linnean Society.

Male frogs were recorded squeezing inside hollow bamboo through small slits, where they attracted females with their calls. After mating, females laid a clutch of eggs inside the bamboo and males stayed in the hollow part of the stem to take care of the eggs, from which froglets emerge.

At night, the devoted dads left the eggs for a few hours to feed before returning to their watchman duties.

The new reproductive mode is the 41st described among frogs and toads, and is unique because the eggs are laid in bamboo without any water, where they develop directly into froglets. And unusually, the adults provide parental care.

The study built on observations of the closely related Ochlandra reed frog (Raorchestes ochlandrae), which also makes use of bamboo. Researchers now believe Ochlandra reed frogs breed in the same way as white spotted bush frogs.

Team member Seshadri KS, a PhD student from the National University of Singapore’s Department of Biological Sciences, said the discovery of a new reproductive mode “opens up a new world for questions on the evolutionary ecology of frogs".

The bamboo-utilising mode is the latest of many terrestrial breeding strategies recorded in frogs and toads. “Frogs have shown the tendency of being increasingly non aquatic," said Mr Seshadri, adding that the Chalazodes group of frogs "seem to have evolved this adaptation under certain pressures of natural selection".

Researchers observed white spotted bush frogs living in the Kalakad Mundanthurai Tiger Reserve in the Western Ghats mountains, which are known as a biodiversity hotspot and listed as a UNESCO (United Nations Educational, Scientific and Culture Organisation) World Heritage site.

While around 100 new species of frog have been described from the Western Ghats, Mr Seshadri said little is known about frog behaviour and reproductive strategy.

The study also highlights bamboo as an important breeding resource, and the team want to investigate ways of conserving the endangered frogs, which may be at threat from overharvesting of bamboo for paper and pulp.

Team member Dr David Bickford, also from the National University of Singapore’s Department of Biological Sciences, said: “[It’s] 2014 and we are still making discoveries like these; natural history is sexy - always was and always will be. No matter what the molecular and genomic revolutions have accomplished for us in the biological sciences, nature is still the ultimate source for everything we do in biology.”

Video courtesy of Seshadri KS