Too cool for school: These frogs skip the tadpole stage

PUNE: Imagine if you never went to school, skipping that phase of your life and instead worked from the day you were born. Some frogs, found in the Western Ghats, seem to be doing just that with their young ones. These frogs are skipping the tadpole stage entirely and emerging from their eggs as fully-formed froglets that grow into adults.
In general, the lifecycle of the frog comprises of them laying eggs, usually in water, called an egg-clutch.When these eggs hatch, an embryo emerges and stays in this form for about eight to nine days following which they develop into tadpoles. "Tadpole feed on algal matter in the water to grow in size. After undergoing the process of metamorphosis for one or two months the tadpoles emerge as frogs," said KV Gururaja, chief scientist at Gubbi Labs LLP.
However, some frogs have evolved a strategy that bypasses the free living tadpole stage completely, known as direct development. "The Western Ghats are home to two groups of these frogs — 52 species of the Raorchestes genus and another three species of the Pseudophilautus genus," Gururaja said.
It is presumed that all 52 species of Raorchestes genus reproduce through direct development, but, so far, the behaviour of only four or five species has actually been studied. There is a need for much more research and this is an area where not only scientists, but nature enthusiasts too can contribute, said KS Seshadri, who is studying the frogs as part of his PhD.
Direct development has been seen in frogs in many parts of the world. Recent molecular DNA studies have revealed interesting insights about how the process came about, Seshadri said. "So far it was thought that direct development is an evolutionary advantage that enables these frogs to reproduce without the aquatic phase. However, it has been found that instead of merely one evolutionary pathway from which all of them evolved, they have emerged between nine to thirteen times. So the frogs that developed this ability in the Western Ghats evolved separately from those in, say South America," he explained.
"These frogs inhabit a variety of habitats ranging from evergreen forests to grasslands to tree canopies. Their ability to reproduce without a tadpole stage reduces their dependency on water since there is no stage in the lifecycle that is completely aquatic," Gururaja added. However, the adaptation has not removed the need for water completely. Even now, the frogs require high humidity, moisture and lay their eggs only in the rainy season," he added.
Breeding in Bamboo
Usually, the adult frogs lay their eggs and then leave them to hatch and develop on their own, but an unusual parental behaviour has been spotted in some species of Raorchestes.
When it is time to mate, Raorchestes chalazodes and Raorchestes ochlandrae frogs find gaps, or openings, in shoots of Ochlandra travancorica — a bamboo that is endemic to the Western Ghats. They enter the bamboo shoots through existing gaps, created by insects, and once the eggs are laid, the female frog leaves as is common. However, the male frog stays behind to take care of the eggs — ward off predators (ants) and keep them moist, Gururaja said. Much like sea-horses, it is the male frog that takes care of the eggs and not the female, he added.
Similar behavior, of breeding inside bamboos, has been observed in some frog species in northeastern India, but in those modes of reproduction, the cavities where the eggs are laid are filled with water. In this case, the internodes of the bamboo are dry, Seshadri said.