PUBLISHED August 24, 2017

The newly discovered Bhupathy's purple frog spends nearly its entire adult life underground—but its tadpoles spend four months suctioned to cliffs behind waterfalls. Photograph by Jegath Janani

Scientists have discovered a new and unusual species of frog in the Western Ghats mountain range in India. The frog has shiny, purple skin, a light blue ring around its eyes, and a pointy pig-nose.

The scientists have called the new species Bhupathy's purple frog (Nasikabatrachus bhupathi), in honor of their colleague, Dr. Subramaniam Bhupathy, a respected herpetologist who lost his life in the Western Ghats in 2014.

While the new amphibians may appear odd, each quirk of the purple frog’s anatomy is the result of countless years of evolution. Small eyes, a long snout, and short limbs equipped with hardened ‘spades’—each enables the frog to spend almost its entire life below ground.

In fact, the amphibians don’t even surface to eat. Instead, the Indian purple frogs use a long, fluted tongue to slurp up ants and termites underground, says Elizabeth Prendini, a herpetologist at the American Museum of Natural History and coauthor of a paper describing the species in the newest issue of the journal Alytes.

Bhupathy’s purple frog is closely related to another purple frog (N. sahyadrensis) found in the region in 2003. Together, the two make up the only known members of their family. The find comes as part of an effort sponsored by the Indian government to sample the DNA of every frog and toad species in the nation.

“This frog lineage is very ancient, and has a very low diversity, so this finding is very special and unusual,” says Prendini.

Singing in the Rain

There is one thing that can coax the purple frogs from their underground burrows—rain.

When the monsoon season begins, the male frogs start making loud calls from beneath the sand in mountain streams, says Ramesh Aggarwal, senior author of the new study and a molecular geneticist at the Center for Cellular and Molecular Biology in Hyderabad, India.

The frog's features—pointy snout, tiny eyes, and stumpy limbs—help it adapt to life almost entirely underground. Photograph by Jegath Janani

Males then mate with females in the streams, where they deposit the fertilized eggs. After a day or two, the eggs hatch into tadpoles.

But unlike the tadpoles of many frog species, which spend their days swimming around puddles and ponds, Bhupathy’s purple frog tadpoles develop mouths more like that of a suckerfish. The tadpoles use these bizarre orifices to cling to the rocks behind waterfalls created by the heavy rains, where they graze on algae with tiny teeth.

The cliff-hanging tadpoles spend about 120 days in the torrent, says Karthikeyan Vasudevan, coauthor, biologist, and colleague of Aggarwal’s at CCMB.

“This is the longest the species appears above ground during its entire lifetime,” says Vasudevan. After the larval phase, Bhupathy’s purple frogs bid adieu to the outside world and set about their lives of subterranean secrecy.

A Wonderful World of Frogs

“Frogs are amazing in their adaptations, and this frog is evidence of this,” says Jodi Rowley, an amphibian biologist at the Australian Museum and National Geographic Explorer who was not involved in the new study.

Rowley says there are frog species all over the world that can burrow to escape periods of dryness, but that Bhupathy’s purple frog has taken this lifestyle to the extreme by finding a way to live underground almost permanently.

India's Western Ghats mountain range is home to a rich array of frog species, including some very tiny ones.

The find is also particularly interesting, says Rowley, because of just how distant the Bhupathy’s purple frogs are from their closest relatives.

“Both species of purple frog have been evolving independently from other frog species for a very long time,” she says. “Their closest relatives are not in India but the Seychelles, which is closer to Africa than India.”

All in all, the new species shows how little we still know about frogs in general.

“Despite being one of the most threatened groups of animals on the planet, with 42% of all known species threatened with extinction, we still don't even know how many species of frogs and other amphibians there are,” says Rowley.

In fact, she says over 100 new frog species are described in scientific journals each year. (Many more have been discovered, but await the time and effort it requires to officially describe them.) And perhaps this curious, pig-nosed species will inspire the next generation of young biologists.

“It's a wonderful world out there, with amazing critters, and so I think we need to celebrate the good news,” says Rowley.