New genus of tree frog discovered in Andaman Islands and Northeast India

A team of Indian, Chinese, Indonesian and Thai researchers have found a new genus of frogs in the Andaman and Nicobar Islands and India’s northeast, according to November 12 issue of Zootaxa, an international animal taxonomy journal. The genus has been named Rohanixalus after Sri Lankan taxonomist Rohan Pethiyagoda.

A genus is a category of classification of animals, plants above a species and below a family. It can include one or many similar species.

Rohanixalus is the 20th recognised genus of the Rhacophoridae family and comprises eight out of the 422 known Old World Tree Frog species in Asia and Africa.

The researchers studied aspects such as external morphology, calls, breeding biology, etc of tree frog species distributed across South, Southeast, and East Asia and confirmed that they represent a new genus.

Frogs from the genus are characterised by a small and slender body (about 2 cm to 3 cm long), a pair of contrastingly coloured lateral lines on either side of the body, and other distinct behavioural traits, the researchers said in a note on Thursday.

Based on DNA studies, the new genus is believed to be of a distinct evolutionary lineage compared to previously known tree frog genera. During the breeding season, these reddish-brown frogs can be found in large numbers on bushes and shrubs surrounding water bodies.

Scientists believe many more unnamed Rohanixalus species are likely to be present and there is a need to understand the diversity of the new genus.

This is the first time a tree frog species has been found in the Andaman Islands.

“Our discovery of a tree frog member from the Andaman Islands is unexpected and once again highlights the importance of dedicated surveys and explorations for proper documentation of biodiversity in a mega-diverse country like India,” said SD Biju, a Delhi University professor, who led the study.

The researchers noticed maternal parental care among the new genus. The mother frog attends the egg clutches until hatching and assists in the release of the tadpoles.

“During the first three days after egg-laying, the mother sits on the eggs and produces a gelatinous secretion with which she glazes the eggs through the clockwise movement of her legs. This provides necessary moisture to the eggs laid on exposed leaf surfaces and protects them from insects,” said the note.

The scientists found that multiple clutches of eggs laid on a single leaf or plant are attended by multiple females in a behaviour pattern described as community egg attendance.

The distinct light green coloured eggs of the new genus are laid in an intermediate form of bubble nests, whereas tree frogs of other genera possess creamy white eggs and their nesting behaviour varies from direct development to foam nests or gel nests.

“Members of the new genus are reported to display territorial behaviour and frequent combats between males involving pushing, kicking and dislodging, in order to successfully mate with a female,” the note said. “The gravid [pregnant] females in species of the new genus such as ‘Rohanixalus vittatus’ possesses translucent skin making their internal organs, including mature eggs, visible on their see-through bodies.”