Guwahati: Scientists have described two new species of slender-armed frogs from secretive habitats in Arunachal Pradesh.
The study also highlights the Brahmaputra River as a significant biogeographical barrier: the newly discovered species occur north of the river, while all previously known members of the genus are restricted to its southern side.
The discoveries are the result of more than three years of intensive expeditions to remote mountain regions of Arunachal Pradesh. The findings were published today in the US-based scientific journal PeerJ.
Arunachal Pradesh lies within the Himalaya biodiversity hotspot—one of the world’s richest regions for biological diversity—known for its exceptional plant and animal life, including a remarkable variety of amphibians.
Among these amphibians are members of the frog family Megophryidae, one of the most diverse frog families globally. The slender-armed frogs (Leptobrachium), belonging to this family, include about 40 species distributed across South and Southeast Asia.
The new species were discovered by a team led by S. D. Biju as part of the PhD research of his student, Akalabya. During extensive fieldwork across five northeastern Indian states, the team documented multiple populations of slender-armed frogs. Detailed laboratory analyses of specimens from Arunachal Pradesh confirmed that two populations represented species new to science.
The study employed an integrative taxonomic approach, combining DNA sequencing, detailed morphological comparisons of adults and tadpoles, bioacoustic analyses, and three-dimensional micro-CT scans of skeletal structures. Molecular data from the new species were compared with all known members of the genus to understand their evolutionary relationships.
“The descriptions of these two new species are supported by multiple lines of evidence, confirming that they represent distinct evolutionary lineages. Our results also demonstrate how riverine barriers—particularly the Brahmaputra—shape the geographic distribution and diversification of slender-armed frogs,” said Prof. S. D. Biju.
The New Species
Soman’s Slender Arm Frog (Leptobrachium somani)
Discovered at Tiwarigaon in Arunachal Pradesh, this small frog measures about 55 mm in length. It has a greyish-brown body with irregular light-grey markings and striking silver-grey to light-blue eyes. An evergreen-forest species, males are typically found calling from the banks of fast- or slow-flowing streams.
The species is named in honour of the late E. Somanath (Ettazhi Somanath), a noted journalist from Kerala who was deeply committed to environmental reporting and frequently accompanied Prof. Biju on frog-search expeditions.
Mechuka Slender Arm Frog (Leptobrachium mechuka)
Measuring about 60 mm, this species inhabits evergreen forests and adjoining grasslands. It has a uniformly brown body with a reddish tinge and distinctive silvery-white eyes.
The frog is named after Mechuka, the town in Arunachal Pradesh where it was first collected. Notably, this species had recently been reported from China under an incorrect identity.