Guwahati, Jan 9: Scientists have described two new species of slender-armed frogs—Soman’s Slender Arm Frog (Leptobrachium somani) and Mechuka Slender Arm Frog (Leptobrachium mechuka)—from secretive habitats in the northeastern Indian state of Arunachal Pradesh.

One of the species has been named in honour of the late journalist E. Somanath, recognising his lifelong commitment to environmental journalism.

The study also provides new insights into the role of the Brahmaputra River as a major biogeographical barrier. Both newly described species are found north of the river, whereas all previously known members of the genus Leptobrachium are restricted to regions south of it.

The discoveries follow more than three years of intensive field expeditions to remote mountainous regions of Arunachal Pradesh and have been published today in the US-based scientific journal PeerJ.

Arunachal Pradesh lies within the Himalaya biodiversity hotspot, one of the world’s most biologically rich regions, renowned for its exceptional diversity of flora and fauna, particularly 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, comprise about 40 species known from 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 surveys across five northeastern Indian states, the researchers documented several populations of slender-armed frogs.

Subsequent laboratory analyses of specimens collected from Arunachal Pradesh confirmed that two populations represented species new to science.

The study adopted 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 those of all known members of the genus to clarify their evolutionary relationships.

“The descriptions of the two new species are supported by multiple lines of evidence, confirming that they represent distinct evolutionary lineages. Our findings also demonstrate how riverine barriers, particularly the Brahmaputra, shape the geographic distribution and diversification of slender-armed frogs,” said Prof. Biju.

Species details

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 distinctive 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 journalist E. Somanath, who frequently accompanied Prof. Biju on field expeditions in search of frogs.

Mechuka Slender Arm Frog (Leptobrachium mechuka)

Measuring about 60 mm, this species occurs in evergreen forests and adjoining grasslands. It has a uniformly brown body with a reddish tinge and striking silvery-white eyes. The species is named after Mechuka, the town in Arunachal Pradesh where it was first collected. Notably, this frog had recently been reported from China under an incorrect identity.

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