Guwahati: Scientists have identified two previously unknown species of slender-armed frogs from the forests of Arunachal Pradesh, adding fresh evidence that major river systems such as the Brahmaputra play a decisive role in shaping species evolution in the Eastern Himalaya.
The discoveries, published in the international peer-reviewed journal PeerJ, are the result of more than three years of field expeditions to remote mountain regions of Arunachal Pradesh, part of the globally significant Himalayan biodiversity hotspot.
The study was led by amphibian expert S. D. Biju of the University of Delhi and carried out as part of the doctoral research of Akalabya, who surveyed frog populations across five northeastern states.
The two new species-Soman's Slender Arm Frog (Leptobrachium somani) and Mechuka Slender Arm Frog (Leptobrachium mechuka)-were found in secretive habitats in Arunachal Pradesh. One species has been named in honour of the late journalist E. Somanath, recognising his lifelong commitment to environmental journalism.
Using an integrative taxonomic approach, the researchers combined genetic sequencing, morphological analyses of adults and tadpoles, bioacoustic data, and three-dimensional micro-CT scans of skeletal structures. Comparative molecular analysis confirmed that the specimens represent two distinct evolutionary lineages within the genus Leptobrachium.
Soman's Slender Arm Frog, discovered at Tiwarigaon, measures about 55 mm in length and has a greyish-brown body with irregular light-grey markings and silver-grey to light-blue eyes. An evergreen forest species, males are typically found calling from the banks of streams. Prof. Biju noted that E. Somanath frequently accompanied him on frog-hunting expeditions.
The Mechuka Slender Arm Frog, measuring about 60 mm, 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 town, where it was first collected, and had earlier been misidentified in reports from China.
A key finding of the study is that both species occur north of the Brahmaputra River, while all previously known slender-armed frogs are restricted to the south, underscoring the river's long-term role as a biogeographical barrier influencing amphibian diversification.
Researchers say the findings highlight how much of Northeast India's biodiversity remains undocumented and stress the need for sustained ecological exploration and habitat protection.
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