Darjeeling's Himalayan frog population genetically isolated, faces hunting pressure: Study
A new study reveals Darjeeling's Marbled Cascade Frog is genetically isolated and faces threats from hunting and low genetic diversity.
A groundbreaking scientific study has revealed that the Marbled Cascade Frog, a resident of the Darjeeling and Kalimpong regions, is facing a critical survival crisis. The species, known locally as ‘Sisne Paha’ or ‘Sisne Paa’, is struggling with extreme genetic isolation and increasing pressure from traditional hunting practices.
A Genetically Unique but Vulnerable Population
The research, which involved a collaborative team of 12 scientists from prestigious institutions including the University of Calcutta, Banaras Hindu University (BHU), and the Zoological Survey of India (ZSI), marks the first time a detailed DNA analysis has been conducted on this species. Published in the international journal BMC Genomics, the findings paint a concerning picture of the frog's biological health.
According to the DNA analysis, the population in the Darjeeling region possesses significantly lower genetic diversity compared to other populations found across Asia. While frogs in Myanmar, Southeast Asia, and China show relatively high genetic variety, the Darjeeling lineage stands apart as being genetically distinct and isolated.
The Science Behind the Isolation
The research team conducted extensive field surveys across 57 locations, ranging from waterfalls to fast-flowing rocky rivulets at altitudes between 200 and 2,400 metres. By analyzing the 16S rRNA and COI genes, scientists were able to trace the evolutionary history of the species:
- Ancient Origins: The common ancestor of the species in Asia lived approximately 17.4 million years ago.
- Lineage Divergence: The South Asian or Darjeeling lineage diverged roughly 11.2 million years ago.
- Regional Spread: The current Darjeeling lineage spread across its specific region approximately 0.94 million years ago.
Dr. Kumaresh Mandal noted that the population likely originated from a small group through a "founder effect" and subsequently expanded. This historical event has left the Darjeeling samples on a distinct branch of the phylogenetic tree, characterized by short branches that signify limited genetic diversity.
Hunting Pressures and Ecological Risks
Beyond the biological threat of isolation, the study highlights a significant modern pressure: local consumption. In the Darjeeling Hills, catching frogs is a common practice, particularly during the monsoon season when the animals are perched on rocks and bushes at night.
While two major species are consumed in the region—Amolops marmoratus and Nanorana liebigii—it is the Marbled Cascade Frog (Amolops marmoratus) that faces the most intense harvesting pressure due to its wider distribution. This traditional use for food and medicine, while culturally established, could further deplete the already fragile genetic pool.
A Call for Urgent Conservation
The researchers emphasized that the combination of geographical isolation, limited gene flow, and historical population events has left this species in a precarious position. Dr. Rakesh Tamang, who led the research from the University of Calcutta, stressed the importance of these findings for future environmental planning.
"The population is distinct and exhibits low diversity; this factor cannot be overlooked when formulating conservation policies," said Dr. Tamang.
Protecting these genetically unique Himalayan populations and their specific stream habitats is now seen as essential for maintaining the overall ecological stability of the Eastern Himalayas.