Gene studies say that the Sunderbans tiger population is identical to the tiger population of central India and has been isolated recently, may be 300-1000 years ago, from the latter.
A study by Wildlife Institute of India (WII) scientist SP Goyal and researchers Sujeet Kumar Singh and Sudhanshu Mishra claimed that historical events, change in the land-use patterns and human pressure have isolated the Sunderbans tiger population from that of central India.
“Our study has found that the gene pattern of the Sunderbans tiger is identical to the big cat population of the central India landscape, including states like Madhya Pradesh, Maharashtra, Chhattisgarh and parts of Andhra Pradesh,” said Goyal.
An earlier study by US scientist Adam Barlow in 2009 had observed that the Sunderbans tiger is morphologically distinct in terms of skull and body size and therefore, the population can be evaluated further to determine if it’s an evolutionary significant unit.
But the WII report — Tigers of Sunderbans Tiger Reserve: Is This Population a Separate Evolutionary Significant Unit — has put to rest such possibilities for now. DNA haplotyping and fragment analysis methods were used during the study. Haplotypes are unique characters present in a genetic composition of a particular tiger population.
Goyal said Sunderbans tiger showed identical allelic or gene pattern as observed in the tigers of MP parks, including Bandhavgarh, Kanha, Pench, and reserves like Tadoba and Nagzira in Maharashtra.
Pulak Lahiri, former Nilratan Sarkar Professor of Zoology at Calcutta University, said: “Geologically, Sunderbans doesn’t have a history as old as central or northern India, so it’s possible that the mangroves’ tigers have isolated from central India landscape.”
Scientists believe while an animal isolated for a period of one million years can be classified as a different species, one that’s genetically isolated for 20,000-50,000 years can be termed as a different sub-species.
But, an earlier study by eminent scientists, John Seidensticker, Sandeep Sharma and Hemendra Panwar claimed that while tigers populated central India about 10, 000 years ago, their population subdivision began only about 1000 years ago and accelerated only 200 years ago owing to habitat fragmentation.
In historian Rajat Roy’s words, in 1756, when Siraj-Ud-Daulah recaptured the city of Kolkata (then Calcutta) from the British, today’s Salt Lake area used to be the main city then and the Lower South Circular Road that’s now known as Chowringhee used to be the city’s southern border. “Beyond that were the forests of Sunderbans and there are beliefs that tigers were often sighted in those forests which now house busy localities like Tollygunge and Behala,” said Roy, also the professor emeritus of Presidency University.
Though Goyal said only further analysis will throw light on the historical events that isolated a part of central Indian tiger population to Sunderbans, he believes that increase in urbanization and agricultural areas are the main triggers.
A key tiger landscape in central India, Satpura-Maikal, has already lost 78% forest cover to farmlands and urbanization. In the last 300 years, there was 22-fold increase in agricultural area and 25-fold rise in urbanization in this landscape.
The WII study has also found highest population differentiation between Sunderbans tigers and north Indian tigers, compared to central Indian tigers, which, according to Goyal, only proves that Sunderbans tigers are genetically more close to central Indian big cat population.
Additional PCCF (wildlife) Pradeep Vyas said the tigers of Sunderbans have definitely come from somewhere. “And this study throws some light on it. If the British rulers didn’t declare the Sunderbans as reserve forest sometime around 1880, the tiger population would have isolated far beyond,” he said, adding that this should not be a conclusive study and further experimentation should be encouraged.