BANGALORE: India's tigers, also known as Bengal tigers, have lost 93% of genetic variation from that of their ancestors, despite their numbers having risen the recent years, says a research report in the Proceedings of the Royal Society B.
There has also been a distinct change in the clustering of Bengal tigers in the past 200 years - from two distinct groups to three - mainly due to loss of habitat, said the report by Samrat Mondol, Michael W Bruford and Uma Ramakrishnan.
Bengal tigers were earlier found in two distinct groups based on their genes - those found south of Madhya Pradesh and the ones found in Terai and semi-arid regions. An additional genetic separation has created a separate group of tigers, consisting of some 100 tigers found in semi-arid regions who have been cut off from their eastern neighbours.
"This has happened due to the loss of habitat across the country, hampering connectivity among tigers," says Uma Ramakrishnan, co-author of the paper, who's with the National Centre for Biological Sciences' ecology and evolution department.
The existing tiger population in the country, which has mostly multiplied from a small number as a large population of the beasts was wiped out in the last 200 years, shares a relatively high percentage of DNA. The lack of genetic diversity is a matter of grave concern. For, it can affect their evolution, especially their ability to respond to new diseases, climate change and other challenges.
Uma Ramakrishnan and her team used samples from Bengal tiger pelts and bones in London museums, 53 museum specimens collected between 1836 and 1955 from the scat of 123 living tigers, and compared them to the DNA of the living Bengal tigers obtained mostly from their faeces and blood. "There were a lot of variations in the mitochondrial DNA which is inherited from the mother and has been lost, although nuclear DNA, inherited from both parents, didn't differ much," she says.
The loss of mitochondrial DNA variation could be due to their behaviour. Ramakrishnan says: "While male tigers roam widely, female tigers inherit their mothers' territories. Since habitats in semi-arid regions of the sub-continent like Pakistan, Afghanistan and the Gangetic plains of the country have been wiped out in the last 200 years, lineages of female tigers living in these areas also seem to be lost."
The challenge ahead
At present, India is home to over half of the world's tiger population. According to the latest tiger census report released on March 28, 2011 by National Tiger Conservation Authority, the estimated tiger population is 1,706 - ranging between a minimum of 1,571 to a maximum of 1,875. The results include figures from 17 Indian states with a tiger population.
What we need to do is to preserve the sub-population of tigers and allow good connectivity between them, says Ramakrishnan. "In the next 40 years, we will witness increasing urbanization of the hinterland. It will be a challenge to sustain this connectivity," she added.
