From C K Nayak
NEW DELHI: It is not just elephants but also tigers which moved from peninsular India to the North East and vice versa, new studies have shown.
Even during the 1930s, 40,000 tigers roamed the forests of India but by the 1970s, tiger numbers had plummeted to less than 2,000. Historically, the tiger ranged from the Caspian Sea to the Russian Far North to the Indonesian islands of Java and Sumatra. Now, they occupy just 7% of this historical range, with India home to over half of the tigers remaining in the wild. And what a world they inhabit.
The habitat the tiger lives in is no longer continuous, but broken up with veritable seas of humanity in-between. These fragmented forests mean tigers occur in very small populations, sometimes as small as two tigers in a particular place.
In this fragile final frontier of the world’s tigers, evaluating how they are faring is crucial.
The study indicated that tigers are moving around and connecting peninsular India with North Eastern India, and females are staying close to their mothers, as usually observed in tigers.
The study conducted by Samrat Mondol and Uma Ramakrishnan from the National Centre for Biological Sciences in Bangalore is about genetic signatures in tigers by analysing their DNA.
The genetic material in any living organism is passed on from parent to offspring. If an organism dies without reproducing, any unique DNA it has is lost forever. Genetic material is like an arsenal – more variation in the DNA means the species is better equipped to deal with different hardships, like a sudden disease outbreak.
Mondol and Ramakrishnan teamed up with Michael Bruford from Cardiff University in the UK. Bruford’s lab specializes in extracting genetic signatures from old, preserved animal samples. Using tiny bits of skin and bone from tiger specimens at the Natural History Museum in London and the National Museum of Scotland in Edinburgh, they obtained a genetic profile of tigers hunted from before 1950. A lot of these museum specimens are from areas where tigers are not found anymore – Afghanistan, Rajputana and Gujarat.
There were two historical tiger populations – the peninsular and the North East Indian population and the north Indian population. Current populations have three sections: the semi-arid tigers, the Terai tigers and the peninsular-Northeastern, each being very different from one another.
The results show that tigers have lost about 93% of the maternally inherited mitochondrial DNA. This sharp drop is also because of the behaviour of tigers – females tend to setup territories next to their mothers, or even inherit the mother’s territory. Females also hold relatively smaller territories (about 20 sq km).
Males move away from where they are born and establish new territories, usually much larger than that of females (60 to 100 sq km). Wiping out tigers from one area means, a lot of related females die out, and their genetic material is lost forever.
After creating a kind of family tree using tiger samples from different areas, the authors could see that the tiger museum samples formed two populations, one with samples from North Eastern India and peninsular India (Western Ghats and Deccan Plateau), and the second with samples from the Terai region and the semi-arid regions in Rajasthan. This means, tigers from the peninsula were moving between the south and the northeast, but the Terai and semi-arid regions were distinct.
When analyzing the current samples, the peninsular India – North Eastern population remained the same. But, the semi-arid and Terai tigers form two populations; what was one population in the early twentieth century is now two.
The fact that populations from North Eastern India and peninsular India are still connected comes as a pleasant surprise. Ramakrishnan feels that the remnant forests along eastern India have allowed tigers from peninsular India move to the Northeast and vice versa. “However, we need more samples from Eastern and Central India to know more about how much these populations are connected,” they added.