Corridors help avoid low genetic diversity

Forest corridors that allowed India’s tiger populations to breed with one another are vital for the conservation of these magnificent animals, according to research that has been just been published in the Proceedings of the Royal Society B.

Where once these animals roamed across much of the subcontinent, they now survive in India in small populations of just 20 to 120 individuals, mostly in tiger reserves. The country holds over half of the world's tigers, and an official assessment carried out in 2010 estimated that there were about 1,700 of these animals in 39 tiger reserves.

Genetic intermingling

Sandeep Sharma of the Smithsonian Conservation Biology Institute in the U.S. and his colleagues studied the extent of genetic intermingling between tiger populations in five tiger reserves in the states of Madhya Pradesh and Maharashtra.

To do so, they analysed the DNA extracted from faecal, hair and claw samples of 273 animals.

When an animal moved and bred with an individual from a different population, its genes propagated in the latter group. Maintaining such gene flow between isolated tiger populations was important in order to avoid the deleterious effects of low genetic diversity and inbreeding, said Dr. Sharma in an email.

The tiger reserves were embedded in a landscape composed of agricultural land and fragmented forest patches, with numerous small villages and town. The scientists found that “there is a drastic reduction in gene flow” between reserves that had lost forest connectivity.

These forest corridors played “an important role in maintaining genetic variation and persistence of tigers in this landscape,” they observed in their paper.

Legal status needed

Such corridors should be given legal status, said Dr. Sharma in his email. Tiger corridors in central India faced imminent threats from activities like road widening, construction of railway lines and coal mining.

Corridor-mediated gene flow was important for India’s leopard populations too.

The necessity of maintaining the genetic diversity of Indian tigers was highlighted in another paper published in the same journal a few months back. In that paper, Uma Ramakrishnan of the National Centre for Biological Sciences in Bangalore and her colleagues noted that a large number of historic genetic variants were not found in modern tiger populations in the country.

As it was, current Indian tiger populations were quite small, she told this correspondent. With further fragmentation of their habitat, these populations could lose connectivity and become isolated.

The resulting loss of genetic variation and greater inbreeding could then make such groups more vulnerable to environmental changes.

Maintaining connectivity between tiger populations was crucial for the conservation of these animals, she emphasised.