|November 17, 1997|
A controversy arises over the purity of the Indian tiger after DNA samples show Siberian tiger genes.
By Subhadra Menon
Blue blood with a hint of A scandalous liaison? That is what a strand of hair and a DNA profile has indicated. A team of wildlife researchers has found the DNA samples of two Royal Bengal tigers (Panthera tigris tigris) from Dudhwa National Park in Uttar Pradesh "polluted" by genes of the Siberian tiger.
Surrounded by feline DNA fingerprints, Lalji Singh, deputy director of the Centre for Cellular and Molecular Biology (CCMB), Hyderabad, who led the research team, says the findings are disturbing. "The genetic purity of the Indian tiger in Dudhwa will be lost," he warns, "and we will end up with a mixed-gene pool." The Royal Bengal is small and brilliant coloured -- tawny, golden yellow, with dark stripes -- and its fur sticks close to its body. It has pointed ears and a lean jawline. In comparison, the Siberian tiger -- hardly 200 of which survive in Russia's far eastern corner -- is the biggest of the five living tiger sub-species: the others being the South Chinese (P. tigris amoyensis), Sumatran (P. tigris sumatran) and the Indo-chinese (P. tigris corbett); the Caspian, Javan and Bali tigers are now extinct. The Siberian is a fine cat with rounded ears, a massive jaw, and thick, soft fur.
The CCMB study has busted the myth that Indian tigers are genetically confined to their own pockets. Working on blood and hair samples from 22 tigers of "known wild origin" from all over the country, Singh studied the vital sequences of the DNA that are peculiar to each species. The readings showed around 21 per cent heterozygosity in Indian tigers, which means that the felines drew genetic characteristics from more than one gene pool. Much of the variation arose out of cross-breeding between tigers from the country's 23 tiger reserves. This low level of variation indicates inbreeding, given that the average variation in wild carnivores is 40 per cent. What is more, on analysing 50 to 125-year-old tiger skins from museum specimens, Singh found almost the same level of genetic variation.
The two samples taken from Dudhwa were of tigers suspected to be hybrids. The genetic information obtained certainly related to the Siberian tiger. The big question is: where did the alien genes come from? The two tigers from Dudhwa could be the offspring of Tara, a tigress controversially released into the wilderness by wildlife enthusiast Billy Arjan Singh in the '70s. Questions had been raised in Parliament about Tara's origins and there was, at some point, the admission that she was not of Indian stock.
"Since the 20 other samples showed no Siberian genes, it is possible that the genes came from Tara," says Lalji Singh. He, however, adds that two specimens constituted too small a sample base to conclusively prove that Tara was the source of Siberian genes. "Ideally, all the tigers in the Dudhwa region should be studied before a definitive statement can be made," he says. If not from Tara, who? There are some theories about the influx of foreign genes (see box). While the Himalayas effectively squashes the probability of tigers from India crossing over to China or Russia, it is possible that an Indian tiger mated with a Chinese tiger along the Myanmar tract. The Chinese tiger could, in turn, have inherited genes from a Siberian parent. Theoretically, tigers of unknown lineage which have escaped from zoos and circuses could also be the source of the Siberian genes.
Will the Siberian genes then make the Royal Bengal a pale shadow of its majestic self? "The big cats are characteristically conservative in their breeding habits," says Ravi Chellam, scientist at Dehradun's Wildlife Institute of India. Which is perhaps why the Indian tiger -- anyway restricted to pockets in the tiger reserves -- has tended to breed within its distinctive population. Scientists are worried about inbreeding depression, where highly inbred animals become sterile, are susceptible to infections and lose their vitality. However, Chellam explains that inbreeding isn't a real problem unless the group shrinks to 50 individuals or less.
This strengthens the case for out-breeding, which takes place, say, when a tiger from Corbett National Park in Uttar Pradesh mates with a tigress from the Sunderbans; in other words, when there is an influx of genes from populations other than the one immediately surrounding the animal. The cubs of such a union could show better resistance to diseases or enjoy a robust physique. This means that the Siberian gene could make the Royal Bengal tiger a bigger animal, if a less beautiful one.
Lalji Singh's Siberian gene finding has people worried. "This kind of genetic pollution could affect the purity of the Royal Bengal stock," stresses R.L. Singh, chief wildlife warden of Uttar Pradesh. While there are many who thumb their noses at the argument about retaining the purity of the Indian tiger, it is in keeping with today's thinking. Maintaining the purity of wild gene pools is the current philosophy of conserving species. This is notwithstanding the fact that different species are known to interbreed in the wild. There is, for instance, a new species called the Brown Langur, the product of the mating between the Nilgiri Langur and the Common Langur.
To a lot of experts, genetics lies on the fringe of conservation programmes. "The role of genetics in the endangerment of a species is highly exaggerated," says Ullas Karanth of the Wildlife Conservation Society of the US. He says that the ecological threats faced by vulnerable animals like the tiger are bigger worries. Still, the genetic identification of wild tiger populations is not something that can be ignored. Which is why Lalji Singh thinks he's only just begun an important task. He feels that immediate and extensive studies should be done on the genetic profiles of tigers in all the reserves of India. That, he says, can become the blueprint for action to save these great cats.
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