Tiger Genes

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Is the tourism lobby of Ranthambore Tiger Reserve, which sees profits slipping if tigers are moved out, really behind the controversy surrounding tiger inbreeding? Or does declining genetic diversity seriously endanger India's national animal?

Akash Bisht Sariska/Jaipur

The Rajasthan forest department was in a celebratory mood recently when they shifted a new tiger from Ranthambore Tiger Reserve (RTR) to Sariska Tiger Reserve (STR) in the state. The endeavour - part of the relocation drive to repopulate the reserve that went tiger-bare after poachers wiped out the entire population in 2005 - is, however, now in jeopardy. 

Wildlife experts have raised doubts on the selection of the newly relocated tiger that has taken the count of tigers in STR to four. Experts believe it is difficult to ascertain whether the tiger sent to STR is actually the one that had been selected after DNA tests. The tests were conducted on eight tigers to ascertain their genetic compatibility with the Sariska tigresses; only two were considered fit for relocation.    
Dharmendra Kandhal, a biologist working in Ranthambore, informed Hardnews that the tiger might not be the one that had been selected after DNA tests. He revealed, "Scat (excreta) samples of tigers were sent to Bangalore for DNA tests to avoid genetic incompatibility. The area from where this tiger was selected was regularly frequented by more than eight tigers - so how did the forest department determine which scat sample belonged to whom?"

SP Yadav, DIG, National Tiger Conservation Authority (NTCA), didn't rule out the possibility and mentioned that "if it has happened, it is just another case of human error". "You can't expect a person to follow the tiger with a bucket in his hand to ensure that the scat samples are genuine," he said. 

To avoid this confusion, Kandhal suggests that a DNA dart could be used - the dart extracts the tissue sample and falls to the ground. "This is a much safer and accurate technology and avoids the uncertainty caused by the obsolete technology of collecting scats," informed Kandhal.   

The whole debate surrounding DNA testing surfaced after reports suggested that the three animals - one tiger and two tigresses - shifted to STR in the first phase of translocation between 2008 and 2009 are siblings. Wildlife authorities later confirmed the allegation. 

Wildlife experts, scientists and NGOs demanded that the new tigers should be brought in only if DNA tests confirmed that they are not closely related to the tigresses already in STR. Thereafter, the Bangalore-based National Centre of Biological Sciences conducted the tests and zeroed down on two tigers for relocation. 

Scientists believe that siblings find it difficult to breed and could trigger 'inbreeding depression' that could amplify the feline mortality rate. "Inbreeding is a condition where genetically similar individuals in a population breed with each other and over time individuals of the population become even more similar to each other. The population suffers from a loss of genetic diversity. This can lead to adverse conditions that result from inbreeding (inbreeding depression) such as muscle degeneration (observed in humans), low sperm count and quality, inability to fight some infections (lowered immunity) etc," apprised Dr Shomita Mukherjee, Principal Scientist, Salim Ali Centre for Ornithology and Natural History. 

However, officials in Rajasthan and Delhi call inbreeding a common phenomenon in the wild and believe that most animals in RTR are closely (or distantly) related to each other.

"The present tiger count in RTR is 40 while it was only 14 a few years ago. So, possibly, siblings mated with each other to take the population to its current numbers. There is an unnecessary issue that is being created by the media and so-called experts. Animals choose the best compatible partner to mate with, even if they are siblings. Weak genes are eliminated either by predation or by infighting and these are the rules of the forest," said RN Mehrotra, Chief Wildlife Warden, Rajasthan.

Mukherjee doesn't rule out this possibility and claims, "It need not always be the case that if related individuals breed, their offspring will always be at risk. But the probability that it will, increases with inbreeding." It is perceived that the genes of the RTR population could be severely damaged because of extensive inbreeding. 

To ensure genetic variation, tigers could be brought in from other geographical locations, especially the central zone comprising Madhya Pradesh and Maharashtra. Media reports had earlier highlighted that the central government tried to persuade Madhya Pradesh and Maharashtra to donate a few tigers so that the gene pool of STR could be diversified. However, MP's forest minister made it clear that they had no surplus tigers to donate and refuted claims of receiving any such request from the ministry. 

Even the NTCA denies knowledge of any such request. "I am not aware of any such request made by the ministry. We are also reviewing the study done by SP Goyal, a Wildlife Institute of India (WII) scientist, wherein he has mentioned that gene pools of different geographical regions should not be mixed," Yadav said.

Hardnews spoke to Goyal and has a copy of the study in which concerns have been raised about mixing tiger populations of different geographical areas - northern, north-eastern, southern, western and central - that have distinct genetics.

This story is from the print issue of Hardnews: AUGUST 2010