Indian tigers are inbreeding due to loss of habitat, which has fragmented populations and kept tigers from finding unrelated mates, finds a new study that aims to update tiger conservation strategies. The inbreeding threatens the tigers’ genetic diversity, which is the highest among all tiger subspecies in the world.
Scientists are as yet unsure how inbreeding will affect the tigers’ population, but genetic diversity within an animal population improves its chances of survival.
Tigers have received significant attention from conservation efforts, both in the country and around the world. However, little is known about the evolutionary history and genomic variation—information that is critical to any endeavors of conservation. This holds especially true for Indian tigers, who make up 70% of the world’s tiger population.
A team of researchers from the National Centre for Biological Sciences (NCBS), Stanford University, and zoological parks and NGOs across the world recently completed a three-year project, published in the journal Molecular Biology and Evolution, that confirms tiger subspecies are genetically distinct — tigers from northeast India more so than other populations in India. The project also reveals that although Indian tigers have the highest genetic variation of all tiger subspecies, there is evidence of inbreeding among them—possibly due to small and fragmented protected areas that have them mating within their own gene pool.
“Given our results, it is important to understand why some Bengal tigers appear inbred and what the consequences of this are,” says Anubhab Khan of the NCBS, an author of the study, in a statement.
As human populations have expanded, so has their imprint on the land. This would have disrupted the ability of the tigers to move freely, leaving them “hemmed into their own protected area,” say the study’s researchers. “Now, they can only mate with the other tigers in their own population,” Uma Ramakrishnan, a study author with the NCBS, told PTI. “Over time, this will result in inbreeding, they will end up mating with their relatives. Whether this inbreeding compromises their fitness, their ability to survive, we do not yet know.”
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In such situations, maintaining structural connectivity and enabling tigers to move between protected areas can help overcome these bottlenecks. “This would require the right types of habitat between protected areas, for example having densely populated human settlements would not work,” Ramakrishnan added.
In the study, the scientists sequenced whole genomes from 65 individual tigers representing the surviving subspecies, with a special emphasis on tigers from India. After conducting a variety of population genomics analyses, they investigated the possible impacts of inbreeding, demographic history, and possible signatures of local adaptations, among other things.
The study also showed recent divergences between tiger subspecies, within the last 20,000 years, which scientists say is consistent with increasing human activity across Asia and a transition from a glacial period of ice coverage to interglacial climate or the warmer period.
The tiger, researchers conclude, is an excellent example of how historic events sculpt species’ genomic diversity. Such information, they say, is critical for the success of rescue efforts. “Population management and conservation action must incorporate information on genetic variation. I hope doing so will help India maintain the gains in tiger conservation achieved so far,” Ramakrishnan said in the statement.
“It is clear from our work here, and a growing number of other studies, that it is crucial to increase our sampling efforts and use caution when interpreting results from limited sample sizes,” Ellie Armstrong, a study author from Stanford University, said in the statement. However, the study calls for further investigation of its findings and for expanded data and analyses of more tiger genomes.
