Fragmentation Of Habitat Is Causing Inbreeding Among Indian Tigers And That Could Be Disastrous

Remember the photos of that 'golden tiger' from Assam's Kaziranga National Park that went viral on social media last year? After the dust settled, the sad reality behind the photo was revealed.

KNP issued a statement, in which the photographed golden tiger has been identified as Golden Tiger of Kaziranga KAZI 106-F and added that there are a total of four golden tigers there.

Parveen Kaswan

But what lead to the colour change was more concerning.

According to Rabindra Sharma, Research Officer, Kaziranga National Park, the skin of tigers is orange-yellow with black stripes and whitish abdominal region, a change that has been brought in genetically due to inbreeding.

Now, a new study has shed light on the extent of inbreeding among Indian tigers and its potential consequences.

Parveen Kaswan

The research, published in the journal Molecular Biology and Evolution found that fragmentation of habitat has already disrupted the natural evolutionary process in wild tigers and will continue to do so in future as anthropogenic pressures increase, leading to higher inbreeding and lower survival.

The researchers from Stanford University, the National Centre for Biological Sciences (NCBS) in Bengaluru, and various zoological parks and wildlife NGOs sequenced 65 genomes from four of the surviving tiger subspecies¡ªAmur tigers, Bengal tigers, Sumatran tigers and Malayan tigers¡ªover a period of three years to gain insight into the genomic variation in tigers.

While Indian tigers have the highest genetic variation compared to other subspecies of the feline across the world, their populations continue to be fragmented by loss of habitat, leading to inbreeding and potential loss of this diversity.

Umred Paoni Karhandla Wildlife Sanctuary/ Representational Image

"As human population started expanding, so also their signatures on the land. We know that some of these signatures would result in disrupting the ability of tigers to move," Uma Ramakrishnan, co-author of the research, published in the journal Molecular Biology and Evolution, told PTI.

According to Ramakrishnan, molecular ecologist and assistant professor at the National Centre for Biological Sciences, Bangalore, this habitat loss from human activities leads to tigers being "hemmed into their own protected area."

"Now, they can only mate with the other tigers in their own population. Over time, this will result in inbreeding, they will end up mating with their relatives," she explained.

"Whether this inbreeding compromises their fitness, their ability to survive, we do not yet know," the molecular ecologist added.

BCCL

While genetic diversity across a population improves their chances of survival in the future, the study said population fragmentation of tigers can decrease this variation, and endanger them further.

Although tigers have received significant conservation attention, the scientists said very little is known about their evolutionary history and genomic variation, especially for Indian tigers.

With 70 per cent of the world's tigers living in India, the researchers said understanding the genetic diversity of tigers in the country is critical to the feline's conservation worldwide.

The results of their three-year long study offer insights into genomic variation in tigers and the processes that have sculpted it.

Based on the results, the scientists believe there have been relatively recent divergences between subspecies, and intense population bottlenecks that may have contributed to inbred individuals.

According to the NCBS scientist, maintaining structural connectivity, enabling tigers to move between protected areas can help overcome these bottlenecks.

AFP/ REPRESENTATIONAL IMAGE

"This would require the right types of habitat between protected areas, for example having densely populated human settlements would not work. Further, there also needs to be functional connectivity, that tigers do actually move," Ramakrishnan added.

In the study investigated the partitioning of genetic variation, possible impacts of inbreeding, and demographic history, and possible signatures of local adaptation.

While the total genomic variation in Indian tigers was higher than in other subspecies, the study found that several individual tigers in the country had low variation, suggesting possible inbreeding.

According to the research, tigers from northeast India were the most different from other populations in India

"Given our results, it is important to understand why some Bengal tigers appear inbred and what the consequences of this are," said Anubhab Khan, co-first author of the research.

The study showed recent divergences between tiger subspecies, within the last 20,000 years, which the scientists believe is concordant with increasing human impacts across Asia and a transition from glacial to interglacial climate change in the continent.

BCCL

However, the scientists believe this finding needs to be investigated further with expanded data and analyses of more tiger genomes.

"Most studies focusing on species of conservation concern use limited numbers of specimens to try to gain understanding into how genomic variation is partitioned," said Ellie Armstrong, co-first and co-corresponding author of the study from Stanford University in the US. "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," Armstrong added.

According to Ramakrishnan, the genomic variation of Indian tigers continues to be shaped by the ongoing loss of connectivity.

"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 added.