JOIN USScientists decode mystery behind Similipal 'black tiger'
Biologists from Bengaluru on Monday unravelled a genetic secret associated with a small set of Indian tigers that are found in a solitary tiger reserve – Similipal in Odisha.
The tigers in Similipal have an unusually broad and fused stripes, which make them appear dark.
The answer to the mystery – why such a unique look and why such tigers are seen only in Simlipal – provided vital clues on what needs to be done to save them from extinction, scientists said.
Going by the 2018 tiger census, India houses an estimated 2,967 tigers, of which 8 are known to be staying within the 2,750 sq km Odisha park, whereas another 12 were using the tiger reserve.
According to the new study conducted by an Indo-US team led by researchers at the National Centre for Biological Sciences, Bengaluru, nearly 30-40 per cent of Similipal tigers are pseudomelanistic. Such tigers have thick stripes so close together that the tawny background is barely visible.
The NCBS team traced the genetic root behind such an unusual look back to a single mutation in the tiger genome that was carried forward in successive generations due to the isolated nature of the tiger population, leading to inbreeding.
“Despite a healthy growth in tiger population in India, there are small isolated populations where we can see such an unique evolutionary pathway. The policymakers should look for options to connect tiger habitats in order to avoid the chances of such populations going extinct,” Uma Ramakrishnan, NCBS scientist and corresponding author of the study, told DH.
“Similipal is far away from other tiger populations. In the absence of another robust source population, there is no gene flow and inbreeding,” she said.
The scientists while conducting their studies were fortunate to find a pseudomelanistic cub at Nandankanan Zoo in Bhubaneswar. Samples from the litter as well as its parents and grandparents were taken for genome sequencing.
The gene maps of the pseudomelanistic tigers bred in captivity were compared with the genomes isolated from faecal samples of 12 tigers visiting Similipal to identify the unique genetic signature.
The mutation increases the chances of a tiger being pseudomelanistic by 200 times but copies of the gene have to come from both parents. If it’s coming from one parent, the unique stripe won’t show.
While comparing the Similipal genomes with another 395 wild tigers, the team realised only the big cats in the Odisha forest bear such a genetic trait. No other tigers carry that specific mutation in their genomes.
This, explained Ramakrishnan, gave the team an opportunity to study rapid evolutionary changes in an endangered species in an isolated condition. “Our study highlights ongoing phenotypic (external look) evolution, potentially from human-induced fragmentation, in endangered large carnivore populations,” the team reported in the Proceedings of the National Academy of Sciences on Monday.