Scientists unravel mystery behind ‘black tigers’

New Delhi, Sept. 15: The enduring mystery behind the black tigers of Similipal in Odisha may finally have been solved with researchers identifying a single mutation in a gene that causes their distinctive stripes to broaden and spread into their tawny pelt, occasionally appearing entirely dark.

Considered mythical for centuries, the ‘black tigers’ have long been a subject of fascination. Now, a team led by ecologist Uma Ramakrishnan and her student Vinay Sagar from the National Centre for Biological Sciences (NCBS), Bengaluru, have discovered that the coat colouration and patterning which make the wild cats appear dark boil down to a single mutation in the Transmembrane Aminopeptidase Q (Taqpep) gene.

“Ours is the first and only study to investigate the genetic basis for this phenotype (look). While the phenotype has been talked about and written about earlier, this is the first time its genetic underpinnings were scientifically investigated,” Ramkrishnan, professor at NCBS said.

The researchers combined genetic analyses of other tiger populations from India and data from computer simulations to show that the Similipal black tigers may have risen from a very small founding population of tigers and are inbred — providing an answer to the question that had perplexed so many for so long.

The study, published in the journal Proceedings of the National Academy of Sciences, noted that tigers in the Similipal Tiger Reserve are an isolated population in eastern India, and gene flow between them and other tiger populations is very restricted.

The researchers noted that this has important implications for tiger conservation as such isolated and inbred populations are prone to extinction over even short periods of time.

They (the black tigers) have not been found in any other places in the wild to the best of our knowledge. Nowhere else in the world, Sagar, a PhD student in Ramakrishan’s lab and lead author of the paper said.

“We used whole genome sequencing from a pedigree (family tree) that includes pseudomelanistic (false coloured) and normally striped individuals to find the mutation responsible for the phenotype,” he explained.

The abnormally dark

or black coat in such tigers is termed pseudomelanistic or false coloured. The most recent sightings of this rare mutant tiger in Similipal, long considered mythical, was reported in

2017 and 2018.

Since the late 1700s, reports of black tiger sightings and supposed captures in central and northeast India have been recorded by locals and British hunters. According to the

2018 tiger census, India has an estimated 2,967 tigers.

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