Melanistic tiger in Similipal of Odisha.
| Photo Credit: PTI

The story so far: A tigress from the Tadoba-Andhari Tiger Reserve, Maharashtra, was sent 800 km away to the Similipal Tiger Reserve on Sunday (October 28, 2024) so as to diversify the genetic pool of the tiger population in Odisha. She is part of a plan by the Odisha government to tackle inbreeding in the tiger population that has resulted in increasing numbers of the once elusive black tigers or pseudo-melanistic tigers. 

Aged two years and seven months, the tigress was released into an enclosure where she is kept for observation. She will be later released in the South Division of Similipal. 

According to Susant Nanda, Principal Chief Conservator of Forest (Wildlife), the presence of so many melanistic tigers in Similipal is not a cause of concern. However, he stressed that the tigress will bring in different genetic matter which would remedy the inbreeding situation.

What are pseudo-melanistic tigers?

As far as appearances go, pseudo-melanistic (pseudo: false; melanistic: dark coloured) tigers appear to have a black coat with white and orange stripes occasionally peaking through. Their pelt looks almost the inverse of a normal tiger. 

Till the 1700s, these tigers were considered mythical. One of the first pieces of evidence of a black tiger was a watercolour painting by a British artist and writer named James Forbes.

Identifying the genetic basis of pseudomelanism in captive tigers. (A) Normal tiger (Left) versus pseudomelanistic tiger (Right). An increase in the surface area of the coat covered by darker stripes gives the pseudomelanistic tiger a darker, blotchy appearance. (B) The pedigree of the captive tigers sampled for this study. 
| Photo Credit:
Proceedings of the National Academy of Sciences

Even two centuries later, there were only sightings recorded by locals and British hunters. This is until 1970, when a tigress at the Oklahoma City Zoo gave birth to a cub with bizarre patterns. The cub was killed soon after by the mother. In the 1990s, an unusual tiger pelt was seized from poachers in New Delhi which finally confirmed the existence of this rare tiger.

The most recent sighting of the black tiger was in 2017-18 in the Similipal Tiger Reserve. 

How do the tigers get their colours?

The pseudo-melanistic tiger is a colour variant of the Bengal tiger. Its strange coat is a result of a mutation in a particular gene. This genetic quirk cause their stripes to widen and spread across the orange or tawny coat and at times give the appearance of being completely black.

Distribution of the genotyped individuals. A total of 428 individuals were genotyped at the Taqpep c.1360C > T mutation site. Wild tigers are shown with a circular marker, and captive tigers (NKB, AAC, and Mysore Zoo) are shown with a square marker. The size of the square/circle indicates the number of individuals genotyped from a given area. In addition to the 399 Bengal tigers shown on the map, we genotyped 12 Amur, 12 Malayan, and five Sumatran tigers from Armstrong et al.
| Photo Credit:
Proceedings of the National Academy of Sciences

A comparison between tiger populations showed that apart from the Similipal population, the mutation of the gene is extremely rare or even non-existent. The only other black tigers that have been found beyond the Similipal population are in captivity—Nandankanan Zoological Park at Bhubaneswar and Arignar Anna Zoological Park at Chennai—whose ancestry could be traced back to the Similipal population. 

Pseudo-melanistic tiger cub at the Arignar Anna Zoological Park.
| Photo Credit:
B Velankanni Raj

The mutated gene

A 2021 study by the National Centre for Biological Sciences (NCBS), Bengaluru, published in the Proceedings of the National Academy of Sciences, looked at the gene which gave the black tigers their colour. 

The team, led by Uma Ramakrishnan, found that the mutation of the Transmembrane Aminopeptidase Q or Taqpep gene was responsible change in colour. This gene gives other cat species their markings too. For instance, tabbies with darker or more blotchy stripes have this mutated gene. A King cheetah’s wider and darker spots are also because of the mutated gene. 

Population genetic analyses of Similipal tigers suggest genetic differentiation of Similipal from other tiger populations, indicating ongoing drift, and simulations suggest past bottlenecks might be responsible for a high frequency of Taqpep p.H454Y in Similipal.
| Photo Credit:
Proceedings of the National Academy of Sciences

The anomalies in colour and patterns are caused due to a missense mutation in the Taqpep gene. This mutation changes the amino acid Cytosine (C) to Thymine (T) in position 1360 of the gene sequence.