Why are melanistic or ‘black’ tigers exclusive to Odisha’s Similipal? Secret explained

In the heart of eastern India lies the Similipal Tiger Reserve, a lush expanse of biodiversity nestled within Odisha's Mayurbhanj district. Beyond its dense forests and waterfalls, Similipal holds a secret that has captivated scientists and wildlife enthusiasts alike by being the only known habitat in the world where melanistic tigers, often referred to as ‘black tigers,’ roam freely in the wild.

These rare creatures, with their distinctive dark coats and bold merged stripes, are not a separate species but a rare genetic variant of the Royal Bengal Tiger. However, their exclusive presence in Similipal raises intriguing questions about genetics, evolution, and conservation. 

What makes this reserve the sole sanctuary for such a unique phenotype? The answer lies at the intersection of genetic mutation, ecological isolation, and human intervention.

The Genetic Mystery: Decoding Answers

Melanism, characterised by an excess of dark pigmentation, is a phenomenon observed in various animal species. In tigers, this manifests as pseudo-melanism—a condition where the black stripes are so broad and closely spaced that they stand above the orange background, giving the tiger a darker appearance.

The root cause of this trait in Similipal's tigers has been traced to a specific mutation in the Transmembrane Aminopeptidase Q (Taqpep) gene.

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Notably, this gene plays a crucial role in determining stripe patterns in felids. A study led by researchers from the National Centre for Biological Sciences (NCBS) in Bengaluru identified a high frequency of the Taqpep p.H454Y mutation among Similipal's tigers.

Curiously, this mutation was absent in over 395 tigers sampled from other regions, giving its exclusivity to Similipal.

Isolation and Inbreeding: The Genetic Bottleneck

The prevalence of the melanistic trait in Similipal is not merely a genetic coincidence but a consequence of the reserve's ecological isolation.

Surrounded by human settlements and lacking connectivity with other tiger habitats, Similipal's tiger population has become genetically insular. This isolation has led to inbreeding, resulting in a higher incidence of homozygosity for the Taqpep mutation.

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Genetic analyses reveal that Similipal's tigers exhibit low genetic diversity, with simulations suggesting that founder effects and genetic drift have contributed to the fixation of the melanistic trait within this isolated population.

Conservation Challenges: Balancing Uniqueness and Genetic Health

While the melanistic tigers of Similipal are a source of fascination, their existence also highlights pressing conservation concerns. The genetic homogeneity resulting from inbreeding poses risks such as reduced fertility, increased susceptibility to diseases, and diminished adaptability to environmental changes.

Raising Awareness: The Melanistic Tiger Safari

To bolster conservation efforts and raise public awareness, Odisha has embarked on an ambitious project by establishing the world's first melanistic tiger safari near Similipal.

This initiative aims to educate visitors about the unique genetic and ecological aspects of these tigers, fostering a deeper appreciation for their conservation.

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As conservationists work to ensure the survival of these rare tigers, Similipal stands as both a sanctuary and a symbol of nature's complex tapestry.