BHUBANESWAR: In the dense forests of Similipal Tiger Reserve (TR), India’s fourth biggest tiger habitat, a unique population of melanistic tigers rove freely. However, in-breeding and a closed population, with almost no migratory flow either in or out, have emerged as a looming threat for the striped predators in the tiger land that has no nearby breeding source population.
The Similipal is the lone habitat for melanistic tigers in the world, which makes it a critical bastion for the conservation of these rare big cats with distinctive dark stripe patterns. Yet, the surge in population of these pseudo-black tigers in recent years has raised concern.
Wildlife conservationists and experts opine that the growing melanistic population could be a result of inbreeding and limited genetic diversity that could put the big cat population of the tiger reserve to a heightened risk of genetic dwarfing and isolation.
As per reports, the first confirmed record of the pseudo-melanistic tigers from Similipal was in 1993. Sources, however, said these rare tigers were first officially documented in 2007. More melanistic tigers were documented in the subsequent years. However, by 2021 the population of the melanistic tigers grew to 10, while the All Odisha Tiger Estimation (AOTE) 2023-24 report released by the Odisha government in February this year put the figure of black tigers in Similipal at 13.
This rapid spike in the number of pseudo-black tigers, that now constitute close to half of Similpal’s total tiger population, became a matter of concern prompting experts to speak more on ways to improve genetic diversity within the population.
As it is, melanistic tigers are not a separate subspecies but rather a colour morph within the RBT population due to gene mutation.
A study by a group of researchers, including scientists from the National Centre for Biological Sciences (NCBS), Bengaluru, headed by senior molecular ecologist Uma Ramakrishnan in 2021 had found that approximately 37% of tigers (Panthera tigris) in the STR were pseudo-melanistic, characterised by wide and merged stripes.
The genetic analysis of other tiger populations in the country and computer simulations by the researchers had suggested that Similipal black tigers were inbred and that it might have arisen from a very small founding population of tigers.
Wildlife conservationist Aditya Chandra Panda said melanism is not necessarily a result of inbreeding but the concentration of melanism within the Similipal population indicates inbreeding.
“As this mutation is being increasingly expressed within the population, it is a sign of inbreeding. The immediate solution to it is introduction of tigers from other unrelated populations to improve the genetic diversity,” Panda said while calling for measures for creation of more source population in the nearby landscapes of STR, as a long term solution for exchange of gene flow.
Retired IFS officer and former field director of STR Suresh Kumar Mishra said inbreeding, in the absence of adequate number of partners, apart from leading to genetic isolation and dwarfing of the population could emerge as a cause of their collapse.
He, however, said the path ahead is challenging as balancing the preservation of the unique genetic heritage and ensuring long-term viability of the present Similipal population, especially the usual morphs, is a formidable task.
He suggested that the introduction of new genetic lineages from other source populations needs to be done at the earliest, while steps should be taken for making tiger corridors functional and natural migration for long term sustainability of the species in the region.
Similipal Field Director Prakash Chand Godineni, on the other hand, said though rare pseudo-melanistic phenotype isn’t a threat for the big cats, the forest department wants to improve genetic diversity of this isolated tiger population. “Accordingly, introduction of female tigers from other landscapes has been planned by the forest department,” he said.
While authorities said that Odisha has already approached the National Tiger Conservation Authority (NTCA) to take up the project in the near future, experts opined that the state government should exercise adequate caution before going ahead with it so as to avoid the mistakes made in the Satkosia tiger relocation project.