Let’s clarify the headline right away: these big cats are not completely black, but rather have yellow stripes on a dark base coat, which gives them their much darker appearance. This striking coloration is more than just a visual curiosity—it may in fact signal trouble for the species.

advertisement

India is home to about three-quarters of the world’s tigers. After several uncertain years due to hunting, human–animal conflict, and habitat loss, the tiger population doubled between 2006 and 2018 thanks to conservation efforts—and their habitat range even expanded by 30%. However, some smaller populations are struggling with a shared problem, one that shows up rather dramatically in the famous orange coat that tigers are known for. The so-called black, or more accurately, pseudo-melanistic tigers have been observed in the Similipal Tiger Reserve (STR) since the mid-1970s, and this is believed to be the only place in the world where these unusual animals are found. They are not a separate species, but a genetically altered form of the Bengal tiger (Panthera tigris tigris).

The Father of All Black Tigers

Nearly half of Similipal’s tigers are pseudo-melanistic, and their symbolic representative is a 10-year-old male named T12, the oldest resident of the reserve. He is believed to be responsible for the growing frequency of this genetic mutation. The phenomenon is both a sign of conservation success and a warning of an impending crisis: although the tiger population in the reserve is at its highest level in decades, the area is geographically isolated—a kind of “tiger island” with a severely limited gene pool, putting the population at risk of inbreeding.

To correct this, conservationists are already searching for suitable mates for T12. This is a key step in a long-planned breeding program that brings together conservation experts, molecular ecologists, and geneticists to save the Similipal tigers.

One of the core principles of tiger reserves is that tigers should be able to move between protected areas through natural “eco-corridors,” which help maintain genetic diversity. Similipal, covering over 1,000 square miles, is one of India’s largest reserves, but its nearest neighbors—Satkosia to the southwest and Sundarban to the east—are more than 160 kilometers away. In theory, this distance would not be insurmountable, but Satkosia no longer has tigers, and there are no natural corridors between Similipal and Sundarban. The intervening areas—urban zones like Kolkata and its suburbs, and rice paddies—have little forest cover. In effect, the Similipal tigers have no way in or out. Fortunately, promising females have been found in Chandrapur district, suitable for pairing with the Similipal males. The first female to be tranquilized and relocated was named Jamuna.

The Mutation Revealed a Deeper Problem

While the gene responsible for the darker coat is harmless in itself, researchers were quick to express concern over the situation: if such a benign mutation can spread so rapidly, harmful ones could just as easily take hold.

To find the right mates for T12 and his descendants, researchers had to study not only today’s tigers but also those of the past. Molecular ecologist Uma Ramakrishnan and her team have been collecting tiger DNA samples across India since 2005 to map the species’ genetic diversity. So far, they’ve gathered about 250 historical samples—from London museums, as well as from wild tigers’ scat, blood, fur, and saliva. These samples have provided vital insights into how the species’ genetics have changed over time.

When the NTCA (National Tiger Conservation Authority) noted the increase of dark-colored tigers in Similipal in 2017, Ramakrishnan was tasked with the genetic analysis. She discovered that the recessive gene was spreading rapidly—a “ticking time bomb” that could prove fatal if not managed. According to domestic cat genetic databases, similar mutations can cause retinal degeneration, kidney disease, and hyperthyroidism—so the risk is real.

Because Similipal is isolated, Ramakrishnan proposed introducing female tigers from other reserves. Genetic comparisons pointed to the most promising candidates in the Tadoba–Andhari Reserve in Chandrapur district. Of course, identifying the right tiger is one thing—relocating a 140-kilogram wild animal across the country is quite another. Fortunately, the transfer of the first tigress, Jamuna, was successful, and in the following months she was joined by another, Zeenat. It seems the efforts have borne fruit: this summer, Zeenat became pregnant. Ramakrishnan and her students continue collecting fur and scat samples to better understand the genetic diversity of the population. Authorities hope Jamuna will also eventually find a mate. Everyone is eager to know whether Zeenat’s cubs will inherit T12’s pseudo-melanism.

advertisement