DNA Reveals the Origin Stories of America’s Captive Tigers

Scientists have wondered if the many captive tigers in the United States could one day help restore the species in the wild.

In 2020, the Netflix documentary series “Tiger King” introduced the world to America’s large population of captive tigers. Estimates by experts suggest there may be as many as 7,000 of the big cats in the United States today, while only around 5,500 tigers survive in the wild in other countries.

More than 99 percent of those American tigers live in unaccredited roadside zoos, private residences or sanctuaries. Conservationists have long wondered what types of tigers make up this population and whether their genetic material could help increase the number of tigers in the wild.

A group of scientists recently examined the DNA of America’s captive tigers for the first time and discovered their muddled origin stories. Based on their findings, the researchers showed that these animals would be of little use to conservation.

In a study published last month in the Proceedings of the National Academy of Sciences, scientists sequenced the ​​genomes of 138 tigers rescued from private ownership, including two once owned by Joe Exotic, the main subject of “Tiger King.”

There is only one species of tiger in the wild, but that species is divided into six surviving subspecies, each with distinctive genetic markers. The subspecies have adapted to survive in very different habitats. For example, the Sumatran tiger is found in the balmy jungles of an Indonesian island, while the Amur tiger inhabits coniferous forests and snowy mountains in Russia, northern China and Korea.

In 2018, Ellie E. Armstrong, an author of the study and an assistant professor of evolutionary genomics at the University of California, Riverside, set out to establish the ancestry of America’s captive tigers.

“There was a lot of hearsay about these tigers but no facts,” Dr. Armstrong said.

Dr. Armstrong and a group of researchers from Stanford began visiting sanctuaries across the United States and collected blood samples from the resident tigers whenever they received veterinary care.

“I was fondly nicknamed ‘the vampire’ by the vets,” she said.

Their efforts led to the largest genetic database for tigers to date. In addition to giving scientists a glimpse into the ancestry of America’s captive tigers, this catalog can be used by conservationists to determine whether a tiger was born in captivity or the wild.

There was no single country of origin for the animals: None were purebred, and every one turned out to be a hodgepodge of all six tiger subspecies.

“They are a very well-mixed population,” Dr. Armstrong said.

According to Dr. Armstrong, the United States became a tiger melting pot in large part because of the rise of a petting industry for cubs, which incentivized people like Joe Exotic and Doc Antle to breed the animals en masse and then ship them across the country.

The genetic data collected by Dr. Armstrong and her team also suggests that America’s captive tiger population has levels of genetic diversity similar to those of most wild tiger populations and fewer harmful genetic mutations found in some wild cats. Because none are purebred, they are most likely not ideal candidates for captive-breeding programs intended to restore populations in the wild.

“Would those individuals be able to persist and thrive in an environment that a single subspecies was adapted to? asked Neil Carter, an associate professor of conservation science at the University of Michigan who was not involved with the study. “I think people are concerned that they probably wouldn’t.”

He added that “there’s a lot that we don’t know about how these genes actually manifest in the wild” among particular subspecies.

Both Dr. Carter and Dr. Armstrong agree that the best way to conserve tigers is to protect their habitat in the wild. If there is nowhere for tigers to live in nature, they argue, then any efforts to conserve the species will be futile.

Nevertheless, Dr. Armstrong suggested that in certain cases, American tigers could become useful. For instance, if populations of genetically pure tigers dwindle both in the wild and in accredited zoos, conservationists may be forced to rely on these motley tigers to maintain wild populations.

In the late 1990s, 20 to 30 Florida panthers remained, and they were becoming severely inbred. State wildlife officials brought in eight wild Texas panthers to make the population more genetically diverse. The plan worked, and by 2007, the Florida panther population had reached roughly 100 animals.

Whether America’s mixed-up captive tigers could be used in such a way is unclear. Tigers born in captivity don’t fare well in the wild. But their genetic material could perhaps be put to use through artificial insemination of wild tigers, though such an effort has never been attempted.

“When we are getting down to these extreme conservation decisions, evolutionary history is an important consideration, but my guess is that people aren’t going to be very picky about where the tiger came from if the other option is extinction,” Dr. Armstrong said. “A tiger is a tiger at the end of the day.”

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