Could captive tigers help restore wild populations?

Captive tigers in the U.S. now outnumber those living in the wild. According to estimates from the World Wildlife Federation, about 5,000 of these big cats reside in the U.S., mostly owned by private citizens. 

Despite their large numbers, the health and genetic diversity of this captive population remain a mystery, posing significant questions for conservationists. 

Could these privately owned tigers help stabilize or restore wild tiger populations, or are they too genetically compromised to be of value? Are they purebred or inbred, or do they exhibit characteristics favored in the illegal trade?

Protecting captive tigers 

In a recent study, experts at Stanford University set out to address these questions. The findings provide a new tool that both conservationists and law enforcement can use to protect captive tigers and prosecute those responsible for their mistreatment.

“We’re trying to leverage genomic technology to be useful in a conservation context – there are so few tigers. We won’t get a second chance if they go extinct,” said lead author Ellie Armstrong, a PhD student at Stanford.

Armstrong conducted this research as part of her doctoral studies in biology at Stanford, working with co-advisors and co-authors Elizabeth Hadly and Dmitri Petrov.

The team initially became interested in captive tigers after studying the genetic impact of isolation on wild tiger populations.

“We were conducting a large study on wild tiger populations and leveraged these data to address the issue of captive tigers in the United States,” Armstrong said. “It was a bit unbelievable, at first, that you could have a tiger living right next door and not know it.”

Enormous number of captive tigers 

Through a partnership with Tigers in America, Armstrong and her team discovered that an enormous number of tigers live outside accredited facilities. 

Many of these tigers were bred for animal encounters, performed in circuses, or were trafficked as exotic pets. However, the team had no idea of their genetic makeup or origin.

The lack of official data on these so-called “generic” tigers (due to their unknown origin) presented a major hurdle. Although documentaries like Tiger King and The Tiger Next Door increased public awareness, accessing these animals for scientific study remained a challenge.

“There was so much hearsay associated with this captive population, and a lot of it contradicts itself,” noted Armstrong.

“People said, ‘All of the cats are really inbred,’ or ‘All of the cats are genetically diverse.’ We had no idea what to expect and thought that genomic technology could help us answer some of these questions.”

Genetics of generic tigers 

Through relationships with sanctuaries that had rescued generic tigers, Armstrong and her team were able to gather samples and collect data on the animals, including their rescue locations. 

The researchers collected samples from 154 generic tigers and compared them with 100 wild tiger samples from the National Center for Biotechnology Information (NCBI) database.

With this data, they developed a reference panel to distinguish individual tigers and identify their genetic ancestry, similar to popular genetic ancestry tests for humans. 

“When we do 23andMe, we’re not sequencing the whole genome – we’re sequencing a portion of it that informs us about your health and ancestry,” Armstrong explained. “That’s what we want to be able to do, but for tigers.”

The genetic database developed by the researchers has uses beyond conservation efforts. It can also assist law enforcement in prosecuting crimes related to wildlife trafficking.

Prosecuting wildlife crimes

The Big Cat Public Safety Act, which went into effect on December 20, 2022, ended private ownership of big cats as pets and placed restrictions on breeding, commerce, and possession of certain species, including tigers. 

However, the U.S. Fish and Wildlife Service still has storerooms full of confiscated tiger pelts, bones, teeth, and other materials that are difficult to identify without a clear way to trace their origins.

Armstrong’s team has already received requests from the agency to apply their research in identifying confiscated materials. 

“We’ll be working with law enforcement to try to apply this in a forensic context to prosecute wildlife crimes like those seen in Tiger King, monitor the populations in the U.S., and track the illegal trade,” Armstrong said.

Urgent applications of the research 

Using only a small portion of a genome, this reference panel can allow wildlife agencies to determine the ancestry of confiscated samples with limited DNA. 

“That’s been the most rewarding part of this research – we know that this work mattered and has immediate future applications.”

The research also sheds light on the genetic makeup of captive tigers in the U.S. Contrary to widespread rumors, these tigers do not show signs of extensive inbreeding relative to wild tiger populations. 

However, they also do not maintain pure subspecies ancestry, as is the case with zoo-bred tigers or wild tigers. Instead, these generic tigers are a mix of different tiger subspecies. 

Genetic diversity in captive tigers 

Armstrong and her team also found that the non-zoo captive tiger population does not possess more genetic diversity than their wild counterparts.

“This absence of unique genetic diversity in captive tigers means that there will be no ‘genetic rescue’ of wild tigers with individuals now in captivity,” said Elizabeth Hadly, one of the study’s co-authors.

“In other words, the genetic diversity of wild tigers is all that evolution has to work with going into the future.”

Since DNA is the only way to distinguish between tiger subspecies, Armstrong believes the reference panel could be used to identify individual tigers with pure subspecies ancestry if tiger management and conservation efforts ever included releasing captive animals into the wild.

“This technology is usually a ‘for fun’ thing for humans, to find out more about your genetic ancestry, but we can use genomics in a very serious way to help our wildlife populations thrive in the wild and keep them from being exploited,” Armstrong concluded.

The research is published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–