Pictured are tigers Nyla (left) and Blanca (right), who were rescued at In-Sync Exotics Wildlife Rescue and Educational Center in Wylie, Texas (2022). Both tigers were confiscated from their previous owners, who supplied animals for circus and fair shows. Credit: Keri Osterman
In the United States, there are more tigers in captivity than in the wild. The World Wildlife Federation estimates that about 5,000 of these big cats live in the United States, most of them privately owned.
The health of this population is a genetic mystery to conservation groups and researchers interested in how captive tigers might help stabilize or restore wild tiger populations. Are privately held animals like wild tigers, or do they reflect traits popular in the illegal trade? Are they a mix of wild tiger ancestry, or are they inbred and detrimental?
A new study from Stanford University, published September 19 in Proceedings of the National Academy of Sciencesexamines these questions and proposes a new tool that conservationists and law enforcement can use to protect animals and prosecute those responsible for their abuse.
“We’re trying to leverage genomic technology to make it useful in a conservation context: there are so few tigers. We don’t get a second chance if they go extinct,” said Ellie Armstrong, Ph.D., lead author of the study.
An unknown population
The study was led by Armstrong, who conducted the research as part of his doctoral studies in biology, with co-supervisors and co-authors Elizabeth Hadly, the Paul S. and Billie Achilles Professor of Environmental Biology, Emerita; and Dmitri Petrov, the Michelle and Kevin Douglas Professor, both in the School of Humanities and Sciences.
The researchers became interested in studying the genetic diversity of privately held tigers – called “generics” because their sources are unknown – after conducting a study on the genetic impact of isolating wild tiger populations.
“We were doing a large study of wild tiger populations and we used that data to address the issue of captive tigers in the United States. At first, it was a little unbelievable that you could have a tiger living right next door and not know it,” said Armstrong, who is now an assistant professor of evolution, ecology and organismal biology at the University of California, Riverside.
“We reached out to Tigers in America, and that’s when we realized there were a huge number of these cats outside of accredited facilities being bred for animal encounters, displayed as circus animals, or trafficked as exotic pets. But we had no idea what type of tiger they were or where they were coming from,” Armstrong continued.
The research team faced a major obstacle: the lack of official data on tigers. Series like Netflix’s “Tiger King” (2020) and the documentary “The Tiger Next Door” (2009) helped raise awareness of the problem of privately owned tigers, but access to the animals for research remained a challenge.
“There were so many rumors associated with this captive population and many of them contradicted each other. People would say, ‘All cats are really inbred,’ or ‘All cats are genetically diverse,’” Armstrong said. “We had no idea what to expect and we thought genomic technology could help us answer some of those questions.”
Building a genetic database
Through its relationships with sanctuaries that have rescued generic tigers, the team obtained samples and learned about tigers, including where many of the animals were rescued.
The researchers collected samples from 154 generic tigers and used another 100 samples from wild tigers available in the National Center for Biotechnology Information (NCBI) database. From their previous work, the team knew that there are six wild subspecies of tigers. Using this data, they developed a tiger reference panel that was used to accurately distinguish individual animals and assign their genetic ancestry. Armstrong compares it to popular genetic ancestry tests for humans.
“When we use 23andMe, we’re not sequencing the entire genome, but a portion of it that tells us about your health and your ancestry,” she said. “That’s what we want to be able to do, but for tigers. It’s difficult and expensive to sequence and analyze an entire genome, especially in a conservation context. The workflow we’ve developed allows us to sequence a portion of the genome and get answers about the tiger and its ancestry.”
A boon for law enforcement
Knowing a tiger’s ancestry has uses beyond conservation and breeding programs: law enforcement can use it to prosecute cases.
The Big Cat Public Safety Act went into effect on December 20, 2022, ending private ownership of big cats as pets and imposing restrictions on the breeding, trade, possession, and use of certain species, including tigers. (People who owned cats before the law was passed must register the animals.) Still, the U.S. Fish and Wildlife Service has hoards full of confiscated tiger skins, bones, teeth, and more, and cases it can’t prosecute because it can’t positively identify the origin and ancestry of the samples. The agency has already asked to work with the researchers.
“We’re going to be working with law enforcement to try to apply this in a forensic context to prosecute wildlife crimes like those seen in ‘Tiger King,’ to monitor populations in the United States and to track illegal trade,” Armstrong said. “Materials like teeth and fur contain a limited amount of DNA, and the reference panel we’ve created here can allow wildlife agencies to determine the ancestry and identity of confiscated samples, even by sequencing just a small portion of the genome. That’s the most rewarding part of this research – we know this work has been important and has immediate applications in the future.”
Putting an end to the rumors
As for those wondering, “What are these animals?” the researchers believe they have the answer. The captive tiger population in the United States does not exhibit widespread inbreeding compared to wild tiger populations. Nor have they demonstrated that generic tigers retain ancestry from a single subspecies, as is the case with zoo-bred or wild tigers.
These generic tigers are a mix of different tiger subspecies. Armstrong and his colleagues also show that the captive tiger population outside zoos in the United States has no more genetic diversity than that found in wild populations.
“This lack of unique genetic diversity in captive tigers means that there will be no ‘genetic rescue’ of wild tigers with individuals currently in captivity,” Hadly said. “In other words, the genetic diversity of wild tigers is all that evolution has to work with in the future.”
DNA is the only way to identify a tiger subspecies: there are no noticeable physical differences between the six recognized subspecies. If the unique evolutionary history of each tiger subspecies remains a priority for tiger management, and we can overcome the enormous hurdles of releasing captive animals into the wild, the reference panel could be used to identify individuals that do not have mixed ancestry.
According to Armstrong, “This technology is generally used for fun and to discover information about the genetic ancestry of humans, but we can use genomics in very serious ways to help our wildlife populations thrive in the wild and avoid being exploited.”
More information:
Ellie E. Armstrong et al., Deciphering the story of genomic diversity and admixture in captive tigers in the United States, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2402924121
Provided by Stanford University
Quote:Can captive tigers help save wild populations? (2024, September 19) retrieved September 20, 2024 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without written permission. The content is provided for informational purposes only.