Research Indicates There Are No Pure North American Bison Left, All Have Domestic Cattle DNA

by Jon D. B.
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Texas A&M researchers cite the “strongest evidence yet” that domestic cattle DNA is present in all living North American bison, regardless of location.

Alongside the bald eagle, the bison is one of America’s greatest conservation success stories. Unlike our national bird, however, saving our national mammal would alter their genetic code forever.

As this new Texas A&M College of Veterinary Medicine & Biomedical Sciences research shows (published by Scientific Reports), all bison in North America carry multiple, clearly identifiable DNA markers originating from domestic cattle.

To reach this conclusion, researchers would compare the DNA genome sequences of “major historical lineages” of American bison to over 1,800 domestic cattle. In doing so, they found that every single bison population tested contains domestic cattle DNA.

In other words, we now have the “strongest evidence yet” that every existing bison left in North America – regardless of location – has some domestic cattle ancestry. And it all comes down to the heavily documented bison population crash, then bottleneck, of the 19th century.

Not Even Yellowstone National Park Bison Are 100% Pure, Study Says

“This comparative study clearly documents that the people responsible for saving the bison from extinction in the late 1800s are also responsible for introducing cattle genetics into this species,” says the study’s co-lead, Dr. James Derr.

North American Bison and their calves, forage for food at Yellowstone National Park, Wyoming. In the early 1800’s, an estimated 65 million bison roamed throughout the continent of North America but hunting and poaching had a devastating effect on their population and by 1890, fewer than 1,000 would remain. (MARK RALSTON/AFP, Getty Images)

Derr has been working on bison DNA research for well over 20 years now. His 2022 publishing comes, in fact, as an update to his series of studies published two decades ago in which his team cites “only a few” bison herds existed that were truly free of domestic cattle introgression. But with advancements in genetic technology come far more detailed – and accurate – results. And those results show that even the bison herds we thought were pristine and historic – like Yellowstone National Park – are not.

“Today, it appears that all major public, private, tribal and non-governmental organization bison herds have low levels of cattle genomic introgression,” explains Sam Stroupe, first author of the study and a Ph.D. student in Derr’s lab. “This includes Yellowstone National Park, as well as Elk Island National Park in Canada… Which were thought to be free of cattle introgression based on previous genetic studies.”

Remarkable, Long-Term ‘Ramifications for Bison Conservation’

Derr’s research has been instrumental in the species’ (wood and plains bison) conservation for the last several decades. And the resulting impact of this 180-degree turn already feels monumental.

Most prominently, specific herds – like Yellowstone – may no longer need to be managed in isolation. Their populations are not free of domestic cattle DNA, as was previously thought.

“For example, these findings really open up a number of opportunities for the establishment of new bison conservation herds. And the augmentation of existing herds,” Derr cites. Indeed, his new findings hold remarkable, long-term “ramifications for bison conservation efforts.”

As for how we got here, American history holds more documentation of the bison population crash and rehabilitation than perhaps any other wildlife species. And that rehabilitation came as the direct result of private ranchers and herd ownership in the 19th century U.S.

History: How Cattle Ranchers Inadvertently Saved North America’s National Mammal

Roaming North America in the 1800s meant sharing the vast plains and woodlands with untold millions of bison. Biologists of the time estimated at leas 30 million individuals called the continent home.

But the arrival of European settlers brought on their catastrophic demise in a shockingly-short amount of time.

19th century engraving depicting men hunting bison. (Photo by: Universal History Archive/Universal Images Group via Getty Images)

Unregulated hunting (for sport, food, and indiscriminately without purpose), would drive the species towards extinction in its natural habitat by the end of the 19th century. The congruent carving of America into cities, territories, and ranches also decimated the bison’s habitat. Diseases from imported domestic livestock would also take a toll.

By 1880, early American conservationists estimated only a few hundred bison were left in the wild. Besides this precious few – of which the majority continued to roam in Yellowstone National Park – only the bison “domesticated” by private ranchers were left to carry on the species’ existence.

As a result, every single existing bison today descends from these few hundred survivors. This bottleneck could have ended very differently, too, if not for five individual cattle ranchers to whom we owe the entire 430,000 bison roaming North America today.

Yet the intentions of these ranchers was not, at the time, to save the species. Instead, it was to cross-breed them with domestic beef cattle. Which they did; extensively. And this is how every extant bison today shows traces of domestic cattle ancestry within their DNA.

‘Without these private herds, it is possible bison would have become extinct’

“The American bison were proven successful on this continent… Surviving glaciation and multiple other climatic events over thousands of years,” Dr. Derr offers of the rancher’s motivation. “By crossing bison and cattle, those intrepid cattlemen hypothesized they could get a beef animal that is as resilient as bison but that produces as much quality meat as beef cattle. In the end, they failed due to inadvertent creation of a lackluster beef animal.”

circa 1933: A herd of wild bison. (Photo by Fox Photos/Getty Images)

But their time, and purpose would still come. The early 20th century saw the onset of the American conservation movement, shepherded by men as influential as President Theodore Roosevelt and William Hornaday. Both men would co-found the American Bison Society. And by 1905, their plan to save the species from annihilation was in motion.

In order to preserve the dwindling wild populations in Yellowstone and Wood Buffalo National Parks, however, the society would have to pull in more bison. And the only place they existed was the private ranches and beef farms of Western America.

“As a result, these well-intentioned hybridization efforts leave a complicated genetic legacy,” Dr. Brian Davis, co-author of the new study, explains. “Without these private herds, it is possible bison would have become extinct. At the same time, this intentional introduction of interspecies DNA resulted in remnant cattle footprints in the genomes of the entire contemporary species.”

“Two primary events, an extremely small bison population size and widespread interest in developing hybrid animals… Changed and shaped the genomes of this species in ways we are just now starting to understand,” Dr. Derr adds. “Nevertheless, this species did survive and now they are thriving across the plains of North America.”

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