UNDESIREABLE WHAT ?
Strands of Undesirable DNA Roam With Buffalo
by Jim Robbins
MALTA, Mont. — The animals certainly looked like bison, with the characteristic humps and beards. But just to make sure, a pick-up truck slowly rolled up to them, and a bison wrangler shot a drug-filled dart into one of several calves.
Researchers in Malta, Mont., taking blood samples from a tranquilized animal to see if it is genetically pure.
A few minutes later the anesthetized animal was on the ground, grunting and squirming. Several men warily moved in to hobble the animal and take blood samples.
This bison wrangling was being done to test the genetics of a herd of 39 animals that is being used by the American Prairie Foundation as seed stock to re-create a large-scale native prairie landscape. The researchers want animals with only pure bison genes, which are not so easy to find.
“The majority of public herds have some level of hybridization with cattle,” said Kyran Kunkel, a World Wildlife Federation biologist who is doing the sampling. “You can’t see any difference visually. But we don’t know what the long-term ecological or biological impacts would be.”
American bison, which teetered on the edge of extinction more than a century ago, are one of the first and perhaps greatest conservation successes, but there is an asterisk next to their species: while bison were being nursed back to viable populations, ranchers who owned them crossed them with cattle.
By the late 19th century, tens of millions of American bison had been reduced to fewer than 1,000, with two dozen or so in Yellowstone National Park, and another 250 in Wood Buffalo National Park in Canada. The balance of the animals were owned by cattle ranchers who wanted to preserve them.
“They purposely crossed bison with domestic cattle to make a better beef animal,” which they called cattelo, said James Derr, a geneticist at the Texas A&M College of Veterinary Medicine. “Bison did better in harsh conditions and are more resistant to parasites and native viral diseases.” (Bison do not contract Texas fever, for example, which afflicts cattle.)
Over time, cattle genes have spread into many of the remaining herds of American bison. Since the late 1990s, Dr. Derr and his graduate students have traveled to public and private bison herds around the country, taking blood samples. They have concluded that the vast majority of the 300,000 or so bison in the United States are hybrids, though they look like pure bison. Fewer than 10,000 bison are genetically uncontaminated.
The research has led to the stark realization that the battle for the long-term preservation of wild bison is not over.
Though cattle genes in affected bison herds make up less than 1 percent of the bison genome, their presence could create serious consequences like weaker disease resistance. “Hybridization makes it hard to predict and hard to manage because their immune response can be all over the place,” Dr. Derr said.
To prevent a “genomic extinction” through hybridization, biologists are focusing on the protection and perpetuation of the herds with pure or nearly pure genetics.
Most immediately, it means separating hybridized from pure bison. The United States Fish and Wildlife Service, for example, has been testing bison on its refuges for several years, moving the pure animals to places where they are isolated or can expand.
What the wildlife service wants, said Matt Kales, a spokesman in Denver, is to avoid “the old eggs-in-one-basket approach.”
Most private herds have some cattle ancestry, which is fine, Dr. Derr said, if the bison are being raised for meat and if long-term conservation is not a concern.
“But if a bison herd has no evidence of cattle genetics, it would be criminal to move bison with cattle genetics into that herd,” he said.
The animals in two federally owned herds, at Yellowstone National Park and Wind Cave National Park, are considered as pure as bison get. (Wind Cave is the source of the American Prairie Foundation herd; lab results are not in yet.)
Other national parks — including Grand Teton, Theodore Roosevelt and Badlands — have bison with very few cattle genes. “The U.S. federal herds are the crown jewels of the bison herd,” Dr. Derr said. “They are healthy, there is no inbreeding, they are pure. That’s an amazingly good thing.”
Though the term “pure” is commonly used in describing such herds, Dr. Derr said, it is technically not accurate because of the limits of DNA testing, which has a 1 percent probability of error. He prefers the phrase “no historic or genetic evidence of hybridization.”
A state-owned herd in Utah and a herd owned by Ted Turner on his Vermejo Park Ranch in New Mexico also show no signs of hybridization.
…..Unhybridized bison are critical in efforts by the American Prairie Foundation, the Nature Conservancy, the Canadian government and even Mr. Turner to restore large tracts of native prairie and plains that include herds of bison. Establishing new and disparate bison herds will help assure the future of the wild bison.
While the effects of hybridization on bison are not known, Dr. Derr hypothesizes that genetic alterations could change behavior or traits like weight gain and fertility, in addition to disease resistance. “When you mix up two different genomes, you get a lot of different traits, and it’s not completely predictable,” he said.
Hybrid vigor, a cross-breeding response in which a more robust animal is the result, is not the case when cows and bison commingle. “We get just the opposite,” Dr. Derr said.
The selection practiced by bison ranchers also affects the gene pool.
“Ranchers might get rid of a cantankerous bull, for example,” said Curt Freese, a biologist who directs Great Plains bison restoration for the World Wildlife Fund. “Breeding bison to be docile and meaty are the kinds of things that affect the wildness of the bison.”
Keepers of the pure herds are weighing options to protect their genetics.
Many of the herds are small and at risk of inbreeding and loss of diversity, and so must be trucked away to breed with other populations.
In Yellowstone, which has the largest, purest and most genetically diverse herd of wild bison, the plan is to keep the number of bison high.
“We agreed to manage at greater than 2,300 animals to assure conservation of the genome,” said Rick Wallen, a Park Service biologist. “Managing our population at relatively high levels should go a long way toward protecting genetic diversity.”
Managers of these herds must also keep a wary eye on hybridized invaders. In Yellowstone, officials found a domestic bison that had wandered into the wild population from a neighboring ranch. And Wind Cave National Park is adjacent to Custer State Park, where the animals are hybridized.
The new approach may change other aspects of management, as agencies move from managing the species to managing the genetics. Dr. Derr is involved in a study, for instance, of whether the hunting of the bison that leave Yellowstone might be selecting certain behaviors from the population because animals that migrate are targeted.
Dr. Derr said was one of the questions of the study, which should be completed in a year, was “Are they removing family groups?”
“If they are, it’s a biased way to remove herds, and does it have an effect, such as reducing diversity? Those are the questions we’re asking.”