Capturing a Grizzly? In the Age of DNA, A Few Hairs May Do

The New York Times

Jackson, Wyo.
Damien Miller let out a loud whistle of warning as he walked toward his study site, hoping to perk up the ears of any grizzly bears that might be lurking in the woods. Mr. Miller, a biologist with the Wyoming Department of Game and Fish, would love to have some grizzlies visit this patch of spruce and pine forest, but he has no desire for a surprise encounter with a 1,000 pound bear.

Whistling, he said, should scare off any lurkers. Actually, Mr. Miller does not need to see his study subjects, either nose to nose or through binoculars. All he needs is a bit of evidence that the animals paid a visit to the enticing bucket of cattle blood suspended among the pines.

Ignoring the flies swarming around the bloody lure, he methodically examined a few lengths of barbed wire that ran around several pines and formed a kind of corral below the lure. On one of the barbs he found his tiny prize: a few silver-tipped hairs from a grizzly bear.

He plucked the hairs off the wire and carefully placed them in a small envelope, noting the time and location.

The hair trap corral, one of three dozen in the area, had worked. A grizzly bear had ducked under the barbed wire to investigate the irresistible smell wafting out of the bucket and had left behind a few hairs. Mr. Miller had the biological samples he needed and the bear, rather than having to endure the stress of being trapped, drugged and handled by humans, had probably felt nothing more than a light scratch on its back.

From those few hairs Mr. Miller and his colleagues will be able to discern the bear’s genetic heritage and might also uncover information that could prove crucial to the recovery of grizzly bears in the 9,500 square-mile Yellowstone ecosystem.

From this wooded hillside in Bridger-Teton National Forest, just east of Grand Teton National Park, the hairs will travel to England. There, Dr. Ryk Ward, a geneticist at Oxford University, will extract the bear’s DNA, analyze it for several characteristics, and build a genetic fingerprint of the animal. When samples have been collected from enough bears, said Steve French, a co-founder of the Yellowstone Grizzly Foundation who is leading the research effort, the researchers should finally be able to answer many long-standing questions:

Just how healthy is this isolated population of grizzly bears? Have they lost precious genetic diversity over the last century? Which bears are related to one another? And most importantly, are there now enough grizzlies in the Yellowstone Ecosystem to move the species off the Endangered Species List, and if not, what might be the best options for recovery? Are the bears, the largest land carnivores on earth, rebounding and expanding their territory or are they in danger of collapse?

As many as 100,000 grizzly bears were found west of the Mississippi River in the early 1800s, but by 1975, the bears had been squeezed by human development into a few isolated habitats, and fewer than 1,000 animals remained. The Yellowstone population, the southernmost group in the U.S., experienced additional problems in the early 1970s. Many of the 230 or so grizzlies then living in Yellowstone National Park had come to rely on garbage dumps for their food, but the last dump closed in 1971, forcing ill-prepared bears to quickly learn how to forage for food.

The United States Fish and Wildlife Service listed the grizzly as a threatened species in 1975. Among the conditions now needed to declare the species recovered and take

it off the list, says the agency, is a population in Yellowstone that includes an annual average of 15 females with first-year cubs, which indicates a total population of about 158 animals.  Some critics say that number is far too low, and to be truly viable the population should be as large as 2,000 bears. Current estimates range from 225 to more than 600 bears, including an annual average of 19 females with first year cubs.

Unfortunately, no one can say exactly how many bears are roaming through the wilderness and ranches. Making a positive identification of each individual would require trapping every bear and fitting it with an ear tag or radio collar, a difficult and expensive undertaking. So population estimates typically rely on observing and counting bears from a distance. But there are pitfalls in using such methods, since animals can easily be counted more than once or not at all. “How many total are out there? No one has the foggiest idea,” said Dr. French.

Dr. French initiated the hair trapping and genetic studies in 1990, in part to answer the numbers question once and for all. Having studied the Yellowstone grizzlies for fourteen years, he believes the population has exploded in recent years, and estimates there may be as many as 500 bears.

“There are so many bears around here that you can’t swing a dead cat without hitting a grizzly,” he said. “But we have to come up with a number that is scientifically valid. We have to finally get off this debate over how many bears there are.”

The first portion of the studies, conducted with Dr. Lisette Waits of the University of Utah and Dr. Ward, looked at the evolutionary relationships between grizzly bear populations worldwide. They analyzed the mitochondrial DNA of several species of bears, getting the DNA not from the current hair samples, but from the tissues and blood of more than 300 bears that zoo curators and other researchers around the world have collected over the years.

Mitochondrial DNA is different from the DNA in cells’ nucleuses in that it passes only from mother to offspring. It also mutates more rapidly than nuclear DNA. By tracking the mutations found in certain parts of the mitochondrial DNA, and knowing how fast or slow mutations are likely to arise in those regions, Drs. Waits and Ward were able to construct an evolutionary tree of bear species, determining how many millions of years ago each species diverged from its ancestors. Grizzly bears, they found, emerged as a separate species about two million years ago.

The researchers also discovered that grizzly bears today are split into four genetically distinct subpopulations around the world, one of which is the grizzly bears of southern Canada and the Lower 48 States. Within that group, they also found, are six distinct maternal lines. Only two of those lines are found today in the Yellowstone bears, but in other areas, as many as all six lines can be found. Knowledge of these maternal lines and where they are found in the world can help conservation efforts, said Dr. French.

Once the broad evolutionary relationships were revealed, Dr. French and his colleagues set out to further define the genetic profile of the Yellowstone bears. To do so, they decided to study nuclear DNA, which is more complex and reveals more information about individuals than does mitochondrial DNA. Dr. French and his colleagues decided to get the DNA from hair samples, and set about designing the barbed wire traps.

For the last two years, in collaboration with the Wyoming Game and Fish Department, the wildlife service, and other agencies, Dr. French has run a pilot study of hair trap corrals in Bridger-Teton and Shoshone National Forests and Yellowstone National Park, fine-tuning the locations used, scent, wire height and other factors. Once the most effective combination is determined, the researchers will set up perhaps 500 or more hair traps in the Yellowstone ecosystem.

While the traps are being perfected, Dr. Ward is analyzing DNA samples for the distinctive characteristics that will enable them to tell one bear from another and track family relationships. He is now identifying numerous distinctive regions of DNA known as microsatellites. Each microsatellite is a particular spot on the DNA strand that is known to contain a repetitive sequence of base pairs, or genetic information. All bears will have this sequence of repeats at that location, but the number of repetitions found can vary considerably from one animal to another. That variability can be identified in the laboratory. And while some bears might be identical in some microsatellites, just as many people have identical genes for green eyes, the researchers believe that by looking at as many as 30 different microsatellites they should be able to identify each individual bear, even distinguishing between siblings. With that information, said Dr. French, “We can quantify bears more accurately than it’s ever been done before. We can come up with an actual count of bears.”

The microsatellite information will also be used to assess the genetic diversity of Yellowstone bears, to see if past population declines have led to dangerously low diversity and the possible loss of valuable genetic traits, as is suspected from preliminary studies. Dr. French has come up with an intriguing way to make those comparisons with the long-gone Yellowstone grizzly population.

“Every single guest ranch and lodge around here has one or two grizzlies mounted on the wall, “he said.” We know where and when each was killed.” Dr. French plans to extract DNA from hair or tooth samples taken from the mounted specimens, assess the maternal lines as well as the overall genetic diversity found in them, and compare that to the existing population. If significant differences are found, it might be advisable to augment the population with outside bears, in particular with bears that are known to carry the missing genetic information.

By knowing what genetic makeup was once there and is now missing, he said, “We won’t be doing it blindly anymore.”

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