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On a trip to the Northwest Territories last year, Jim Martell spent more than $45,000 for the right to shoot a polar bear. But the animal he killed turned out to have puzzling characteristics - long claws, a humped back and brown patches in its white fur. Had he shot a grizzly by mistake? If so, the American tourist faced up to a year in jail for hunting without a proper licence.

DNA tests showed that the animal in question was not, in fact, a grizzly. But neither was it a polar bear. It was the only confirmed case of a hybrid - born of a polar bear mother and grizzly father - in the wild. This let Mr. Martell off the hook. He even got to take the "grizzlar" home. As he told one newspaper, "It will be quite a trophy."

For conservationists, however, the animal has become more of a booby prize - a symbol of the troubling questions posed by cross-breeding between at-risk species. For example, should the offspring of "animals of special concern" such as grizzlies and polar bears be protected from hunters? Or even encouraged to breed? Or could hybrids actually weaken genetically pure populations of disappearing wildlife?

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In Alberta, for instance, hybridization has contributed to the 80-per-cent decline in threatened cutthroat trout. Cross-breeding has similarly affected populations of golden-winged warblers in Manitoba, Ontario and Quebec. And in British Columbia, mating with other species is an insidious threat to the province's tiny population of spotted owls. Such hybridization could also have an impact on other animals and plants in these ecosystems.

"It's godawfully complicated," says Marco Festa-Bianchet, a biologist with Université de Sherbrooke. This week, he led a meeting of wildlife experts in Ottawa for the Committee on the Status of Endangered Wildlife in Canada. The group is drafting recommendations on how to deal with hybridization to be released next year.

"People may say, 'So what if we have no more cutthroat trout and instead we have a swarm of hybrids?' Well, cutthroat trout were selected for a certain ecosystem. We don't know what impact the hybrid will have on the ecosystem," Prof. Festa-Bianchet says. "Hybrids occur in nature, but we're facing a situation worsened by the actions of man."

BREEDING HYBRIDS

Before the 1800s, hybrids were rare. But European arrivals began removing barriers that separated related species.

Take the eastern wolf in Ontario. As settlers cut down trees to create farmland, the animals' forest habitat disappeared and put them in close quarters with gun-toting humans trying to protect livestock. Wolf populations plummeted.

At the same time, coyotes living in the prairies moved east into newly cleared land. According to Brad White, a geneticist at Trent University in Peterborough, Ont., the two species started mating in the early 20th century. And by 1995, DNA tests of eastern wolves in Algonquin Park showed that they all carried some proportion of coyote genes.

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"Western coyotes and eastern wolves had reached an equilibrium and along we came and broke everything down," Prof. White says.

Habitat destruction could also be pushing cross-breeding among spotted owls. Extensive logging cut down 80 per cent of the old-growth forest they live in and allowed for the invasion of barred owls. This has resulted in cases of hybridization between the two species - and today the David Suzuki Foundation calls the spotted owl the most endangered bird in Canada.

Climate change is another factor in the rise of interspecies mating. Because of changing temperatures, the blue-winged warbler has been moving north - both competing and mating with its closely related golden-winged cousins.

This also could explain the "grizzlar." Wildlife geneticist David Paetkau, whose company tested the hybrid's DNA, thinks that warming temperatures may have caused the grizzly father to spend less time hibernating, giving him more time to wander farther afield. And once he found himself so far out of his usual range, he may have chosen to mate with a polar bear because he could find no females of his own kind.

In fact, grizzlies and polar bears separated into two distinct species less than one million years ago. In evolutionary terms, this is a blink of an eye, and the bears' genes are so similar that Mr. Paetkau suspects that the offspring, like other hybrid species, was probably fertile.

PREVENTION OR PROTECTION

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Yet none of this answers the question of what - now that humans have altered their habitats - should be done about hybrids. Should they be allowed to proliferate, further changing fragile ecosystems? Or should conservationists put a stop to cross-breeding?

In New Brunswick, officials have decided to protect the hybrid offspring of bobcats and lynx - dubbed bob-o-lynx - from hunters. "We treat the animal as its most restricted parent," says Cade Libby, a wildlife biologist with the Department of Natural Resources.

In contrast, a government project in the southern United States stresses the importance of genetic uniqueness. To keep coyotes from over-hybridizing with at-risk eastern wolves (also called red wolves), officials have captured purebreds and put them into a special breeding program.

But others say hybrids need not be controlled at all. They see them as a part of evolution - nature's answer to habitat destruction and climate change.

"What matters is the ecosystem, not the individual populations within it," Mr. Paetkau says. "You can spend an incredible amount of energy preserving animals on a landscape when that landscape is changing underneath them because of deforestation and climate change. The issue is how to preserve a functioning ecosystem that can evolve in the face of change."

Trent's Prof. White agrees. "The most important thing in biology is to facilitate the evolutionary process and not be a preservationist," he says. "You can't turn the clock back to before the Pilgrim fathers landed. All individuals will be dead relatively soon. The only thing that will go on is genetic information and it's that information that will allow animals to adapt to change. So we celebrate genetic diversity."

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Still, Prof. Festa-Bianchet is concerned about the implications of such celebrations. "I worry it could be used as an excuse not to act at the local habitat level," he says. "It could be used as an excuse for doing nothing."

As for hunters such as Jim Martell? As long as he buys the right licence, he is free to shoot whatever species he sets his sight on. Since snagging his "grizzlar," he reportedly has returned to Yellowknife to kill a grizzly.

Sharon Oosthoek is a freelance science writer based in Toronto.

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