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Grolar Bears and Narlugas: Rise of the Arctic Hybrids

Four years ago photographer Steven Kazlowski shot this image of a strangely colored bear east of Barrow, Alaska. “Locals told me it was a cross-breed,” Kazlowski says, but it’s impossible to know without DNA testing. There was a lot of discussion about whether Kazlowski’s photo should accompany a new report on Arctic hybridization in the journal Nature. “It looks compelling," co-author Brendan Kelly says, "but the discoloring in the fur could, for all we know, be dried seal blood.” The picture ultimately ran with the article.
Climate change appears to be igniting a sexual revolution among Arctic mammals -- and that’s not good news for some endangered species.

In 2006 an American hunter shot an animal in the far north of Canada’s Northwest Territories that shared characteristics of a polar bear and a grizzly. Earlier this year, a similar bear was killed less than 200 miles away, and DNA tests confirmed it was a mixture of the two species. The "grolar bear" thus joined a growing list of cross-species couplings -- beluga whales and narwhals, right whales and bowhead whales, various seal mixtures -- all confirmed to varying degrees by scientists in the Arctic over the past two decades.

What’s going on here?

In the December 16 issue of Nature, three American researchers argue that global warming is encouraging the formation of hybrid offspring among Arctic mammals. "The rapid disappearance of the Arctic ice cap is removing the barrier that’s kept a number of species isolated from each other for at least ten thousand years," says the article’s lead author, University of Alaska evolutionary biologist Brendan Kelly. That’s leading to some unusual pairings that could have dire consequences for endangered species in the Arctic.

As formerly isolated animals come into contact, write Kelly and co-authors Andrew Whiteley and David Tallmon, "they will mate, hybrids will form and rare species are likely to go extinct." As the genes of Arctic species mix through successive generations, they write, the adaptive gene combinations that allow species to flourish in the extreme environmental conditions of the far north "will be lost."

"By melting the seasonal ice cap," Kelly says, "we’re speeding up evolution."

The grizzly-polar bear mixtures provide some of the study’s most compelling evidence. The most recent confirmed hybrid was killed on April 2010 by a native Inuvialuit hunter who observed it scavenging through unoccupied cabins. Biologists used DNA tests to confirm that the bear -- which had thick white fur but a wide grizzly-like head, brown legs, and brown paws-- was indeed a cross between the two species.

But those tests revealed something more: The 2010 specimen was a second-generation hybrid. "That clearly indicates that these hybrids are fertile in the wild," Kelly says. One of the common complications of cross-breeding is infertility; the lineage of the horse and donkey, for example, stops at the mule. A fertile grolar bear "suggests that we’re not just seeing one or two crosses, but something more common," Kelly says. "This has been going on for a matter of decades now" as the Arctic has warmed.

The same could be true in marine mammals, which are more prone to hybridization because of their genetic makeup, Kelly says. Many pinnipeds (seals, sea lions, and walruses), for example, share the same number of chromosomes, which helps produce fertile offspring. Donkeys and horses have a different number of chromosomes, which prevents their mule offspring from producing sperm or eggs.

In their Nature article, Kelly, Whiteley, and Tallmon list 34 potential hybridizations between discrete populations, species, and genera of marine mammals in the Arctic and near-Arctic. Some of those potential matings have already been realized. Using photographic evidence, whale experts last year confirmed the existence of a bowhead-right whale hybrid in the Bering Sea. A narwhal-beluga whale mix has been found in Greenland. Its intermediate form, however, raises questions about the potential success of its genetic line. The narwhal-beluga (narluga?), write the authors, "had teeth combining qualities of each species, but lacked the narwhal’s tusk -- an important determinant of narwhal breeding success."

NRDC: Hybrid Law

Andrew WetzlerAndrew Wetzler

Q&A with Andrew Wetzler, co-director of NRDC’s Land and Wildlife Program and an expert on the Endangered Species Act and legal issues regarding threatened and endangered species.

Does the increasing number of hybrids in the Arctic present a concern for the preservation of endangered or threatened species?

Yes, hybridization can be a real problem for some endangered species. For example, the Northern Spotted Owl has suffered from hybridization in recent decades.  When a species hybridizes, its gene pool can be compromised or even lost.  Eventually, the "species" you were trying to protect simply doesn’t exist anymore.

Read the rest here.

Hybridization occurs occasionally in nature, of course, and cross-breeds have proven to be box office draws at zoos. (Think the lion-tiger hybrid, the liger.) What’s different about the Arctic is that melting ice is erasing a continent-size geographic barrier between isolated species. That kind of thing usually happens gradually, over geologic time; now it’s happening over a matter of decades.

Sudden contact may lead to an endangered species being subsumed by a higher-population species. "It’s partly a numbers game," says Whiteley, a conservation geneticist at the University of Massachusetts at Amherst. If a lonely narwhal encounters nothing but beluga whales during mating season, cross-species sparks may fly. Repeat enough times, and pretty soon you’re left with few pure narwhals. "At the very least [the rarer species] is wasting its reproductive efforts," Whiteley says. "It’s one more factor in the species’ decline."

It’s happened before. Mallard ducks, introduced to New Zealand in the 1860s, mated with native gray ducks and overwhelmed the gray duck species, which is now listed by New Zealand as critically endangered. In the southeastern United States, the decimated red wolf population began mating with coyotes in the mid-20th century -- because lonely wolves, bereft of mates, decided coyotes were better than nothing -- leading to the loss of nearly all genetically pure red wolf populations.

Could polar bears suffer the same fate? Melting sea ice is forcing more polar bears to come ashore, and the warming climate is making Arctic habitat more welcoming to grizzly bears. Result: More grizzly-polar bear meetings, and, perhaps, opportunities for mating.  The concern is that polar bears could be subsumed into the larger grizzly population, which is better adapted for warmer temperatures, and essentially disappear as a separate species.

"The main question we want to raise for scientists and policy makers is this: How do we handle hybrids?" Whiteley says. The Endangered Species Act has no official policy for dealing with hybrid species. In some cases, wildlife managers have culled hybrid offspring in order to keep the genetic line of an endangered species pure. "What we need is a widescale genetic monitoring program," Whiteley says -- something overseen by an international organization like the IUCN (World Conservation Union) -- "to get a sense of what’s going on up there."

Hybridization could, in theory, lead to fitter, more well-adapted animals. But that’s not likely, Kelly says. First-generation hybrids often exhibit excellent survival characteristics. Biologists call it "hybrid vigor." But successive generations rapidly fall off in fitness, which is known as "outbreeding depression."

"People often talk about species adapting to climate change," Kelly says. "But the kind of adaptation that’s necessary is a change toward genes that fit the new climatic environment better than the old genes. Individuals don’t adapt genetically. Populations do. That requires generations, which requires time. Bears, seals, whales -- these are long-lived animals. They need decades and centuries to adapt. But we’re talking about losing the Arctic summer sea ice in a matter of a few decades. So the time for adaptive response may not be there."

Editor’s note: Bruce Barcott is writing about changing Arctic food webs for the Spring 2011 issue of OnEarth magazine. Sign up for our e-mail newsletter to be notified when his story is published.

image of Bruce Barcott
Bruce Barcott was a 2009 Guggenheim Fellow in nonfiction and is the author of The Last Flight of the Scarlet Macaw and The Measure of a Mountain: Beauty and Terror on Mount Rainier. He writes frequently about the outdoors and the environment for such... READ MORE >
How is interbreeding bad, exactly, for endangered species? It will allow their genetics to live on, and, you know, create new species that will inhabit our planet in the future. It's literally the way things have always, always worked. Humans seem to have lost sight of evolution. Breeding yourself out of a species is a wonderful thing, a thing to be celebrated, because it's the only way life has progressed. 99.9+% of all species that have ever existed are gone. And that's given rise to the world we live in today. That's some sort of awful concept? While I agree that diversity is a wonderful thing, and conservation is great, we have to remember the concept of survival of the fittest, and/or luckiest. We cannot, and should not, stop this. Humans themselves are crossbreeds of crossbreeds of crossbreeds of crossbreeds.... etc. Are you suggesting that we'd have been better off if that hadn't happened? If your species is so terrible at living where it's always lived... maybe it's just your time. Life has decided you should move on. Do so. Change, adapt. Because the world is always changing. I like the part about "lacking the tusk so important to narwhal breeding." Well, the lack of tusk obviously wasn't that big a problem for the narwhal that mated with the non-tusk-having beluga!
Oh, one last thought. That whole "keeping the blood lines of endangered species pure." That really smacks of racism and the indignities suffered by multiracial children in a world where national and racial purity is (still, unfortunately) held so highly. Do we really want to enforce these ignorant attitudes upon the natural world?
"That whole "keeping the blood lines of endangered species pure." That really smacks of racism and the indignities suffered by multiracial children in a world where national and racial purity is (still, unfortunately) held so highly. Do we really want to enforce these ignorant attitudes upon the natural world?" What a load of rubbish! This has nothing to do with racism. This is about species, not race. Most hybrid animals are sterile, so interbreeding is generally a genetic dead end that could (in combination with the damage done by humans) contribute to the destruction and ultimate extinction of the species.
Seconded. Don't draw obscure links where there are none. Keeping bloodlines pure in evolutionary terms is important because natural selection has ensured that these species have the inherited ability to survive whatever environment they in habit. Seriously bro, think before you speak.
I'm curious to whether hy-breeding makes a species more compatible to a broad environment or not. In the short mind two bear mixes seems more effective to handle environments in the instinctive end, but mentioning two bears drowns the genetic integrity is inconclusive( resource would be nice, but I guess I can look that up later).
For starters, from the article: 'Hybridization could, in theory, lead to fitter, more well-adapted animals. But that’s not likely, Kelly says. First-generation hybrids often exhibit excellent survival characteristics. Biologists call it "hybrid vigor." But successive generations rapidly fall off in fitness, which is known as "outbreeding depression."' When you interbreed two populations, you're basically engaging in a massive game of chance -- throwing all the pieces (genes) into a big bucket, and then randomizing and re-selecting according to new rules. Rules that neither genome was evolved to accommodate. So you lose traits. It's easier to see with plants, because they're easier to breed and we have so many examples of losing valuable traits such as resistance to certain diseases, ability to accommodate certain insects and parasites, nutritional content, climate-tolerance, drought-tolerance, etc. That's why there's such an effort to reclaim "heirloom" varieties before they're marginalized out of existence. That said, I think a lot of the concern is knee-jerk and overblown. Yes, it would be sad to say that we wiped out the polar bear, but what's happening is in fact a normal evolutionary phenomenon.
What's happening is not "normal" at all, as the habitat shifts making these hybrid offspring more likely are due to human-propelled climate change.
What's not "Normal" because it's human-propelled. Humans are God's Creatures, too... and as such-- an integral part of the Ecosystem. Anything that happens is "Normal"-- because it was meant to be... such as a comet slamming into the Earth approximately 65 Million years ago & wiping out the Dinosaurs. I agree, though, that we are supposed to be Stewards of the Land and definitely help protect species from Extinction. The problem is that the minds of human beings... the Hyppocratic Oath has Backfired by humans creating vaccines-- leading to Overpopulation. Virus' and Bacteria were our "Apex Predators"-- like wolves over deer & sharks over smaller fish. Our "Apex( top of the pyramid in the Food Chain ) Predators" have disappeared because of Noble Efforts by people such as Jonas Salk, etc.. There are no Real Dragons except the Komodo-- yet our real dragons such as Small Pox, Polio, etc. have virtually been eradicated. What we're faced with now is twice as much CO2 from cars and factories than the Earth can tolerate. People need to slow down their usage of these things. I forget the date, but 400 or 450 Million years ago there was a mass Extinction( more species died that in the 65 Million Dinosaur die off ). Before it happened it wouldn't have been considered "Normal"-- but now we know it was because it was pure science. The Seas turned to acid. The bottom of our Food Chain in the Oceans is Phytoplankton & Zooplankton( which also produce O2 out of CO2 ). 60 % of our Phytoplankton is NOW DEAD. The Eastern 1/3 of The Great Barrier Reef is now dead... with ocean PH/acid levels continuing to rise. People Wake Up! Ocean Acid levels rising just a little more to create holes being punched in our many foods chains causing havoc to be wreaked upon the planet is NOT far away!! It's going to happen with Lightning Fast "More Than Exponential Progression"... and by the time "Enough People" Start Doing Something About It-- there might very well be little if anything that we'll be able to do to stop it. I urge everyone to take an "Alarmist Position"... precisely because IT IS an Alarming Situation: Action Now!!!! Tom III-- who wrote # 4( below )
The "narluga" from Greenland was no hybrid at all, as recent genetic tests have shown it was actually a pure Monodon, yet a very freakish specimen.
If the Polar bear keeps on trying to hunt the way it does... then 100 % of it's genes-- that are already adapted to cold-- will perish/go extinct. Then, someday when the ice returns... the Grizzly will try to occupy that land-- and it will take many deaths and many many generations to eventually adapt to the cold. The Polar Bear is merely Diversifying it's Risk against extinction by "Storing it's genes in the Grizzly line for awhile. The Polar Bear is dying & going extinct the way it hunts-- due to drowning because the ice bergs are too few & far between. The grizzly will survive( carrying recessive Polar Bear genes ) because it eats salmon out of the stream-- and honey, nuts & berries. Eventually someday when it's cold up there again the hybrids will return. Up there the superior way to hunt & survive will be as the Polar Bear( today ) used to do. Iceberg hopping for seals and hollow white hairs to bring the suns radiance down to the skin will again be the most efficient and superior survival mechanisms. Even if the Polar bears genes comprise only 25 % of these new hybrids-- that's OK. That 25 % will be the recessive genes and 1 out of 4 of this new hybrid will be born with Polar Bear traits. There will be more deaths amongst the 3 with primary Grizzly traits because they won't know how to survive in the Polar Bears original/cold environment-- and so they won't procreate. The 25 % Polar bears will continue procreating at a higher proportionate amount. Eventually Natures Survival of the fittest will dictate 50/50 genes in these Hybrids, then 75 % Polar Bear 25 % Grizzly... until finally we're back to Square One-- pretty close to 100 % Polar Bear. This "Shortened Evolution" might only take 1,000 or 2,000 years because of the Polar Bears recessive traits being stored in the Grizzly. If there were no Polar Bear recessive traits in the Grizzly-- then when cold comes back it might take 10, 30 or 100,000 years for the Grizzly to adapt from scratch-- to try to develop white hollow hair to keep warm from the sun and to try to evolve or develop the swimming & hunting skills. A few thousand years of repeat evolution is way better than 100,000 years or so!! :) Tom
What can I say that hasn't already been said? I agree with Tom & Nick.
This article smacks of bad science. Actually there is nothing remotely scientific about it. It is based upon the unsupported opinions of so-called scientists, which are presented as fact. Just because a person gives himself the title of "scientist" does not mean he knows what he is talking about. The extinction of arctic species will not be due to hybridization, as the "scientists" claim, but to climate change. Climate change is a long-term problem, for which hybridization is a long-term solution. In the case of hybridization due to temporary factors, then yes, I could see a reason for people to interfere in the natural process of evolution. This is especially true in cases where hybridization is occurring because humans have introduced species to ecosystems where they didn't belong (Mallards in New Zealand, for example.) These cases of hybridization in the arctic are the only natural mechanism for survival of very important, unique genetic material. Why would the author prefer the polar bear to die off in lonely genetic purity rather than live on in whatever way it can? It is such an egocentric, selfish thing, "If we can't have the polar bear the way it used to be, then we won't have it at all." If the genetic purists have their way, someday the last pure polar bear carrying the very last polar bear genes will be swimming alone in a vast sea devoid of icebergs. When he finally is exhausted he will drown, and what good will his genetic purity be to him then? Or to us, for that matter?
Funny you should say it's "bad science" when you're practicing "bad science" yourself. Using a few logical fallacies (straw man, ad hominem) doesn't help your cause any, either. Calling Kelly a "so-called scientist" is blatantly obtuse. He's a polar biologist who's been in the field for well over thirty years study all sorts of polar mammals. If anyone knows what he's talking about when it comes to polar biology, he is the man. What part of the article did you not understand? Grizzly bears have been introduced to an eco-system they don't belong, simply because the ice has melted enough for them to cross upwards north into polar bear territory. We haven't introduced them, but nonetheless they have been inadvertently introduced to an region they should not be in, and as Dr. Kelly has already stated (based on evidences gathered throughout his decade of experience, but simply does not have the time & space to lay it out in a simple magazine article), the likelihood that this would lead to beneficial evolutionary traits is very unlikely, and thus is *not* a good thing.