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Mating
a polar bear with grizzly bear might be awesome to behold but does it
happen in the wild? And if it does, what might the consequences be for
the two species involved? If you’re a polar …
If You're Not A Grizzly Bear, Is Mating With One A Good Idea?
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Credit: Mark Newman/Getty Images
Although they descend from the same branch of the evolutionary tree, polar bears and grizzly bears are two very different animals. Polar bears are categorized as marine mammals because they live most of their lives on polar sea ice and depend on the ice to hunt ringed seals, their main source of food. They do not hibernate. Grizzly bears are omnivorous terrestrial mammals that eat fish, meat, insects, plants, birds and carrion. They also hibernate between five and seven months each year. Although they are very different, grizzlies and polar bears can crossbreed and produce fertile offspring.
In the past, hybrids between polar and grizzly bears – called pizzlies or grolars – were not seen very often in the wild because there was relatively little contact between their sea-ice and terrestrial habitats. Recently, however, hybrids have been showing up more frequently in the wilds of Alaska and Northwestern Canada. Climate change caused by global warming is usually given as the reason. As the polar ice shrinks, a larger proportion of the polar bear’s habitat comes into contact with the territory occupied by grizzly bears and the opportunities for crossbreeding increase.
Credit: Wikipedia
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In addition, hybrids living in the grizzly bear’s habitat are very
likely to mate with grizzlies because the polar bear males rarely
roam into warmer climates. Hybrids living in the polar bear’s habitat
may mate with grizzly bears because grizzly males will roam into arctic
climates. Theoretically, this imbalance favors the spread of grizzly
bear genes at the expense of the polar bear. There is empirical evidence
that this imbalance is occurring because second generation hybrids in
the wild tend to have a genetic makeup that is biased in favor of
the grizzly bear.
Does this mean that polar bears could become extinct as a result of their genotype becoming dilluted by grizzly bear genes? It’s possible, but it would take a very long time and there are factors in play that are much more likely to result in the extinction of polar bears long before crossbreeding with grizzlies could wipe them out.
At first glance, the loss of arctic ice caused by global warming
appears to make a compelling case for gradual extinction through
crossbreeding. The situation is not as simple as it first appears,
however.
The likelihood that the two species will come into contact increases as the polar ice melt increases during the course of the summer. They are most likely to meet during mid-to-late summer when the annual loss of polar ice is at it’s greatest. However, both polar and grizzly bears breed in the spring when the ice melt has not advanced very far. This means that roaming males are most likely to come into contact with females of the other species when the females are not breeding. Hybridization in the wild is rarer than you might think if all you consider is the yearly loss of polar ice without taking the bear’s breeding season into account.
The severe decline in polar ice in the mid and late summer is much more of a threat to polar bears than the possibility of genetic dilution through crossbreeding. Polar bears depend on a thick cover of sea ice in order to hunt ringed seals. The seals claw breathing holes in the ice and the bears camp out at the holes and take the seals when they surface. Loss of sea ice because of climate change, or thinning of the ice so that it cannot support the bear’s great weight, can drastically reduce the polar bears’ food supply.
This video produced by NOAA (National Oceanic and Atmospheric Administration) shows the loss of sea ice every year from 1987 to 2014. The oldest ice that the polar bears could depend on year in and year out is shown in white. If global warming is not brought under control, polar
bears will become extinct from the loss of their natural habitat as a
result of climate change long before they might be threatened by the
consequences of crossbreeding with grizzly bears.
Returning to the original question, is mating with a grizzly bear a good idea? It depends on who’s asking. If you’re a polar bear that’s worried about the possible dilution of your gene pool, you’re asking the wrong question. You’d be better served if you worried about the humans who are destroying your habitat. If you’re a female polar bear near the end of your breeding season who isn’t pregnant, taking advantage of a randy male grizzly who wandered into your neighborhood is probably a good idea. If you’re a human, trying to mate with a grizzly is not recommended.
Kevin Murnane covers science & tech for Forbes. You can find more of his writing about these and other topics at The Info Monkey and Tuned In To Cycling. Follow on Twitter@TheInfoMonkey.
Does this mean that polar bears could become extinct as a result of their genotype becoming dilluted by grizzly bear genes? It’s possible, but it would take a very long time and there are factors in play that are much more likely to result in the extinction of polar bears long before crossbreeding with grizzlies could wipe them out.
Credit: Alan D. Wilson/Wikimedia Commons
The likelihood that the two species will come into contact increases as the polar ice melt increases during the course of the summer. They are most likely to meet during mid-to-late summer when the annual loss of polar ice is at it’s greatest. However, both polar and grizzly bears breed in the spring when the ice melt has not advanced very far. This means that roaming males are most likely to come into contact with females of the other species when the females are not breeding. Hybridization in the wild is rarer than you might think if all you consider is the yearly loss of polar ice without taking the bear’s breeding season into account.
The severe decline in polar ice in the mid and late summer is much more of a threat to polar bears than the possibility of genetic dilution through crossbreeding. Polar bears depend on a thick cover of sea ice in order to hunt ringed seals. The seals claw breathing holes in the ice and the bears camp out at the holes and take the seals when they surface. Loss of sea ice because of climate change, or thinning of the ice so that it cannot support the bear’s great weight, can drastically reduce the polar bears’ food supply.
Returning to the original question, is mating with a grizzly bear a good idea? It depends on who’s asking. If you’re a polar bear that’s worried about the possible dilution of your gene pool, you’re asking the wrong question. You’d be better served if you worried about the humans who are destroying your habitat. If you’re a female polar bear near the end of your breeding season who isn’t pregnant, taking advantage of a randy male grizzly who wandered into your neighborhood is probably a good idea. If you’re a human, trying to mate with a grizzly is not recommended.
Kevin Murnane covers science & tech for Forbes. You can find more of his writing about these and other topics at The Info Monkey and Tuned In To Cycling. Follow on Twitter@TheInfoMonkey.
