When polar bears and grizzlies breed, they can produce fertile offspring. Why can't other species?
A grizzly–polar bear hybrid is a rare ursid hybrid that has occurred both in captivity and in the . Grizzlies given the same bags do not demonstrate this hurling behavior. The hybrids were also observed lying down similar to polar bears: on their. Should the bears meet, the grizzlies could do some serious damage. "This is worrying for the polar bears because grizzly bears would likely. Meet the Pizzly, or should that be Grolar Bear? other, and it's likely that it will be polar bears that integrate into brown bears,” say Lorenzen.
And we only have to look at our own species for evidence of this. They diverged for a couple of hundred thousand years and then came back into contact. Oldest human genome reveals a story of sex and migration Polar bears and grizzlies have interbred before Studies of bear DNA shows that polar bears and brown bears have also interbred before, says Lorenzen, who has previously mapped the genome of 89 polar bears.
She discovered that polar bears and brown bears first diverged as a species betweenandyears ago. Since then, the two species have met and interbred several times, and today, brown bears also referred to as grizzly bears still retain some of this ancient polar bear DNA, and vice-versa.
But I know of four individuals that are three quarters grizzly and one quarter polar bear. So these will likely be lost. No new species of bear expected any time soon So could these hybrids and their offspring become a new species? Until now, they have been considered more of a scientific curiosity, but they are receiving more attention as their numbers continue to rise. But asked whether they expect a new species of bear to arise any time soon, both Derocher and Lorenzen say, no.
It would take somewhere in the order of hundreds of thousands of years for a new species to arise, and it certainly could not occur within our life times, says Lorenzen. Country Denmark Related content. Why can some interbreeding species produce fertile offspring, while others—like horses and donkeys—cannot?
Grizzly–polar bear hybrid
Because they have more recent common ancestry. When geographical barriers—such as rising sea levels or retracting ice floes—separate populations, they may develop genetic, physiological, or behavioral differences ; changes in chromosome structure or number; differently shaped genitalia; or incompatible mating times and rituals—any of which can prevent successful reproduction. Take horses and donkeys, which probably diverged about 2.
- The truth about polar bears
- When polar bears and grizzlies breed, they can produce fertile offspring. Why can't other species?
- Grizzly-polar bear hybrids spotted in Canadian Arctic
Horses have 64 chromosomes, while donkeys have 62, and when they mate, their chromosomes don't pair up properly, inhibiting meiosis in their offspring. As a result, mules are sterile.
Grizzly-polar bear hybrids spotted in Canadian Arctic | ScienceNordic
Brown bears and polar bears, by contrast, evolved from the same ancestor only aboutyears ago—a relatively brief period—and have not developed significant genetic differences.
Advertisement The prevailing theory holds that polar bears diverged from brown bears at the end of the last ice age the Pleistocenewhen a population followed retreating ice northward. As they adapted to their new arctic home, the separated population lost the brown bear's hump and developed the polar bear's characteristic hair which is actually clearnarrower shoulders, longer neck, smaller head, and partially webbed toes.
Despite appearances, polar bears and grizzlies are still genetically quite similar. In fact, there are multiple instances of the two species successfully interbreeding in zoos.
The reason grizzlies and polar bears rarely interbreed in the wild is that, generally speaking, they don't cross paths during mating season. Barren-ground grizzlies live primarily on land, where they feast on caribou and berries, and mate from May to July; meanwhile, polar bears mate from April to June while hunting for seals along the sea ice. But four years ago, a sports hunter shot a male grizzly-polar bear hybrid near Banks Island just west of Victoria Islandproving that at least a couple of wild bears bridged their differences.