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Melting Arctic ice heralds new polar hybrids: Pizzlies and more

A pizzlie is a cross between a polar bear and a grizzly bear, and this new hybrid animal may foreshadow as many as 34 hybrids to come as Arctic ice melts, say scientists.

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Chromosomes that are unmatched in number cannot pair during meiosis, a special type of cell division necessary for sexual reproduction. During meiosis, chromosomes duplicate and the cell divides to form daughter cells, which split apart to form gametes, or mature sexual reproductive cells. But with unmatched chromosomes, the split into gametes would be uneven, creating sterility.

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Over the short term the hybrid offspring from these Arctic animal matings will likely be strong and healthy, because unlike inbreeding, which magnifies deleterious genes, so-called outbreeding can mask these genes. Most of these genes are recessive, meaning the offspring need a pair to actually show the trait. Different species or different genera generally don't have the same bad recessive alleles, and so there's not a high chance of a pair turning up. (Alleles are different versions of the same gene.)

But over time, as the hybrids mate randomly, those harmful genes will come out of hiding and make the offspring less fit and less capable of surviving, Whiteley warned.

Kelly said that breeding between species usually isn't beneficial when it's caused by accelerated environmental change, because the hybrid animals don't have time to evolve survival traits. "This change is happening so rapidly that it doesn't bode well for adaptive responses."

For instance, a cross between a narwhal and a beluga whale spotted in Greenland lacked the narwhal's spiral tusk, which contributes to breeding success. The polar–grizzly hybrid bears in a German zoo showed behaviors associated with seal hunting, but not the strong swimming abilities of polar bears.

Animals already threatened with extinction could take a hit from hybridization. The breedings between the North Pacific right whale, whose numbers have fallen below 200, and the more numerous bowhead whale, could push the former to extinction. (Over time, the hybrids would begin to outnumber the sparse right whales.)

Climate Crisis

"This is one of the consequences of the rapid changes we're inducing in that environment and one more reason to consider whether we really want to continue warming the climate as rapidly as we are," Kelly told LiveScience.

The Arctic Ocean may lack summer ice by the end of the century, "removing a continent-sized barrier to interbreeding," the researchers wrote. As such, Kelly and his collaborators urge scientists to model the prevalence and outcomes of hybridization, genetically monitor at-risk populations, and generate a priority list.

And they're pushing policy-makers to incorporate hybrids into their management and protection plans. Currently, the Endangered Species Act doesn't protect hybrid animals, Kelly said. "It's just not something that has been on people's radar screen, and we think it should be."

IN PICTURES: Hybrid animals

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