A Strange New Gene Pool of Animals Is Brewing in the Arctic
Scientists have seen the future and it is “grolar bears.”
The journey began in spring 2010, just as the sea ice surrounding the North Pole began its annual melt. Two bowhead whales, 50-foot-long behemoths that scour the Arctic seas for plankton, each started from their homes on opposite sides of North America—one in the Beaufort Sea north of Alaska, the other in Baffin Bay on the west side of Greenland. As the summer progressed, sea ice shrank (to its third-lowest cover in the last 30 years), and the whales swam toward each other through the now ice-free passage above the continent. Two independent teams of scientists from Canada and the United States watched the whales closely via satellite. “We were all pretty excited,” recalls Kristen Laidre, a biologist at the University of Washington and member of the U.S. team.
In September, in an inlet some 1,800 miles north of Fargo, North Dakota, where the North American landmass dissolves into the Arctic Ocean, the whales met in the middle. They spent two weeks together, and although not much happened before they turned around, the meeting was historic. The fossil record indicates the last time Pacific and Atlantic bowhead whales came into contact was at least 10,000 years ago.
In the last 40 years, the Arctic has warmed by about 3.5 degrees Fahrenheit, more than twice the overall global rise in that same period. Already grizzly bears are tromping into polar bear territory while fish like cod and salmon are leaving their historic haunts to follow warming waters north. One tangible result of the migration, scientists report, is that animals will learn to live with new neighbors. But polar biologists worry that animals could get a little too friendly with each other. With less ice clogging Arctic seas, whales are ranging farther; meanwhile, animals like seals that breed on the ice have fewer places to go. In both cases, the chances of encountering a different species jump. “All of a sudden, hybridization will skyrocket,” says Brendan Kelly, a polar ecologist at the National Science Foundation.
While it’s tempting to imagine a strange new Arctic teeming with “grolar bears” and “narlugas,” hybridization comes at a cost.
The first confirmed cross between a polar bear and a grizzly bear—a white bear with brown patches—was documented in 2006; genetic analysis of a second, found in 2010, revealed that its mother was also a hybrid, suggesting that more instances are happening under scientists’ radar. In 2009, a biologist at the National Marine Mammal Laboratory photographed a probable bowhead/right whale hybrid in the Bering Sea. More hybrids are possible. Kelly and his coauthors have counted 34 opportunities for hybridization across 22 Arctic or near-Arctic species, based on the animals’ genetic compatibility and geographic range. The list includes potential hybrids of ringed and ribbon seals, Atlantic walrus and Pacific walrus, and beluga whales and narwhals.
While it’s tempting to imagine a strange new Arctic teeming with “grolar bears” and “narlugas,” hybridization comes at a cost. Arctic biodiversity will be reduced through gradual consolidation, taking with it a blend of genes that have evolved by natural selection over millennia. “There’s going to be a whole bunch of organisms containing genes that we’re going to lose,” Kelly says. Which genes, exactly, is unclear.
A hybrid’s success, like any organism’s, hinges on its fitness to its environment. Because the Arctic is changing rapidly, it’s hard to predict which traits will be most important for, say, a population of grolar bears. Merging features of two well-adapted parent species might help hybrids cope with shifting conditions. But more often than not, Kelly thinks, genetic incompatibilities in hybrids will erase traits crucial to the long-term survival of both parent species. If that happens, he says, “then we can expect a great reduction in those populations, and possibly extinctions.”
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