Expert: Expect "a Lot More" Arctic Hybrids
Polar biologist Brendan Kelly has been studying Arctic pinnipeds -- seals, sea lions, and walruses -- for more than thirty years. His interest in marine mammal hybrids grew out of a simple question: What happens when the Arctic ice melts? Bruce Barcott recently interviewed Kelly at his office at the University of Alaska at Fairbanks. Barcott is writing about changing Arctic food webs for our Spring 2011 print issue.
Are the hybrids you describe in your new Nature paper (see "Grolar Bears and Narlugas: Rise of the Arctic Hybrids") just "Ripley’s Believe It Or Not" freaks?
Some people may say these are just a few freaks. Others will say the sky is falling. What we’re saying is that these are a few of the many examples of hybridization happening among marine mammals in the Arctic right now. It fits with what we would expect as a result of the rapid change in Arctic habitat. This sort of hybridization may be happening with more frequency, and we should pay attention.
Why the Arctic? Why now?
For terrestrial mammals, oceans are a barrier to dispersal and gene flow. Continental drift separated mammals in South America from those in Africa, and they evolved on different tracks. But for marine mammals, it’s the other way around. Continents are barriers, oceans are corridors. And in the case of Arctic species, you’ve had a continent-size mass of sea ice keeping species isolated for thousands of years.
And if the ice continues to melt?
If you remove that sea ice barrier, you can re-establish contact. Right now, the sea ice is melting quite rapidly. So we’re suddenly going to see a lot of previously isolated populations come back into contact -- and we’re likely to see a lot more hybridization.
Does the existence of "grolar" bears come as a surprise?
Grizzlies and polar bears have mated in captivity and produced fertile offspring, so we knew that it could happen. But the polar-grizzly hybrid confirmed earlier this year was a second-generation hybrid. DNA tests found that its mother was a hybrid, and its father was a grizzly. That clearly indicates that this particular hybrid combination is fertile in the wild, and this may have been going on for a matter of decades, if not longer. These are very long-lived animals, and the second-generation hybrid bear wasn’t a cub.
Is hybridization a form of adaptation to climate change? Is this how evolution happens?
Yes and no. Sometimes the parent species remain, and hybridization leads to a new third species. But sometimes the final loss of an endangered species happens when it’s absorbed into the gene pool of a more populous species. The danger here is that the rate of environmental change in the Arctic may proceed faster than these long-lived, slow-reproducing mammals can adapt from generation to generation. With a fast-reproducing organism like bacteria, they’re producing many generations per minute. They can adapt to changes pretty fast. With a long-lived mammal, it takes decades for them to produce the number of generations it takes for a genetic response. With walruses, seals, whales, or polar bears, the time necessary for adaptive response -- what we think of as evolution -- may not be there.