セミクジラ
Recently, scientists have begun to notice that the warming Arctic Ocean and land is resulting in changed distribution of species with the result of breaking down climate barriers that have prevented hybridization between closely related species. The most reported examples have been the three confirmed grizzly–polar bear hybrids. In 2010, a team led by National Marine Mammal Laboratory ecologist Brendan Kelly counted 34 possible hybridizations between distinct populations or species of Arctic marine mammals, many of which are endangered or threatened. These observed hybridizations included in 2009, a cross between a bowhead whale and a North Pacific right whale in the Bering Sea. Kelly stated that "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.)" Co-author Andrew Whitely wrote: "Breedings between these marine mammals near the North Pole are likely to result in fertile offspring, because many of these animals have the same number of chromosomes...[and] 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 ... 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."