One of the most well-known animals, the polar bear, is a newcomer on the world stage, according to research published in the Proceedings of the National Academy of Sciences. By studying the DNA of an ancient polar bear jawbone uncovered in 2004 in Norway scientists have for the first time pinpointed the time when the polar bear split from its closest relative, the brown bear.
“Our results confirm that the polar bear is an evolutionarily young species that split off from brown bears some 150,000 years ago and evolved extremely rapidly during the late Pleistocene, perhaps adapting to the opening of new habitats and food sources in response to climate changes just before the last interglacial period,” says Charlotte Lindqvist, PhD, research assistant professor in the UB Department of Biological Sciences and lead author on the paper.
 Polar bear with carcass. Photo courtesy of the USGS. |
By comparing the DNA of the 110,000 to 130,000-year-old ancient polar bear fossil to DNA of modern polar bears and brown bears, researchers were able to sequence the mitochondrial genome of the fossil. The work resulted in the oldest mammal mitochondrial genome yet sequenced.
“The fact that our ancient polar bear lies almost directly at the splitting point between this unique group of brown bears and polar bears, that is, close to their most recent common ancestor of the two species, was very intriguing. It provided an ideal opportunity to ultimately settle the time of polar bear origin,” Lindqvist says.
The timing of the appearance of the polar bear reveals some interesting points about the world’s biggest land carnivore’s history. For instance, the polar bear survived past climatic changes. However, researchers caution not to assume past adaptability will save the polar bear in today’s warming world.
“We have found that polar bears actually survived the interglacial warming period, which was generally warmer than the current one,” Lindqvist explains, “but it’s possible that Svalbard might have served as a refugium for bears, providing them with a habitat where they could survive. However, climate change may now be occurring at such an accelerated pace that we do not know if polar bears will be able to keep up. The polar bear may be more evolutionarily constrained because it is today very specialized; morphologically, physiologically and behaviorally well-adapted to living on the edge of the Arctic ice, subsisting on a few species of seals.”
Øystein Wiig, polar bear expert and co-author at the University of Oslo’s Natural History Museum, says that the fossil jawbone was a particularly lucky find.
“Very few polar bear fossils have been found, leading to widely varying estimates of exactly when and how polar bears evolved,” he explains. “Because polar bears live on the ice, their dead remains fall to the bottom of the ocean or get scavenged. They don’t get deposited in the sediments like other mammals.”
Citation: Charlotte Lindqvist, Stephan Schuster, Yazhou Sun, Sandra Talbot, Ji Qi, Aakrosh Ratan, Lynn Tomsho, Lindsay Kasson, Eve Zeyl, Jon Aars, Webb Miller, Ólafur Ingólfsson, Lutz Bachmann, and Øystein Wiigd. Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear. PNAS.
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