Genes Reveal how Polar Bears Can Survive on High-Fat Diet
In a genetic analysis published Thursday in the journal Cell, an international team of scientists unveiled the reasons why polar bears, eating their fill of blubbery marine mammals, can survive a high-fat diet.
Researchers compared the polar bear genome to that of its closest relative, the brown bear. They found that the polar bear is a much younger species than previously believed, having diverged from brown bears less than 500,000 years ago.
Since this separation of ways, polar bears have undergone remarkable genetic changes related to cardiovascular function and fatty acid metabolism permitting the high-fat diet they need in their native, frigid Arctic conditions.
Unlike humans, they can tolerate such a high-fat diet without worrying about clogging their arteries and developing heart disease. Scientists may be able to learn how to prevent fat-related heart disease in humans.
"For polar bears, being very fat is no problem," Eline Lorenzen, a molecular ecologist at the University of California, Berkeley, told Reuters.
In fact, fat is a key to their survival. In the Arctic regions where they live, fat is a key source of their energy needs - up to half their body weight can be fat. And without regular access to fresh water, they rely on metabolic water - water that is a by-product of the breakdown of fat in the body, Lorenzen said.
"They essentially live in a polar desert," Lorenzen added.
Nursing cubs also rely on milk from their mothers that can be up to 30 percent fat, the news release notes.
Researchers deciphered the genome of the polar bear based on blood and tissue samples from 79 polar bears from Greenland. They also used samples from 10 brown bears as a comparison.
Some previous estimates had placed the origin of polar bears as long as 5 million years ago, but now it seems it was much more recent.
"In this short amount of time, polar bears have adapted to the cold environment of the Arctic and to a new diet. We see the footprints of this adaptation in the genome of the polar bear," evolutionary geneticist Rasmus Nielsen told Reuters.
There are only 20,000 to 25,000 polar bears worldwide, and climate change is melting the ice they depend on. They may need to rely on their genes, arguably which also gave polar bears the ability to swim long distances.