Polar bears diverged from brown bears more rapidly than initially thought

Analysis of 89 complete genomes of polar bears showed that the species diverged from brown bears more recently than initially thought, according to a study published in Cell¹. 

By comparing nuclear genomes of polar bears from Greenland with those of brown bears from other areas, the study reveals that the two species diverged approximately 400,000 years ago.

“In this short 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,” says Rasmus Nielsen, a computational biologist from the University of California, Berkeley, who led an international team that included Jun Wang from King Abdulaziz University, Jeddah.

The team found that polar bears living in Arctic regions adapted to a high-fat diet, primarily consisting of seals and their blubber, in fewer than 20,500 generations. During the evolution of polar bears there were mutations in genes related to blood coagulation, heart development and adipose tissue development. The study reports that: “Such a drastic genetic response to chronically elevated levels of fat and cholesterol in the diet has not previously been reported.”

 

The researchers add that the adaptive changes in the polar bear’s APOB gene – which encodes apolipoprotein B, the lipid-binding protein that facilitates entry of cholesterol into cells – has enabled them to cope with a high-fat diet by clearing cholesterol from the blood.