Population Genomics Reveal Recent Speciation and Rapid Evolutionary Adaptation in Polar Bears

Polar bears are uniquely adapted to life in the High Arctic and have undergone drastic physiological changes in response to Arctic climates and a hyperlipid diet of primarily marine mammal prey. We analyzed 89 complete genomes of polar bear and brown bear using population genomic modeling and show that the species diverged only 479–343 thousand years BP. We find that genes on the polar bear lineage have been under stronger positive selection than in brown bears; nine of the top 16 genes under strong positive selection are associated with cardiomyopathy and vascular disease, implying important reorganization of the cardiovascular system. One of the genes showing the strongest evidence of selection, APOB, encodes the primary lipoprotein component of low-density lipoprotein (LDL); functional mutations in APOB may explain how polar bears are able to cope with life-long elevated LDL levels that are associated with high risk of heart disease in humans. [Display omitted] [Display omitted] •de novo assembly of a polar bear reference genome•Polar bears and brown bears diverged only ca. 400,000 years ago•Genes on the polar bear lineage have been under stronger selection than brown bears•Strong selection in polar bears restructured metabolic and cardiovascular function Strong selection in genes related to fatty acid metabolism, pigmentation, and cardiovascular function are found in the polar bear genome, reflecting the unique adaptations of polar bears to the extreme High Arctic compared to brown bears.