Polar bear genomics

Abstract

Rasmus Nielsen, Eske Willerslev, Jun Wang and colleagues have performed a population genomics study of polar bears to gain insights into their evolutionary history and the genetic mechanisms underlying their adaptation to the Arctic environment (Cell 157, 785–794, 2014). The authors generated a de novo assembly of the polar bear genome through deep sequencing of a single polar bear and obtained population diversity data by performing lower-depth sequencing of 79 polar bears and 10 brown bears. From these data, they estimate that polar bears diverged from brown bears roughly 400,000 years ago, with continuous gene flow from polar bears into North American brown bears since their divergence. They also looked for genomic signatures of adaptation and found evidence that genes associated with cardiovascular function and adipose tissue development have evolved under strong positive selection in the polar bear population. The strongest signature of positive selection was found at APOB, which encodes a protein important for the transport of lipids in blood and their uptake by cells. They also found signatures of positive selection at two pigmentation genes that might underlie the phenotype of white coat color in polar bears.