A study suggests a key role for gene copy number changes in polar bear evolution. Polar bears and brown bears occupy distinct ecologies, despite having diverged comparatively recently--less than 500,000 years ago. Differences between individuals in the number of times a DNA segment repeats in a genome, known as copy number variation (CNV), can drive ecological adaptation over short time periods. To examine the extent to which polar bear/brown bear divergence was driven by CNV, John Gibbons and colleagues analyzed gene copy numbers in 17 individual polar bears and 9 brown bears. The authors identified nearly 200 genes whose copy numbers differed significantly between polar bears and brown bears. Nearly half of these genes encoded olfactory receptors. Other genes whose copy numbers differed between species include the gene for salivary amylase, an enzyme involved in digesting starch, and genes involved in fatty acid metabolism. The results suggest that copy number differences between the species reflect differences in dietary requirements between polar bears, which have a primarily carnivorous diet, and brown bears, which have an omnivorous diet. According to the authors, natural selection may have driven rapid gene copy loss in polar bears, playing an integral role in polar bear adaptation to the arctic environment.
Article #19-01093: "Polar bear evolution is marked by rapid changes in gene copy number in response to dietary shift," by David C. Rinker, Natalya K. Specian, Shu Zhao, and John G. Gibbons.
MEDIA CONTACT: John G. Gibbons, University of Massachusetts Amherst, MA; tel: 413-545-1025; e-mail: jggibbons@umass.edu
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Proceedings of the National Academy of Sciences