Study reveals new genomic roots of ecological adaptation in polar bear evolution

How natural selection shaped gene copy numbers

Date:  June 17, 2019

Source:  University of Massachusetts at Amherst

Scientists from the University of Massachusetts Amherst, Vanderbilt University and Clark University have shed new light on the genomic foundation of the polar bear's ecological adaption by pinpointing rapid changes in the bear's gene copy numbers in response to a diet shifting from vegetation to meat.

In a paper published Monday, June 17 in the Proceedings of the National Academy of Sciences and chosen for the cover of PNASVol. 116, issue 27, John G. Gibbons and Ph.D. student Shu Zhao of UMass Amherst, David C. Rinker of Vanderbilt and Natalya K. Specian of Clark discuss the first population-level study to characterize genome-wide patterns of copy number variation (CNV) in the polar bear and brown bear.

CNV refers to differences among individuals in the number of copies of a particular portion of the genome, and the study's results suggest this variation played an important role in the adaptation of polar bears to the Arctic.

"This research addresses a big-picture evolutionary question of how diet shapes the genome," explains Gibbons, assistant professor of food science.

Since the brown or grizzly bear (Ursus arctos) and polar bear (Ursus maritimus) diverged less than 500,000 years ago, the polar bear has evolved unique traits to adapt to the Arctic climate and ecology, such as a camouflaging coat of pigment-free fur. Previous population genomic studies of polar bears and brown bears analyzed single-nucleotide polymorphisms, or changes in a single base pair in a DNA sequence.

"CNVs were traditionally harder to detect so they weren't always analyzed," Gibbons says. "With recent advances in DNA sequencing technologies over the last 15 years or so, computational approaches to detect and quantify CNVs from genomic data have been developed. The polar bear data gave us a nice opportunity to fill in the gap."

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