Population genomics reveals historical divergence and local adaptation
in polar bears
Abstract
Single-nucleotide polymorphisms (SNPs) have numerous advantages over
microsatellites, including greater power to infer population structure
and history and to detect loci undergoing selection. Here, we conduct
the first continental-level SNP study of polar bears (Ursus maritimus)
using genotypes from an array of 5441 SNP loci genotyped in 16–30 polar
bears sampled in each of 16 geographic regions in Canada and West
Greenland. Our study aimed to assess population history and genetic
structure and to identify evidence of adaptive loci. Using these data,
we confirmed the existence of four broad-scale genetic clusters in North
America (FCT = 0.035) and identified nine fine-scale subclusters using
more powerful spatial methods. An assessment of historical patterns of
migration suggests that polar bears migrated into North America from the
Beaufort Sea after the last glacial maximum. Using a conservative
approach, we identified 17 loci that may represent adaptive variation,
including one SNP in the 3’ untranslated region of PDLIM5 (PDZ And LIM
Domain 5), a gene involved in cardiovascular function, which has
undergone substantial selection in polar bears since their divergence
from brown bears. Outlier loci differentiated the Norwegian Bay genetic
cluster more strongly from remaining clusters than did our complete
dataset, suggesting possible adaptive differences in the High Arctic.
Through careful consideration of SNP loci, sample inclusion, and
analytical approaches, we provide a comprehensive picture of polar bear
population structure at a continental level. This study provides a model
for the analysis of wide-ranging species that can contribute to their
conservation and management.