Genetic diversity within and between bear species.

<p>(A) Pairwise differences between individuals estimated as the average number of differences per 10 thousand bases (kb) in 42,000 non-overlapping 50 kb regions. After strict quality filtering, within-sample heterozygosity was resolved by selecting a single, high-quality base at random. The Lancaster Sound polar bear showed an excess of postmortem damage, as expected for historic specimens <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003345#pgen.1003345-Green2" target="_blank">[32]</a>, and is shown in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003345#pgen.1003345.s001" target="_blank">Figure S1</a>. Polar bears are remarkably homogenous compared to brown bears, and both polar bears and brown bears are approximately equally diverged from the American black bear. Consistent with the results of the <i>D-</i>statistic test, pairwise distance between the ABC Islands brown bear and all polar bears (yellow lines) is less than that between the mainland brown bear and all polar bears (red lines). (B) Schematic diagram of a representative gene tree within brown bear, polar bear, and black bear populations, with the present day at the left of the diagram. For this locus, admixture occurring more recently than the population divergence of polar bears leads to the introgression of a polar bear haplotype into brown bears. Estimate of average genomic distance for brown, black, and polar bears and for population divergence between brown bears and polar bears given different calibration points are provided in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003345#pgen-1003345-t001" target="_blank">Table 1</a>.