Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution (original) (raw)
Figure 4
Simulated admixture reveals the direction of gene flow on the X chromosome.
(A) Pairwise distance as in Figure 2 but limited to the 12 scaffolds identified as X-chromosome. (B) 100 replicate simulations in which 6.5% of the female West Hudson Bay polar bear X-chromosome is replaced with that of the mainland Alaska brown bear in randomly inserted 20 kb fragments, simulating admixture from the brown bear genome into polar bear ∼50kya. Pairwise differences are calculated between the simulated genome (light brown lines; mean highlighted in dark brown) and the plot comparing the two female polar bears (blue line), to maximize the number of informative sites in the test. The addition of brown bear DNA to the polar bear genome markedly increases the number of high-diversity bins (>10 differences/10 kb), indicating that any introgression of brown bear DNA into polar bears should be easily detectable. (C). As in (B), but with 6.5% of the mainland Alaska brown bear X-chromosome is replaced with that of the female West Hudson Bay polar bear. In this instance, we find no difference between the simulated (blue lines) and real (brown line) data.