Figure 2. Reconstructed Spatial Diffusion Pathways of Brown and Polar Bear Matrilines over the Last 120,000 Years.

Map indicating the 13 locations to which each matriline was assigned and the 14 significant diffusion pathways that describe the maternal phylogeographic history of brown bears and polar bears over the last circa 120 kya. For the phylogeographic analyses, we assigned all polar bears to a single geographic location, depicted here as Svalbard. Nonreversible diffusion rates are estimated across the entire distribution of posterior trees and therefore reflect average rates of diffusion over time. Rates are considered to be significantly different from zero with Bayes factor (BF) > 8. The significant diffusion pathways are shown in pink, with increasing significance indicated by darker shades and arrows indicating the direction of diffusion. An interactive visualization of the diffusion process of the ancestral bear matrilines over time is available at http://www.phylogeography.org/BEARS.html. Figure S2 describes the results of two sensitivity analyses performed to assess the phylogeographic results depicted here and in Figure 1.