Hybridization between related species is frequently observed in the wild and sometimes leads species to adaptation to a new environment. The brown bear (Ursus arctos), distributed widely in the Northern Hemisphere, is known to have hybridized with some related species, such as the polar bear (Ursus maritimus) and cave bear. However, its timing and scale are still unclear due to the complex demographic history resulting from the multiple hybridization and dispersals.
In this study, we analyzed whole-genome resequencing data of Ursidae to investigate (1)When, (2)Where, and (3)How much hybridization has occurred between the brown bear and related species. Our phylogenetic analysis showed incomplete lineage sorting, possibly caused by male-biased migration. ƒ4 statistics and ƒ4 ratio indicated that the brown bears in North America, Hokkaido, and Etorof islands have hybridized with polar bears more than Far Eastern individuals distributed between North America and Hokkaido. In addition, hybridization between brown bears of West Asia and Kazakhstan, and Caucasus cave bears was also possible. These patterns could be formed due to not only the difference in which species the brown bear hybridized with but also the difference in male-biased dispersal during the last glacial period.