Bidirectional dispersals during the peopling of the North American Arctic

It is thought that Paleo-Inuit were the first people that settled the American Arctic about 5000 BP (before the present) from a migration that crossed Beringia from Northeast Asia. It is theorized that this group initially migrated to the North Slopes of Alaska and subsequently expanded eastward, eventually reaching Greenland. A second circumpolar dispersal of Neo-Inuit from the North Slopes associated with the Thule-Inuk culture has been postulated to have extended eastward around 800 BP, totally replacing the original Paleo-Inuit without admixing. Although generally accepted, this migration scenario is incompatible with previously reported indications of east to west gene flow across the American Arctic. Here we report on the Y-chromosome haplogroup and Y-STR diversity of the four circumpolar populations of the Tuva Republic (N = 24), Northeast Siberia (N = 9), Bethel, Alaska (N = 40), and Barrow, Alaska (N = 31). Four haplogroup lineages (Q-NWT01, Q-M3, Q-M346, and Q-M120) were detected, Q-NWT01 and Q-M3 being the most abundant at 11.11 and 66.67% in Northeast Siberia, 32.50 and 65.00% in Bethel, and 67.74 and 32.26% in Barrow, respectively. The same samples genotyped for Y-chromosome SNPs were typed for 17 Y-STYR loci using the AmpFlSTR Yfiler system. Age estimates and diversity values for the Q-NWT01 and Q-M3 mutations suggest extensive movement of male individuals along the entire longitudinal stretch of the American circumpolar region. Throughout the entire region, Q-M3 exhibits a west to east decreasing gradient in age and diversity while Q-NWT01 indicates the opposite with older TMRCA and higher diversity values running from east to west with the most recent estimates in Canada and Alaska. The high age and diversity values in Greenland are congruent with an origin of the Q-NWT01 mutation in the east of the circumpolar range about 2000-3000 ya. This scenario is incompatible with a complete biological replacement starting about 700 BP of Paleo-Inuit like the Dorset by the Thule-Inuit (Neo-Inuit), as is currently thought, and more parsimonious with gene flow carrying the NWT01 mutation from a pre-Thule population to the ancestors of the present-day Inuit.