Beringian standstill and spread of Native American founders

Abstract

Native Americans derive from a small number of Asian founders who likely arrived to the Americas via Beringia. However, additional details about the initial colonization of the Americas remain unclear. To investigate the pioneering phase in the Americas we analyzed a total of 623 complete mtDNAs from the Americas and Asia, including 20 new complete mtDNAs from the Americas and seven from Asia. This sequence data was used to direct high-resolution genotyping from 20 American and 26 Asian populations. Here we describe more genetic diversity within the founder population than was previously reported. The newly resolved phylogenetic structure suggests that ancestors of Native Americans paused when they reached Beringia, during which time New World founder lineages differentiated from their Asian sister-clades. This pause in movement was followed by a swift migration southward that distributed the founder types all the way to South America. The data also suggest more recent bi-directional gene flow between Siberia and the North American Arctic.

Figure 1. Schematic representation of phylogeny of human mtDNA outside of Africa.

Branches encompassing Native Americans and their immediate Asian ancestral and sister lineages, represented by complete sequences, are shown in black with coalescence ages indicated and geographic location identified by colours. Lineages in brown correspond to the main haplogroups, found in Eurasia and Oceania, but absent in Native Americans. For complete phylogenetic tree see Supplementary figure 1.

Figure 2. Schematic illustration of maternal geneflow in and out of Beringia.

Colours of the arrows correspond to approximate timing of the events and are decoded in the coloured time-bar. The initial peopling of Berinigia (depicted in light yellow) was followed by a standstill after which the ancestors of the Native Americans spread swiftly all over the New World while some of the Beringian maternal lineages–C1a-spred westwards. More recent (shown in green) genetic exchange is manifested by back-migration of A2a into Siberia and the spread of D2a into north-eastern America that post-dated the initial peopling of the New World.