Mitochondrial DNA and Y-Chromosome Variation of Eastern Aleut Populations: Implications for the Genetic Structure and Peopling of the Aleutian Archipelago

Abstract

The Aleuts are the native inhabitants of the Aleutian archipelago off the southwest coast of Alaska and, since Russian contact in 1741, have experienced a series of demographic transitions. This study investigates the impact of historical events on the genetic structure of the Aleut population through analysis of mitochondrial and Y-chromosome DNA variation in five eastern Aleut communities in relation to previous molecular research conducted on communities located further to the west. Results from HVS-I sequencing and Y-SNP and Y-STR typing reveal patterns of variability that exhibit geographic differentiation in an east-west manner. Mitochondrial haplogroups A and D represent the two major maternal lineages observed in the Aleut samples, with haplogroup D more prevalent in the Pribilofs and island groups located to the west. This distribution pattern is likely the result of founder effect related to the forced population resettlements organized by Russian fur traders in the late 18th and early 19th centuries. In the eastern Aleutian Islands and lower Alaska Peninsula, higher frequencies of haplogroup A and its subclades were observed and based on archaeological and phylogeographic evidence may represent the genetic signature of sustained cultural and demic exchange with neighboring Eskimo and Na-Dene groups. The relationship between geography and mtDNA variation is further evident from the highly significant correlation of geographic and genetic distance matrices (r = 0.717) and the decreasing correlogram of spatial autocorrelation values that present a clinal pattern to mtDNA structure. For the Aleut Y-chromosomes, the vast majority were characterized to European haplogroups (approximately 85%), which contrasts the mtDNA picture that reveals only 6.1% non-native matrilines in the eastern region and thus indicating asymmetrical gene flow between European men and Aleut women. Russian paternal lineages are common in the western islands, whereas the predominantly Scandinavian patriline I1a is observed at elevated frequencies in the eastern communities, a consequence of the American purchase of Alaska and the subsequent influx of Scandinavian and US European fishermen into the region. The application of Monmonier's algorithm and genetic surface interpolations for both genetic systems reveal geographic zones of discontinuity at Umnak and Akutan Islands, underscoring the east-west substructure for the Aleut population. Lastly, phylogeographic analysis of mtDNA data and the results of recent ancient DNA studies suggest that subhaplogroup D2 evolved in Beringia and may represent the ancestral gene pool for both Paleo-Eskimos and Aleuts. Overall, this study identifies a significant relationship between geography and genetic variation in the Aleut population, with a distinct substructure along an east-west axis. These regional differences are due to a combination of historical founder effects, male-biased gene flow from European populations, and the peopling of the Aleutian Archipelago during the postglacial period.