Analysis of mitochondrial DNA diversity in the aleuts of the commander islands and its implications for the genetic history of beringia

Abstract

The Aleuts are aboriginal inhabitants of the Aleutian archipelago, including Bering and Copper (Medny) Islands of the Commanders, and seem to be the survivors of the inhabitants of the southern belt of the Bering Land Bridge that connected Chukotka/Kamchatka and Alaska during the end of the Ice Age. Thirty mtDNA samples collected in the Commanders, as well as seven mtDNA samples from Sireniki Eskimos in Chukotka who belong to the Beringian-specific subhaplogroup D2, were studied through complete sequencing. This analysis has provided evidence that all 37 of these mtDNAs are closely related, since they share the founding haplotype for subhaplogroup D2. We also demonstrated that, unlike the Eskimos and Na-Dene, the Aleuts of the Commanders were founded by a single lineage of haplogroup D2, which had acquired the novel transversion mutation 8910A. The phylogeny of haplogroup D complete sequences showed that (1) the D2 root sequence type originated among the latest inhabitants of Beringia and (2) the Aleut 8910A sublineage of D2 is a part of larger radiation of rooted D2, which gave rise to D2a (Na-Dene), D2b (Aleut), and D2c (Eskimo) sublineages. The geographic specificity and remarkable intrinsic diversity of D2 lineages support the refugial hypothesis, which assumes that the founding population of Eskimo-Aleut originated in Beringan/southwestern Alaskan refugia during the early postglacial period, rather than having reached the shores of Alaska as the result of recent wave of migration from interior Siberia.

Figure 1

Map of the Bering Sea region, showing locations of the Commander and Aleutian Islands

Figure 2

Lineage D2 sequence variation in Aleuts and Siberian Eskimos. “M” is macrohaplogroup M, which is shared by all of the Aleut and Eskimo mtDNA samples. Four diagnostic variants for haplogroup D mtDNAs are underlined. These were inferred through comparisons with four complete sequences (three Native Siberian and one Native American mtDNA) belonging to haplogroup D lineages other than D2, as well as with the data given by Herrnstadt et al. (2002). Asterisks (*) indicate the Aleut-specific 8910A transversion. Only those nucleotide positions that differ from the Cambridge Reference Sequence (Andrews et al. 1999) are shown. Mutations are transitions, unless specified explicitly. The Aleuts were sampled in the Commanders, and the Eskimo sample consists of Sireniki Eskimos from the Chukchi Peninsula. Note that site 8683 AluI+, reported by Starikovskaya et al. (1998), was incorrectly mapped and, instead, is 8700 AluI+ (because of transitions at nps 8701 and 8703).

Figure 3

Schematic phylogenetic representation of the sequence types, numbered from I to XIV. The sizes of the circles (Aleuts) and squares (non-Aleuts) are proportional to the number of individual mtDNA samples. The 8910A mutation is a transversion. The rest of the mutations are transitions. The founding sequence type (VIII) for lineage D2 is shown in the square with a bold outline.

Figure 4

Intraspecific phylogeny of haplogroup D, rooted with the macrohaplogroup M haplotype as an outgroup, which, in turn, has been inferred from the complete sequences of Siberian haplogroup C, D, Z, and G mtDNAs and an American Indian D mtDNA sample. The complete sequences of three Siberian and one Native (Central) American used for phylogenetic reconstructions are as follows—Ulchi number 1: 73, 195, 263, 489, 750, 1438, 2706, 3010, 4769, 4883, 4907, 5178A, 7028, 8414, 8701, 8860, 9077, 9540, 10398, 10400, 10646, 10873, 11719, 12705, 13812, 14016, 14668, 14766, 14783, 15043, 15301, 15326, 16093, 16223, 16232, 16290, 16362; Ulchi number 2: 73, 263, 489, 750, 961, 1438, 2706, 3010, 3336, 3644, 4769, 4883, 5048, 5178A, 7028, 8269, 8414, 8701, 8860, 9540, 10398, 10400, 10873, 11719, 12705, 13879, 14668, 14766, 14783, 15043, 15236, 15301, 15326, 16223, 16278, 16325, 16362, 16519; Nganasan: 73, 239, 263, 297, 489, 722, 750, 951, 1438, 2706, 3010, 4023, 4769, 4883, 5178A, 6374, 7028, 8020, 8414, 8701, 8860, 9540, 9785, 10181, 10398, 10400, 10873, 11719, 12705, 14034, 14668, 14766, 14783, 15043, 15301, 15326, 15440, 15951, 16223, 16319, 16362; and Native American: 73, 263, 489, 750, 1438, 2092, 2706, 3010, 4769, 4883, 5178A, 7028, 8414, 8701, 8860, 9540, 9966, 10398, 10400, 10873, 11092, 11719, 12705, 13879, 14459, 14668, 14766, 14783, 15043, 15301, 15326, 16223, 16291, 16325, 16362, 16519. Mutation positions, relative to the Cambridge Reference Sequence (Andrews et al. 1999), are transitions unless the base change is specified.