Jomon: Paleolithic Contingent in Modern Japanese Mar 27, 2018 18:47:13 GMT
Post by Admin on Mar 27, 2018 18:47:13 GMT
Regional classification of the population sample sites. Geographic locations of the sites are indicated by black dots. Numbers in parentheses denote the numbers of samples from each site that were successfully analyzed
As described earlier, previous morphological studies have indicated possible regional differences in the Ainu people. These studies divided Hokkaido Island in several different ways. Among them, Dodo et al. (2012) explicitly explained their particular system of division as follows. The area that is southwest of Ishikari Low Land (southwestern Hokkaido, classified by the dashed line in Figure 3) often shared the same culture as the northern part of Honshu since the Jomon era. Moreover, the influence of the Kofun culture of northern Honshu, which played an important role in the formation of the Satsumon culture, extended into this area. Therefore, this area is expected to have been genetically more influenced by the mainland Japanese than the other areas of Hokkaido. On the other hand, the area along the coast of the Sea of Okhotsk was intensively inhabited by the Okhotsk culture people; therefore, their influence is expected to be more evident in this area. The other area is considered to be less influenced by mainland Japanese and the Okhotsk people, and is expected to have retained the characteristics of the indigenous Jomon people. We adopted this classification and analyzed the observed haplogroups in each region and their frequencies to elucidate the regional differences of the Ainu. However, the number of samples from along the coast of the Sea of Okhotsk that were successfully analyzed was small (seven individuals from four sites, see Figure 3), so we combined this area with the central area and analyzed this as “northeastern/central Hokkaido.”
Aside from the Hokkaido Jomon and the Okhotsk culture people, the populations inhabiting the neighboring area of Hokkaido are expected to have contributed to the establishment of the Ainu. Therefore, to elucidate the regional differences of the haplogroups observed in the Edo Ainu, we classified them into four types as follows: (1) Hokkaido Jomon type (the haplogroups that are observed in the Hokkaido Jomon); (2) Okhotsk type (the haplogroups that are observed in the Okhotsk culture people, but are absent from the Hokkaido Jomon); (3) mainland Japanese type (the haplogroups that are absent from the Hokkaido Jomon and the Okhotsk culture people, but are observed in modern-day mainland Japanese at higher frequencies than in modern-day native Siberians); and (4) Siberian type (the haplogroups that are absent from the Hokkaido Jomon and the Okhotsk culture people, but are observed in modern-day native Siberians at higher frequencies than in modern-day mainland Japanese). Based on the frequencies of these four haplogroup types, regional differences of the Ainu between southwestern Hokkaido and northeastern/central Hokkaido were examined by Fisher's exact probability test by using R version 3.4.1 (R Core Team, 2017).
Genetic characteristics of the Ainu mtDNAs
Twenty-one haplogroups and their subhaplogroups were identified in 94 Edo Ainu individuals (Supporting Information Table S1). As described earlier, conventionally, the Ainu are considered to be descended from the Hokkaido Jomon people, with little admixture with other populations. Among the haplogroups observed in the Hokkaido Jomon (N9b1, N9b4, N9b*, D4h2, G1b*, M7a2, M7a*; Adachi et al., 2011), haplogroups N9b1, G1b*, and M7a2 are also observed in the Edo Ainu. Above all, haplogroup N9b1, which is the most frequently observed haplogroup in the Hokkaido Jomon people (55.6%, 30 of 54 individuals; Adachi et al., 2011), is also observed at a relatively high frequency (20.2%, 19 of 94 individuals) in the Edo Ainu. These findings indicate the genetic continuity between the Hokkaido Jomon and the Ainu. This possible genetic continuity is corroborated by Y chromosome DNA analysis of the modern Ainu. Y chromosomal DNA haplogroup D1b, which is considered to be a strong candidate for the Jomon paternal lineage, was observed at high frequency in the modern Ainu (Hammer et al., 2006; Tajima et al., 2004).
However, there is a crucial difference between the Hokkaido Jomon people and the Ainu. Four haplogroups (N9b4, N9b*, D4h2, M7a*) are missing in the Edo Ainu, whereas they have 19 haplogroups that are not observed in the Hokkaido Jomon. This raises questions about the conventional hypothesis that the Ainu are the direct descendants of the Hokkaido Jomon people.
To clarify the matrilineal genetic relationship between the Edo Ainu and the other populations, pairwise Fst values between each pair of populations (Supporting Information Table S2) were calculated from the mtDNA haplogroup frequencies of the Edo Ainu and the 14 ancient and modern-day East Asian and Siberian populations (Table 1, Figure 1). In the frequency-based clustering of compared populations determined by neighbor-joining based on the Fst values described earlier, the Ainu of the Edo era was located almost in the median center between the Hokkaido Jomon/Udegey cluster and the Lower Amur region cluster including the Okhotsk culture people (Figure 4). This confirmed our hypothesis (Adachi et al., 2011) that the genetic characteristics of the Ainu are based on the Hokkaido Jomon people and the subsequent input of Lower Amur region Siberian genes through the Okhotsk culture people. However, when examining in detail the haplogroups observed in the Ainu examined in the present study, haplogroups M7a1, M7b1a1a1, D4 (except for D4h2), M8a, Z1a, M9a, F1b, N9a, A5a, and A5c are observed neither in the Hokkaido Jomon nor in the Okhotsk culture people. This suggests the presence of populations other than the Hokkaido Jomon and the Okhotsk culture people that contributed to the formation of the Ainu. Mainland Japanese and the native Siberians are considered to be the major candidates for the origin of these haplogroups because of the proximity of their distributions to Hokkaido.