Non-metric dental variation of Sakishima Islanders, Okinawa, Japan: a comparative study among Sakishima and neighboring populations

Abstract

Twenty-four non-metric tooth crown traits of Miyako and Ishigaki Islanders, from the southernmost Ryukyu Islands, were investigated and compared with those of neighboring populations. The frequency of double-shoveling in Sakishima samples, and especially, Ishigaki Island, is lower than that found among Atayal people (Taiwan) and main-island Japanese. The frequencies of protostylid and cusp 6 in Miyako and Ishigaki Islanders are comparable to those in Hokkaido Ainu and lower than in main-island Japanese and Atayal. Miyako and Ishigaki Islanders, as well as other Ryukyuans, are basically more similar to main-island Japanese than to Ainu, while being situated between main-island Japanese and Ainu in terms of both mean measure of divergence (MMD) and R-matrix methods. However, Ishigaki and Miyako Islanders are relatively close to Hokkaido Ainu among Ryukyu people and main-island Japanese, as suggested in some previous preliminary studies. The estimated Fst (the ratio of among-group variation to total variation), using an average heritability rate = 0.55 for the non-metric tooth crown traits used in this study, displayed low levels of interregional variation, as already indicated in analyses of genetic, cranial and dental metric data. Meanwhile, the relatively large diversity of Ryukyu Islanders based on Fst suggested long-term isolation or poor intra-island contact among the Ryukyu Islands. The lower observed variation compared with the expected variation in most Ryukyu samples may reflect a greater degree of genetic drift in the Ryukyu Island chain.

Genome-Wide SNP Analysis Reveals Population Structure and Demographic History of the Ryukyu Islanders in the Southern Part of the Japanese Archipelago

“…Indeed, relatively few studies have examined the population structure of the inhabitants of the Ryukyu Islands to date. However, of the studies that have been undertaken, some have reported the existence of local variations in morphological and genetic characteristics (Naito 1976;Omoto et al 1976;Haneji et al 2007;Toma et al 2007;Matsukusa et al 2010). However, the population structure within the Ryukyu Islands remains unclear due to a lack of comprehensive data and due to incompatibilities between the findings of previous studies.…”

Nonmetric dental characteristics of the early modern population of Okinawa Island in Nansei Islands, Japan

“…However, not all studies have supported the Ainu‐Ryukyu common origin theory. Many studies do not support the theory from the viewpoint of somatology (Suda, 1950; Terakado, 1976; Ikeda & Tagaya, 1980), craniometry (Hsü, 1948; Ikeda, 1974; Tagaya and Ikeda, 1976; Pietrusewsky, 1994, 1999, 2004; Doi et al , 1997; Doi, 1998, 2003, 2004; Asato & Doi, 1999), cranial nonmetric traits (Mouri, 1986; Dodo, 1992; Dodo et al , 1998, 2000), dental morphology (Manabe et al , 1999a, 1999b, 2001, 2003a, 2008; Higa et al , 2003; Haneji et al , 2007), mitochondrial DNA (Horai et al , 1996), and the human leukocyte antigen (HLA) gene (Hatta et al , 1999; Tokunaga, 2003). Thus, even among studies involving similar methods, no consensus has been reached with regard to the genealogical position of the Nansei islanders in the Japanese archipelago and East Asia.…”

A Common Variation in EDAR Is a Genetic Determinant of Shovel-Shaped Incisors

“…For this purpose, plaster casts of permanent dentition ( Figure 1A) were obtained from 102 individuals at Showa University Dental Hospital, Tokyo, and from 100 individuals in Sakishima Islands (Miyako and Ishigaki), the southernmost Ryukyu Islands (Figure 2). 27,28 The Sakishima subjects were selected as individuals who had no ancestor derived from other regions for at least three generations. We also collected a blood, buccal mucosa, or saliva specimen from each individual to prepare a DNA sample.…”

“…To reduce the metric data to a small number of dimensions, we applied a principal-component analysis (PCA) with the data for 751 Japanese individuals (375 males and 376 females) from Honshu, Okinawa, and the Sakihima Islands. 27,28,30 The procedure is as follows: the metric dental data, from which missing values were removed, were standardized for each sex. Then, merging the standardized data of both sexes, we created a correlation-coefficient matrix.…”