Metric dental diversity of Ryukyu Islanders: a comparative study among Ryukyu and other Asian populations

Abstract

Mesiodistal and buccolingual crown diameters were examined to describe and compare patterns of metric dental variation in five modern samples from the Ryukyu Island chain (Miyako, Ishigaki, Tokunoshima, and two samples from Okinawa Island). Principal component analysis applied to two separate datasets, raw measurement and standardized (C-score) data, for 32 Asian and Pacific samples, including the five Ryukyu Islander series, produced an overall size factor and three shape factors (relative size of mesiodistal diameters versus buccolingual diameters and two kinds of front-back polarity). Ryukyu Islanders have similar crown dimensions as those of the predominant eastern Asian groups, characterized by mesodont dentition. In terms of shape factors, Ryukyu Islanders are distinctive among eastern Asian population groups on the one hand, and show diversity among themselves on the other hand. The inter-regional variation of Ryukyu Island groups estimated by F st falls within the range of 4-6% of the total variance, which is greater than those of Arctic population samples (Aleuts and Eskimos). The average within-group variance of the Ryukyu Island series measured by the R-matrix method (intra-regional variation) is compatible with those of East and Northeast Asians, Micronesians, and Polynesians. These findings suggest that differential patterns of long-term gene flow from an outside source, geographical isolation, and genetic drift in each island of the Ryukyu Island chain has produced the morphological diversification of modern Ryukyu Islanders.

Craniometric divergence history of the Japanese populations

“…The Ryukyu Islanders were also considered probable descendants of the Jomon people according to the "dualstructure model"; however, successive Japanese migration and/or genetic contribution from the south probably contributed to phenotypic changes leading to the recent Ryukyu Islanders (Hatta et al, 1999;Fukumine et al, 2006). Because of the northeastern continental scope of the present study, no comparative samples from southeastern Asia were included so that hypotheses of genetic contribution to the Ryukyu Islanders could not be specified; however, the greater phenotypic variance seen in the Ryukyu Islanders in this study (Table 2) and other studies Toma et al, 2007;Komesu et al, 2008) supports a possible external genetic contribution in the Ryukyu Islanders.…”

“…The Yayoi immigrants showed clear modern East Asian features (Nakahashi and Li, 2002). Although the basic approach of this model is quite valid, the dual-structure hypothesis is too simple to explain the population history for all of the Japan Islands Toma et al, 2007); in particular, after the Yayoi immigration to the Japanese main islands, the people of the Okhotsk culture came from northeastern Asia to the Sakhalin and Hokkaido Islands during the 5th-12th centuries AD (Kikuchi, 1999;Amano, 2003). Archeological evidence and isotopic analysis show that the Okhotsk culture had developed a considerable maritime infrastructure (Yoneda, 2002).…”

Effects of an Asian-specific nonsynonymous EDAR variant on multiple dental traits

“…We also used specimens from 73 individuals from the Sakishima Islands, the western islands of Okinawa, that had also participated in previous studies (Japanese set 3). 14,34,35 All the subjects gave informed consent for their participation in this study. This study was conducted with the approval of ethical committees of the Showa University, the Pusan National University and the University of the Ryukyus.…”

A comparative study of craniofacial measurements between Ryukyuan and mainland Japanese females using lateral cephalometric images

“…The craniofacial morphology of ancient and modern people in the Japanese archipelago has been well studied (von Baelz, 1911;Ikeda, 1974;Brace and Nagai, 1982;Hanihara, 1991;Ishida, 1992;Pietrusewsky, 1999;Dodo et al, 2000;Higa et al, 2003;Fukumine et al, 2006;Haneji et al, 2007;Toma et al, 2007;Fukase et al, 2012;Miyazato et al, 2014). Such studies have revealed that craniofacial features, including dental characteristics, show regional differences even within Japan, especially between the mainland Japanese, Ryukyu Islanders, and Ainu.…”