Mitochondrial DNA Diversity and its Determinants in the Southwest Pacific

Abstract

The purpose of this study is to examine mitochondrial DNA variation in the Southwest Pacific and determine what factors contribute to the degree and patterning of the observed variation. Population variation is known to be influenced by factors including demographic history, natural selection, climate, isolation, island area/complexity, and population age, as older populations are generally more diverse. The groups compared are from three regions in the Southwest Pacific; (a) northeast New Guinea, (b) Manus in northern Island Melanesia and (c) Easter Island in eastern Polynesia. MtDNA surveys have revealed highly significant differences in molecular variance across these populations. According to traditional biogeographical theory, the likely determinants of these differences are (a) length of time since initial settlement, (b) the comparative isolation of particular islands or regions since settlement, and (c) the size and complexity of settlement areas. Evidence from archaeology and linguistics provides the necessary framework for the study. Detailed archaeological surveys for several of the study regions provides evidence for settlement dates as well as evidence for isolation and/or frequent contact with other areas, usually in the form of trade and translocation of animals and artifacts. Linguistics, though not as informative as archaeology for settlement dates, provides detailed evidence for isolation and/or contact in the form of language isolates, language families, borrowing and linguistic divergence. The mtDNA haplogroups found in this study belong to several documented haplogroups, some of Melanesian origin, and some of Southeast Asian origin. The distribution of mtDNA variants and the pattern and degree of variation was examined using Analysis of Molecular Variance, standard diversity measures and partial Mantel matrix correlations. There were strong positive correlations between insular area, isolation and degree of variation. There were also measurable differences between inland and coastal populations on the larger islands where diversity in the isolated inland populations was greater than diversity in the coastal population. While there was some confounding of the variables, the results of our analysis indicate that insular area/complexity and isolation influence the pattern of variance more than length of settlement time.