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, 95 (15), 9047-52

Testing Migration Patterns and Estimating Founding Population Size in Polynesia by Using Human mtDNA Sequences

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Testing Migration Patterns and Estimating Founding Population Size in Polynesia by Using Human mtDNA Sequences

R P Murray-McIntosh et al. Proc Natl Acad Sci U S A.

Abstract

The hypervariable 1 region of human mtDNA shows markedly reduced variability in Polynesians, and this variability decreases from western to eastern Polynesia. Fifty-four sequences from New Zealand Maori show that the mitochondrial variability with just four haplotypes is the lowest of any sizeable human group studied and that the frequency of haplotypes is markedly skewed. The Maori sequences, combined with 268 published sequences from the Pacific, are consistent with a series of founder effects from small populations settling new island groups. The distributions of haplotypes were used to estimate the number of females in founding population of New Zealand Maori. The three-step simulation used a randomly selected founding population from eastern Polynesia, an expansionary phase in New Zealand, and finally the random selection of 54 haplotypes. The results are consistent with a founding population that includes approximately 70 women (between 50 and 100), and sensitivity analysis shows that this conclusion is robust to small changes in haplotype frequencies. This size is too large for models postulating a very small founding population of "castaways," but it is consistent with a general understanding of Maori oral history as well as the results of recent canoe voyages recreating early trans-oceanic voyages.

Figures

Figure 1
Figure 1
Distribution of distances between pairs of individuals within Polynesian populations and within Melanesia. From left to right for each set, New Zealand Maori, other eastern Polynesians, western Polynesians, and Melanesians. There is decreasing mitochondrial diversity going from Melanesia to New Zealand Maori and a bimodal distribution.
Figure 2
Figure 2
Distribution of distances within: New Zealand Maori; all other Polynesians; Asians; Africans; and the Turkana of East Africa. (A few (≈6%) of the values of differences between Turkana sequences are not shown, lying between 17 and 20 bases.) Maori and Turkana were similar medium-sized populations but have, respectively, the lowest and highest mitochondrial diversity of populations studied at present.
Figure 3
Figure 3
Effect of the founding maternal population size on the expected number of haplotypes for the New Zealand Maori sample. The size of the founding population from eastern Polynesian is indicated on the x axis; the y axis shows the frequency of 20,000 simulations that the indicated number of alleles (–10) are present in a sample of 54 sequences after the founding population has expanded to 50,000 females is on the y axis. The estimated founding population size on this criterion is 40–90 females to give four haplotypes as observed.
Figure 4
Figure 4
The frequency, relative to founding maternal population size, of final samples with a highly unequal distribution of four haplotypes (two haplotypes occur only once in the 54 sequences). Larger founding population sizes are more likely to lead to an unequal distribution of haplotypes, and the estimated founding population size is now ≈70 (50–100) females. The 95% confidence interval on a one-tailed test excludes a founding population size of less than ≈50 (see Table 3).

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