MBE Advance Access published online on December 18, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm279
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Research Article |
Contrasting Signatures of Population Growth for Mitochondrial DNA and Y Chromosomes among Human Populations in Africa
1 Department of Anthropology, University of Arizona, Tucson AZ 85721
2 ARL Division of Biotechnology, University of Arizona, Tucson AZ 85721
3 Department of Biology, Williams College, Williamstown MA 01267
4 Department of Ecology and Evolutionary Biology, University of Arizona, Tucson AZ 85721
5 Department of Animal and Human Biology, University La Sapienza, Rome, Italy
6 Human Genomic Diversity and Disease Research Unit, National Health Laboratory Service and University of the Witwatersrand, Johannesburg, South Africa
7 Department of Anthropology, University of Michigan, Ann Arbor MI
Corresponding Author: Michael Hammer, ARL Division of Biotechnology, University of, Arizona, Tucson, AZ 85721 USA. Email: mfh{at}u.arizona.edu; Phone: (520) 621-982; Fax: (520) 626-8050
A history of Pleistocene population expansion has been inferred from the frequency spectrum of polymorphism in the mitochondrial DNA (mtDNA) of many human populations. Similar patterns are not typically observed for autosomal and X-linked loci. One explanation for this discrepancy is a recent population bottleneck, with different rates of recovery for haploid and autosomal loci as a result of their different effective population sizes. This hypothesis predicts that mitochondrial and Y chromosomal DNA will show a similar skew in the frequency spectrum in populations that have experienced a recent increase in effective population size. We test this hypothesis by re-sequencing 6.6 kb of non-coding Y chromosomal DNA and 780 basepairs of the mtDNA cytochrome c oxidase subunit III (COIII) gene in 172 males from five African populations. Four tests of population expansion are employed for each locus in each population: Fu's Fs statistic, the R2 statistic, coalescent simulations and the mismatch distribution. Consistent with previous results, patterns of mtDNA polymorphism better fit a model of constant population size for food-gathering populations and a model of population expansion for food-producing populations. In contrast, none of the tests reveal evidence of Y chromosome growth for either food-gatherers or food-producers. The distinct mtDNA and Y chromosome polymorphism patterns most likely reflect sex-biased demographic processes in the recent history of African populations. We hypothesize that males experienced smaller effective population sizes and/or lower rates of migration during the Bantu expansion, which occurred over the last five thousand years.
Key Words: population growth • Homo sapiens • sub-Saharan Africa • mtDNA • NRY • hunter-gatherer