About two weeks ago, I blogged on how variation mtDNA was used to reconstruct an idea of Pleistocene population growth. That study was very remarkable because illuminated a large 5 fold increase in South Asian populations about 50,000 years ago. But we haven’t been able to use polymorphisms in autosomal loci to the same. A new paper in Molecular Biology and Evolution tries to figure out a way to overcome this limitation, by testing to see whether or not mitochondrial and Y chromosomal DNA show similarities in the spread of polymorphisms in populations that have experienced a recent increase in effective population size.
The paper, “Contrasting Signatures of Population Growth for Mitochondrial DNA and Y Chromosomes among Human Populations in Africa,” honed in a large sequence from the Y-chromosome and the cytochrome c gene in the mtDNA from 172 males from 5 African populations. Four different statistical tests were applied to test for population expansion: Fu’s Fs statistic, the R2 statistic, coalescent simulations, and the mismatch distribution.
The authors find,
“…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 5,000 years.”
- Pilkington, M.M., Wilder, J.A., Mendez, F.L., Cox, M.P., Woerner, A., Angui, T., Kingan, S., Mobasher, Z., Batini, C., Destro-Bisol, G., Soodyall, H., Strassmann, B.I., Hammer, M.F. (2008). Contrasting Signatures of Population Growth for Mitochondrial DNA and Y Chromosomes among Human Populations in Africa. Molecular Biology and Evolution, 25(3), 517-525. DOI: 10.1093/molbev/msm279