Originally published as Genetics Published Articles Ahead of Print on July 29, 2007.
Genetics, Vol. 177, 469-480, September 2007, Copyright © 2007
doi:10.1534/genetics.107.074922
Distinctly Different Sex Ratios in African and European Populations of Drosophila melanogaster Inferred From Chromosomewide Single Nucleotide Polymorphism Data
Stephan Hutter*,1,
Haipeng Li*,
,
Steffen Beisswanger*,
David De Lorenzo*,2 and
Wolfgang Stephan*
* Section of Evolutionary Biology, Biocenter, University of Munich, 82152 Planegg-Martinsried, Germany and
Institute of Genetics, University of Cologne, 50674 Cologne, Germany
1 Corresponding author: Section of Evolutionary Biology, Biocenter, University of Munich, Grosshaderner Strasse 2, 82152 Planegg-Martinsried, Germany.
E-mail: hutter{at}zi.biologie.uni-muenchen.de
It has been hypothesized that the ratio of X-linked to autosomal sequence diversity is influenced by unequal sex ratios in Drosophila melanogaster populations. We conducted a genome scan of single nucleotide polymorphism (SNP) of 378 autosomal loci in a derived European population and of a subset of 53 loci in an ancestral African population. On the basis of these data and our already available X-linked data, we used a coalescent-based maximum-likelihood method to estimate sex ratios and demographic histories simultaneously for both populations. We confirm our previous findings that the African population experienced a population size expansion while the European population suffered a population size bottleneck. Our analysis also indicates that the female population size in Africa is larger than or equal to the male population size. In contrast, the European population shows a huge excess of males. This unequal sex ratio and the bottleneck alone, however, cannot account for the overly strong decrease of X-linked diversity in the European population (compared to the reduction on the autosome). The patterns of the frequency spectrum and the levels of linkage disequilibrium observed in Europe suggest that, in addition, positive selection must have acted in the derived population.
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Copyright © 2007 by the Genetics Society of America.