Abstract
An important goal of population genetics is to determine the forces that have shaped the pattern of genetic variation in natural populations. We developed a maximum likelihood method that allows us to infer demographic changes and detect recent positive selection (selective sweeps) in populations of varying size from DNA polymorphism data. Applying this approach to single nucleotide polymorphism data at more than 250 noncoding loci on the X chromosome of Drosophila melanogaster from an (ancestral) African population and a (derived) European, we found that the African population expanded about 60,000 y ago and that the European population split off from the African lineage about 15,800 y ago, thereby suffering a severe population size bottleneck. We estimated that about 160 beneficial mutations (with selection coefficients s between 0.05% and 0.5%) were fixed in the euchromatic portion of the X in the African population since population size expansion, and about 60 mutations (with s around 0.5%) in the diverging European lineage.
Highlights
A long-standing interest in evolutionary biology has been to estimate the rate of adaptive substitution
It has been found that positive selection could play a role in the human-chimpanzee lineages [3] and that as much as 45% of all amino-acid substitutions have been fixed by natural selection in Drosophila [4]
We found that the level of genetic polymorphism of a locus is significantly positively correlated with divergence between D. melanogaster and D. simulans (Figure 2)
Summary
A long-standing interest in evolutionary biology has been to estimate the rate of adaptive substitution. Since only few beneficial mutations with strong selection coefficients exist (Figure 5), we suggest that recent strong selection (affecting genetic polymorphism within multiple windows) does not affect the estimated rate of adaptive substitution. We confirmed this by checking the pattern of polymorphism in the African population along an 11-Mb region with densely spaced loci (from Fin114 to Fin432; see [16,18]). More selection events may be needed to explain the larger discrepancies Despite these caveats, our estimated rates of strong adaptive substitutions are only slightly lower than the published rate (0.092 3 10À9 per site per generation [4]), which was obtained by averaging over a long time period (since the divergence of D. melanogaster and D. simulans). Considering the fact that the published rate [4] takes relatively weak selection into account, our results may indicate an accelerated rate of adaptation in both populations due to recent environmental changes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
