High rate of strong adaptation in Drosophila

In a study just published in Genetics and authored by Macpherson, J.M., Sella, G., Davis, J.C., and D. A. Petrov, we study the correspondence between divergence at protein-coding sites and neutral polymorphism using genomewide data from Drosophila simulans. We find that neutral polymorphism is both lower and less homogeneous where nonsynonymous divergence is higher and that the spatial structure of this correlation is best explained by the action of strong positive selection. We introduce a method to infer the rate and selective strength of adaptation. Our results independently confirm a high rate of adaptive substitution (~1/3000 generations) and newly suggest that many adaptations are of surprisingly great selective effect (~1%), reducing the effective population size by ~15% even in highly recombining regions of the genome.