Characterizing recurrent positive selection at fast-evolving genes in Drosophila miranda and Drosophila pseudoobscura

Characterizing the distribution of selection coefficients in natural populations remains a central challenge in evolutionary biology. We resequenced a subset of 19 fast-evolving protein-coding genes in the sister species Drosophila miranda and D. pseudoobscura and their flanking regions to characterize the spatial footprint left by recurrent and recent selection. Consistent with previous findings, fast-evolving genes and their flanking regions show reduced levels of neutral diversity compared with randomly chosen genes, as expected under recurrent selection models. Applying a variety of statistical tests designed for the detection of selection at different evolutionary timescales, we attempt to characterize parameters of adaptive evolution. In D. miranda, fast-evolving genes generally show evidence of increased rates of adaptive evolution relative to random genes, whereas this pattern is somewhat less pronounced in D. pseudoobscura. Our results suggest that fast-evolving genes are not characterized by significantly different selection coefficients but rather a shift in the distribution of the rate of fixation.