Figure 4 .
Levels of nonsynonymous and synonymous DNA polymorphism among populations. DNA diversity for nonsynonymous mutations (scaled to DNA diversity for synonymous mutations) is plotted against DNA diversity for synonymous mutations (an estimate of population size). πS is a proxy for population size if mutation rates are similar among the species compared. Note that statistical analyses of such data must account for the contribution of πS to both axes (Piganeau and Eyre-Walker 2009; Elyashiv et al. 2010). Common symbols in each plot indicate the same set of genes compared among species. Data are shown for taxa for which six or more independent populations have been sampled for ≥20 nuclear genes. See Table S1 for species names, sample numbers, number of loci, and references (as well as data for a more limited number of Drosophila species).