Quantifying Adaptive Evolution in the Drosophila Immune System
The estimated number of adaptive substitutions per non-synonymous site between D. melanogaster and D. simulans, for 131 immune genes (A; red) and 265 control genes (B; blue). The mean and variance is higher for immune genes than control genes: 0.011 vs. 0.006 (p = 0.022) and 0.00054 vs. 0.00026 (p = 0.018) respectively, though the modes are extremely similar (the modal class in both (B) and (C) is centred on zero [−0.003,0.003]). (C) shows number of adaptive substitutions per non-synonymous site, plotted against gene length. We used a in place of α for this analysis because α is poorly estimated for single genes (see Materials and Methods).