The most extreme values were observed for MT-ATP6, with 10 nonsynonymous and seven synonymous changes (pN/pS = 0.67), and MT-ND4, with one nonsynonymous and 20 synonymous changes (pN/pS = 0.02); when MT-ATP6 and MT-ND4 are removed from the analysis, the pN/pS ratios do not vary significantly among the remaining 11 genes (P = 0.23).