mtDNA synonymous diversity (πs) and substitution rate. Open circles and dotted regression line are for mammals (n = 123), close circles and solid regression line for birds (n = 46). Substitution rates are in log-transformed and are in unit of substitution per third codon position per million years.
Nabholz et al. BMC Evolutionary Biology 2009 9:54 doi:10.1186/1471-2148-9-54