Brief description of models.

aIn the models specified with the suffix “F”, equilibrium codon frequencies are assumed to be equal to codon frequencies in codon sequences. dGm[rs], i.e., dGmr or dGms, means that the variation of mutation rate or selective constraint over site is approximated by a discrete gamma distribution with m categories [32], respectively; means no variation and the suffix dG1[rs] is omitted.