We compared the selection profiles on protein coding genes of genotypes I and II, which include strains that are circulating in the face of homotypic vaccination pressure (designated as the vaccinerelated group), and genotypes III-VII (designated as the nonvaccine-related strains) (Table 3) . Overall, the global rate of nonsynonymous to synonymous substitutions (dN/dS) for all protein coding genes were less than 1, indicating purifying selection has been the major driving force in the evolution of class II aPMV-1 viruses. There were no codons identified to be under positive selection in M and L genes in either group (Table 3) . However, there was a clear difference in the codon based selection profiles of N, P, F and HN genes between the vaccine-and nonvaccinerelated groups. In the vaccine-related group, only the surface protein encoding genes, F and HN, had positively selected codons. Both groups had a single site identified in F; these were at codon 115 within the F 0 cleavage site for the vaccine-related group and codon 28 in the signal peptide for the nonvaccine-related group. There were 3 positively selected sites identified in the HN gene in the vaccine-related group and one in the non vaccine-related group. In contrast, the P gene of nonvaccine-related genotypes III-VII had three sites predicted to be under positive selection but no sites were identified in the vaccine-related group. Thus, selection is focused on HN in vaccine-related groups and on P in nonvaccine- 