Natural selection and correlated evolution of substitution rates and allelic variation in the DRB1*03 lineage of primates. The interspecific relationship between non-synonymous (dN) and synonymous (dS) substitution rates at the a) ABS contact residues and b) ABS non-contact residues. c) The association between non-synonymous (dN) substitution rate at the ABS and allelic variation of the lineage (the number of alleles when the number of animals were held constant). Each data point represents the polymorphism of the DRB1*03 lineage in different species, and was obtained from the appropriate statistical model (see text) that considers the phylogenetic relatedness of species. Symbols represent different taxonomical groups of primates. Solid line is the regression line laid on the entire dataset; dotted line is the regression line that is obtained for New World primates only; dashed line indicates y = x. For illustration; we also included data from human (HLA-DRB1*03, HLA-DRB1*11, HLA-DRB1*12, HLA-DRB1*13 and HLA-DRB1*14 combined; data were subtracted from the IMGT/HLA database, http://www.ebi.ac.uk/imgt/hla/). We could not add human data to c), because the number of individuals screened for the 324 detected alleles is unknown and thus relative allele numbers cannot be calculated.