Figure 2

Evolutionary rate. Number of nucleotide substitutions compared to the oldest strain in each lineage is plotted. Evolutionary rates are calculated from the slope of the tangent of a simple regression line (number of substitutions/site/year), for canine/equine (A), swine (B), avian (C), and human (D). Correlation coefficient (r) was estimated using the Pearson correlation. Reference strains are A/chicken/Brescia/1902(H7N7) for Av1, A/turkey/Massachusetts/3740/1965(H6N2) for Av2, A/equine/Miami/1/1963(H3N8) for CE, A/Brevig Mission/1/1918(H1N1) for Hu1 and Hu2, A/swine/Iowa/15/1930(H1N1) for Sw1, and A/swine/Netherlands/25/80(H1N1) for Sw2. Mean and 95% confidence interval (shown in parentheses) are calculated by SPSS.