BEAST inference 4: refining estimates for tMRCA(Neudoerfl-Hypr) Due to its sampling, the E_161 alignment allows access to the antiquity of additional divergence events. Posteriors obtained from BEAST inference 3 were included as priors, with an additional uniform prior distribution over [7.28610 25 -6.29610 24 substitutions/site/year] set on the meanRate parameter. This value reflects previously observed substitution rates for the E gene in the Tick-borne encephalitis virus: the lower bound comes from the value of 7.28610 25 substitutions/site/year estimated for nonsynonymous substitutions [38] , while the upper bound comes from an estimation of 4.78610 24 substitutions/site/year with a standard error of 1.51610 24 [39] for synonymous substitutions. Because the analysis of selection pressure (see results) inferred that a strong purifying selection acts on the proteins, we expect to see higher rate of synonymous substitutions than of nonsynonymous substitutions. As the mean rate takes both types of substitutions into account, its estimate should be intermediate between their two values.