Co-evolution of foamy viruses (FVs) and their mammalian hosts. (A) FV Bayesian phylogeny (left) is compared to that of their hosts (right, previously published in ). Curved branches indicate outgroups. Numbers on branch nodes are Bayesian posterior probabilities. Solid lines between the two trees indicate FV-host associations. FV and host phylogeny scale bars are in units of amino-acid substitutions per site and million years, respectively. Weak support for the sister-taxon relationship of RhiFV and PSFVaye (dotted branches, posterior probability = 0.56) was inferred. Among 17 FV and host sequences, 3 apparent mismatches have been inferred using co-phylogenetic reconstruction. Branches corresponding to FV-host co-evolution were identified and used in FV-host divergence correlation analysis (B). Branch lengths of FV tree and host divergence time were determined to have a linear correlation with a statistically strong support for its coefficient (linear regression: N = 23, R2 = 0.823, p = 3.48E-8), represented by the solid red line. Dotted lines represent the 95% confidence interval of the estimated linear relationship. Outliers determined by Cook’s distances (solid dots), including the bovine foamy virus (BFV) branch (red), the ChrEFV branch (green), and the ancestral branch leading to the exafroplacentalian FVs (blue), were not included in the linear regression. The colors of the outliers correspond to the colors of the branches in A.