Viral-host co-evolution. The tree on the left shows observed viral sequence relationships [82, 91] and references therein) and the tree on the right represents host species relationships . FIV polymerase sequences (158 amino acids included in analysis) were analyzed phylogenetically from nine feline species representing six out of the eight feline lineages . Asterisks indicate significant bootstrap values (≥ 70%). The branch lengths are not in scale. Numbers next to node define estimated time of divergence for each the felid lineages and for the Felidae/Hyaenidae split in million years.