Figure 4. Putative emergence of mutations resulting in observed amino acid substitutions at positively selected codons.

Possible historic occurrence of relevant point mutations at sites ¤24; ¤144, ¤147; ¤221, and ¤222 is indicated by tandem nucleotide triplets with a nucleotide change in one codon position. > stands for direction of change. Single triplets between branching points indicate maintenance of unchanged sequence. Nucleotide triplets refer to tree branches below (horizontal lines) or at right hand side (vertical lines). Lineage labels with sign * represent majority of designated lineage members, with one or more individual strains showing different amino acid (or just different codon). Most latter strains are also labelled with coloured symbols to mark separation from lineage. Note that on many occasions there are multiple possible evolutionary pathways of which only a single hypothetical alternative is presented.