M2 PhyloMap. (A) The PhyloMap for 2016 M2 protein sequences. Each spot in the plot corresponds to one sequence, and the first two dimensions represent 44.9% of the total variation. The phylogenetic tree mapped onto the plot is shown in (B). The mapping error is 0.013. The strain names that stand for the numbers in the plot are shown in the phylogenetic tree in (B). (B) The NJ tree of M2 protein sequences built using distances inferred by the JTT model, 40 sequences have been selected by PhyloMap as data centers, the other 2 sequences (in bold italics) have been added manually. This tree has been mapped onto the PCoA result as shown in (A). Bootstrap values (1000 replications) for key nodes are shown.