Phylogenetic stability of gag subgroups without phylotypes 10–14. The gag Neighbor-Joining tree contains sequences representing 16 of 21 gag phylotypes identified in Figure 2. Numbers located at outer taxonomic units represent phylotype designations. Numbers at internal nodes of the trees represent bootstrap values. Yellow and blue shaded regions represent subgroups 1 and 2, respectively. The scale bar represents substitutions per site.