Number of R7 core genes and strain-variable ORFs placed at different nodes of the species tree. The relative proportions of R7 core genes (open boxes) and strain-variable open reading frames (ORFs; black boxes) are indicated at each node of the tree. Arrows show the nodes that contain the majority of core genes (ROW*) and strain-variable ORFs (R8). Species abbreviations are as in Figure 3, plus Ot (O. tsutsugamushi), wMel (W. pipientis [Drosophila melanogaster]), and wBm (W. pipientis [Brugia malayia]). The underlying phylogenetic tree was constructed using the maximum likelihood method from a concatenated alignment of adenylate kinase, SecY, and ribosomal proteins S3, S8, S10, S11, S13, S14, S19 and L2, L3, L4, L5, L6, L14, L16, L18, L22, L23, L24 and L29.