Fig. 2

Phylogenetic relationships between USPs in the Platyhelminthes. The maximum-likelihood phylogenetic tree (method aLRT-SH for branch support, see text for more details) shows several USP sequences shared by platyhelminthes and annelids, referred as ancestral USP genes (highlighted in yellow). On the other hand, the Trematoda and Cestoda (highlighted in green) classes show species-specific expansions and losses (one asterisk indicates losses in the Taeniidae family; while two asterisks represent losses in the genus Echinococcus). For simplification (and to facilitate associations with Fig. 1), we grouped the Cestoda sequences according to the IDs of E. granulosus based on the ortholog relationship (see Additional file 1: Table S1). Gene names are in italic. Prefix species are as follow: CapteP for C. teleta, HelroG for H. robusta, Gsa for G. salaris, Mli for M. lignano, SMU for S. mediterranea, Smp for S. mansoni, Csin for C. sinensis, TsM for T. solium, HmN for H. microstoma, and EgrG for E. granulosus. The number in parenthesis beside SMU and Mli correspond to the number of collapsed sequences in S. mediterranea and M. lignano, respectively. The USPs clustered in the chromosome (see Fig. 1) are also grouped together in the phylogenetic tree, suggesting an origin by subsequent tandem duplications. Identical sequences from M. lignano (~ 35) were excluded in the analysis. Three molluscs (L. gigantea, C. gigas, and O. bimaculoides) and two annelids (H. robusta and C. teleta) were used as outgroups. A minor ID for M. lignano and G. salaris was used (Additional file 1: Table S5). For an extended tree, see Additional file 3: Figures S1 and S2. Branch support values obtained by Bayesian Inference are in bold font. Only values with a branch support greater than 0.7 are showed