Figure 6

Origin and duplication of 2DBD-NRs in metazoans. A. Deduction from traditional view of metazoan phylogeny. The common ancestor of 2DBD-NR originated from DBD duplication in a common bilaterian ancestor (red branch). The fact that 2DBD-NRs are present in both Acoelomates and Coelomates supports this view. Star indicates duplication event(s). B. Deduction from the molecular view of metazoan phylogeny. The common ancestor of 2DBD-NR might originate in a common Protostome ancestor (red branch). The fact that 2DBD-NRs are present in both Ecdysozoa and Lophotrochozoa supports this view. Another possibility is that 2DBD-NR might originate in a common ancestor of the Bilateria and was lost in the Deuterostome lineage after the split of Protostomes and Deuterostomes (blue branch). Ac: Acoelomates, Ar: Arthropoda, B: Bilateria, C: Chordates, Ce: Caenorhabditis elegans, Cn: Cnidarians, Co: Coelomates, De: Deuterostomes, Dp: Daphnia pulex, Dr: Drosophila, E: Ecdysozoans, Ec: Echinoderms, Lg: Lottia gigantean, Lo: Lophotrochozoans, M: metazoa, Pl: Platyhelminths, Po: Poriferans, Pr: Protostomes, Ps: Pseudocoelomates, Se: Schmidtea mediterranea, Sm: Schistosoma mansoni, Ec: Echinoidea. indicates 2DBD-NR, the number of indicates the number of 2DBD-NRs found in that taxon.