Fig. 6

Schematic representation of proposed evolution of TNF signaling in platyhelminths. Here, we hypothesize that an ancestor free-living platyhelminth displayed genes that code for TNF receptor (represented by green sticks) and TNF ligand (represented by orange spheres). The event of parasitism implicated in the substitution of the platyhelminth TNF ligand by the host TNF causing the loss of the coding gene for the former. Probably the loss of the TNF ligand is ancestral, occurring at the base of the monophyletic branch of parasitic platyhelminths. X axis represents a putative temporal line and Y axis in the right represents the conservation level of DD (from the most conserved at the bottom to the lowest conserved at the top)