Figure 2.

Phylogenetic distribution, evolutionary scenarios and models of regulation of regA. (a) Simplified volvocine phylogeny (adapted from [18]) showing the distribution of RLS1/rlsD and the regA cluster (red, blue and green indicate species that are unicellular, multicellular with no soma and multicellular with soma, respectively). (b) Scenarios for the co-option of an environmentally regulated ancestral RLS1/rlsD into a developmentally regulated regA by (i) replacing the environmental regulation or (ii) adding the developmental regulation. (c) Models for the dual regulation of regA involving either shared components of the ancestral signalling pathway or the evolution of a parallel pathway (RE-regulatory elements); adapted from [20].