In previous research, I found that many of the genes for multicellularity in the volvocine green algae appear to have evolved very early in the transition between unicellular and multicellular life history (preliminary results from the genomic analysis of Gonium pectorale). The exception is the evolution of regA, a gene which regulates somatic cells in a multicellular species, Volvox carteri. Given the importance of the evolution of division of labor (i.e., cellular differentiation in the evolution of multicellularity), understanding the evolutionary history of genes regulating somatic cells is critical to understanding the evolution of multicellularity.
In order to understand the evolutionary history of regA in the volvocine algae, we have investigated the presence of regA in divergent species of Volvox (V. ferrisii and V. gigas, see below). Using the presence of regA in other species of Volvox, particularly V. ferrisii (see below), we argue that regA evolved early in the volvocine algae though after the Gonium lineage split from the Eudorina-Volvox clade (see right). The ancestor in which regA likely evolved is predicted to not have somatic cells, suggesting an alternative selection pressure for regA. This result is similar to the current view of volvocine genomics, where the genetic basis for multicellularity largely evolved before the phenotypes thought to arise from these genes. Because the common ancestor of V. ferrisii and V. carteri is predicted to have given rise to multiple lineages with and without somatic cells, this suggests a more complex relationship between somatic cells and fitness than previously appreciated (see right). This research raises a number of questions, including under what evolutionary and ecological conditions would species with the genetic potential for soma not evolve somatic cells, and how many pathways are available for the volvocine algae to regulate somatic cells.