Abstract
The transition from unicellular to multicellular organisms is not a well understood process in evolution. A common trait often associated with multicellularity is cellular differentiation, which is a separation of tasks through the division of labor. Using mathematical models of population dynamics, and phylogenetic analyses, I focus on the possible evolutionary paths leading to terminal differentiation in cyanobacteria. I show evidence indicating that multicellularity evolved early in the cyanobacterial lineage. Furthermore, in line with studies indicating that group or spatial structure are ways to evolve cooperation and protect against the spread of cheaters, the results I discuss provide theoretical and phylogenetic evidence that differentiated single-celled populations of cyanobacteria are not stable. The compartmentalization afforded by multicellularity is required to maintain the vegetative/heterocyst division of labor and for selection to optimize the carrying capacity. Hence in cyanobacteria, multicellularity is a necessary condition for both the evolutionary stability of terminal differentiation and for the optimization of the division of labor. I will also discuss some ecological conditions that would favor either differentiated or undifferentiated developmental strategies.
Prof. Homayoun C. Bagheri, University of Zurich