Matthew Herron (University of Montana)
Abstract. The transition to multicellular life was one of a few major events in the history of life that created new opportunities for more complex biological systems to evolve. Indeed, multicellularity is a prerequisite for the evolution of large, complex organisms such as plants and animals. An understanding of the ecological conditions and evolutionary mechanisms that favor this key innovation is necessary to determine where and with what likelihood complex life may have arisen beyond Earth. I address the evolution of multicellularity using both retrospective (comparative) and prospective (experimental) approaches, both using green algae of the volvocine clade as a model system. The comparative results comprise the most detailed reconstruction of a Major Transition currently available. The experimental results include de novo origins of simple (undifferentiated) multicellularity in two separate experiments in a species that has not had multicellular ancestors. Furthermore, the form of multicellularity observed differs substantially between experiments, suggesting that the particulars of the transition to multicellular life depend not only on the nature of the unicellular ancestor, but on the specific selective pressures driving the transition as well.