Meeting Abstract

S1-12  Friday, Jan. 4 15:00 - 15:30  The distinct evolutionary trajectories of C4 and CAM photosynthesis EDWARDS, Erika J; Yale University

Evolutionary convergence provides a special opportunity to dissect the environmental and organismal context surrounding the repeated origins of similar features. Often times, convergence itself is phylogenetically patterned, with certain lineages having evolved particular characteristics multiple times, while other lineages never have. C4 and CAM photosynthesis are two plant adaptations that are remarkably convergent, together evolving hundreds of times, and mostly within the last 10 million years. They stand as exceptional model systems for understanding the repeated evolution of complex phenotypes, and in understanding the phylogenetically clustered nature of this convergence. In this talk I will highlight what we have learned about the evolution of C4 and CAM syndromes, focusing on the increasingly predictable stepwise evolutionary integration of anatomy, biochemistry, and molecular optimization. I propose a general model that explains and unites C4 and CAM evolutionary trajectories, and also highlights some key differences in their dynamics. Available data suggest that in both C4 and CAM evolution, it is the anatomical rather than biochemical modifications that act as the “macroevolutionary bottleneck” in each trajectory. In the case of C4, I'll argue that the anatomical changes precede the assembly of a new biochemical cycle, whereas in CAM the biochemistry is assembled in relatively unspecialized tissue, and the anatomical bottleneck occurs subsequently. Whether this bottleneck occurs early or late in the evolutionary assembly of a new phenotype may have profound implications for the distribution of certain adaptations across the Tree of Life.