Morphological and functional diversification during kelp evolution

Kelps are highly successful ecosystem engineers that substantially increase the productivity of nearshore ecosystems, forming nursery habitat for other species. Despite the importance of kelps to the modern ecology of temperate ecosystems, we have a limited understanding of their evolutionary relationships, the diversification dynamics that led to their modern distributions, and the factors that determine where they are found in nature. In this dissertation, I quantitatively explore how distributions and modern ecological strategies have arisen through kelp evolution. I utilize phylogenomic approaches to determine the evolutionary relationships between kelp species and the timing of their diversification, elucidating many previously unknown phylogenetic relationships between kelps (Ch. 2). I then investigate the strategies that kelps use to survive on wave-swept shores and test for trade-offs that may have constrained their broad range of morphological variation. I use flow tank experiments and field mechanical testing to investigate how external forces from the environment interact with morphology. I show that kelps with high mechanical support also experience greater environmental forces than weaker, more streamlined species, consistent with well known trade-offs of stress resistance in other organisms (Ch. 3). I also investigate the interspecific scaling of biomass allocation in organs of kelp that are analogous to those of land plants and showed that there are shared features of how size influences morphology in both groups (Ch. 4). Lastly, I combine trait and phylogenetic information to explore patterns of trait evolution and determine how species that specialize in different environments are distributed across the phylogeny. I assess whether phylogenetic relatedness or trait differences explain the assembly of kelp communities and demonstrate that kelp communities are composed of distantly related species that have converged on similar traits (Ch. 5). Taken together, these studies offer a multifaceted perspective on the morphological and ecological diversification of kelps and demonstrate that ecological strategies are convergent among phylogenetically divergent lineages.Science, Faculty ofBotany, Department ofGraduat