One of the most fundamental issues in evolutionary biology is the nature of transitions from single cell organisms to multicellular ones, with accompanying cellular differentiation and specialization. Not surprisingly for microscopic life in fluid environments, many of the relevant physical considerations involve diffusion, mixing, and sensing, for the efficient exchange of nutrients and metabolites with the environment is one of the most basic features of life. This proposal describes a combination of experimental and theoretical research aimed at some of the key mysteries surrounding transport and sensing by and in complex, multicellular organisms, and the implications of those findings for the explanation of driving forces behind transitions to multicellularity. There are two main components of the research. The first involves studies of single and multicellular algae which serves as model systems for allometric scaling laws in evolution. Of particular importance are the synchronization dynamics of the eukaryotic flagella that provide motility, enhance nutrient transport, and allow phototaxis in these organisms. The second thrust involves investigation of the ubiquitous phenomenon of cytoplasmic streaming in aquatic and terrestrial plants. Despite decades of research, there is no clear consensus on the metabolic role of this persistent circulation of the fluid contents of cell. Building on recent theoretical developmnts we will study its implications for internal transport and mixing, homeostasis, and development in large cells. In each case, state-of-the art experimental methods from physics, fluid dynamics, and cell biology will be used in combination with advanced theoretical methods for the study of the stochastic nonlinear PDEs that form the natural description of these systems.
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