| Most organisms live and evolve in environments that are spatially structured. The research presented here is focused on understanding the role of spatial structure on the outcomes and dynamics of adaptive evolution using mathematical models and experiments using bacteriophages (phages).;In our first project, we showed that for a parasite evolving in a spatially structured environment, an evolutionarily advantageous strategy may be to reduce its transmission rate. We demonstrated this empirically using phage from an evolution experiment where spatial structure was maintained over 550 phage generations on agar plates. We found that a single substitution in the major capsid protein led to slower adsorption of phage to hosts with no change in lysis time or burst size. Resulting plaques were larger and contained more phage per unit area. Using a spatially explicit, individual-based model, we showed that when there is a trade-off between adsorption and diffusion, slow adsorption can maximize plaque size, plaque density and overall productivity.;In the second project, we used the model developed previously to perform a detailed study of phenotype-fitness maps for phage in various environments. We found that mappings depend on the degree of structure and on other factors including competition, spatial configuration of the starting population and choice of fitness measure. In general, well-mixed environments select for rapid adsorption, while optimal latent period was less sensitive to population structure and depended on the fitness measure being optimized. Short lysis times increased rate of initial population growth while long lysis times maximized end population. We also used the model to investigate the role of periodic population bottlenecks on populations. While bottlenecks lead to a loss of diversity in all simulations, but the effect is most severe in well-mixed environments. Bottleneck size and spatial configuration both play a role in determining the diversity and composition of the end population. Recombination can help reverse some of this loss of diversity, but this benefit is primarily seen in spatially structured environments where waves of phage types meet and create zones of co-infection. |
