Abundant ecological opportunity is thought to drive adaptation and diversification. The presence of multiple opportunities leads to divergent selection, which can slow adaptation when niche-specific beneficial mutations have antagonistically pleiotropic effects. Alternately, competition for multiple opportunities can generate divergent selection leading to high rates of adaptive differentiation. Which outcome occurs may depend on the spatial structure of those ecological opportunities. In a mixture of resources, competition for multiple opportunities can drive divergent selection; however if each resource is available in a spatially distinct patch, competition for multiple opportunities simultaneously cannot occur. We report the effects of extent and spatial structure of ecological opportunity on the evolutionary dynamics of populations of Pseudomonas fluorescens over 1000 generations. We varied extent of ecological opportunity by varying the number of sugar resources (mannose, glucose, and xylose), and varied spatial structure by providing resources in either mixtures, or spatially distinct patches. We saw that a particularly novel resource (xylose) drove the rate of adaptation when in a mixture but had no effect on diversity. Instead we saw the evolution of a single adaptive strategy that differed with respect to phenotype and degree of specialization, depending on both the extent and spatial structure of ecological opportunity.
Relative fitness measures over time of Pseudomonas fluorescens SBW25 populations evolving in environments containing mannose, glucose, xylose, and all three sugars. Fitness measures are estimates from 24 hour competitions against the ancestor.
Relative fitness of genotypes isolated from evolving populations of Pseudomonas fluorescens SBW24 every 200 generations for 1000 generations, assayed in mannose, glucose and xylose. Fitness measures are estimated from 24 hour competitions against the ancestor.
Growth measures from BIOLOG assays of genotypes isolated from Pseudomonas fluorescens SBW25 populations evolved for 1000 generations in mannose, glucose, xylose, and the combination of all three sugars. Growth was measured as the difference between final and initial optical density (after 24 hours) in each well a BIOLOG GN2 plate. BIOLOG GN2 plates are comercially available 96-well plates containing different 95 different carbon sources plus a carbon-absent control well. A1 - H12 indicate well.
Pseudomonas fluorescens SBW25:lacZ+ fitness relative to Pseudomonas fluorescens SBW25:lacZ- measured on each selection environment used in our evolution experiment. Fitness was estimated via 24 hour competitions.
replicated population fitness
Additional replicated population fitness data for select evolved Pseudomonas fluorescens SBW25 lines. These fitness measures are a replication of some of the data in "population fitness.xls".
Nal mutant fitness
Difference between fitness of Pseudomonas fluorescens SBW25 naladixic acid-resistant mutants and Pseudomonas fluorescens SBW25, measured in mannose, glucose, and xylose environments. Fitness differences were estimated from 24 hour competitions in three replicate assays.
Population density of Pseuodomonas fluorescens SBW25 populations evolving in environments containing mannose, glucose, xylose, and a combination of all three sugars over 1000 generations. Population density was measured by counting colony forming units after 24 hours of growth in the selection environment every 30 - 100 generations.