Experimental evolution with bacteria in complex environments

Abstract

Experiments with microbes are a powerful tool for addressing general questions in evolutionary ecology. Microbial evolution is also interesting in its own right, and often clinically relevant. I have used experimental evolution of bacteria (Pseudomonas spp.) in controlled laboratory environments to investigate the role of environmental heterogeneity in the evolution of phenotypic diversity. Some of my results provide insight on general processes, while others are specific to bacteria. (1) I have shown that variation in resource supply affects the evolution of niche breadth in complex environments containing a range of available resources, leading to a peak in phenotypic diversity at intermediate levels. (2) I have found that resource availability also affects selection against redundant phenotypic characters, which is strongest when resources are scarce. (3) Using experiments with bacteria and their protozoan predators, I have found that selection for predator resistance varies with resource supply during a model adaptive radiation. (4) I have looked at the role of periodic bottlenecks in population size in the evolution of antibiotic-resistant bacteria. My results highlight the importance of biochemical constraints specific to different resistance mutations. (5) Finally, I have shown that bacterial adaptation to novel carbon substrates affects different growth parameters simultaneously, and that the same response is seen in environments that maintain different levels of phenotypic diversity. These findings emphasize the role of environmental heterogeneity in the evolution of phenotypic diversity, but also show how ecological and genetic factors can constrain adaptation to a given niche within a heterogeneous environment.