Rapid adaptation and increased genetic parallelism in experimental metapopulations of Pseudomonas aeruginosa

Natural populations are often spatially structured, meaning they are best described as metapopulations composed of subpopulations connected by migration. We know little about how the topology of connections in metapopulations impacts adaptive evolution. Topologies that concentrate dispersing individuals through a central hub can accelerate adaptation above that of a well-mixed system in some models, however empirical support is lacking. We provide evidence to support this claim and show acceleration is accompanied by high rates of parallel evolution resulting from a reduced probability that rare beneficial mutations are stochastically lost. Our results suggest metapopulation topology can be a potent force driving evolutionary dynamics and patterns of genomic repeatability in structured landscapes such as those involving the spread of pathogens or invasive species.