Experimental evolution of evolvability

Capacity to generate adaptive variation can evolve by natural selection. However, the idea that mutation becomes biased toward specific adaptive outcomes is controversial. Here, using experimental bacterial populations, we report the evolution of enhanced evolvability via localised hyper-mutation. Key to realisation was a lineage-level birth-death dynamic, where lineage success depended upon capacity to mutate between two phenotypic states, each optima in a cycling environment. The evolved mechanism is analogous to “contingency loci” in pathogenic bacteria, whose origin was previously unclear. Subsequent evolution showed lineages with localised hyper-mutability were more likely to acquire additional adaptive mutations. Our results provide a detailed mechanistic account of the adaptive evolution of evolvability.