Ultra-local adaptation due to genetic accommodation

Models of "plasticity-first" evolution suggest that phenotypic plasticity precedes and facilitates the rapid evolution of new adaptations. Previous work has emphasised how new adaptations arise through the loss of plasticity, when populations split to occupy new environments and become reproductively isolated from the ancestral population. Here we analyse the role of "plasticity-first" evolution in generating divergent new adaptations when populations are still connected by gene flow. We report that neighbouring populations of burying beetles Nicrophorus vespilloides , in different Cambridgeshire woodlands, have divergently adapted to breed on different-sized carrion despite ongoing gene flow. We show experimentally that this ultra-local adaptation is due to evolution of the reaction norm linking clutch size to carrion size, a process known as genetic accommodation. Plasticity is not lost in the derived population, but instead is fine-tuned by evolution to match the greater range in carrion available naturally. Accordingly, we find that loci associated with oogenesis have become differentiated in beetles from the different woodlands. We suggest that genetic accommodation can enable organisms to rapidly and specifically adapt to very fine-scale differences in their local environment, even while gene flow persists.