Experimental assessment of the impact of rapid evolution on population dynamics

Background: It is generally assumed that short-term population dynamics are too slow to be influenced by evolution. Question: Can evolution occurring within only weeks (four to five generations) impact concurrent population dynamics? Organism: Green peach aphid (Myzus persicae) growing on an undomesticated host (Hirschfeldia incana). Aphid clones were collected from a single wild population. Site of experiment: Greenhouse experiment lasting 4 weeks. Methods: A preliminary experiment found that aphid clonal lineages differed by up to 17% in intrinsic growth rate (fitness). Using a subset of clones, we manipulated the amount of genetic variation in intrinsic growth rate within replicated aphid populations by manipulating aphid clonal composition. We compared the population dynamics of evolving populations (clonal frequencies free to vary) with that of non-evolving controls (populations without clonal variation). Results: Two of the three evolution treatments rapidly evolved by changing in clonal frequencies. These evolving populations grew 28–34% faster, reaching higher densities, compared with non-evolving control populations.