Experimental Tests of Rapid Eco-Evolutionary Dynamics in a Plant-Herbivore System

Examples of rapid evolution, occurring within a few dozen generations or less, have recently increased substantially. Evolution on these timescales suggests the possibility that rapid evolution could reciprocally interact with short-term ecological dynamics, a process termed `Eco-Evolutionary Dynamics'. My dissertation experimentally tests these interactions in an aphid (Myzus persicae) and an undomesticated mustard host (Hirschfeldia incana). Aphid clonal lineages were collected from a local population, and found to differ by up to 17% in intrinsic growth rate. This variation was used to conduct experimental evolution. Experiment 1 quantified how aphid rapid evolution impacts concurrent aphid population dynamics in the greenhouse. I manipulated the amount of genetic variation in intrinsic growth rate by manipulating the genetic composition of aphid populations, which altered rates of evolution. Significant changes in clonal frequencies (or gene frequencies) occurred within a few weeks. Evolving populations grew significantly faster, up to 34%, and reached higher densities compared to non-evolving control populations. I then tested whether rapid evolution significantly impacts population dynamics in the wild. Evolving populations grew significantly faster, up to 42%, and reached up to 67% higher densities compared to non-evolving controls even in the face of environmental variation. Yet evolution only had this impact in the natural uncaged treatments highlighting that ecological context alters the strength of eco-evolutionary dynamics. Finally, the last experiment tested the full eco-evolutionary dynamic cycle of dual causality between ecological dynamics (density) and evolutionary dynamics in the greenhouse. Initial aphid density altered the rate and outcome of evolution. Density also quantitatively and qualitatively altered how rapid evolution impacts population growth rate sometimes accelerating or decelerating growth. This experiment also revealed that rapid evolution and intraspecific density have similar relative impact sizes on population growth rate. My dissertation experimentally quantified strong reciprocal causal interactions between rapid evolution and population dynamics on short-timescales in both greenhouse and in the field in a plant-herbivore system for the first time. Such interactions strongly countermand the assumption that evolution is too slow to influence population dynamics and suggests that ecological and evolutionary predictions would be improved if these interactions were integrated into predictive models