Living fast on the edge: Adaptive evolution in founding populations of an invasive plant

Introduced species face a variety of challenges and opportunities in their introduced ranges. We have been examining how isolated founding populations of the invasive shrub Hypericum canariense have responded to these novel ecological and evolutionary environments. Our comparisons of invasions in California and Hawaii to native populations in the Canary Islands have revealed a suite of evolutionary changes in life history, mating system, and chemical defense. Invading plants show local adaptation in flowering phenology, overall increased growth and decreased defense (preliminary results), and a shift toward a self-fertilizing mating system, particularly at invasion fronts. These changes fit some of the predictions regarding the ecological traits that should benefit colonizing species.  Furthermore, evolution appears to have occurred over less than 50 years, and in populations with strongly diminished genetic diversity. This suggests that populations with few founders (small propagule pool) may not lose opportunities for rapid adaptive change, at least over the short term. We consider how this might contribute to aggressive spread and community dominance in H. canariense.