The rapid evolution of an invasive plant due to increased selection pressures throughout its invasive history

Invasive plants are highly successful because they can quickly adapt to selection pressures imposed by both biotic and abiotic stressors. Since selection pressures may vary across temporal and biogeographical gradients, the growth and fitness of invasive plants varies across time. However, only a few studies have focused on the evolutionary potential of invasive plants following their establishment. In this study, the impacts of cadmium (Cd) on the germination and seedling growth of an invasive plant, Ageratina adenophora, were examined. The seeds were collected from different historical populations at the invasion stage (during the early, middle, and new stages of invasion). Plant performance was tested under both heavy metal and simulated herbivory treatments to examine the evolution of A. adenophora under different selection pressures. It was found that early stage A. adenophora populations have higher germinability and weaker seedling growth than the new stage populations. Compared with new stage populations, early-stage populations are more tolerant to simulated herbivory and their germination potential tends to be higher under high Cd stress. It seems that the adaptive strategy of A. adenophora is to invest more energy in growth during the initial stage of invasion. As selection pressures increases over time, more energy seems to be shifted to the improvement of seed quality as well as to the vegetative growth system which improves its ability to tolerate stressful environments. It is important to consider the invasion history of a species when studying the invasive and evolutionary potential of plant species.