Multiple Genetic Routes to the Evolution of Invasiveness in a Perennial Sunflower

It has long been recognized that invasive species exert important ecological and economic impacts. Yet, despite substantial incentive, we are only beginning to understand the phenotypic, evolutionary, and genetic determinants of invasion success. Here, we investigate these topics in the perennial sunflower Helianthus tuberosus, a tuber crop that escaped cultivation and is currently listed as one of the most widespread invasive plants in Europe. By surveying genome-wide variation, we show that invasive H. tuberosus originated repeatedly, with most genotypes deriving from breeding material obtained from crosses between domesticated and wild material. We also show that some invasive clones of H. tuberosus have persisted in Europe for over three decades, and currently span hundreds of kilometers in range. Using a common garden experiment, we show that increased clonal growth is an important invasiveness trait in this system, with invasive samples producing twice the number of tubers of non-invasive samples. Our results additionally indicate that increased tuber number production can be achieved in H. tuberosus either by hybridization and heterosis, or independent of hybridization, through the contribution of a small number of alleles of large additive effect. Finally, we show that widespread invasive clones of H. tuberosus exploited both of these genetic routes during the evolution of invasiveness.