A tale of two continents: The role of different evolutionary forces in life history shifts during biological invasions

One explanation for invasiveness is that selection resulting from enemy escape favors a shift in investment from defense to traits enhancing growth and reproduction. Silene latifolia was introduced from Europe (EU) to North America (NA) approximately 200 years ago. Field studies and common garden experiments conducted in EU and NA have revealed major differences between the two continents: 1) Silene has escaped a number of specialist enemies during colonization and the resulting damage levels are lower in NA; 2) NA plants display a ‘weedier' and more reproductively prolific phenotype, and; 3) NA plants invest less in defense and have lower resistance to fungal infection and fruit predation. These results are consistent with the notion that the invasive NA phenotype has evolved at the expense of defensive abilities due to altered selection pressures in enemy-free NA. Yet, while it may be parsimonious to invoke natural selection as the driving mechanism for this life history shift, in this talk I will evaluate the potential role of other evolutionary forces. Specifically, how did the colonization history influence the amount and structure of genetic diversity in the introduced range via bottlenecking and founder effect? Did the subsequent population expansion in NA lead to gene flow among previously distinct lineages resulting in admixture and the evolution of novel phenotypes? Taken together, the evidence from S. latifolia provides insight into how historical and contemporary forces play crucial roles in the fate of introduced species.