No abstract

For introduced species that have spread across a wide distributional range, phenotypic plasticity (PLA) has often been proposed as an important contributor to invasion success, because it increases the survival rate during initial colonization. In contrast, local genetic variation (LOC) has also been proposed to be important, because it could allow invaders to evolve high performance in a new habitat. While evolutionary ecologists have long been interested in understanding genetic mechanisms that allow rapid colonization and spread of species, until recently experimental tests of these concepts have been limited. As a step towards generalization in our understanding of the importance of PLA and LOC, we review the current state of the literature on this topic using meta-analysis. Here, we focused on three fundamental questions: 1) which strategy, PLA or LOC, better explains the phenotypic divergences during invader range expansion across different environmental gradients? 2) Which species characteristics correlate with the occurrence of these different phenomena? And 3) does the detection of PLA versus LOC depend on the trait studied? Using meta-analysis we found that plasticity explained a higher proportion of phenotypic variation regardless of the environmental gradients studied or plant growth forms. PLA predominated in clonal, self-compatible and perennial species, while LOC predominated in annual species. The patterns were trait-dependent: LOC was significantly more important than PLA in phenology, while opposite patterns were found in fecundity and biomass allocation. The frequent simultaneous detection of PLA and genotypic variation in PLA among invasive populations suggested that PLA might benefit from LOC to some extent. Our results also indicate that the contribution of plasticity to the competitive advantages of invasive plants may be more informative than the level of plasticity itself.

Rapid range expansion of invasive plants provides a unique opportunity to explore evolutionary changes of dispersal-related traits during the invasion process. Increasing evidence now suggests that a higher dispersal rate is favored at the invasion front. However, little is known about the role of genetic diff erentiation and phenotypic plasticity on patterns of dispersal ability during the invasion process. In this study, we combined a fi eld survey and a common garden transplant experiment to test for evidence of genetically based dispersal ability in Mikania micrantha , a highly invasive vine, across its invaded range in southern China. Th ree dispersal-related traits, plume loading, seed mass and pappus radius, were measured in both natural and common garden populations. We found that in natural conditions, plume loading and seed mass signifi cantly decreased with expanding distance from the source population, but in controlled conditions, these two traits exhibited a signifi cant humped trend against percent fi eld cover, indicating that dispersal ability of M. micrantha was selected for during range expansion and that the related traits were likely to be under genetic control. Furthermore, rebounding dispersal ability was detected in highly competitive sites in the range core, which suggested that this evolutionary process was likely partially driven by intraspecifi c competition. Because more and more plant species are under spatial nonequilibirum due to climate change, this study can serve to provide hints at the fate of spatially fl uctuant populations.