Contrasting levels of evolutionary potential in populations of the invasive plant Polygonum cespitosum

Abstract

The amount of quantitative genetic variation within an invasive species influences its ability to adapt to conditions in the new range and its long-term persistence. Consequently, this aspect of genetic diversity (or evolutionary potential) can be a key factor in the success of species invasions. Previous studies have compared the evolutionary potential of populations in introduced versus native ranges of invasive species, but to date no study has examined differences among introduced-range populations of such species in levels of quantitative genetic variation expressed in ecologically relevant environments. We assessed quantitative variation of fitness, life-history, and functional traits in six geographically separate introduced-range populations of the invasive annual Polygonum cespitosum, by comparing norms of reaction for a large sample of genotypes (16–19 per population) expressed in response to two glasshouse environments simulating contrasting habitats in this new range. Patterns of reaction norm diversity varied considerably among the 6 populations studied. Two populations showed very little quantitative genetic variation in both environments. In contrast, two other populations contained significant genetic variation for fitness and life-history traits in the form of genotypes with low performance in both habitats. Finally, two populations showed significant norm of reaction diversity in the form of cross-over interaction: genotypes that performed relatively well in one environment did poorly in the other. Differences among populations in potential selective response are likely to affect the dynamics and future spread of P. cespitosum, since specific populations will likely contribute differently to the invasion process. More generally, our results suggest that the evolutionary component of long-term invasion success may depend on population rather than on species-level processes.