Evolutionary potential for increased invasiveness: High-Performance Polygonum cespitosum genotypes are competitively superior in full sun.

PREMISE OF STUDY The presence of genetic variation for traits that contribute to ecological range expansion can provide the potential for introduced taxa to evolve greater invasiveness. Genotypes that contribute to the spread of introduced range populations must have the ability to maintain fitness under changing environmental stress and competitive intensity. Previously, we identified a subset of genotypes in populations of the invasive annual Polygonum cespitosum that express consistently high reproductive fitness in diverse (shaded, dry, and resource-rich) conditions. Here, we investigated whether these broadly adaptive (High-Performance) genotypes also show a competitive advantage over conspecifics in full sun and/or shade. METHODS We grew a population-balanced sample of 13 High-Performance and 13 'Control' genotypes in intraspecific competitive arrays, comprising all four possible combinations of High-Performance vs. Control target plants and competitive backgrounds, in both full sun and shaded glasshouse environments. KEY RESULTS In full sun, High-Performance genotypes (1) better maintained growth and reproductive output despite competition and (2) more strongly suppressed growth and reproduction of target plants. However, genotypes did not differ significantly in shade. CONCLUSIONS Competitive superiority in open conditions may contribute to increasing predominance of these broadly adapted genotypes in introduced-range Polygonum cespitosum populations, and hence to the evolution of greater invasiveness. This study provides insight into the role of genotypic variation for ecological traits in the range expansion of a contemporary plant invader. It also highlights how such variation can be differently expressed in alternative environments (gene by environment interaction).