High-performance genotypes in an introduced plant: insights to future invasiveness.

Maintaining high reproductive output in diverse conditions has consistently been found to promote invasiveness in introduced taxa. Following on this key observation, studies have compared the performance across environments of invasive vs. native congeners, and of introduced vs. native populations within invasive species. Performance differences among genotypes within introduced species have received far less attention, although such genetic variation could be critical to invasive potential. If an introduced species contains genotypes that can maintain high fitness across contrasting environments, such broadly adaptive, high-performance genotypes could promote and shape the species' immediate spread across multiple habitats. Furthermore, their presence could lead to the evolution of greater aggressiveness in the species, as these high performers increase in frequency. We investigated the existence and distribution of high-performance genotypes in Polygonum cespitosum, a newly invasive Asian annual. We raised 416 genotypes, collected from 14 North American populations, under resource-rich conditions to identify potential high-performance genotypes (the top 5% in total reproductive output). We then compared their fitness, life history, and functional traits to a random group of the remaining genotypes in three contrasting environments to ask the following: (1) Do consistently high-performance genotypes (i.e., genotypes with high relative fitness in diverse conditions) exist within introduced-range populations? (2) If so, do these high-performance genotypes possess distinctive life history and/or functional traits? (3) Do these genotypes occur in all populations or in only a subset of populations? Genotypes initially identified as high-performance in favorable conditions also had higher reproductive output in resource-limited environments. Their fitness advantage compared with control genotypes varied in magnitude from one environment to another but was significant within all three test environments. High-performance genotypes shared a developmental syndrome characterized by rapid and high germination, fast seedling growth, early reproductive onset, and high reproductive allocation, but they did not differ in other functional traits. P. cespitosum includes a subset of genotypes with accelerated development and significantly greater fitness in both favorable and stressful conditions. The nonrandom distribution of these high-performance genotypes among populations in the species' introduced range highlights the importance of genotypic and population-level variation for invasion dynamics.