Angela Walczyk

Polyploidy commonly occurs in invasive species, and phenotypic plasticity (PP, the ability to alter one's phenotype in different environments) is predicted to be enhanced in polyploids and to contribute to their invasive success. However, empirical support that increased PP is frequent in polyploids and/or confers invasive success is limited. Here, we investigated if polyploids are more pre‐adapted to become invasive than diploids via the scaling of trait values and PP with ploidy level, and if post‐introduction selection has led to a divergence in trait values and PP responses between native‐ and non‐native cytotypes. We grew diploid, tetraploid (from both native North American and non‐native European ranges), and hexaploid Solidago gigantea in pots outside with low, medium, and high soil nitrogen and phosphorus (NP) amendments, and measured traits related to growth, asexual reproduction, physiology, and insects/pathogen resistance. Overall, we found little evidence to suggest that polyploidy and post‐introduction selection shaped mean trait and PP responses. When we compared diploids to tetraploids (as their introduction into Europe was more likely than hexaploids) we found that tetraploids had greater pathogen resistance, photosynthetic capacities, and water‐use efficiencies and generally performed better under NP enrichments. Furthermore, tetraploids invested more into roots than shoots in low NP and more into shoots than roots in high NP, and this resource strategy is beneficial under variable NP conditions. Lastly, native tetraploids exhibited greater plasticity in biomass accumulation, clonal‐ramet production, and water‐use efficiency. Cumulatively, tetraploid S. gigantea possesses traits that might have predisposed and enabled them to become successful invaders. Our findings highlight that trait expression and invasive species dynamics are nuanced, while also providing insight into the invasion success and cyto‐geographic patterning of S. gigantea that can be broadly applied to other invasive species with polyploid complexes.