Altered patterns of growth, physiology and reproduction in invasive genotypes of Solidago gigantea (Asteraceae)
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Introduced plants may leave their specialized herbivores behind when they invade new ranges. The Evolution of Increased Competitive Ability (EICA) Hypothesis holds that this escape from herbivory could lead to reduced investment in defenses, thereby freeing resources for growth and reproduction. We tested the prediction that introduced genotypes of Solidago gigantea would outperform native genotypes when grown in the absence of herbivores, and examined whether tolerance to insect herbivory has changed in introduced genotypes. S. gigantea is native to North America and an exotic invasive in Europe. Insect damage reduced plant growth and biomass for both native and exotic genotypes. While there was no evidence that continent of origin influenced the degree to which plants compensated for herbivory, the mechanisms contributing to recovery differed for native and exotic plants. Damaged US plants showed enhanced photosynthetic rates to a greater extent than damaged European plants, while damaged European plants carried more leaves than damaged US plants. At the end of the season, leaf mass of European plants was significantly greater than that of US plants. Contrary to the predictions of the EICA hypothesis, US plants were more likely to flower than European plants. European plants invested significantly more of their total reproductive biomass into rhizomes rather than flowers than US plants. While other work with S. gigantea has supported some aspects of the EICA hypothesis, the results reported here generally do not. We conclude that multiple factors influence the success of introduced plants.
KeywordsEvolution of increased competitive ability Tolerance Solidago gigantea Reproductive allocation Compensatory photosynthesis Invasive plant
We thank Terry Bott and Lou Nelson for help in the garden. Jeff Karron suggested helpful literature. Special thanks to Stephen Sanders. Financial support was provided by NSF Grant DEB-0315430 to G. Meyer. This is publication #251 from the University of Wisconsin—Milwaukee Field Station.
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