Invasive Spartina alterniflora exhibits increased resistance but decreased tolerance to a generalist insect in China.

CHINA; UNITED States

Several theories explaining the post-introduction evolution of invasive plants predict that specialist-enemy release often leads to decreased defense in introduced plants, but how novel generalist consumers in the introduced ranges affect plant-defense evolution remains largely unexplored. According to the shifting defense hypothesis, the decreased defense against specialist enemies may result in the increased defense against generalists. We compared resistance and tolerance of native (from the USA) and invasive populations (from China) of Spartina alterniflora to the dominant generalist insect Laelia coenosa in China. We also compared leaf traits between Spartina population origins. We found that Laelia had lower performance on invasive than on native Spartina populations. Native Spartina populations, however, had a greater capacity to compensate for leaf damage by Laelia than invasive ones. Although specific leaf area and leaf carbon content did not significantly vary between Spartina origins, invasive Spartina populations had lower leaf-nitrogen content than native populations. These results suggest that, following its introduction to China, Spartina has developed increased resistance but decreased tolerance to the generalist herbivore, which may be related to evolutionary increases in leaf carbon-to-nitrogen ratio. These findings enhance our understanding of invasive plant defense against generalist herbivores in the introduced ranges and highlight the trade-off between resistance and tolerance. [ABSTRACT FROM AUTHOR]