Comparison of the herbivore defense and competitive ability of ancestral and modern genotypes of an invasive plant, Lespedeza cuneata

The evolution of increased competitive ability (EICA) hypothesis provides a compelling explanation for the success of invasive species. It contends that because alien plants have escaped their coevolved natural enemies, selection pressures favor a diversion of resources from herbivore defense to traits that confer increased competitive ability. Here, we provide evidence for EICA in the noxious grassland invader Lespedeza cuneata, by comparing the ancestral genotype introduced to North America in 1930 with modern-day invasive (North American) and native (Japanese) genotypes. We found that the invasive genotype was a better competitor than either the native or the ancestral genotype. Further, the invasive genotype exhibited greater induced resistance but lower constitutive resistance than the ancestral and native genotypes. Our results suggest that selection has played a pivotal role in shaping this invasive plant species into a more aggressive, but less constitutively defended competitor.