Evidence for a Growth-Defense Trade-off in Centaurea solstitialis

Abstract

An important question in invasion ecology is why certain introduced species become invasive. It is thought that some invasive plants escape their natural enemies, and therefore might adapt to devote more resources to growth under a general trade-off between growth and defense. Yellow starthistle (Centaurea solstitialis) has previously been shown to grow larger in its invaded range. This study sought to test whether yellow starthistle is evolving differences in immune activity along a growth-defense trade-off or through local adaptation to its pathogen communities. This study used a high-throughput peroxidase assay to quantify immune activity after leaves were exposed to bacteria from native and invaded ranges. Immune activity was measured using the light absorbance of a substrate for peroxidase enzymes. Plant genotypes from the invaded range showed a lower immune response when exposed to bacteria from all ranges. Three bacteria strains from the invaded range elicited a lower immune response when exposed to plant genotypes from both ranges. These results support the hypothesis that yellow starthistle is evolving to invest less in defense, and future work should investigate the connections between these changes and investment in growth.