Increased reproductive capacity and physical defense but decreased tannin content in an invasive plant

Abstract Plant invasions create novel plant–insect interactions. The EICA (evolution of increased competitive ability) hypothesis proposes that invasive plants will reallocate resources from defense to growth and/or reproduction because they have escaped from their co‐evolved insect natural enemies. Testing multiple herbivory by monophagous and oligophagous herbivores and simultaneous measurement of various plant traits will provide new insights into the evolutionary change of invasive plants. In this context, we conducted a common garden experiment to compare plant growth and reproduction, chemical and physical defense, and plant responses to herbivory by different types of herbivores between invasive North American populations and native East Asian populations of mile‐a‐minute weed, Persicaria perfoliata. We found that invasive mile‐a‐minute exhibited lower biomass, flowered earlier and had greater reproductive output than plants from the native range. Compared with native populations, plants from invasive populations had lower tannin content, but exhibited higher prickle density on nodes and leaves. Thus our results partially support the EICA hypothesis. When exposed to the monophagous insect, Rhinoncomimus latipes and the oligophagous insects, Gallerucida grisescens and Smaragdina nigrifrons, more damage by herbivory was found on invasive plants than on natives. R. latipes, G. grisescens and S. nigrifrons had strong, moderate and weak impacts on the growth and reproduction of mile‐a‐minute, respectively. The results indicate that mile‐a‐minute may have evolved a higher reproductive capacity in the introduced range, and this along with a lack of oligophagous and monophagous herbivores in the new range may have contributed to its invasiveness in North America.