General purpose genotypes and evolution of higher plasticity in clonality underlie knotweed invasion

Many widespread invasive plant species express high phenotypic variation across novel environments, providing a unique opportunity to examine ecological and evolutionary dynamics under global change. However, biogeographical studies often lack information about the origin of introduced populations, limiting our understanding of post-introduction evolution of introduced species in the new range. Here, we assessed the responses of Reynoutria japonica from 128 populations spanning three latitudinal transects in the native ranges of China and Japan, and the introduced ranges of North America and Europe. When grown in two common gardens in the native range, plants from introduced populations in North America and Europe differed in almost all traits from those from native Chinese populations, but were similar to plants from native Japanese populations. Compared to Chinese populations, North American, European and Japanese populations expressed lower trait values and plasticity in most traits. However, plants from both introduced ranges and from Japanese populations expressed higher clonality and plasticity in clonality than plants from Chinese populations. In addition, introduced populations expressed higher plasticity in clonality but lower plasticity in basal diameter compared to Japanese populations. Our study showed heritable differences in phenotypes between plants from the native ranges of Japan and China, and those from the introduced ranges were similar to the putative source of origin in Japan. However, we found that introduced populations may have evolved higher plasticity in clonal growth. Our findings emphasize the critical role of clonality and plasticity in invasion success, demonstrating the importance of discriminating between source and non-source native populations to identify ecological and evolutionary responses of invasive plants to novel environments.