Geographical Variation Of Invasive Alternanthera Philoxeroides In Its Native And Introduced Ranges

Natural environments are not uniform but heterogeneous, and genetic differentiation is an important strategy for organisms to cope with heterogeneous habitats. Due to spatial variation of selection regime, morphological, physiological and life history traits of widely-distributed species may vary genetically among geographic populations. Spatial variation of resource availability and natural enemy pressure are among the most important factors driving geographical variation of plant species, and are also considered as impetuses for rapid evolution of invasive exotic plants.This study framed a conceptual model for the geographical variation of invasive exotic plants. In a common garden experiment, morphology and growth-defense strategy were compared among six geographic populations of Alternanthera philoxeroides from both its native (Argentina) and introduced (USA and China) ranges. The aim was to test the theoretical predictions of our conceptual model, and to explore the role of resource-enemy interaction in plant invasions.The main conclusions were summarized as follows:(1) A. philoxeroides showed significant geographical variation in morphology and growth-defense strategy in its native range, and the pattern appeared to be latitudinally clinal. The high-latitude population represented the extreme of "low-resource ecotype" in the variation continuum (low innate growth, low growth plasticity and high resistance to specialist herbivore). The low-latitude population represented the extreme of "high-resource ecotype" in the variation continuum (high innate growth, high growth plasticity and low resistance to specialist herbivore). The mid-latitude population represented the transitional "intermediate-resource ecotype".(2) A. philoxeroides showed similar latitudinal variation in USA as in its native range, however, introduced populations spanned a narrower ecological breadth, i.e. there were only high- and intermediate-resource ecotypes in USA and China. These conclusions provide new clues concerning the origin of invasive phenotypes of A. philoxeroides in USA and China, and indicate that increase in resource availability and release from specialist herbivore may interact to facilitate successful invasion of A. philoxeroides. In addition, this study also provides new insights to the management and control of A. philoxeroides and other invasive exotic plants.