Rapid evolution of latitudinal clines in growth and defense of an invasive weed

Re-estabishment of heritable latitudinal clines in growth-related traits has been recognized as evidence for adaptive evolution in invasive plants. However, less is known about latitudinal clines in defense and joint clinal evolution of growth and defense in invasive plants.

We planted 14 native Argentinean populations and 14 introduced Chinese populations of Aternanthera philoxeroides in repicate common gardens in China. We investigated the latitudinal clines of traits related to growth and defense, and plasticity of these traits in relation to experiment site and soil nitrogen.

We found that chemical defense decreased with latitude in native populations but increased with latitude in introduced populations. For growth rate, latitudinal clines were positive in introduced populations but nonexistent in native populations. There were also parallel positive latitudinal clines in total/shoot biomass and specific leaf area. Experiment site affected the occurrence or magnitude of latit...