Adaptive geographical clines in the growth and defense of a native plant

Broad-scale geographical gradients in the abiotic environment and interspecific interactions should select for clinal adaptation. How trait clines evolve has recently received increased attention because of anticipated climate change and the importance of rapid evolution in invasive species. This issue is particularly relevant for clines in growth and defense of plants, because both sets of traits are closely tied to fitness and because such sessile organisms experience strong local selection. Yet, despite widespread recognition that growth and defense traits are intertwined, the general issue of their joint clinal evolution is not well-resolved. To address heritable clinal variation and adaptation of growth and defense traits of common milkweed (Asclepias syriaca), we planted seed from 22 populations encompassing the species' latitudinal range in common gardens near the range center (New York [NY]) and towards the range edges (New Brunswick [NB] and North Carolina [NC]). Populations we...