REACTION NORMS OF ARABIDOPSIS (BRASSICACEAE) .3. RESPONSE TO NUTRIENTS IN 26 POPULATIONS FROM A WORLDWIDE COLLECTION

The study of phenotypic plasticity, the ability of a given genotype to express different phenotypes as environments change, is becoming a central focus of ecological genetics and evolutionary theory. To help address the most pressing questions about plasticity (its genetic control, ecological relevance, and macroevolutionary consequences) we advocate the use of Arabidopsis thaliana (and eventually other related species of the same genus) as a model system. In this study we present experimental data concerning: (a) the extent of reaction norm variation to two levels of nutrients in a worldwide collection of 26 A, thaliana populations; and (b) the existence of multivariate associations among key phenotypic characters, and their reaction to changes in the environment. We found significant among-population genetic variation for eight of the nine traits measured, as well as plasticity in four traits. Five traits showed significant differences in genetic variation between the two environments. The multivariate association of the nine traits defines four major groups of covarying characters, each of which may be plastic or not, depending on the particular population. The use of populations that can be easily obtained by any researcher, because they are part of a worldwide collection, implies that it will be easy to build on our results during future investigations of phenotypic plasticity in this species.