Touchy and bushy:: Phenotypic plasticity and integration in response to wind stimulation in Arabidopsis thaliana

Thigmomorphogenesis, or touch response, is a widespread and ecologically significant, yet understudied, form of phenotypic plasticity in plants. I investigated uni- and multivariate differentiation for plasticity in response to mechanical stimulation induced by wind in several populations of Arabidopsis thaliana (Brassicaceae). I set out to test specific hypotheses based on three different scenarios predicting patterns of character correlations among morphological and life history traits in this annual opportunistic weed. A complex model of phenotypic integration, including developmental correlations and trade-offs, fit the data remarkably well, with little variation from the environment. Wind was found to influence only the degree of branching of the plant, which had a direct effect on a component of fecundity. When exposed to no or little wind, the overall phenotypic similarities among populations seemed random; sustained winds clearly elicited distinct phenotypic syndromes, with eight populations developing a highly "bushy" (branched) phenotype, one population failing to do so, and two more showing intermediate phenotypes. Arabidopsis thaliana seems to be characterized by few and distinct plasticity syndromes, which may help our understanding of the ecology and evolution of phenotypic plasticity better than what can be achieved with more widely plastic species where distinctive patterns are difficult to recognize or to relate to specific ecological conditions.