Genetic differences in plastic responses to density between ecotypes of Arabidopsis thaliana

One of the most promising directions in the study of phenotypic plasticity is its detailed analysis in organisms that are also well-studied in other aspects. Conclusions based on plasticity studies in environmental gradients that closely mimic natural variation are shown to be the most relevant. Following those directions, we conducted this study of phenotypic plasticity on the currently best available model system in flowering plants, Arabidopsis thaliana, and utilized one of the most common variations experienced in the wild: variation in density. Four Arabidopsis thaliana commonly used inbred lines (ecotypes) were grown in densities from one to seven plants per pot. Both phenotypic plasticity and its genetic variability were detected for almost all of 11 analyzed traits, with analyzed ecotypes responding strongly to density of just two plants per pot. Density had small effect on life history and moderate effect on size traits, while vegetative and reproductive traits responded strongly. Mortality of plants during the experiment was almost absent, showing that all densities corresponded to the medium density phase in which carrying capacity is not yet reached. Genetic variability for phenotypic plasticity was in mast cases the result of profound deviation of only one ecotype from the response of others. In the case of reproductive output, however, G x E interaction was the result of greater between-ecotype variability at lower densities. If we reasonably assume that dense stands are more common in the wild, this difference between ecotypes (populations) closely resembles the cases of so-called potential variability within populations.