Phenotypic plasticity is the major determinant of changes in phenotypic integration in Arabidopsis

The way in which novel genetic variation affects the patterns of phenotypic integration in natural populations is addressed here. An experimental study is presented of the variability in integration caused by interpopulation hybridization and consequent genetic reshuffling, as we ll as by changes in the physical environment in the model system Arabidopsi s thaliana (Brassicaceae). Our results show a basic invariance of sets of covarying traits in A. thali ana, with changes in nutrient availability as the principal factor accounti ng for major departures from the general pattern and where differences in t he genetic background of the recombinant lines are less important. In A. th aliana, the relationships among vegetative and reproductive traits form dis tinct clusters in multivariate space. A high degree of congruence was found between differences in the multivariate mean phenotype and the pattern of phenotypic integration, as expected on the basis of recent theoretical mode ls. This relationship might indicate strong selective constraints acting on the specialized life history of these populations, which are spring ephemerals inhabiting ruderal habitats and prone to competition avoidance.