Mutational effects on constraints on character evolution and phenotypic plasticity in Arabidopsis thaliana

Although the concept of genetic constraints plays an important role in our understanding of the evolution of natural populations, there are still few empirical investigations probing the nature and limits of constraints in pl ant and animal species, aside from some studies in Drosophila. In the work reported here, we use an induced mutation - artificial selection protocol t o analyse constraints on character means and phenotypic plasticity to nutri ents in Arabidopsis thaliana, an annual crucifer. We induced point mutation s in a highly inbred line characterized by an extreme phenotype (very fast life cycle, early flowering, reduced leaf production) and little plasticity . We then selected individuals with increased leaf numbers. The goals were to determine if: (i) it is possible to increase leaf production; (ii) this has an effect on reproductive fitness; (iii) a mutation-selection process s imultaneously alters the environmental insensitivity of the plant, thereby allowing phenotypic plasticity; and (iv) changes in the target trait affect other characters or their plasticities. The results demonstrate that: (a) mutations do increase leaf number; (b) this yields a much higher reproducti ve fitness, owing to the extension of the very short life cycle of the base inbred line; (c) there are no changes in plasticity of leaf number or of a ny other trait, possibly because few loci are involved in the control of pl asticity; (d) changes in leaf number are related to alterations in three ot her traits comprising a strong set of covarying characters in A. thaliana. Two uncorrelated traits are capable of independent evolution from the const rained set. We therefore suggest that environmentally insensitive ecotypes of A. thaliana can quickly evolve to form ecologically specialized, relativ ely environmentally invariant genotypes.