Beschreibung:
<jats:p>Research on the genetics of development and on reactions to environmental changes (phenotypic plasticity) is important to understand the evolution of natural populations, mostly because of the possible adaptive meaning of some plastic responses, and because of the suggested role of plasticity in maintaining genetic variation. In this paper, we present a study of developmental norms of reaction of two populations of Lobelia siphilitica (Lobeliaceae) to three levels of light availability. We investigated: (1) the plasticity to light of characters determining phenological timing and of end—of—season traits, and (2) the shape of the ontogenetic reaction norms of plant height and number of leaves in the (Time, Environment, Phenotype) space. We found genetic variation for bolting time, fruit production, final leaf number, rate of stem elongation, and rate of leaf production. We detected plasticity for final height, number of leaves, and rates of height growth and leaf production, and genetic variation for plasticity of height growth rate. The ontogenetic reaction norms for leaf number reveal differences among populations and genotypes both in their average (i.e., across environments) ontogenies and in the plastic responses of the ontogenetic trajectories. The ontogenetic reaction norms for plant height, on the other hand, show only a significant Time by Treatment by Genotype effect. The variation among genotypes for both characters can be due to differences in either the rate of growth or its duration. In addition, the same final phenotype may be produced by different ontogenetic trajectories, e.g., rapid early height growth and short duration vs. slower growth and longer duration. The response to selection on plant height or leaf number will depend on the degree of separation in their genetic control and on the amount of genetic variation for these aspects of development. These results suggest that including ontogenetic data in plasticity studies broadens considerably our understanding of how phenotypes may respond to selection and evolve.</jats:p>