A developmental morphologist's perspective on plasticity

This series of essays addresses plasticity from the perspective of developmental morphology. The first essay deals with the problem of distinguishing between plasticity and other types of ontogenetic variation. In a temporally varying environment, morphological plasticity may be expressed as the production of a succession of different metamers. However, even in a constant environment, plant metamers can vary dramatically, a phenomenon known as heteroblasty. Because heteroblasty and plasticity can yield similar patterns of ontogenetic variation, the two are often confounded in analyses of developmental plasticity. The second essay discusses the integration of plant phenotypic responses and finds that the evidence for integration is equivocal. The third section shows that developmental properties can constrain the expression of morphological plasticity. Developmental lags and the 'epiphenotype problem' are particularly important features for analyses of the evolution and expression of plasticity. Finally, in answer to the question of strategies for studying plasticity, I emphasize the need for research at multiple levels and for the inclusion of a historical or phylogenetic perspective.[PUBLICATION ABSTRACT]