Title

Developmental and adult phenotypic plasticity in plants: Environmentally induced changes in character correlations and effects on fitness

Date of Completion

January 1994

Keywords

Biology, Botany|Biology, Ecology|Biology, Genetics

Degree

Ph.D.

Abstract

Phenotypic plasticity is the ability of an organism to produce different phenotypes in response to different environments. Plasticity has received much attention in the last decade due to its theoretical importance for adaptive phenotypic evolution, allowing persistence of populations under unfavorable conditions, and supposed role in maintaining genetic variation within populations.^ Notwithstanding the amount of work recently published on plasticity, there are major areas of investigations that have been rarely addressed. In particular, we still know little about the development, genetic control, and ecological relevance (i.e., effects on fitness) of plastic responses.^ This thesis deals with aspects of these problems, using two experimental systems characterized by very different life histories, yet particularly suitable for plasticity studies: two species of Lobelia (L. cardinalis and L. siphilitica), family Lobeliaceae, and Arabidopsis thaliana, family Brassicaceae.^ The first chapter shows genetic variation for the plasticity of ontogenetic trajectories in two populations of L. siphilitica responding to different shade conditions, while the second one contains data of the same type referring to two populations of L. cardinalis and two of L. siphilitica responding to differences in nutrients. The existence of plasticity and genetic variation for plasticity during ontogeny means that selection has more opportunities to act in order to change crucial developmental events in these two species.^ The third chapter shows the environmental-dependence of character correlations in four populations of A. thaliana, while the fourth chapter summarized how the same genotypes respond to three types of abiotic stress. The last chapter concentrate on the complex relationship between fitness and several traits measured in 55 genotypes of A. thaliana. These results point to the complexity of response to environmental variation at the whole-organism level, suggesting the existence of genetic as well as functional constraints on the evolution of plant's phenotypes.^ Taken together, the data gathered during these studies help in the understanding of the complexities of the developmental, genetic, and ecological aspects of plastic responses. They also bear on the currently intense theoretical debate over the contribution of phenotypic plasticity toward macroevolutionary patterns, alternatively seen as a constraint or as an avenue for evolutionary novelties. ^