Phenotypic plasticity

Plasticity of morphological characters is an inherently developmental phenomenon. Nevertheless, the role of development in the evolution and expression of phenotypic plasticity has been virtually ignored. This research has two primary foci: 1) identification of developmental constraints on the potential for expression of phenotypic plasticity, and 2) construction of developmental models to distinguish between true phenotypic plasticity and architectural effects on phenotypic expression in metameric organisms. I have shown that the developmental fate of meristems and primordia is contingent upon the ontogenetic milieu in which they are initiated (ontogenetic contingency). Both past responses to the environment (plasticity) and positional information (architecture) affect the final phenotype of each developing structure.

Architecture

Because plants are composed of repeating metameric units, there is a persistent underlying assumption that all metamers should be inherently phenotypically similar. As a consequence, much intra-individual phenotypic variation among metamers is interpreted as plastic responses to temporal changes in the internal or external environment. Experimental work has detected significant, repeatable variation among metamers that is inherent in plant axes; positional variation is the rule, rather than the exception. Positional variation not only affects our interpretation of underlying controls on development (especially epigenetic factors), it may also provide the raw material for evolutionary diversification of metamers within axes.

Sexual Systems

Plants possess a diversity of sexual systems, ranging from hermaphroditism to monoecy to dioecy. Although the selective advantages of the various plant sexual systems have been studied extensively, the developmental transformations that underlie the origin and diversification of most sexual systems are unknown. Recent work has focused on andromonoecy, a sexual system in which individual plants bear both hermaphroditic and staminate flowers. Comparisons of andromonoecious taxa with hermaphroditic outgroups are underway to identify the developmental antecedents of this sexual system.