My research concerns the evolution of morphological diversity among plants with particular emphasis on understanding how features of development shape the dynamics of evolutionary change. My approaches range from analyses of developmental responses of individuals to contrasting environmental conditions, to understanding how development has evolved over time in groups of closely related plants, to understanding differences across all of flowering plants. I examine development at the level of gene expression, the features of cells and tissues, and the features of whole plants as they unfold over an individual’s lifetime. Current work includes:
1) The evolution of unisexual flowers: Flowers of most species include both “male” and “female” parts, that is, they are bisexual. Single sexed (unisexual; male or female) flowers, however, have evolved hundreds of times among distantly related taxa. Although this evolutionary transition is very common, we understand very little about how or why unisexuality evolves. My NSF funded work has detailed the developmental basis for this transition in a large group of closely related plants (Solanum) and has demonstrated the critical role of phenotypic plasticity (developmental responses to the environment) in the evolution of novel flower types. This work also demonstrated the importance of considering “whole organism” properties (what I have termed architectural effects) to understand the developmental properties and evolution of sub-organismal structures such as flowers. Ongoing and future work includes a meta-analysis of published literature on species that produce both male and female flowers on the same individual. My hypothesis is that unisexual flowers evolve within plant groups that that have a distinctive type of architecture that facilitates formation of a signaling gradient. Once I have identified the global architectural patterns common among plants with unisexual flowers, I will focus on understanding the details of the signaling system that underlies the development of distinct flower types.
2) Floral assembly rules: In a collaboration that began with a National Science Foundation-NESCent working group that I co-organized, I and my colleagues have begun to investigate how suites of floral traits have been assembled over evolutionary time to generate the diversity of forms among flowering plants. We find that the traits that contribute most to explaining the distribution of characters across flowering plants are those associated with the generation of new species (i.e., diversification). The occurrence of bursts of diversification over an evolutionary time scale, however, is greatly delayed by the multiple trait origin events (transitions) that are necessary to assemble of the “best” trait combinations. Our group has generated an extensive data set and developed new tools for the analysis of character combinations that we will continue to use to test specific hypotheses about the evolution of floral form.
3) Evolution of embryo nourishing tissue: The embryos of all flowering plants are nourished by a tissue called endosperm. Endosperm provides about two-thirds of the calories consumed by humans world wide (e.g., it is the starchy part of the corn, rice, and wheat kernel) and is thus of great economic significance. The evolutionary origin of this tissue that is unique to flowering plants is unknown and the many hypotheses that have been proposed to explain the origins of endosperm have proven very difficult to test. A graduate student in my lab was able to test one hypothesis and show that the unique degree of genetic relatedness between endosperm and embryo causes the endosperm to behave altruistically. I have, in collaboration with a colleague, initiated new experiments that further manipulate the genetic relatedness of endosperm and embryo. These experiments will recreate the hypothesized genetics of the earliest flowering plants in order to examine the evolutionary origin of this mysterious tissue.
4) Nurturing plant evolutionary-developmental biology (evo-devo): In addition to my own sole-PI and collaborative research, I am committed to fostering advances in botanical research and education across the scientific community. I lead two projects aimed at enhancing interdisciplinary research in plant evolution and plant evo-devo. The first is “microMorph” a National Science Foundation Funded, Research Coordination Network that promotes interactions between the intellectually diverse disciplines of evolutionary ecology, population genetics, developmental morphology, phylogenetics, molecular developmental biology, and genomics. MicroMorph organizes workshops and provides research funding for interdisciplinary training. The second project is a summer intensive course in plant developmental morphology. This course was launched in 2013 to provide basic training in comparative development. I fear that as a scientific community, our ability to delve deeply into the complexity of genomes has already outpaced our ability to understand the structures that those genomes construct. It is my goal to remedy that widening gap in student research training. To that end, I funded and hosted 12 students at the Arnold Arboretum of Harvard University for two weeks of intensive training.