My research and that of my lab group is focused on the ecology and genetics of plant populations. We study the mechanisms regulating genetic diversity and phenotypic evolution in plants, and, conversely, how evolutionary processes (drift, gene flow, adaptation, genetic diversity) affect the ecological function of populations (reproduction, growth, persistence, extinction). To understand these relationships we focus mainly on plant genetic systems, those reproductive attributes that govern mutation, gamete formation, pollination, fertilization, and organization of genetic diversity in populations.
Currently, my lab is involved in four related research areas:
I. Ecology and genetics of small populations
All populations contain a finite number of individuals, particularly those populations in restricted or marginal habitats. This can have a profound effect on mating patterns and ecology, but the significance of population size for the evolutionary process is heavily debated. We have explored this issue through studies on effective population size, metapopulation dynamics, the effects of drift on mating system evolution, inbreeding depression, and the mechanisms by which hybridization causes extirpation of rare species.
II. Evolutionary significance of genome duplication.
Genome duplication above the diploid state (a.k.a. polyploidy) is widespread among plants and animals and is particularly common in flowering plants and ferns. Its prevalence in plants (and absence in many animals) has long puzzled biologists and recent mathematical models still argue that polyploidy should rarely evolve in sexual organisms with non-overlapping generations. Our research uses plant species with natural variation in ploidy (Chamerion, Galax, Malus) and mutagens that induce genome duplication to explore two major hypotheses: 1) genome duplication has a disproportionately large influence on rates of species diversification; 2) it enhances the adaptive potential and, hence, persistence of lineages that bear it.
III. Function and evolution of plant reproductive systems.
Plants exhibit a bewildering array of breeding systems, reflected by variation in gender, floral form and display, mechanisms of pollen transfer, and pathways of fertilization and seed maturation. Accounting for this sexual diversity is important because of its significance for population persistence, reproductive isolation and the organization of genetic diversity within and among populations. It also provides a useful focal point for studying the mechanisms of microevolution such as gene flow, genetic drift and selection. Our research currently focuses on two aspects of plant reproduction: the evolution of self-fertilization versus cross-fertilization (mating system), and the adaptive significance of dichogamy (temporal separation of male and female function). In both cases we are using comparative analyses, manipulative experiments and multi-generational selection studies to understand the evolution of these traits.
IV. Ecological impacts of hybridization and gene flow?
The importance of genetic diversity (mutation, gene flow, drift, heritability) to adaptive evolution is widely recognized, but it is less clear whether and how it affects ecological function and viability of populations. Understanding the ecological consequences of genetic diversity also have implications for conservation, restoration practices. Using a combination of genetic markers and manipulative studies, our research on hybridization between American and Eurasian chestnut (Castanea), Asian and native mulberry (Morus) and domestic and native apples (Malus) has allowed us to explore the conditions favouring gene exchange between species and the impacts on seed production and establishment. In addition, paternity analysis, flow cytometry and experimental crosses are being used to examine patterns of mating and the effects of mate diversity on reproductive success in domestic and native species.
V. Development and applications of plant barcoding
We are part of a national collaborative effort (comprising 4 labs) to develop barcoding tools for plants. The group has published one of the most extensive evaluations of potential barcode regions and has been instrumental (along with 3 other international groups) in facilitating an international agreement on a standard barcode region for land plants . Equally important we are advancing and exploring the applications of this tool for studies in ecology (belowground community structure and function) and evolutionary biology (phylogeography).