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Sonia Sultan
Harvard University
Campus Extension: 3493
Evolutionary ecology of plant response to environment.
Current understanding of the evolutionary process rests on the simplifying assumption that genetic differences rigidly determine the relative success or failure of organisms in their environments. However, the organism's own capacity to respond to its environment (phenotypic plasticity) lends an important element of flexibility to this process. In addition, random microenvironmental influences on individual success will affect the outcome of natural selection in unpredictable ways. These largely unexplored areas of evolutionary ecology are the focus of our research.
Work in this lab centers on the morphological, physiological, and reproductive responses of plants to their environments, and how these responses influence natural selection. Study systems include several widespread species of colonizing annuals, primarily in the genus Polygonum. We take an interdisciplinary approach that draws on ideas and methods from physiological ecology as well as developmental, quantitative, and population genetics to examine plant response in both functional and evolutionary terms. Controlled experimentation in the greenhouse is complemented by field studies of natural populations, including genetic sampling where appropriate.
My previous research on phenotypic plasticity showed that single Polygonum genotypes expressed dramatically different, functionally appropriate phenotypes when clones were grown in different environmental treatments, and that these broad repertoires of response would promote the maintenance of genetic diversity within populations. A follow-up study revealed that these plants not only adjusted their own growth characteristics in response to their environments, but also altered the size and structure of their seeds in ways likely to promote offspring success in those environments.
Our current research addresses the evolutionary implications of phenotypic plasticity at the species and population levels. One ongoing project is a comparative study of phenotypic plasticity in four Polygonum species that are ecologically either very broadly or very narrowly distributed. The goal of this study is to determine whether greater phenotypic plasticity of individuals in a species allows that species to occupy numerous habitats, compared with species composed of less plastic individuals. In addition to developmental, physiological, and life-history plasticity, we have compared cross-generational plasticity in these species: ways that plants subjected to environmental stresses may alter the size and specific growth traits of their offspring. This complex aspect of environmental response may influence the ability of species to maintain viable populations in sites subject to poor or variable conditions. The results bear on several issues of broad biological interest, including the nature of generalist versus specialist organisms, the evolution of "weedy" species, and attributes of species likely to become rare or endangered. In a related study, we are testing the hypothesis that plastic response to environment can substitute for the evolution of locally specialized populations. By comparing patterns of population differentiation in highly plastic and less plastic species, we will explore the extent to which the plasticity of individuals in a species can influence patterns of evolutionary diversification. This study complements our recent theoretical examination of this issue (Sultan and Spencer 2002).They will also inform the design of a related study of differentiation among populations of highly plastic versus less plastic species. In this second study, we will explore the extent to which the plasticity of individuals in a species influences patterns of evolutionary diversification.
A second area of research activity is the evolutionary role of seed banks in plant populations. Although it has long been known that a population's "bank" of dormant seeds provides a buffer against local extinction, very little is known about the genetic effects of this buffer. Since random environmental factors largely determine which seeds (and therefore which genetic variants) are released into the breeding population, immigration from seed bank may be a significant factor in maintaining genetic diversity in the face of both natural selection and genetic drift.
Funding: National Science Foundation (Population Biology Panel); USDA; Andrew Mellon Foundation (Conservation and the Environment); Mathers Charitable Trust Links |
Professor