Research
In plants, survival and reproductive success depend on the ability to coordinate development, growth, and reproduction with variable factors in the external environment. Such factors may be highly predictable (photoperiod) or vary considerably from season to season (temperature). The predictability of any given factor may be disrupted by larger scale phenomena such as long-distance migration or long-term climate change. An improved understanding of how individual plants and plant populations integrate environmental complexity is a major goal in plant organismal biology. Such an understanding would make it easier to successfully breed or engineer crop species, or to forecast how the ranges of crop, native, or exotic plant species will respond to migration or climate change. By focusing on Arabidopsis thaliana, which is a model plant species and the focus of an international plant genome sequencing initiative, research focusing on this type of complex adaptive evolution is made more tractable (Callahan et al. 1997).
My lab is actively
studying the phenotypic plasticity of flowering time in Arabidopsis thaliana, a
weedy, cosmopolitan species that typically flowers in early spring. Very generally,
phenotypic plasticity is a change in phenotype induced by the environment. For example,
flowering time in Arabidopsis responds plastically to at least three seasonally
variable and light-related factors: light intensity, light spectral quality, and
photoperiod (daylength). It also responds to a fourth seasonally variable factor,
vernalization (extended exposure to cold temperatures). All four factors may change in an
imperfectly concordant fashion during the transition from winter to spring. Molecular
biologists are actively studying how multiple photoreceptors and other light- or
vernalization-sensitive genes are integrated in Arabidopsis. Our work complements
these mechanistic studies by investigating flowering time plasticity from ecological and
evolutionary perspectives.
We are studying natural
phenotypic and genetic variation using several approaches. The first approach uses wild Arabidopsis
populations collected all over the world, from habitats with varying climatic and local
light and temperature regimes. We use this collection to examine patterns of
differentiation among and within populations. A second approach uses a collection of
nearly 100 full-sib families drawn from a spring-flowering population in Michigan and
subject to several generations of artificial selection. With these families, we are
studying flowering time in different types of environments using quantitative genetics
(e.g., estimates of heritability). Yet a third approach takes advantage of artificial
crosses between pairs of ecologically divergent natural genotypes; these crosses generate
genetically variable offspring. From these offspring, it is possible to establish and
maintain separate inbred sub-populations, called recombinant inbred (RI) lines. With these
RI lines, we plan to initiate long-term studies of how natural selection regimes can alter
flowering time and its plasticity to various seasonal factors. 
We are also interested in studying seasonal phenotypic plasticity and other syndromes of phenotypic plasticity with other plant species (Callahan and Waller 2000). We are particularly interested in comparing invasive species and native species that compete poorly with invaders. Such studies may be conducted in natural habitats, including a series of sites already established by other researchers along a gradient from very urban to very rural sites. This series of sites is likely to include forested areas in New York City parks and at the New York Botanical Garden’s forest in the Bronx, the Black Rock Forest in the Hudson Valley, or other small natural areas in rural New York and Connecticut.
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