Local adaptation and phenotypic plasticity
Many plants show a remarkable degree of phenotypic plasticity, drastically altering gene expression, physiology and morphology according to the environment. I am interested in understanding how plants can respond adaptively to their environment through sensing and/or integration of environmental cues, and how these responses affect the geographic range and niche breadth of plants.
For plants that occupy a wide range of habitats, what constitutes an appropriate response to a given environmental cue in one habitat may not be adaptive in another. My current research with Johanna Schmitt at Brown University seeks to elucidate how geographic variation in selection pressure shapes plant response using a synthetic approach that brings together phenotypic, genetic and developmental modeling data.
The wide distribution of Arabidopsis thaliana and its well-characterized developmental genetics make it an ideal system in which to study the genetic architecture of environmental responsiveness. Like many species, the model plant A. thaliana exhibits multiple different life histories in natural environments. We grew mutants impaired in different signaling pathways in field experiments across the species' native European range in order to dissect the mechanisms underlying this life history variation. A genetically informed photothermal model of progression toward flowering, developed in conjunction with our collaborator Stephen Welch, explained most of the observed variation in flowering time and predicted an abrupt transition from autumn flowering to spring flowering in later summer germinants (Wilczek et al., Science, doi:10.1126/science.1165826). We are now working to extend our phenology model to a broader range of climates (both current and future). The model approach could also be applied to alternate genetic architectures, including economically important seasonal traits in other species.
In collaboration with Arabidopsis laboratories at five field sites in Spain, Germany, England, and Finland, we are continuing to explore 1) how variation in climate may favor different life history characteristics across sites and seasons and 2) the extent to which natural variation in populations shows the signature of local adaptation. In 15 total seasonal field plantings across the five common gardens in 2006-2008, we have collected life history data on a large set of genetically diverse lines drawn from throughout A. thaliana's range as well as controlled background genotypes harboring alternate alleles of key genes in flowering time pathways. These data, which we are currently analyzing and preparing for publication, will further our understanding of the geographic variation in natural selection on life history across the native range of Arabidopsis thaliana, the relationship between natural genetic variation, climate and local adaptation, and the role that different developmental pathways play in shaping adaptive responses. For example, we have determined that natural variation in the polymorphic candidate gene FRIGIDA experiences contrasting patterns of selection across sites and seasons. Natural loss of FRIGIDA accelerates flowering, with positive fitness consequences in spring- and summer-germinating cohorts. Populations that contain natural null alleles are more likely to be located in areas with high summer precipitation, even though there appears to be no distinction in the monthly temperature profiles of allele types. Thus the ability to complete a rapid cycling generation in the summer, which may be correlated with the spread of agricultural tilling, appears to be driving the rapid, recent spread of null alleles.
With Sonia Sultan at Wesleyan University, I took part in an ongoing project investigating the relationship between individual plasticity, response breadth and population differentiation in a group of four co-occurring species in the genus Polygonum (doi: 10.1046/j.1365-2745.1998.00265.x; doi: 10.1007/s004420050554 ). More recently, we studied how phenotypic plasticity and maternal effects can in combination affect plant adaptation to environment (Ecology, doi: 10.1890/08-1064.1), an area of research I explore further below.
Photo of Arabidopsis in snow by Judith L. Roe.
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