Northern Blazing Star

My lab is interested in the adaptive evolution of developmental, physiological, and life history traits in natural plant populations. We use quantitative genetics, QTL mapping, and association studies of candidate loci to examine the genetic basis of natural variation in ecologically important traits. We also measure natural selection on these traits and the loci underlying them by experimentally manipulating environments, phenotypes, and genotypes in the field. Recently we have explored the evolution of adaptive plasticity using phytochrome-mediated “shade avoidance” responses to crowding and vegetation shade as a model system. Another major research objective is to elucidate the genetic and ecological mechanisms of adaptation to seasonal and geographic variation in climate. Our research takes advantage of the genomic tools available for the genetic model species Arabidopsis thaliana, but we also work with natural populations of other species, especially Impatiens capensis (jewelweed or touch-me-not). We also have interests in conservation biology of rare plants, particularly in threatened New England habitats.

Ecological genomics of Arabidopsis thaliana
The annual weed Arabidopsis thaliana is a genetic model, but it also grows in natural populations in a wide range of climates, and exhibits substantial natural variation in ecologically important traits. Our goal is to identify specific loci associated with naturally occurring variation in life history traits and their plasticity in natural seasonal environments, and to examine natural selection on those loci in the wild. By mapping QTL (quantitative trait loci) for major life history traits in natural seasonal environments, we have found geographical and seasonal variation in the genetic control of those traits and in the specific loci under selection. We have also detected associations between natural allelic variation in candidate genes, trait expression, climate in the site of origin, and fitness in a wide range of Arabidopsis ecotypes grown in common gardens in different natural environments. We are using these data to understand mechanisms of adaptation to seasonal and geographic variation in climate, and to predict evolutionary responses to future climate change. We also study the effect of genetic modification at specific candidate loci on performance and fitness in different ecologically relevant environments.

We are now expanding the scope of this work to ask: How do multiple signaling pathways interact to produce an integrated phenotype in complex environments, and how does natural selection shape the function and architecture of signaling networks in the real world? In order to flower at the right time, plants integrate information from multiple environmental cues, such as day length, growth temperature, and past winter chilling. Different responses to these cues are favored in different climatic regions. Our research objective is to understand how plants integrate multiple environmental signals in the real world, and how the genetic pathways underlying these responses evolve in different climates. This is a large interdisciplinary project in collaboration with research teams headed by plant molecular biologist Richard Amasino (U. of Wisconsin), gene network modeler Stephen Welch at Kansas State U., and molecular evolutionary geneticist Michael Purugganan (NCSU), with support.from the NSF Frontiers in Integrative Biological Research program (FIBR). Our lab is involved in the following projects as part of this effort: 1) screening for natural variation in integrated responses to multiple environmental signals under controlled conditions; 2) testing whether natural sequence variation in candidate genes is causally associated with variation in flowering responses to different environments; 3) testing for evidence of local adaptation to climate by examining geographic associations between ecotype flowering responses, candidate gene variation, and climate in the site of origin; and 4) measuring geographic variation in natural selection on flowering time pathways and investigating the genetic basis of adaptation to climate in a large-scale experiment in which a set of European ecotypes will be grown under natural field conditions at 6 sites across the native European range of A. thaliana in collaboration with 7 leading European Arabidopsis laboratories. Because the same ecotypes can be replicated across experiments in this inbreeding species, it will be possible to integrate phenotypic data from multiple experiments, data on molecular polymorphisms at candidate gene loci and neutral markers, and geographic information on the climatic provenance of each ecotype into a common data base.

The evolution of adaptive plasticity: phytochrome-mediated shade avoidance responses
Many plants display a characteristic suite of developmental “shade avoidance” responses, such as stem elongation and accelerated reproduction, to the low ratio of red to far-red wavelengths (R:FR) reflected or transmitted from green vegetation. This R:FR cue of crowding and vegetation shade is perceived by the phytochrome family of photoreceptors. Phytochrome-mediated responses provide an ideal system for investigating the adaptive evolution of phenotypic plasticity in natural environments. We have used genetic, phenotypic, and environmental manipulation to demonstrate that shade avoidance responses may be adaptive, resulting in phenotypes with high relative fitness in the environments that induce those phenotypes. Our field experiments with Impatiens capensis have shown that the adaptive value of shade avoidance depends upon resource availability as well as the competitive environment. We have found evidence of adaptive divergence in shade avoidance responses between woodland and clearing habitats, which may result from population differences in the frequency of selection on shade avoidance traits, as well as differences in the reliability of the R:FR cue. One current project will compare patterns of molecular and quantitative genetic differentiation in shade avoidance among Impatiens populations to understand the evolutionary history of local adaptation in this species. We are also investigating the adaptive evolution of phytochrome mediated plasticity in early seedling development (emergence and deetiolation) and how these early seedling events might constrain the evolution of shade avoidance traits.

Function-valued traits in natural populations
Many of the traits that we study, such as growth curves, photosynthetic response curves, and reaction norms to continuous environmental variables such as plant density, R:FR, or light availability, can be described as continuous functions. We are collaborating with a consortium of researchers headed by Richard Gomulkiewicz and Patrick Carter (Washington State University) to understand the evolution of such “function-valued” traits. We are using new methods developed by our theoretical and statistical collaborators to describe genetic variation for function-valued traits in natural populations, and to predict how they will evolve in response to natural selection in course-grained environments.

Plant conservation biology
My lab also has ongoing interests in local adaptation, inbreeding depression, maternal effects, and plant responses to stress, and their implications for plant conservation. We have recently become involved in studies of demography, reproductive biology, genetic structure, and spatial analysis of habitat for several threatened plant species, notably Liatris scariosa var novae-angliae (Northern Blazing Star).

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