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Current Research
	Evolution in response to climate change
	Polyploidy and evolutionary potential
	Invasive species
	Parental effects
	Genetic divergence among populations
	Inbreeding
Current Graduate Students
	Tim McAulay
	Kyle Snell
Former Graduate Students
	Becky Anderson
	Jessica Grochowski
Undergraduate Research
	Undergraduate Research Opportunities Program (UROP)
	McNair SholarsProgram
	Directed Research
	Work study
	Lab Technicians
Courses
	Ecological Genetics (BIOL 5240)
	Evolution (BIOL 4802)
	Plant Diversity (BIOL 3601)
	General Biology II (BIOL 1012)
Complete CV - Link

Our lab uses the tools of ecological genetics to understand factors that influence the persistence of native plant populations in response to anthropogenic changes in the environment including climate change, competition with invasive species, inbreeding due to small population size, introduction of nonnative genotypes during habitat restoration, and increased intensity of deer herbivory. Our goal is to examine how natural plant populations change phenotypically and genetically in response to these agents of selection. We use quantitative genetics to understand the underlying genetic architecture of traits and to attain insight into the potential for ongoing adaptive evolution in response to a changing environment. Using this approach, we can also predict the limits to natural selection to further molding of populations. Molecular techniques are used in our lab to quantify the extent of divergence among populations, the degree of inbreeding within populations, and as tools to distinguish between local and nonlocal genotypes of plants that were introduced for restoration purposes. Main menu

Climate change is expected to alter patterns of natural selection across species’ ranges and pose strong evolutionary challenges to native plant populations. The magnitude of evolutionary response that will occur in any given population depends critically upon the genetic architecture of traits that are the targets of selection. Previous reserach

One important aspect of plant genetic architecture is polyploidy, or the duplication of a whole genome, which has received no empirical attention in this context. It is often assumed that polyploids possess greater evolutionary potential than their diploid progenitors because: 1) organisms with many gene copies harbor greater genetic diversity which is the fundamental substrate of evolutionary change, 2) genetic redundancy creates opportunities for duplicated genes to diverge and acquire new functions without compromising the original function, and 3) gene duplication increases the number of gene interactions, some combinations of which may enhance fitness. Thus, polyploidy may allow organisms to evolve faster or in novel directions compared to their diploid progenitors. Although this is a provocative idea and a compelling hypothesis, it has never been explicitly tested. This research will examine the relationship between ploidy level and evolutionary potential. Unique data will brought to bear on this issue by comparing response to artificial selection of diploid, tetraploid, and hexaploid cytotypes sampled from a single population. Results from this research will increase our understanding of the nature of genetic variation in polyploid taxa that may be selected upon and may ultimately increase the persistence of populations in the face of climate change. The long-term goal of this research is to increase our understanding of genetic properties of plant populations that promote adaptive evolution in response to human-mediated environmental disturbances. The proposed research focuses on one prevalent aspect of plant genetic architecture, namely polyploidy, that may play a critical role in this process. The central hypothesis of this work is that polyploids possess greater evolutionary potential than diploids and will, therefore, adapt more readily to climate change.

Impending climate change will test the capacity of plant populations to evolve heat and drought tolerance.

The goal of this research was to assess the evolutionary potential of populations of an annual legume, Chamaecrista fasciculata, to novel conditions due to global warming employing a quantitative genetic approach. Climate models suggest that southern populations currently experience a climate similar to that which is predicted for northern populations in the future. Investigation into the magnitude and nature of genetic variation for performance of northern populations across a range of environments provided insight into limits to adaptation. I sampled populations from an aridity gradient

in the Great Plains in Minnesota, Iowa, Kansas, northern Oklahoma, and southern Oklahoma. In a pair of greenhouse drought experiments, I found clinal variation among these populations with respect to morphological traits, phenotypic plasticity, and physiological response to drought. Furthermore, there was a reversal in the effect of watering such that northern populations had higher fecundity in well-watered conditions whereas the opposite was true for the most southern population. Pedigreed lines from three populations (MN, KS, and southern OK) were produced by controlled crosses in the greenhouse and progeny were reciprocally planted into field sites in MN, KS, and OK. Phenotypic selection analysis demonstrated that selection regimes differ among the field sites. Short phenology and thin leaves are favored in the north, whereas slower phenology and thick leaves are favored in the south. With few exceptions, quantitative genetic analyses indicated that all populations harbor substantial genetic variance for these traits in all environments. However, although the northern population exhibited relatively high mean fitness in terms of fecundity and expressed significant genetic variance in the intermediate site, it had substantially lower fitness and no significant additive genetic variation in the southern site. The additive genetic correlation structure of northern populations across environments did not indicate a constraint to evolutionary response. However, selection response is predicted to be severely constrained by among-trait additive genetic correlations that are not in accord with the direction of selection (see figure below. However, modest responses to selection may prove biologically significant in an incrementally changing environment. [PDF Science 294:151-154] Main menu

Illustration of the influence of genetic correlations among traits on selection response. (A) Hypothetical positive genetic correlation between two traits (each point represents the breeding value for each of two traits). There are two selection scenarios. For R (reinforcing), selection is in the same direction on traits; the depicted genetic correlation is in accord with the direction of selection, enhancing evolutionary response; thus, the genetic correlation is reinforcing. For A (antagonistic), selection is in the opposite direction for both traits; the genetic correlation is antagonistic to the direction of selection, inhibiting evolutionary response. (B) Scatter plot of MN population reproductive stage and leaf number breeding values (centered on the phenotypic mean), showing significant negative genetic correlation that is antagonistic to the positive vector of joint selection on these traits. (C) Scatter plot of the MN population leaf thickness and leaf number breeding values (centered on the phenotypic mean), showing significant positive genetic correlation that is antagonistic to the negative vector of joint selection.

I am interested in the role that both ecological and evolutionary dynamics play in the persistence of native plant populations that are experiencing invasion. Specifically, I am interested in how evolutionary and ecological dynamics interact to determine the fate of populations. I have recently initiated reserach into an invasive species that only occurs in the Duluth area in North America, Campanula cerviarcia. This species was first collected in this region in 1943 but was not correctly identified until 2003. I have begun to study the demographics and quantitative genetics of the invasive populations in this region.. In the next few years, I will add studies of the native plant populations that compete with this exotic invader. Main Menu

Parental effects
This collaboration with Dr. Laura Galloway at the University of Virginia examines the extent to which offspring phenotype is influenced by genetic inheritance and by environmental factors. Specifically, we are interested in effects of the parental environment that are transmitted from maternal or paternal parent to offspring. In Campanula ameriana both maternal and paternal environmental effects have been shown to influence morphological and phenological traits. In a previous experiment, Laura and I found that parental light levels influence offspring germination and life history patterns. Our current quantitative genetics experiment will allow us to quantify genetic and environmental maternal effects and evaluate the potential that such effects contribute to adaptive evolution. Publications. Main menu

I am initiating research into genetic divergence of populations of Tall goldenrod, Solidago altissima, across the prairie-forest border in Minnesota. A common garden experiment of six populations (pairs of prairie and forest populations at three different latitudes) showed that distinct prairie and forest ecotypes exist in this species. Solidago altissima is an autopolyploid species with diploid, tetraploid and hexaploid cytotypes. My graduate student, Jessica Grochowski, and I are trying to determine the extent to which with geographic variation is attributable to differences in the frequency of cytotypes across the biome border (Jessica Grochowski's web page). We are using the technique of flow cytometry to map the ploidy distribution of this species across the state. In addition, we are trying to relate the cytotype distribution to environmental factors that differ across the biome border, especially water availability. I am also just initiating a project that will test the hypothesis that higher ploidy levels harbor greater evolutionary potential. Main Menu

Populations of the same species diverge genetically due to local adaptation by natural selection and random genetic drift. A central debate in evolutionary biology has been which of these two processes plays a more central role in population divergence. It is likely that both processes are important and interact to result in genetic divergence when populations are not connected by gene flow. Both processes produce genetic differences among populations that may accrue to such an extent that the populations are no longer sexually compatible or have severe reductions in fitness when hybridized (i.e. less vigorous plants, lower seed production). Such incompatibility and other reductions in fitness are referred to as outbreeding depression.

This research focuses on three populations of American bellflower, Campanula americana, which were sampled from the eastern United States in Bloomington Indiana (I), Wintergreen Resort near Charlottesville Virginia (W), and along the Blue Ridge Parkway in North Carolina (P) (See map on right). Populations I and W are farthest apart (~570 km), the distance between I and P is intermediate (~360 km), and W and P are the closest (~190 km). In 2001, seed from these populations were sampled in the field and seedlings raised in the greenhouse at the University of Virginia (Charlottesville, Virginia). Flow cytometry was conducted on a subsample of these plants to determine differences in genome size (See figure on left). These data show that populations I and P have similar genome sizes, whereas population W has a significantly smaller genome than any other population (ANOVA: F2, 22 = 7.86, P = 0.003). These populations were crossed in all pairwise combinations to produce new parental seed, F1, F2, and backcross generations. Seeds from these plants are currently being planted and will be grown to maturity in the greenhouse.

The central questions of this work are as follows:
• Do hybrids among these populations exhibit outbreeding depression?
• Do hybrids of distant populations exhibit stronger outbreeding depression than nearby populations?
• Do populations with different genome sizes exhibit stronger outbreeding depression than those with similar genome sizes?
• What is the mode of gene action that has contributed to population divergence?

Parallel research using a different collection of populations is being conducted in Dr. Laura Galloway's lab at the University of Virginia. Laura Galloway's web page. Main Menu

Inbreeding Depression

Campanulastrum americana is an insect-pollinated self-compatible protandrous herb. Thus, inbreeding is most likely to occur as a result of pollinator movement among flowers of the same plant that are in different gender phases. However, Laura Galloway and I found that multilocus outcrossing rate was 94 % and did not differ significantly from unity. This result was unexpected since previous work demonstrated that pollinators frequently move from male- to female-phase flowers on the same plant.C. americana is also an autotetraploid species. Theory predicts that inbreeding depression should be lower in polyploids relative to diploids. In a greenhouse study, we found that inbreeding depression was not significant for most seed and germination characters. However, all later life traits except flowering date differed between inbred and outcrossed individuals resulting in a 26% reduction in cumulative fitness for inbred plants. Limited early- and moderate later-life inbreeding depression suggest it is buffered by the higher levels of heterozygosity found in an autotetraploid. A three-year field study confirmed the strong impact of inbreeding on mortality rates and fecundity. Publications. Main menu

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©2007 Julie Etterson
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