Browsing by Subject "Local adaptation"

Now showing 1 - 4 of 4
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    Floral traits and pollination of Solidago altissima: mechanisms of local adaptation among and within biomes
    (2013-07) Hafdahl, Claire Elizabeth
    Solidago altissima is an herbaceous, clonal plant that has differentiated into two subspecies in the prairie and forest biomes in Minnesota. The mechanisms that have driven the divergent evolution of these subspecies are not well understood. The evolution of floral traits is influenced by the trade-off between sexual and asexual reproduction. Floral traits can evolve rapidly, and this often occurs in response to interactions with pollinators. I found differences in floral traits between plants from the two biomes, and these differences strongly affected pollinator abundance. Forest plants allocate proportionally more resources to flowering than to vegetative reproduction via rhizomes compared to plants in the prairie. I hypothesize that there is stronger competition among plants for resources in the prairie, where selection favors greater allocation of resources to vegetative reproduction. I also tested the hypotheses that pollinator abundance is influenced by differences among plant genotypes and the genotypes of neighboring plants. I conducted an experiment and found that the number of pollinators on a plant was influenced by the genotype of a plant, but not by the genetic diversity of neighboring plants. I also found that the abundance of neighboring flowers affected pollinator abundance. Plant genotypes varied in floral size, flowering time, and nectar quantity. Floral size of the individual stem had the strongest effect on pollinator abundance. The variation in floral traits among genotypes may be a result of selection to optimize the tradeoff between vegetative growth and flowering, which can vary spatially and temporally.
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    Limits to range expansion in the native annual legume Chamaecrista fasciculata.
    (2011-08) Stanton-Geddes, John Louis
    Species range limits are determined by historical (e.g., range expansion), ecological (e.g., biotic interactions) and genetic (e.g, gene flow) processes, but comprehensively understanding the relative role of these processes in limiting any single species‟ range has been elusive. This research is timely for understanding species‟ responses to climate change. The goal of this research was to examine the processes that limit the range of the native annual legume Chamaecrista fasciculata, by integrating ecological-genetic field studies and population genetic laboratory studies. In Chapter 1, I investigate the extent to which C. fasciculata is in demographic range edge equilibrium at its western and northern range edges, and the effect of biotic interactions at these range edges. I find that C. fasciculata fitness is reduced to zero when planted beyond the western and northern range limits, indicating it is in equilibrium with its range. Neighbors increase early-season survival, but decrease seedpod production. The goal of Chapter 2 was to examine if the mutualism between C. fasciculata and its associated rhizobia was disrupted beyond the range edge, potentially limiting range expansion. The results demonstrate that compatible rhizobia are nearly absent beyond both range edges, which may limit range expansion. In Chapter 3, I ask how the habitat where C. fasciculata establishes may change with range shifts. I conclude that habitat type influences C. fasciculata fitness, but the outcome depends on both the substrate and competitive environments. Finally, in Chapter 4, I use population genetic methods to gain insight into the history of range expansion, population structure and gene flow. Population genetics indicate that the edge populations have reduced genetic diversity compared to the southernmost interior population, and are highly differentiated from each other. However, there is little evidence for contemporary gene flow between populations at the scale investigated. Overall, this work suggests that ecological-genetic or metapopulation dynamics are likely to be involved in setting the northern and western range limits. Further, it highlights the value of integrated approaches to studying species‟ range limits.
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    Phenotypic and Genetic Variation for Rhizosphere Acidification, a Candidate Trait for pH Adaptability, in Deciduous Azalea (Rhododendron sect. Pentanthera)
    (2016-07) Susko, Alexander
    In breeding ornamental plants, selection for aesthetic qualities have predominated with less focus on improving certain physiological traits such as pH tolerance. Deciduous azaleas (Rhododendron sect. Pentanthera) are a prime example, where selections from the Woody Plant Breeding Program at the University of Minnesota have introduced 16 cold-hardy, ornamental plants but lack tolerance to high pH and calcareous soils common in many parts of the United States. High pH stress typically manifests in deciduous azalea as iron deficiency chlorosis; a yellowing of plant leaves due to reduced photosynthetic capacity. Chlorosis results in diminished aesthetic appeal and ultimately can lead to plant death. We present research on the quantitative trait variation for pH adaptability in deciduous azaleas; focusing on wild and cultivated populations, as well as novel phenotyping approaches to get a better picture of the phenotypic and genetic variation for pH adaptability in each. The Woody Plant Breeding program initiated its azalea breeding program in 1954 and has kept crossing records ever since. Unfortunately, the location and habitat details for many of the parents of popular cultivars are unavailable. We first categorize one North American species, Rhododendron viscosum (L.) Torr., which is commonly used as a parent in crosses for its white flowers, late season flowering and also for it’s potential to contribute stress adaptation. We developed 14 SSR loci from a sequenced transcriptome of a wild collected R. viscosum plant to help us estimate subpopulation differentiation and admixture throughout the southeastern U.S. range for the species for eventual comparison with trait additive variation. Population level Rst values (0.49) indicated a strongly differentiated population, and STRUCTURE analysis revealed limited admixture between subpopulations in the western part of the R. viscosum range. Next, we present the development of an in vitro phenotyping assay designed to expedite the Rhododendron breeding process and measure rhizosphere acidification, a candidate trait for pH adaptability. Increased iron solubility in soil and root tissue is critical to mitigating iron deficiency chlorosis, though iron solubility is limited in high pH and or calcareous soils. One way that plants make this iron reduction reaction more favorable is through rhizosphere acidification, resulting in lower soil pH near roots allowing newly soluble iron to be reduced and transported into root tissues. New image analysis methods using the technical programming language MATLAB (MathWorks, Inc.) were developed to measure and quantify rhizosphere acidification in tissue-cultured Rhododendron seedlings. Germination of immature Rhododendron seed in vitro was significantly enhanced by gibberellic acid (GA3) applications, resulting in progeny that were screenable for pH tolerance as early as 5 months after crossing as opposed to the usual 8 months. We were able to colorimetrically detect rhizosphere acidification for plants grown in tissue culture media, which correlated with root mass in the breeding populations tested. However, using root mass as the sole predictor of the variation in rhizosphere acidification failed to replicate the observed phenotypic variation across these breeding populations. This indicated that other sources of variation, possibly genetic, could explain a significant portion of the phenotypic variation in rhizosphere acidification. Finally, we employed our in vitro assay to phenotype progeny from two separate deciduous azalea mating designs: a factorial crossing scheme consisting of advanced selections from the UMN breeding program and half sib families from different R. viscosum subpopulations sampled throughout the southern United States. We also developed another MATLAB script to quantify growth rates and leaf color in seedlings of the factorial crossing scheme to correlate with rhizosphere acidification data for each family. Rhizosphere acidification had a narrow-sense heritability of 0.38 in the factorial design and 0.83 in the half-sib design when measured over three calcium carbonate liming rates. The additive variation for rhizosphere acidification was significant in the half sib design, though it was not so in the factorial design. The effect of an endophytic bacterium infection on rhizosphere acidification was found to be significant where present among half sib families derived from Arkansas and Texas subpopulations. Comparisons of trait to molecular variation within and among populations for rhizosphere acidification in R. viscosum revealed that rhizosphere acidification was not locally adapted, as the trait Qst value was 0.20, lower than our molecular differentiation estimate (Rst) of 0.49. Rhizosphere acidification quantified in vitro correlated positively with the growth rate of soil grown seedlings measured in the greenhouse (R2 = 0.49), with families possessing the highest rhizosphere acidification also having the highest growth rates. We conclude that increased rhizosphere acidification in deciduous azalea improves adaptability to high pH soils, and can be screened relatively early to expedite the breeding process of these popular woody ornamental plants.
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    Seedling recruitment in fragmented populations of Echinacea angustifolia
    (2013-02) Dykstra, Amy Beth
    Human activities have resulted in extensive habitat fragmentation, one consequence of which is the reduction in size of remnant plant populations. Small populations may experience increased inbreeding and genetic drift, and are more vulnerable than large populations to demographic and environmental stochasticity. This dissertation describes three research questions related to the effects of habitat fragmentation on Echinacea angustifolia, a species native to the Great Plains of North America. First, I ask whether small remnant populations of E. angustifolia are declining relative to larger populations. Population projection matrices, parameterized with data from two transition years, predicted population declines. A matrix for the 5 smallest populations had significantly lower population growth rate than a matrix for the large populations. Mortality was higher for seedlings than for other stages of the life cycle; however, survival of vegetative and reproductive plants made a greater contribution to population growth rate than did either emergence or survival of seedlings. This is one of only a few studies to find a correlation between population size and population growth rate. Second, I ask whether genetic declines in remnant E. angustifolia populations can be remedied by outcrossing. I performed within-population and between-population crosses using six populations of varying size. Responses to cross type depended on the populations represented and on the fitness trait evaluated. Between-population crosses involving the smallest populations resulted in offspring with higher fitness than the offspring of within-population crosses (i.e., heterosis), while other between-population crosses showed outbreeding depression. Due to the risks of outbreeding depression, managers are cautioned against attempting genetic rescue by performing between-population crosses. Third, I ask whether E. angustifolia populations exhibit local adaptation. I collected and reciprocally sowed seeds from three widely-separated populations located along a 500-km transect from western South Dakota to western Minnesota. Seed source and sow site had significant effects on seedling emergence and survival, but no clear evidence of local adaptation among the three populations was observed. All three source populations had highest emergence in Minnesota and lowest emergence in western South Dakota. The western South Dakota and Minnesota-sourced seed had higher emergence than the central South Dakota seed at all three sowing sites. The western South Dakota seedlings had the highest survival and the Minnesota seedlings had the lowest survival over the first growing season at all three sites.