Browsing by Subject "Switchgrass"

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Ecological and evolutionary analyses of range limits and biodiversity patterns
(2011-12) Behrman, Kathrine Delany; Keitt, Timothy H.; Kirkpatrick, Mark, 1956-
The goal of this dissertation is to further our understanding of how spatially heterogeneous landscapes may impact the formation of range boundaries that then aggregate to form large-scale biodiversity patterns. These patterns have been analyzed from many different perspectives by ecologists, evolutionary biologist, and physiologists using a variety of different theoretical, statistical, and mechanistic models. For some species, there is an obvious abrupt change in the environment causing a range boundary. Other environments change gradually, and it is unclear why species fail to adapt and expand their range. The first chapter develops a novel theoretical model of how the establishment of new mutations allows for adaptation to an environmental gradient, when there is no genetic variation for the trait that limits the range. Shallow environmental gradients favor mutations that arise nearer to the range margin, have smaller phenotypic effects, and allow for proportionately larger expansions than steep gradients. Mutations that allow for range expansion tend to have large phenotypic effects causing substantial range expansions. Spatial and temporal variation in climatic and environmental variables is important for understanding species response to climate change. The second chapter uses a mechanistic model to simulate switchgrass (Panicum virgatum L.) productivity across the central and eastern U.S. for current and future climate conditions. Florida and the Gulf Coast of Texas and Louisiana have the highest predicted current and future yields. Regions where future temperature and precipitation are anticipated to increase, larger future yields are expected. Large-scale geographic patterns of biodiversity are documented for many taxa. The mechanisms allowing for the coexistence of more of species in certain regions are poorly understood. The third chapter employs a newly developed wavelet lifting technique to extract scale-dependent patterns from irregularly spaced two-dimensional ecological data and analyzes the relationship between breeding avian richness and four energy variables. Evapotranspiration, temperature, and precipitation are significant predictors of richness at intermediate-to-large scales. Net primary production is the only significant predictor across small-to-large scales, and explains the most variation in richness (~40%) at an intermediate scale. Changes in the species-energy relationship with scale, may indicate a shift in the mechanism governing species richness.
The genetic architecture of quantitative traits in locally adapted plant ecotypes
(2015-08) Milano, Elizabeth Rose; Juenger, Thomas; Kirkpatrick, Mark; Linder, Craig R; Lloyd, Alan; Martin, Noland
Locally adapted ecotypes are a common phenomenon generating plant diversity within species, yet we know surprisingly little about the genetic mechanisms that lead to locally adapted traits. The genetic architecture underlying traits can indicate evolutionary history and predict response to selection, with applications in evolutionary ecology, conservation, and crop development. This research broadly investigates the genetic architecture of quantitative traits in paired ecotypes from different plant species. I used multivariate comparative methods and quantitative trait loci (QTL) mapping to quantify genetic correlations and population divergence, between ecologically relevant traits, both at the phenotypic and genotypic level. I tested for adaptive floral trait evolution in a perennial wildflower by comparing differentiation at neutral loci to differentiation in a suite of quantitative floral traits in an Ipomopsis aggregata hybrid zone. I used multivariate comparisons to incorporate the genetic covariance architecture underlying floral display and reward traits, and found a strong signal for divergent selection. Non-neutral divergence for multivariate quantitative traits suggests that selection by pollinators is maintaining a correlation between floral display and reward. In Panicum virgatum, a native perennial grass, I used a genetic mapping population, segregating ecotypic variation, to construct a linkage map, and map QTL for nine ecological traits. Most QTL had intermediate to small effects and clustered on a limited number of linkage groups. I also found over half of the functional allelic effects displayed patterns associated with fixed differences between ecotypes. These results suggest there is considerable standing genetic variation within local populations, as well as between ecotypes for ecologically relevant traits. Lastly, I explored the genetics of plant tissue quality in Panicum hallii, a model lignocellulosic grass system. Cell wall components compose the bulk of lignocellulosic biomass and contribute to the recalcitrance of plant tissue. I characterized the divergence of four major cell wall components between ecotypes, identified 14 QTL, and found half of the QTL localized to a single linkage group. Exploring the genetic architecture of tissue traits in a tractable system will lead to a better understanding of cell wall structure and function as well as provide genomic resources for bioenergy crop improvement.