Browsing by Subject "Local adaptation"
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Item 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, NolandLocally 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.Item Geographic variation in male nuptial color across multiple scales in threespine stickleback, Gasterosteus aculeatus(2015-12) Brock, Chad Daniel; Bolnick, Daniel; Cummings, Molly E.; Hofmann, Johann A; Kirkpatrick, MarkMost species exhibit geographic variation in phenotypic traits, and this variation can occur across a broad range of spatial scales. Consistent phenotype-environment correlations are often invoked as evidence for adaptation in response to spatially varying natural selection. Both theoretical and empirical work suggests that local adaptation can occur most readily when the strength of selection exceeds the homogenizing effect of gene flow. Consequently, adaptive phenotype-environment correlations are typically studied at broad spatial scales at which gene flow is weak and environmental variation is pronounced. Despite this, a number of species show adaptive phenotypic divergence across microspatial scales. Signal detectability in animal communication is frequently contingent on the local environment. Consequently, to maintain optimal detectability, signal design should covary with the signaling environment, resulting in predictable phenotype-environment correlations. We investigated whether spatial variation in nuptial color of male threespine stickleback, Gasterosteus aculeatus, varies predictably with optical environment at two spatial scales: 1) between lakes 2) within lakes. We demonstrate that male nuptial color varies significantly between 15 lakes on Vancouver Island, BC. Male orange/red reflectance negatively covaries with the amount of orange/red in the optical background, suggesting that nuptial color tracks the local optical environment to maintain signal contrast. However, visual model results indicate that male signal contrast varies between lakes. Some lakes showed evidence of local adaptation, while others did not. A number of ecological characteristics also covary with male color and contrast, and we suggest these factors may constrain males’ ability to track local signaling optima. Within lakes, we found ’microclines’ across a small spatial gradient: male nuptial color changes across a 2-meter vertical range of nest depths. The color microcline is repeatably associated with depth gradients in ambient light, suggesting that these microclines reflect adaptation to local optical environments. Visual modeling demonstrates that these signals vary in contrast with background, depending on a male’s nest depth. Deeper-nesting males reflected more UV/blue and were more conspicuous than shallow-nesting males. Experimental manipulation of male nesting depth induced plastic changes in nuptial color that replicated the natural gradients in color and conspicuousness, implicating plasticity as the primary mechanism driving microcline formation.Item Germination studies in Arabidopsis thaliana and Sinapis arvensis : genetical and ecological perspectives(2013-08) Morrison, Ginnie Denise; Linder, C. RandalThe environment can exert strong selective pressures on an organism. When selective pressures on traits differ between environments local adaptation may occur. If there is gene flow between the environments, local adaptation may be slowed or prevented. In plants, particularly weedy ephemerals, germination is a life-history trait that can be a strong determinant on fitness. In this dissertation, I explore the germination traits of two weedy Brassicaceae species, Arabidopsis thaliana and Sinapis arvensis, having populations in different habitats to determine whether germination traits within and between populations vary based on environmental conditions and to assess the extent of local adaptation. In Chapter 1, I assessed which genomic regions of A. thaliana were associated with differences in germination traits due to genotype-by-environment interactions. I performed a genome-wide association study using 100 natural accessions of A. thaliana under four light and nutrient combinations. I found 20 single nucleotide polymorphisms significantly associated with different environments, but none associated specifically with genotype-by-environment interactions. In Chapter 2, I assessed germination traits of S. arvensis collected from agricultural and non-agricultural habitats in the Bitterroot Valley of Montana. I discovered that the agricultural collection studied exhibited significantly different germination timing and amounts than the non-agricultural collections, which were statistically indistinguishable from each other. I also found evidence of a strong maternal effect on germination traits. In Chapter 3, I tested whether patterns of genetic variation between agricultural and non-agricultural collections of S. arvensis supported local adaptation to the two habitats even in the face of gene flow. While I expected to see some genetic differentiation between habitats, as seen in Chapter 2, no genetic differentiation was detected and markers putatively under selection were not associated with a particular habitat. I discuss why this might have occurred even though I have evidence for genetically-based phenotypic differentiation between agricultural and non-agricultural populations of S. arvensis.Item The interface between metacommunity ecology and microevolution in freshwater zooplankton(2009-12) Pantel, Jelena Holly; Leibold, Mathew A.; Juenger, Thomas E.; Hawkes, Christine; Bolnick, Daniel I.; Caceres, CarlaIn many habitats, species’ traits correspond strongly to local environmental conditions. The cause of this pattern may be in-situ evolution, where initially mal-adapted resident species evolved traits that increased their fitness. Alternatively, species with suitable traits may have colonized the focal habitat and replaced resident species. Since theories in the fields of evolutionary biology and community ecology developed independently, few guidelines tell us when to expect evolutionary adaptation or ecological species replacement as the primary driver of species and trait composition in a given habitat. The goal of my dissertation research was to explain how evolutionary adaptation and ecological species replacement together determine the composition of pond zooplankton communities. I combined theoretical models with thorough surveys of natural pond communities and manipulative experiments. I discovered that one particular zooplankton species, Daphnia pulex, evolved to have different trait values in ponds with different environments. The evolutionary divergence within D. pulex profoundly affected its ecological interactions with other zooplankton species. D. pulex populations diverged from one another so much that they differed in their ability to successfully colonize ponds full of competing zooplankton species. I also used a computer simulation model to determine when a community’s trait changes were explained by evolutionary adaptation or ecological species replacement. The dispersal rate of species among habitats and the amount of genetic variance within these species both influenced adaptive trait change in a community. The group of research studies that indicate evolutionary and ecological processes operate on a similar time scale is small but growing. My dissertation research provides another crucial demonstration that evolution within individual species, such as D. pulex, influences their community ecological interactions with other species. I also identified key parameters (dispersal rate among and genetic variance within species) that may help biologists predict whether evolution or ecological species replacement explained adaptive trait change. My projects mostly concern the community and trait distributions that result from the assembly of species in new habitats. However, this framework may inform studies of community response to environmental changes such as invasive species or habitat destruction.Item Local adaptation to parasites and selection on major histocompatibility genes in ecologically divergent populations of three-spine stickleback (Gasterosteus aculeatus)(2013-08) Stutz, William Edward; Bolnick, Daniel; Kirkpatrick, Mark, 1956-As individuals and populations diverge ecologically, they become exposed to new parasites and pathogens with potentially harmful fitness consequences. Populations are therefore expected to evolve resistance, possibly at a cost of less resistance to parasites rarely encountered parasites. This trade-off in resistance should generate local adaptation to parasites in different habitats. In chapter one, I show how local adaptation can potentially evolve in response to variation in parasite exposure among eighteen ecologically variable populations of threespine stickleback (Gasterosteus aculeatus). Within populations infection appeared to reflect morphology/diet based exposure differences among individuals. Among populations, however, these patterns were absent or reversed, consistent with the evolution of local adaptation. In chapters two and three I set out to test whether variation major histocompatibility (MHC) genes can underly such local adaptation in stickleback. MHC genes are important components of vertebrate immunity; however, there is little direct empirical support for spatially divergent selection driving local adaptation on MHC loci in the wild. In chapter two I tested for the action of parasite mediated balancing and divergent selection on on MHC loci using naturally infected stickleback in three replicate lake-stream pairs. Despite consistent divergence in parasites and MHC alleles, lakes tended to show decreased parasite burdens with increased allelic richness (consistent with balancing selection), while streams showed some support for divergent selection between lake and stream types. In chapter three I use the same lake-stream pairs to investigate how divergent selection could instead be reflected in variation in the effects of individual MHC alleles among populations. When comparing parapatric populations experiencing gene flow, MHC alleles maintained at relatively high frequency in one population were more likely to be associated with reduced, rather than increased, parasite abundances in that population. Allopatric populations experiencing no gene flow showed no such general relationship between allele frequency and resistance. These results are only consistent with spatially divergent selection, and imply that gene flow and environmental heterogeneity can be important for maintaining MHC diversity.