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Johanna Schmitt - One of the best experts on this subject based on the ideXlab platform.
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Across-environment genetic correlations and the frequency of selective environments shape the evolutionary dynamics of growth rate in Impatiens Capensis.
Evolution; international journal of organic evolution, 2010Co-Authors: John R. Stinchcombe, M. Shane Heschel, Brechann V. Mcgoey, Rima Izem, Johanna SchmittAbstract:Trade-offs can exist within and across environments, and constrain evolutionary trajectories. To examine the effects of competition and resource availability on trade-offs, we grew individuals of recombinant inbred lines of Impatiens Capensis in a factorial combination of five densities with two light environments (full light and neutral shade) and used a Bayesian logistic growth analysis to estimate intrinsic growth rates. To estimate across-environment constraints, we developed a variance decomposition approach to principal components analysis, which accounted for sample size, model-fitting, and within-RIL variation prior to eigenanalysis. We detected negative across-environment genetic covariances in intrinsic growth rates, although only under full-light. To evaluate the potential importance of these covariances, we surveyed natural populations of I. Capensis to measure the frequency of different density environments across space and time. We combined our empirical estimates of across-environment genetic variance-covariance matrices and frequency of selective environments with hypothetical (yet realistic) selection gradients to project evolutionary responses in multiple density environments. Selection in common environments can lead to correlated responses to selection in rare environments that oppose and counteract direct selection in those rare environments. Our results highlight the importance of considering both the frequency of selective environments and the across-environment genetic covariances in traits simultaneously.
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Partitioning adaptive differentiation across a patchy landscape: shade avoidance traits in Impatiens Capensis.
Evolution; international journal of organic evolution, 2007Co-Authors: Eric J. B. Von Wettberg, David L. Remington, Johanna SchmittAbstract:Adaptation to different habitat types across a patchy landscape may either arise independently in each patch or occur due to repeated colonization of each patch by the same specialized genotype. We tested whether open- and closed-canopy forms of Impatiens Capensis, an herbaceous annual plant of eastern North America, have evolved repeatedly by comparing hierarchical measures of F(ST) estimated from AFLPs to morphological differentiation measured by Q(ST) for five pairs of populations found in open and closed habitats in five New England regions. Morphological differentiation between habitats (Q(HT)) in elongation traits was greater than marker divergence (F(HT)), suggesting adaptive differentiation. Genotypes from open- and closed-canopy habitats differed in shade avoidance traits in several population pairs, whereas patterns of AFLP differentiation suggest this differentiation does not have a single origin. These results suggest that open- and closed-canopy habitats present different selective pressures, but that the outcome of diversifying selection may differ depending on specific closed- and open-canopy habitats and on starting genetic variation. Hierarchical partitioning of F(ST) and Q(ST) makes it possible to distinguish global stabilizing selection on traits across a landscape from diversifying selection between habitat types within regions.
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Maternal effects of drought stress and inbreeding in Impatiens Capensis (Balsaminaceae)
American journal of botany, 2007Co-Authors: Corinna Riginos, M. Shane Heschel, Johanna SchmittAbstract:Maternal effects can have substantial impacts on plant fitness and plant populations. Stressful environmental conditions can cause a maternal plant to inadequately provision its progeny, resulting in poor seedling growth, low reproductive success, and decreased competitive ability. Maternal effects consist of environmental and genetic load components, but the interactions between these two components have rarely been considered. To determine the effects of maternal drought stress and maternal inbreeding on progeny biomass (a fitness correlate) and physiological responses to drought stress, we conducted a greenhouse experiment with genetic lines from two populations (mesic site vs. dry site) of the herbaceous annual Impatiens Capensis (Balsaminaceae). Seeds were collected from cleistogamous flowers of inbred or outcrossed maternal plants that were subject to either a drought or control treatment. These seeds were grown into juvenile plants that were also subject to either a drought stress or a control treatment. Plants from the mesic site had significantly reduced biomass from maternal drought stress, while plants from the dry site maintained biomass despite adverse maternal environmental conditions. Juvenile plants of both populations had reduced biomass only as a result of maternal inbreeding. Interestingly, inbreeding depression was more apparent when maternal environmental conditions were benign.
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Ecosystem engineers as selective agents: the effects of leaf litter on emergence time and early growth in Impatiens Capensis.
Ecology letters, 2006Co-Authors: John R. Stinchcombe, Johanna SchmittAbstract:By physically modifying the abiotic environment, ecosystem engineers can have dramatic effects on the distribution and abundance of species in a community. However, ecosystem engineering can also change the selective environment and evolutionary dynamics of affected species, although this remains relatively understudied. Here, we examine the potential for an ecosystem engineer – oak trees – to affect the evolutionary dynamics of the herbaceous, understory annual, Impatiens Capensis, through leaf litter deposition. Using a quantitative genetic experimental approach, we found that: (i) the presence of leaf litter significantly affected a suite of germination, growth and phenological traits in I. Capensis; (ii) I. Capensis does not exhibit performance trade-offs across litter and bare soil environments in the form of negative across-environment genetic correlations; (iii) the presence or absence of leaf litter significantly alters the pattern of natural selection germination timing and hypocotyl length; and (iv) the frequency of leaf litter environments can dramatically change which combinations of hypocotyl length lead to highest mean fitness across both bare soil and leaf litter environments. More generally, our results demonstrate the potential for ecosystem engineers to alter both the ecological and the evolutionary dynamics of the species they affect.
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Testing for stress-dependent inbreeding depression in Impatiens Capensis (Balsaminaceae).
American journal of botany, 2005Co-Authors: M. Shane Heschel, Neil Hausmann, Johanna SchmittAbstract:The relevance of inbreeding depression to the persistence of plant populations can depend upon whether stress magnifies inbreeding depression for fitness-related traits. To examine whether drought stress exacerbates inbreeding depression in gas exchange traits and biomass, we grew selfed and outcrossed progeny of inbred lines from two populations of Impatiens Capensis in a greenhouse experiment under water-limited and moist soil conditions. Drought stress did not magnify the degree of inbreeding depression for any of the traits measured. In fact, in one population there was a trend for stronger inbreeding depression under well-watered, benign conditions. Furthermore, significant inbreeding depression for carbon assimilation rate and stomatal conductance was only detected in the lines from one population. In contrast, inbreeding depression for biomass was detected within both populations and differed among lines. Drought stress exerted significant selection on physiological traits, favoring increased carbon assimilation rates and decreased stomatal conductance in drought-stressed plants. Patterns of selection did not differ between inbred and outcrossed plants but did differ marginally between populations. Thus, estimates of selection were not biased by the mixed mating system per se, but may be biased by combining individuals from populations with different histories of selection and inbreeding.
M. Shane Heschel - One of the best experts on this subject based on the ideXlab platform.
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Effects of population site and maternal drought on establishment physiology in Impatiens Capensis meerb. (Balsaminaceae)
Rhodora, 2016Co-Authors: Christina Maruyama, Zander Goepfert, Kate Squires, Thayer Maclay, Quill Teal-sullivan, M. Shane HeschelAbstract:Abstract Populations of Impatiens Capensis can differentiate across a range of soil moisture conditions. Differences in the plasticity of drought response at both the physiological and morphological level have been documented in populations across the North American range of this species. Impatiens populations tend to utilize whichever drought response mechanism will be most helpful in ensuring their survival and persistence in their particular environment. Here, we examine whether populations from a range of moisture environments exhibit tolerance/avoidance strategies in early life-history and whether maternal effects are important to seedling stress responses. Populations from Pennsylvania across a range of three moisture conditions all responded to maternal drought by decreasing stomatal conductance in seedlings; this maternal drought response was ephemeral and only observed during the first few weeks of growth. Moreover, abscisic acid content covaried with this conductance plasticity for two of the th...
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POPULATION DIFFERENTIATION OF Impatiens Capensis (BALSAMINACEAE) AT THE RANGE LIMIT
International Journal of Plant Sciences, 2011Co-Authors: Katherine Bibee, Katie Shishido, Ronald P. Hathaway, M. Shane HeschelAbstract:A plant species that occupies a large geographic range must survive in a variety of environments. Impatiens Capensis, an herbaceous annual that grows contiguously from the east coast of North America to the Colorado Rocky Mountains, prefers moist environments and is easily susceptible to drought. Impatiens populations at the species’ western range limit (Colorado) must endure a dramatically different environment than eastern populations do (Rhode Island and Illinois). This study investigated the stress response of a weedy annual at its range limit by examining how regional populations of I. Capensis morphologically, physiologically, and phenologically adjust to drought. The results suggest that each population has evolved along a different evolutionary axis; each population exhibits a unique strategy for responding to drought stress. Rhode Island populations have evolved along a temporal axis to avoid stress with an accelerated phenology. An Illinois population has evolved along a physiological axis and e...
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Across-environment genetic correlations and the frequency of selective environments shape the evolutionary dynamics of growth rate in Impatiens Capensis.
Evolution; international journal of organic evolution, 2010Co-Authors: John R. Stinchcombe, M. Shane Heschel, Brechann V. Mcgoey, Rima Izem, Johanna SchmittAbstract:Trade-offs can exist within and across environments, and constrain evolutionary trajectories. To examine the effects of competition and resource availability on trade-offs, we grew individuals of recombinant inbred lines of Impatiens Capensis in a factorial combination of five densities with two light environments (full light and neutral shade) and used a Bayesian logistic growth analysis to estimate intrinsic growth rates. To estimate across-environment constraints, we developed a variance decomposition approach to principal components analysis, which accounted for sample size, model-fitting, and within-RIL variation prior to eigenanalysis. We detected negative across-environment genetic covariances in intrinsic growth rates, although only under full-light. To evaluate the potential importance of these covariances, we surveyed natural populations of I. Capensis to measure the frequency of different density environments across space and time. We combined our empirical estimates of across-environment genetic variance-covariance matrices and frequency of selective environments with hypothetical (yet realistic) selection gradients to project evolutionary responses in multiple density environments. Selection in common environments can lead to correlated responses to selection in rare environments that oppose and counteract direct selection in those rare environments. Our results highlight the importance of considering both the frequency of selective environments and the across-environment genetic covariances in traits simultaneously.
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Maternal effects of drought stress and inbreeding in Impatiens Capensis (Balsaminaceae)
American journal of botany, 2007Co-Authors: Corinna Riginos, M. Shane Heschel, Johanna SchmittAbstract:Maternal effects can have substantial impacts on plant fitness and plant populations. Stressful environmental conditions can cause a maternal plant to inadequately provision its progeny, resulting in poor seedling growth, low reproductive success, and decreased competitive ability. Maternal effects consist of environmental and genetic load components, but the interactions between these two components have rarely been considered. To determine the effects of maternal drought stress and maternal inbreeding on progeny biomass (a fitness correlate) and physiological responses to drought stress, we conducted a greenhouse experiment with genetic lines from two populations (mesic site vs. dry site) of the herbaceous annual Impatiens Capensis (Balsaminaceae). Seeds were collected from cleistogamous flowers of inbred or outcrossed maternal plants that were subject to either a drought or control treatment. These seeds were grown into juvenile plants that were also subject to either a drought stress or a control treatment. Plants from the mesic site had significantly reduced biomass from maternal drought stress, while plants from the dry site maintained biomass despite adverse maternal environmental conditions. Juvenile plants of both populations had reduced biomass only as a result of maternal inbreeding. Interestingly, inbreeding depression was more apparent when maternal environmental conditions were benign.
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Testing for stress-dependent inbreeding depression in Impatiens Capensis (Balsaminaceae).
American journal of botany, 2005Co-Authors: M. Shane Heschel, Neil Hausmann, Johanna SchmittAbstract:The relevance of inbreeding depression to the persistence of plant populations can depend upon whether stress magnifies inbreeding depression for fitness-related traits. To examine whether drought stress exacerbates inbreeding depression in gas exchange traits and biomass, we grew selfed and outcrossed progeny of inbred lines from two populations of Impatiens Capensis in a greenhouse experiment under water-limited and moist soil conditions. Drought stress did not magnify the degree of inbreeding depression for any of the traits measured. In fact, in one population there was a trend for stronger inbreeding depression under well-watered, benign conditions. Furthermore, significant inbreeding depression for carbon assimilation rate and stomatal conductance was only detected in the lines from one population. In contrast, inbreeding depression for biomass was detected within both populations and differed among lines. Drought stress exerted significant selection on physiological traits, favoring increased carbon assimilation rates and decreased stomatal conductance in drought-stressed plants. Patterns of selection did not differ between inbred and outcrossed plants but did differ marginally between populations. Thus, estimates of selection were not biased by the mixed mating system per se, but may be biased by combining individuals from populations with different histories of selection and inbreeding.
Eric J. B. Von Wettberg - One of the best experts on this subject based on the ideXlab platform.
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Partitioning adaptive differentiation across a patchy landscape: shade avoidance traits in Impatiens Capensis.
Evolution; international journal of organic evolution, 2007Co-Authors: Eric J. B. Von Wettberg, David L. Remington, Johanna SchmittAbstract:Adaptation to different habitat types across a patchy landscape may either arise independently in each patch or occur due to repeated colonization of each patch by the same specialized genotype. We tested whether open- and closed-canopy forms of Impatiens Capensis, an herbaceous annual plant of eastern North America, have evolved repeatedly by comparing hierarchical measures of F(ST) estimated from AFLPs to morphological differentiation measured by Q(ST) for five pairs of populations found in open and closed habitats in five New England regions. Morphological differentiation between habitats (Q(HT)) in elongation traits was greater than marker divergence (F(HT)), suggesting adaptive differentiation. Genotypes from open- and closed-canopy habitats differed in shade avoidance traits in several population pairs, whereas patterns of AFLP differentiation suggest this differentiation does not have a single origin. These results suggest that open- and closed-canopy habitats present different selective pressures, but that the outcome of diversifying selection may differ depending on specific closed- and open-canopy habitats and on starting genetic variation. Hierarchical partitioning of F(ST) and Q(ST) makes it possible to distinguish global stabilizing selection on traits across a landscape from diversifying selection between habitat types within regions.
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Physiological mechanism of population differentiation in shade-avoidance responses between woodland and clearing genotypes of Impatiens Capensis.
American journal of botany, 2005Co-Authors: Eric J. B. Von Wettberg, Johanna SchmittAbstract:Forest understory plants often respond less intensely to reduced ratios of red to far red (R : FR) light, an important signal of foliage shade, than conspecific or congeneric plants from open-canopy sites. Reduced responsiveness to low R : FR in plants from closed-canopy sites could be caused by two physiological mechanisms. First, closed-canopy plants could have less sensitive shade-avoidance responses to low R : FR. Second, the high irradiance response to FR (FR-HIR), which allows seedling de-etiolation under low R : FR, might be stronger or persist longer after de-etiolation in closed-canopy plants, thus counteracting shade-avoidance responses to low R : FR. These hypotheses were tested using diodes that emit red and far-red light to distinguish the responses to altered R : FR of genotypes of Impatiens Capensis collected from a pair of open- and closed-canopy populations that have previously been shown to differ in sensitivity to R : FR. Genotypes from the open-canopy environment exhibited typical shade-avoidance responses, elongating in response to supplemental FR. However, genotypes from the closed-canopy environment responded to supplemental FR by elongating less than under ambient control conditions, indicating a persistent FR-HIR. Thus, the observed population differentiation in response to low R : FR may be linked to population differences in FR-HIR.
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Interacting effects of microsite quality, plasticity and dispersal distance from the parental site on fitness in a natural population of Impatiens Capensis
Evolutionary Ecology Research, 2005Co-Authors: Eric J. B. Von Wettberg, Heidrun Huber, Johanna SchmittAbstract:Hypothesis: Induced plastic responses, environmental heterogeneity and local adaptation may have interacting and counteracting effects on the performance of organisms. Organism: The North American herbaceous annual Impatiens Capensis. Site of experiment: This experiment was performed in a forest understory site in Bristol, RI, USA, where previous experiments have shown declines in fitness with transplanting up to 12 m from parental sites. Methods: Eight replicated genotypes were pre-treated in a glasshouse to induce or suppress shade avoidance responses and then transplanted into 50 randomly chosen microsites within 50 m of the site from which their parents were originally collected. Results: Overall plant fitness was significantly autocorrelated at distances less than 4 m, the primary dispersal distance of Impatiens seeds and the distance with greatest environmental spatial autocorrelation. The fitness of transplants was affected by site quality but not by distance from the site of original collection. In addition, genotypes were more sensitive to environmental factors when induced to elongate in response to neighbour shading. Finally, the genotypes most responsive to increasing site quality were the most fit.
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Frequency and microenvironmental pattern of selection on plastic shade-avoidance traits in a natural population of Impatiens Capensis.
The American naturalist, 2004Co-Authors: Heidrun Huber, M. Shane Heschel, Nolan C. Kane, Eric J. B. Von Wettberg, Joshua A. Banta, Anne Marie Leuck, Johanna SchmittAbstract:Abstract: The frequency and predictability of different selective environments are important parameters in models for the evolution of plasticity but have rarely been measured empirically in natural populations. We used an experimental phytometer approach to examine the frequency, predictability, and environmental determinants of heterogeneous selection on phytochrome‐mediated shade‐avoidance responses in a natural population of the annual plant Impatiens Capensis. The strength and direction of selection on shade‐avoidance traits varied substantially on a fine spatial scale. The shade‐avoidance phenotype had high relative fecundity in some microsites but was disadvantageous in other microsites. Local seedling density proved to be a surprisingly poor predictor of microenvironmental variation in the strength and direction of selection on stem elongation in this study population. At least some of this unpredictability resulted from microenvironmental variation in water availability; the shade‐avoidance pheno...
John R. Stinchcombe - One of the best experts on this subject based on the ideXlab platform.
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Across-environment genetic correlations and the frequency of selective environments shape the evolutionary dynamics of growth rate in Impatiens Capensis.
Evolution; international journal of organic evolution, 2010Co-Authors: John R. Stinchcombe, M. Shane Heschel, Brechann V. Mcgoey, Rima Izem, Johanna SchmittAbstract:Trade-offs can exist within and across environments, and constrain evolutionary trajectories. To examine the effects of competition and resource availability on trade-offs, we grew individuals of recombinant inbred lines of Impatiens Capensis in a factorial combination of five densities with two light environments (full light and neutral shade) and used a Bayesian logistic growth analysis to estimate intrinsic growth rates. To estimate across-environment constraints, we developed a variance decomposition approach to principal components analysis, which accounted for sample size, model-fitting, and within-RIL variation prior to eigenanalysis. We detected negative across-environment genetic covariances in intrinsic growth rates, although only under full-light. To evaluate the potential importance of these covariances, we surveyed natural populations of I. Capensis to measure the frequency of different density environments across space and time. We combined our empirical estimates of across-environment genetic variance-covariance matrices and frequency of selective environments with hypothetical (yet realistic) selection gradients to project evolutionary responses in multiple density environments. Selection in common environments can lead to correlated responses to selection in rare environments that oppose and counteract direct selection in those rare environments. Our results highlight the importance of considering both the frequency of selective environments and the across-environment genetic covariances in traits simultaneously.
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Interspecific competition alters natural selection on shade avoidance phenotypes in Impatiens Capensis.
The New phytologist, 2009Co-Authors: Brechann V. Mcgoey, John R. StinchcombeAbstract:Summary • Shade avoidance syndrome is a known adaptive response for Impatiens Capensis growing in dense intraspecific competition. However, I. Capensis also grow with dominant interspecific competitors in marshes. Here, we compare the I. Capensis shade-avoidance phenotypes produced in the absence and presence of heterospecific competitors, as well as selection on those traits. • Two treatments were established in a marsh; in one treatment all heterospecifics were removed, while in the other, all competitors remained. We compared morphological traits, light parameters, seed output and, using phenotypic selection analysis, examined directional and nonlinear selection operating in the different competitive treatments. • Average phenotypes, light parameters and seed production all varied depending on competitive treatment. Phenotypic selection analyses revealed different directional, disruptive, stabilizing and correlational selection. The disparities seen in both phenotypes and selection between the treatments related to the important differences in elongation timing depending on the presence of heterospecifics, although environmental covariances between traits and fitness could also contribute. • Phenotypes produced by I. Capensis depend on their competitive environment, and differing selection on shade-avoidance traits between competitive environments could indirectly select for increased plasticity given gene flow between populations in different competitive contexts.
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Ecosystem engineers as selective agents: the effects of leaf litter on emergence time and early growth in Impatiens Capensis.
Ecology letters, 2006Co-Authors: John R. Stinchcombe, Johanna SchmittAbstract:By physically modifying the abiotic environment, ecosystem engineers can have dramatic effects on the distribution and abundance of species in a community. However, ecosystem engineering can also change the selective environment and evolutionary dynamics of affected species, although this remains relatively understudied. Here, we examine the potential for an ecosystem engineer – oak trees – to affect the evolutionary dynamics of the herbaceous, understory annual, Impatiens Capensis, through leaf litter deposition. Using a quantitative genetic experimental approach, we found that: (i) the presence of leaf litter significantly affected a suite of germination, growth and phenological traits in I. Capensis; (ii) I. Capensis does not exhibit performance trade-offs across litter and bare soil environments in the form of negative across-environment genetic correlations; (iii) the presence or absence of leaf litter significantly alters the pattern of natural selection germination timing and hypocotyl length; and (iv) the frequency of leaf litter environments can dramatically change which combinations of hypocotyl length lead to highest mean fitness across both bare soil and leaf litter environments. More generally, our results demonstrate the potential for ecosystem engineers to alter both the ecological and the evolutionary dynamics of the species they affect.
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Natural selection on light response curve parameters in the herbaceous annual, Impatiens Capensis
Oecologia, 2004Co-Authors: M. Shane Heschel, Kent E Holsinger, John R. Stinchcombe, Johanna SchmittAbstract:We tested for genetic variation in light response curves and their acclimation to sun versus shade in recombinant inbred lines (RILs) of the annual species Impatiens Capensis derived from a cross between sun and shade populations. We exposed replicates of 49 RILs to experimentally manipulated light levels (open versus shade) in a greenhouse and measured photosynthetic light response curves, height, biomass, and reproduction. Plants were taller in the shade treatment, but we were unable to detect differences between light treatments (i.e., acclimation) in the maximal rate of photosynthesis, the light compensation point, or the quantum efficiency of photosynthesis. Genotypic selection analyses indicated that higher maximal rates of carbon assimilation and higher light compensation points (typical of sun-acclimated light curves) were favored by natural selection in both light treatments. Thus, it appears that the pattern of selection on photosynthetic parameters may not depend on light environment in this species.
Keith Clay - One of the best experts on this subject based on the ideXlab platform.
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Spatial and Temporal Patterns of Rust Infection on Jewelweed (Impatiens Capensis)
International Journal of Plant Sciences, 2010Co-Authors: Jennifer M. Koslow, Keith ClayAbstract:Disease epidemiology has rarely been examined in natural plant‐pathogen systems exhibiting obligate alteration of host species. We quantified rust infection in populations of jewelweed; its effect on host mating system, potential biotic and abiotic correlates of infection; and spatial patterns within populations. Jewelweed (Impatiens Capensis) is a woodland annual that can become infected with the heteroecious rust, Puccinia recondita, whose alternate hosts are often grasses. It produces dimorphic self‐pollinated cleistogamous (CL) flowers and open‐pollinated chasmogamous (CH) flowers. Infected plants may have fewer resources, so we predicted a decrease in CH flowering relative to that of uninfected plants. Infection occurred early in the growing season and disappeared by midsummer, although plants continued to grow and flower until the frost. We found no clustering of infection within populations. Infection prevalence did not vary among sites in 2005, but one site had more disease in 2004 than in 2005. R...
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THE MIXED MATING SYSTEM OF Impatiens Capensis AND INFECTION BY A FOLIAR RUST PATHOGEN: PATTERNS OF RESISTANCE AND FITNESS CONSEQUENCES
Evolution; international journal of organic evolution, 2007Co-Authors: Jennifer M. Koslow, Keith ClayAbstract:Outcrossing by hosts may offer protection from natural enemies adapted to parental genotypes by creating diverse progeny that differ from their parents through genetic recombination. However, past experimental work addressing the relationship between mating system and disease in offspring has given conflicting results, suggesting that outcrossing might also cause the dissolution of resistant genotypes. To determine if selfed progeny are more susceptible to disease caused by the heteroecious rust, Puccinia recondita, or if selfing preserves existing resistant genotypes, we used a factorial design to compare levels of infection of selfed and outcrossed progeny of Impatiens Capensis, a woodland annual with a mixed mating system. We compared the level of host infection when exposed to three pathogen sources in the field: the sympatric rust population, and two allopatric rust populations. Outcrossed progeny exposed to sympatric rust had higher infection scores than selfed progeny exposed to the same rust, suggesting that outcrossing breaks up resistant genotypes. In addition, there was a trend for the rust to be more infective on sympatric rather than allopatric hosts. We also examined whether rust infection differentially alters the fitness of selfed and outcrossed progeny. Outcrossed plants that escaped infection had higher fitness, as measured by fruit production, than selfed plants, but there was no difference in fitness between infected selfed and infected outcrossed plants. Thus, outcrossing was advantageous in the absence of disease, but there was no fitness difference between selfed and outcrossed progeny in the presence of disease. In sum, our results indicate that interactions with pathogens can eliminate or reverse the advantage of outcrossing.
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Thinning Reduces the Effect of Rust Infection on Jewelweed (Impatiens Capensis)
Ecology, 1995Co-Authors: Curtis M. Lively, Steven G. Johnson, Lynda F. Delph, Keith ClayAbstract:We examined the relationship between plant density and the probability of infection by a rust (Puccinia recondite) in a natural population of jewelweed (Impatiens Capensis). We also reduced plant density in field manipulations to determine whether there is any synergism between intraspecific competition and infection by the rust. The results showed no relationship between plant density and the probability of infection. However, we found that the effect of infection depends on plant density. Uninfected plants grew significantly faster than infected plants under natural conditions of high density, but in- fection had no significant effect on growth where density was experimentally reduced. Hence, the effect of disease on jewelweed depends on the plant's competitive environment. Such interactions between competition and disease are likely to be important to the pop- ulation biology and breeding-system evolution of plants.
