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Christina M. Holzapfel - One of the best experts on this subject based on the ideXlab platform.
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natural variation and genetics of photoperiodism in Wyeomyia smithii
Advances in Genetics, 2017Co-Authors: William E. Bradshaw, Christina M. HolzapfelAbstract:Seasonal change in the temperate and polar regions of Earth determines how the world looks around us and, in fact, how we live our day-to-day lives. For biological organisms, seasonal change typically involves complex physiological and metabolic reorganization, the majority of which is regulated by photoperiodism. Photoperiodism is the ability of animals and plants to use day length or night length, resulting in life-historical transformations, including seasonal development, migration, reproduction, and dormancy. Seasonal timing determines not only survival and reproductive success but also the structure and organization of complex communities and, ultimately, the biomes of Earth. Herein, a small mosquito, Wyeomyia smithii, that lives only in the water-filled leaves of a carnivorous plant over a wide geographic range, is used to explore the genetic and evolutionary basis of photoperiodism. Photoperiodism in W. smithii is considered in the context of its historical biogeography in nature to examine the startling finding that recent rapid climate change can drive genetic change in plants and animals at break-neck speed, and to challenge the ponderous 80+ year search for connections between daily and seasonal time-keeping mechanisms. Finally, a model is proposed that reconciles the seemingly disparate 24-h daily clock driven by the invariant rotation of Earth about its axis with the evolutionarily flexible seasonal timer orchestrated by variable seasonality driven by the rotation of Earth about the Sun.
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Evolutionary Divergence of Circadian and Photoperiodic Phenotypes in the Pitcher-Plant Mosquito, Wyeomyia smithii
2016Co-Authors: Derrick Mathias, William E. Bradshaw, Laura K Reed, Christina M. HolzapfelAbstract:Abstract For decades, chronobiologists have investigated the relationship between the circadian clock that mediates daily activities and the photoperiodic timer that mediates seasonal activities. The main experiment used to infer a circa-dian basis for photoperiodic time measurement is the Nanda-Hamner protocol (NH). Herein, the authors compare additive and nonadditive (dominance and epistasis) genetic effects that lead to the divergence of populations of the pitcher-plant mosquito, Wyeomyia smithii, for critical photoperiod (CPP) and amplitude of the rhythmic response to NH for 3 temporal-geographic scales: 1) Over geolog-ical time between populations in northern and southern clades, 2) over millennial time between populations within the northern clade, and 3) over generational time between lines selected for long and short CPP from within a single popu-lation. The authors show that the pattern of additive, dominance, and epistatic effects depends on the time scale over which populations or lines have diverged. Patterns for genetic differences between populations for CPP and response to NH reveal similarities over geological and millennial time scales but differences over shorter periods of evolution. These results, and the observation that neither the period nor amplitude of the NH rhythm are significantly correlated with CPP among populations, lead the authors to conclude that the rhythmic response to NH has evolved independently of photoperiodic response in populations of W. smithii. The implication is that in this species, genetic modification of the cir-cadian clock has not been the basis for the adaptive modification of photoperi-odic time measurement over the climatic gradient of North America. Key words circadian rhythm, critical photoperiod, evolutionary divergence, genetic architecture, Nanda-Hamner, photoperiodic time measuremen
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replicate phylogenies and post glacial range expansion of the pitcher plant mosquito Wyeomyia smithii in north america
PLOS ONE, 2013Co-Authors: Clayton R Merz, William E. Bradshaw, K J Emerson, Julian M Catchen, Victor Hansonsmith, Christina M. HolzapfelAbstract:Herein we tested the repeatability of phylogenetic inference based on high throughput sequencing by increased taxon sampling using our previously published techniques in the pitcher-plant mosquito, Wyeomyia smithii in North America. We sampled 25 natural populations drawn from different localities nearby 21 previous collection localities and used these new data to construct a second, independent phylogeny, expressly to test the reproducibility of phylogenetic patterns. Comparison of trees between the two data sets based on both maximum parsimony and maximum likelihood with Bayesian posterior probabilities showed close correspondence in the grouping of the most southern populations into clear clades. However, discrepancies emerged, particularly in the middle of W. smithii's current range near the previous maximum extent of the Laurentide Ice Sheet, especially concerning the most recent common ancestor to mountain and northern populations. Combining all 46 populations from both studies into a single maximum parsimony tree and taking into account the post-glacial historical biogeography of associated flora provided an improved picture of W. smithii's range expansion in North America. In a more general sense, we propose that extensive taxon sampling, especially in areas of known geological disruption is key to a comprehensive approach to phylogenetics that leads to biologically meaningful phylogenetic inference.
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footprints in time comparative quantitative trait loci mapping of the pitcher plant mosquito Wyeomyia smithii
Proceedings of The Royal Society B: Biological Sciences, 2012Co-Authors: William E. Bradshaw, K J Emerson, Julian M Catchen, William A Cresko, Christina M. HolzapfelAbstract:Identifying regions of the genome contributing to phenotypic evolution often involves genetic mapping of quantitative traits. The focus then turns to identifying regions of ‘major’ effect, overlooking the observation that traits of ecological or evolutionary relevance usually involve many genes whose individual effects are small but whose cumulative effect is large. Herein, we use the power of fully interfertile natural populations of a single species of mosquito to develop three quantitative trait loci (QTL) maps: one between two post-glacially diverged populations and two between a more ancient and a post-glacial population. All demonstrate that photoperiodic response is genetically a highly complex trait. Furthermore, we show that marker regressions identify apparently ‘non-significant’ regions of the genome not identified by composite interval mapping, that the perception of the genetic basis of adaptive evolution is crucially dependent upon genetic background and that the genetic basis for adaptive evolution of photoperiodic response is highly variable within contemporary populations as well as between anciently diverged populations.
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resolving postglacial phylogeography using high throughput sequencing
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: K J Emerson, William E. Bradshaw, Clayton R Merz, Julian M Catchen, Paul A Hohenlohe, William A Cresko, Christina M. HolzapfelAbstract:The distinction between model and nonmodel organisms is becoming increasingly blurred. High-throughput, second-generation sequencing approaches are being applied to organisms based on their interesting ecological, physiological, developmental, or evolutionary properties and not on the depth of genetic information available for them. Here, we illustrate this point using a low-cost, efficient technique to determine the fine-scale phylogenetic relationships among recently diverged populations in a species. This application of restriction site-associated DNA tags (RAD tags) reveals previously unresolved genetic structure and direction of evolution in the pitcher plant mosquito, Wyeomyia smithii, from a southern Appalachian Mountain refugium following recession of the Laurentide Ice Sheet at 22,000–19,000 B.P. The RAD tag method can be used to identify detailed patterns of phylogeography in any organism regardless of existing genomic data, and, more broadly, to identify incipient speciation and genome-wide variation in natural populations in general.
William E. Bradshaw - One of the best experts on this subject based on the ideXlab platform.
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natural variation and genetics of photoperiodism in Wyeomyia smithii
Advances in Genetics, 2017Co-Authors: William E. Bradshaw, Christina M. HolzapfelAbstract:Seasonal change in the temperate and polar regions of Earth determines how the world looks around us and, in fact, how we live our day-to-day lives. For biological organisms, seasonal change typically involves complex physiological and metabolic reorganization, the majority of which is regulated by photoperiodism. Photoperiodism is the ability of animals and plants to use day length or night length, resulting in life-historical transformations, including seasonal development, migration, reproduction, and dormancy. Seasonal timing determines not only survival and reproductive success but also the structure and organization of complex communities and, ultimately, the biomes of Earth. Herein, a small mosquito, Wyeomyia smithii, that lives only in the water-filled leaves of a carnivorous plant over a wide geographic range, is used to explore the genetic and evolutionary basis of photoperiodism. Photoperiodism in W. smithii is considered in the context of its historical biogeography in nature to examine the startling finding that recent rapid climate change can drive genetic change in plants and animals at break-neck speed, and to challenge the ponderous 80+ year search for connections between daily and seasonal time-keeping mechanisms. Finally, a model is proposed that reconciles the seemingly disparate 24-h daily clock driven by the invariant rotation of Earth about its axis with the evolutionarily flexible seasonal timer orchestrated by variable seasonality driven by the rotation of Earth about the Sun.
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Evolutionary Divergence of Circadian and Photoperiodic Phenotypes in the Pitcher-Plant Mosquito, Wyeomyia smithii
2016Co-Authors: Derrick Mathias, William E. Bradshaw, Laura K Reed, Christina M. HolzapfelAbstract:Abstract For decades, chronobiologists have investigated the relationship between the circadian clock that mediates daily activities and the photoperiodic timer that mediates seasonal activities. The main experiment used to infer a circa-dian basis for photoperiodic time measurement is the Nanda-Hamner protocol (NH). Herein, the authors compare additive and nonadditive (dominance and epistasis) genetic effects that lead to the divergence of populations of the pitcher-plant mosquito, Wyeomyia smithii, for critical photoperiod (CPP) and amplitude of the rhythmic response to NH for 3 temporal-geographic scales: 1) Over geolog-ical time between populations in northern and southern clades, 2) over millennial time between populations within the northern clade, and 3) over generational time between lines selected for long and short CPP from within a single popu-lation. The authors show that the pattern of additive, dominance, and epistatic effects depends on the time scale over which populations or lines have diverged. Patterns for genetic differences between populations for CPP and response to NH reveal similarities over geological and millennial time scales but differences over shorter periods of evolution. These results, and the observation that neither the period nor amplitude of the NH rhythm are significantly correlated with CPP among populations, lead the authors to conclude that the rhythmic response to NH has evolved independently of photoperiodic response in populations of W. smithii. The implication is that in this species, genetic modification of the cir-cadian clock has not been the basis for the adaptive modification of photoperi-odic time measurement over the climatic gradient of North America. Key words circadian rhythm, critical photoperiod, evolutionary divergence, genetic architecture, Nanda-Hamner, photoperiodic time measuremen
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replicate phylogenies and post glacial range expansion of the pitcher plant mosquito Wyeomyia smithii in north america
PLOS ONE, 2013Co-Authors: Clayton R Merz, William E. Bradshaw, K J Emerson, Julian M Catchen, Victor Hansonsmith, Christina M. HolzapfelAbstract:Herein we tested the repeatability of phylogenetic inference based on high throughput sequencing by increased taxon sampling using our previously published techniques in the pitcher-plant mosquito, Wyeomyia smithii in North America. We sampled 25 natural populations drawn from different localities nearby 21 previous collection localities and used these new data to construct a second, independent phylogeny, expressly to test the reproducibility of phylogenetic patterns. Comparison of trees between the two data sets based on both maximum parsimony and maximum likelihood with Bayesian posterior probabilities showed close correspondence in the grouping of the most southern populations into clear clades. However, discrepancies emerged, particularly in the middle of W. smithii's current range near the previous maximum extent of the Laurentide Ice Sheet, especially concerning the most recent common ancestor to mountain and northern populations. Combining all 46 populations from both studies into a single maximum parsimony tree and taking into account the post-glacial historical biogeography of associated flora provided an improved picture of W. smithii's range expansion in North America. In a more general sense, we propose that extensive taxon sampling, especially in areas of known geological disruption is key to a comprehensive approach to phylogenetics that leads to biologically meaningful phylogenetic inference.
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footprints in time comparative quantitative trait loci mapping of the pitcher plant mosquito Wyeomyia smithii
Proceedings of The Royal Society B: Biological Sciences, 2012Co-Authors: William E. Bradshaw, K J Emerson, Julian M Catchen, William A Cresko, Christina M. HolzapfelAbstract:Identifying regions of the genome contributing to phenotypic evolution often involves genetic mapping of quantitative traits. The focus then turns to identifying regions of ‘major’ effect, overlooking the observation that traits of ecological or evolutionary relevance usually involve many genes whose individual effects are small but whose cumulative effect is large. Herein, we use the power of fully interfertile natural populations of a single species of mosquito to develop three quantitative trait loci (QTL) maps: one between two post-glacially diverged populations and two between a more ancient and a post-glacial population. All demonstrate that photoperiodic response is genetically a highly complex trait. Furthermore, we show that marker regressions identify apparently ‘non-significant’ regions of the genome not identified by composite interval mapping, that the perception of the genetic basis of adaptive evolution is crucially dependent upon genetic background and that the genetic basis for adaptive evolution of photoperiodic response is highly variable within contemporary populations as well as between anciently diverged populations.
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resolving postglacial phylogeography using high throughput sequencing
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: K J Emerson, William E. Bradshaw, Clayton R Merz, Julian M Catchen, Paul A Hohenlohe, William A Cresko, Christina M. HolzapfelAbstract:The distinction between model and nonmodel organisms is becoming increasingly blurred. High-throughput, second-generation sequencing approaches are being applied to organisms based on their interesting ecological, physiological, developmental, or evolutionary properties and not on the depth of genetic information available for them. Here, we illustrate this point using a low-cost, efficient technique to determine the fine-scale phylogenetic relationships among recently diverged populations in a species. This application of restriction site-associated DNA tags (RAD tags) reveals previously unresolved genetic structure and direction of evolution in the pitcher plant mosquito, Wyeomyia smithii, from a southern Appalachian Mountain refugium following recession of the Laurentide Ice Sheet at 22,000–19,000 B.P. The RAD tag method can be used to identify detailed patterns of phylogeography in any organism regardless of existing genomic data, and, more broadly, to identify incipient speciation and genome-wide variation in natural populations in general.
K J Emerson - One of the best experts on this subject based on the ideXlab platform.
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replicate phylogenies and post glacial range expansion of the pitcher plant mosquito Wyeomyia smithii in north america
PLOS ONE, 2013Co-Authors: Clayton R Merz, William E. Bradshaw, K J Emerson, Julian M Catchen, Victor Hansonsmith, Christina M. HolzapfelAbstract:Herein we tested the repeatability of phylogenetic inference based on high throughput sequencing by increased taxon sampling using our previously published techniques in the pitcher-plant mosquito, Wyeomyia smithii in North America. We sampled 25 natural populations drawn from different localities nearby 21 previous collection localities and used these new data to construct a second, independent phylogeny, expressly to test the reproducibility of phylogenetic patterns. Comparison of trees between the two data sets based on both maximum parsimony and maximum likelihood with Bayesian posterior probabilities showed close correspondence in the grouping of the most southern populations into clear clades. However, discrepancies emerged, particularly in the middle of W. smithii's current range near the previous maximum extent of the Laurentide Ice Sheet, especially concerning the most recent common ancestor to mountain and northern populations. Combining all 46 populations from both studies into a single maximum parsimony tree and taking into account the post-glacial historical biogeography of associated flora provided an improved picture of W. smithii's range expansion in North America. In a more general sense, we propose that extensive taxon sampling, especially in areas of known geological disruption is key to a comprehensive approach to phylogenetics that leads to biologically meaningful phylogenetic inference.
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footprints in time comparative quantitative trait loci mapping of the pitcher plant mosquito Wyeomyia smithii
Proceedings of The Royal Society B: Biological Sciences, 2012Co-Authors: William E. Bradshaw, K J Emerson, Julian M Catchen, William A Cresko, Christina M. HolzapfelAbstract:Identifying regions of the genome contributing to phenotypic evolution often involves genetic mapping of quantitative traits. The focus then turns to identifying regions of ‘major’ effect, overlooking the observation that traits of ecological or evolutionary relevance usually involve many genes whose individual effects are small but whose cumulative effect is large. Herein, we use the power of fully interfertile natural populations of a single species of mosquito to develop three quantitative trait loci (QTL) maps: one between two post-glacially diverged populations and two between a more ancient and a post-glacial population. All demonstrate that photoperiodic response is genetically a highly complex trait. Furthermore, we show that marker regressions identify apparently ‘non-significant’ regions of the genome not identified by composite interval mapping, that the perception of the genetic basis of adaptive evolution is crucially dependent upon genetic background and that the genetic basis for adaptive evolution of photoperiodic response is highly variable within contemporary populations as well as between anciently diverged populations.
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Genetic correlations and the evolution of photoperiodic time measurement within a local population of the pitcher-plant mosquito, Wyeomyia smithii
Heredity, 2012Co-Authors: W E Bradshaw, K J Emerson, C M HolzapfelAbstract:The genetic relationship between the daily circadian clock and the seasonal photoperiodic timer remains a subject of intense controversy. In Wyeomyia smithii , the critical photoperiod (an overt expression of the photoperiodic timer) evolves independently of the rhythmic response to the Nanda–Hamner protocol (an overt expression of the daily circadian clock) over a wide geographical range in North America. Herein, we focus on these two processes within a single local population in which there is a negative genetic correlation between them. We show that antagonistic selection against this genetic correlation rapidly breaks it down and, in fact, reverses its sign, showing that the genetic correlation is due primarily to linkage and not to pleiotropy. This rapid reversal of the genetic correlation within a small, single population means that it is difficult to argue that circadian rhythmicity forms the necessary, causal basis for the adaptive divergence of photoperiodic time measurement within populations or for the evolution of photoperiodic time measurement among populations over a broad geographical gradient of seasonal selection.
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resolving postglacial phylogeography using high throughput sequencing
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: K J Emerson, William E. Bradshaw, Clayton R Merz, Julian M Catchen, Paul A Hohenlohe, William A Cresko, Christina M. HolzapfelAbstract:The distinction between model and nonmodel organisms is becoming increasingly blurred. High-throughput, second-generation sequencing approaches are being applied to organisms based on their interesting ecological, physiological, developmental, or evolutionary properties and not on the depth of genetic information available for them. Here, we illustrate this point using a low-cost, efficient technique to determine the fine-scale phylogenetic relationships among recently diverged populations in a species. This application of restriction site-associated DNA tags (RAD tags) reveals previously unresolved genetic structure and direction of evolution in the pitcher plant mosquito, Wyeomyia smithii, from a southern Appalachian Mountain refugium following recession of the Laurentide Ice Sheet at 22,000–19,000 B.P. The RAD tag method can be used to identify detailed patterns of phylogeography in any organism regardless of existing genomic data, and, more broadly, to identify incipient speciation and genome-wide variation in natural populations in general.
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microarrays reveal early transcriptional events during the termination of larval diapause in natural populations of the mosquito Wyeomyia smithii
PLOS ONE, 2010Co-Authors: K J Emerson, William E. Bradshaw, Christina M. HolzapfelAbstract:Background The mosquito Wyeomyia smithii overwinters in a larval diapause that is initiated, maintained and terminated by day length (photoperiod). We use a forward genetic approach to investigate transcriptional events involved in the termination of diapause following exposure to long-days. Methods/Principal Findings We incorporate a novel approach that compares two populations that differentially respond to a single day length. We identify 30 transcripts associated with differential response to day length. Most genes with a previously annotated function are consistent with their playing a role in the termination of diapause, in downstream developmental events, or in the transition from potentially oxygen-poor to oxygen-rich environments. One gene emerges from three separate forward genetic screens as a leading candidate for a gene contributing to the photoperiodic timing mechanism itself (photoperiodic switch). We name this gene photoperiodic response gene 1 (ppdrg1). WsPpdrg1 is up-regulated under long-day response conditions, is located under a QTL for critical photoperiod and is associated with critical photoperiod after 25 generations of recombination from a cross between extreme phenotypes. Conclusions Three independent forward genetic approaches identify WsPpdrg1 as a gene either involved in the photoperiodic switch mechanism or very tightly linked to a gene that is. We conclude that continued forward genetic approaches will be central to understanding not only the molecular basis of photoperiodism and diapause, but also the evolutionary potential of temperate and polar animal populations when confronted with rapid climate change.
Peter Armbruster - One of the best experts on this subject based on the ideXlab platform.
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geographic variation and the evolution of reproductive allocation in the pitcher plant mosquito Wyeomyia smithii
Evolution, 2001Co-Authors: Peter Armbruster, William E. Bradshaw, Kirsten Ruegg, Christina M. HolzapfelAbstract:We measured the egg size of six geographic populations of the pitcher-plant mosquito, Wyeomyia smithii, from Florida (30°N) to Ontario (49°N). Populations from northern latitudes produced larger eggs than populations from southern latitudes. Egg size increased with increasing latitude more rapidly when larvae were reared under low rather than high density. One southern (30°N) and one northern (49°N) population of W. smithii that persisted through 10 generations of selection for increased persistence under conditions of chronic thermal- and nutrient-limiting stress (conditions similar to southern rather than northern habitats) produced smaller eggs more rapidly than unselected control lines. However, there were no differences in lifetime fecundity or fertility between control and selected lines. Thus, laboratory evolution in an environment representative of extreme southern latitudes caused evolutionary changes consistent with geographic patterns of egg size. These results implicate temperature as a selective factor influencing the geographic variation of egg size in W. smithii, and demonstrate a novel trade-off in reproductive allocation between egg size and egg maturation time.
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Evolutionary responses to environmental stress by the pitcher-plant mosquito, Wyeomyia smithii
Heredity, 1999Co-Authors: Peter Armbruster, William E. Bradshaw, Angela L Steiner, Christina M. HolzapfelAbstract:We performed truncation selection for increased fitness ( r _c) under conditions of chronic stress from the combined effects of low nutrients and high temperature, representative of extremes likely to be encountered in nature by the pitcher-plant mosquito, Wyeomyia smithii . We performed selection on geographical parental populations and their hybrids to determine whether hybridization would facilitate or constrain adaptation under our selection protocol. The stressful environment decreased fitness ( r _c) by 54% averaged across all populations relative to near-optimal conditions. After ≈10 generations of selection under chronically stressful conditions, exactly one-half of the parental and one-half of the hybrid populations had gone extinct. Thus hybridization had no effect on the likelihood of population persistence. Fitness ( r _c) of the surviving populations did not show any response to selection. Despite initial hybrid vigour under stressful conditions, the fitness ( r _c) of surviving hybrid populations was either equal to, or worse than, the fitness ( r _c) of surviving parental populations after ≈10 generations of selection. These results suggest that outcrossing populations to augment genetic variation and facilitate adaptation to a rapidly changing environment may not be useful over longer time scales, even in cases where hybridization does initially increase fitness. Although we detected no direct response to selection for increased fitness ( r _c) under lifetime chronic stress, selected populations showed a strong correlated response for survivorship through transient, acute heat and desiccation shock. In evaluating how organisms might respond to future climate change, biologists must maintain a clear distinction between lifelong performance in chronically stressful environments and short-term survivorship through transient, acute stress.
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effects of postglacial range expansion on allozyme and quantitative genetic variation of the pitcher plant mosquito Wyeomyia smithii
Evolution, 1998Co-Authors: Peter Armbruster, William E. Bradshaw, Christina M. HolzapfelAbstract:We determined allozyme variability of 34 populations of the pitcher-plant mosquito, Wyeomyia smithii, from Florida (30?N) to northern Manitoba (54?N) and compared allozyme variability with the additive genetic variance for preadult development time and photoperiodic response determined previously for six populations over a similar range (30-50?N). Phylogenetic analysis of allozymes shows a well-defined split between Gulf Coast and lowland North Carolina populations, similar to previously observed phylogeographic patterns in a wide variety of taxa. A deeper split in the phylogeny of W. smithii coincides with the location of the maximum extent of the Laurentide Ice Sheet. Furthermore, both average heterozygosity and patterns of isolation-by-distance decline in populations north of the former glacial border. It is likely that northern populations are the result of a range expansion that occurred subsequent to the late-Wisconsin retreat of the Laurentide Ice Sheet and that these populations have not yet reached a drift-migration equilibrium. The northern decline in allozyme heterozygosity contrasts sharply with the northern increase in additive genetic variance of development time and photoperiodic response found in previous studies. These previous studies also showed that the genetic divergence of populations has involved stochastic variation in the contribution of dominance and epistasis to the genetic architecture underlying demographic traits, including preadult development time, and photoperiodic response. When taken together, the present and prior studies identify the genetic processes underlying the lack of concordance between geographic patterns of allozyme and quantitative genetic variation in natural populations of W. smithii. In the presence of nonadditive genetic variation, isolation and drift can result in opposite patterns of genetic variation for structural genes and quantitative traits.
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fitness consequences of hibernal diapause in the pitcher plant mosquito Wyeomyia smithii
Ecology, 1998Co-Authors: William E. Bradshaw, Peter Armbruster, Christina M. HolzapfelAbstract:The mosquito, Wyeomyia smithii, develops only within the water-filled leaves of the purple pitcher plant, Sarracenia purpurea, where it overwinters in larval diapause. We reared uniform-aged cohorts in the leaves of intact plants in three environments: near-optimal summer conditions, intentionally stressful summer conditions, and a 23-wk simulated winter. Overwintering W. smithii suffered a 60% loss in fitness (R0), comparable to the 68% loss in fitness imposed by the summer stress. Overwintering cohorts lost fitness through reduced survivorship, fecundity, fertility, adult longevity, and mass-specific fecundity. We argue that very real trade-offs occur between summer performance and winter performance among temperate insects in general. Survivorship and reproduction of the overwintering generation should therefore be an important source of selection shaping not only the seasonal expression of dormancy, but also the evolution of summer life-history syndromes as well.
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evolution of the genetic architecture underlying fitness in the pitcher plant mosquito Wyeomyia smithii
Evolution, 1997Co-Authors: Peter Armbruster, William E. Bradshaw, Christina M. HolzapfelAbstract:We examined the genetic basis for evolutionary divergence among geographic populations of the pitcher-plant mosquito, Wyeomyia smithii, using protein electrophoresis and line-cross analysis. Line-cross experiments were performed under both low density, near-optimal conditions, and at high, limiting larval densities sufficient to reduce fitness (rc ) in parental populations by approximately 50%. We found high levels of electrophoretic divergence between ancestral and derived populations, but low levels of divergence between two ancestral populations and between two derived populations. Assessed under near-optimal conditions, the genetic divergence of fitness (rc ) between ancestral and derived populations, but not between two derived populations or between two ancestral populations, has involved both allelic (dominance) and genic (epistatic) interactions. The role of dominance and epistasis in the divergence of rc among populations affects its component traits in a pattern that is unique to each cross. Patterns of genetic differentiation among populations of W. smithii provide evidence for a topographically complex "adaptive landscape" as envisioned by Wright in his "shifting balance" theory of evolution. Although we cannot definitively rule out the role of deterministic evolution in the divergence of populations on this landscape, ecological inference and genetic data are more consistent with a stochastic than a deterministic process. At high, limiting larval density, hybrid vigor is enhanced and the influence of epistasis disappears. Thus, under stressful conditions, the advantages to fitness due to hybrid heterozygosity can outweigh the deleterious effects of fragmented gene complexes. These results have important implications for the management of inbred populations. Outbreeding depression assessed in experimental crosses under benign lab, zoo, or farm conditions may not accurately reveal the increased advantages of heterozygosity in suboptimal or marginal conditions likely to be found in nature.
Aaron M. Ellison - One of the best experts on this subject based on the ideXlab platform.
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proteomic characterization of the major arthropod associates of the carnivorous pitcher plant sarracenia purpurea
Proteomics, 2011Co-Authors: Nicholas J. Gotelli, Aidan M Smith, Aaron M. Ellison, Bryan A BallifAbstract:The array of biomolecules generated by a functioning ecosystem represents both a potential resource for sustainable harvest and a potential indicator of ecosystem health and function. The cupped leaves of the carnivorous pitcher plant, Sarracenia purpurea, harbor a dynamic food web of aquatic invertebrates in a fully functional miniature ecosystem. The energetic base of this food web consists of insect prey, which is shredded by aquatic invertebrates and decomposed by microbes. Biomolecules and metabolites produced by this food web are actively exchanged with the photosynthesizing plant. In this report, we provide the first proteomic characterization of the sacrophagid fly (Fletcherimyia fletcheri), the pitcher plant mosquito (Wyeomyia smithii), and the pitcher-plant midge (Metriocnemus knabi). These three arthropods act as predators, filter feeders, and shredders at distinct trophic levels within the S. purpurea food web. More than 50 proteins from each species were identified, ten of which were predominantly or uniquely found in one species. Furthermore, 19 peptides unique to one of the three species were identified using an assembled database of 100 metazoan myosin heavy chain orthologs. These molecular signatures may be useful in species monitoring within heterogeneous ecosystem biomass and may also serve as indicators of ecosystem state.
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a keystone predator controls bacterial diversity in the pitcher plant sarracenia purpurea microecosystem
Environmental Microbiology, 2008Co-Authors: Celeste N Peterson, Benjamin E. Wolfe, Aaron M. Ellison, Roberto Kolter, Anne PringleAbstract:Summary The community of organisms inhabiting the waterfilled leaves of the carnivorous pitcher-plant Sarracenia purpurea includes arthropods, protozoa and bacteria, and serves as a model system for studies of food web dynamics. Despite the wealth of data collected by ecologists and zoologists on this food web, very little is known about the bacterial assemblage in this microecosystem. We used terminal restriction fragment length polymorphism (T-RFLP) analysis to quantify bacterial diversity within the pitchers as a function of pitcher size, pH of the pitcher fluid and the presence of the keystone predator in this food web, larvae of the pitcher-plant mosquito Wyeomyia smithii. Results were analysed at two spatial scales: within a single bog and across three isolated bogs. Pitchers were sterile before they opened and composition of the bacterial assemblage was more variable between different bogs than within bogs. Measures of bacterial richness and diversity were greater in the presence of W. smithii and increased with increasing pitcher size. Our results suggest that fundamental ecological concepts derived from macroscopic food webs can also be used to predict the bacterial assemblages in pitcher plants.
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A keystone predator controls bacterial diversity in the pitcher-plant (Sarracenia purpurea) microecosystem. Environ. Microbiol
2008Co-Authors: Celeste N Peterson, Benjamin E. Wolfe, Aaron M. Ellison, Roberto Kolter, Stephanie Day, Anne PringleAbstract:Summary The community of organisms inhabiting the waterfilled leaves of the carnivorous pitcher-plant Sarracenia purpurea includes arthropods, protozoa and bacteria, and serves as a model system for studies of food web dynamics. Despite the wealth of data collected by ecologists and zoologists on this food web, very little is known about the bacterial assemblage in this microecosystem. We used terminal restriction fragment length polymorphism (T-RFLP) analysis to quantify bacterial diversity within the pitchers as a function of pitcher size, pH of the pitcher fluid and the presence of the keystone predator in this food web, larvae of the pitcher-plant mosquito Wyeomyia smithii. Results were analysed at two spatial scales: within a single bog and across three isolated bogs. Pitchers were sterile before they opened and composition of the bacterial assemblage was more variable between different bogs than within bogs. Measures of bacterial richness and diversity were greater in the presence of W. smithii and increased with increasing pitcher size. Our results suggest that fundamental ecological concepts derived from macroscopic food webs can also be used to predict the bacterial assemblages in pitcher plants
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Reverse latitudinal trends in species richness of pitcher-plant food webs
Ecology Letters, 2003Co-Authors: Hannah L. Buckley, Thomas E. Miller, Aaron M. Ellison, Nicholas J. GotelliAbstract:Latitudinal patterns in species richness have been well documented for guilds and individual trophic groups, but comparable patterns for entire, multitrophic communities have not been described. We studied the entire food web that inhabits the water-filled leaves of the pitcher plant Sarracenia purpurea across North America at two spatial scales: among sites and among leaves within sites. Contrary to the expectation, total species richness at both scales increased with latitude, because of increasing species richness at the lower trophic levels. This latitudinal pattern may be driven by a top-down effect. The abundance of the mosquito Wyeomyia smithii, a ubiquitous top predator in this system, decreases from south to north and may permit greater species richness of prey trophic levels at higher latitudes.
