The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform
David M. Kingsley - One of the best experts on this subject based on the ideXlab platform.
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Evolving New Skeletal Traits by cis-Regulatory Changes in Bone Morphogenetic Proteins
Cell, 2016Co-Authors: Vahan B. Indjeian, Garrett A. Kingman, Felicity C. Jones, Catherine A Guenther, Jane Grimwood, Richard M Myers, Jeremy Schmutz, David M. KingsleyAbstract:Changes in bone size and shape are defining features of many vertebrates. Here we use genetic crosses and comparative genomics to identify specific regulatory DNA alterations controlling skeletal evolution. Armor bone-size differences in sticklebacks map to a major effect locus overlapping BMP family member GDF6. Freshwater fish express more GDF6 due in part to a transposon insertion, and transgenic overexpression of GDF6 phenocopies evolutionary changes in Armor-Plate size. The human GDF6 locus also has undergone distinctive regulatory evolution, including complete loss of an enhancer that is otherwise highly conserved between chimps and other mammals. Functional tests show that the ancestral enhancer drives expression in hindlimbs but not forelimbs, in locations that have been specifically modified during the human transition to bipedalism. Both gain and loss of regulatory elements can localize BMP changes to specific anatomical locations, providing a flexible regulatory basis for evolving species-specific changes in skeletal form.
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A recurrent regulatory change underlying altered expression and Wnt response of the stickleback Armor Plates gene EDA
eLife, 2015Co-Authors: Natasha M O'brown, Felicity C. Jones, Brian R. Summers, Shannon D. Brady, David M. KingsleyAbstract:Armor Plate changes in sticklebacks are a classic example of repeated adaptive evolution. Previous studies identified ectodysplasin (EDA) gene as the major locus controlling recurrent Plate loss in freshwater fish, though the causative DNA alterations were not known. Here we show that freshwater EDA alleles have cis-acting regulatory changes that reduce expression in developing Plates and spines. An identical T → G base pair change is found in EDA enhancers of divergent low-Plated fish. Recreation of the T → G change in a marine enhancer strongly reduces expression in posterior Armor Plates. Bead implantation and cell culture experiments show that Wnt signaling strongly activates the marine EDA enhancer, and the freshwater T → G change reduces Wnt responsiveness. Thus parallel evolution of low-Plated sticklebacks has occurred through a shared DNA regulatory change, which reduces the sensitivity of an EDA enhancer to Wnt signaling, and alters expression in developing Armor Plates while preserving expression in other tissues. DOI: http://dx.doi.org/10.7554/eLife.05290.001
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the genetic architecture of parallel Armor Plate reduction in threespine sticklebacks
PLOS Biology, 2004Co-Authors: Pamela F Colosimo, Catherine L Peichel, Kirsten S Nereng, Benjamin K Blackman, Michael D Shapiro, Dolph Schluter, David M. KingsleyAbstract:How many genetic changes control the evolution of new traits in natural populations? Are the same genetic changes seen in cases of parallel evolution? Despite long-standing interest in these questions, they have been difficult to address, particularly in vertebrates. We have analyzed the genetic basis of natural variation in three different aspects of the skeletal Armor of threespine sticklebacks (Gasterosteus aculeatus): the pattern, number, and size of the bony lateral Plates. A few chromosomal regions can account for variation in all three aspects of the lateral Plates, with one major locus contributing to most of the variation in lateral Plate pattern and number. Genetic mapping and allelic complementation experiments show that the same major locus is responsible for the parallel evolution of Armor Plate reduction in two widely separated populations. These results suggest that a small number of genetic changes can produce major skeletal alterations in natural populations and that the same major locus is used repeatedly when similar traits evolve in different locations.
J E Giraldo - One of the best experts on this subject based on the ideXlab platform.
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numerical and experimental analysis of microstructure evolution during arc welding in Armor Plate steels
Journal of Materials Processing Technology, 2009Co-Authors: C M Garzon, J E GiraldoAbstract:Abstract A modeling approach is presented for assessing microstructure evolution in the solid state after arc welding Armor steel Plates. Reliability of the proposed approach is appraised using the case study methodology; predictions of microstructure and hardness for as-welded samples of a specific alloy are compared with results of in-depth quantitative microstructure characterization and microhardness measurements. The experimental work was carried out on MIL A46100 Armor steel Plates welded with AWS E11018M covered electrodes. The modeling approach is implemented in a modular algorithm consisting of diverse tasks, each one of them based on methods described in full in literature. The original contribution of the present work consists the proposed hypothesis that at each point of the weldment the microstructure established at peak temperature during thermal cycles can be (i) assumed to be the same which corresponds to the local equilibrium condition as dictated by thermodynamics, when peak temperature is above AC 1 temperature, or (ii) assumed to be the one corresponding to non-equilibrium martensite decomposition during annealing, when peak temperature is below AC 1 temperature. The most important applications of the algorithm presented are debated.
Kevin J. Hemker - One of the best experts on this subject based on the ideXlab platform.
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microstructural characterization of a commercial hot pressed boron carbide Armor Plate
Journal of the American Ceramic Society, 2016Co-Authors: Kanak Kuwelkar, Jerry C. Lasalvia, Richard A. Haber, Kevin J. HemkerAbstract:Detailed microstructural characterization was carried out on a commercial-grade hot-pressed boron carbide Armor Plate. The boron carbide grains have close to B4C stoichiometry, and most of them have no planar defects. The most prominent second phase is intergranular graphite inclusions that are surrounded by multiple boron carbide grains. Submicrometer intragranular and intergranular BN and AlN precipitates were also observed. In addition, fine dispersions of AlN nanoprecipitates were observed in some but not all grains. No intergranular films were found. These microstructural characteristics are compared with the lab-consolidated boron carbide and their effects on the mechanical properties of boron carbide are addressed.
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Microstructural Characterization of a Commercial Hot‐pressed Boron Carbide Armor Plate
Journal of the American Ceramic Society, 2016Co-Authors: Kanak Kuwelkar, Jerry C. Lasalvia, Richard A. Haber, Kevin J. HemkerAbstract:Detailed microstructural characterization was carried out on a commercial-grade hot-pressed boron carbide Armor Plate. The boron carbide grains have close to B4C stoichiometry, and most of them have no planar defects. The most prominent second phase is intergranular graphite inclusions that are surrounded by multiple boron carbide grains. Submicrometer intragranular and intergranular BN and AlN precipitates were also observed. In addition, fine dispersions of AlN nanoprecipitates were observed in some but not all grains. No intergranular films were found. These microstructural characteristics are compared with the lab-consolidated boron carbide and their effects on the mechanical properties of boron carbide are addressed.
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Microstructural Characterization of a Commercial Hot-Pressed Boron Carbide Armor Plate
Journal of the American Ceramic Society, 2016Co-Authors: Kelvin Y. Xie, Kanak Kuwelkar, Jerry C. Lasalvia, Richard A. Haber, Kevin J. Hemker, R. HayAbstract:Two commercial hot-pressed boron carbide ceramics were investigated by transmission electron microscopy. Atomic-scale observations suggest that the grain boundaries of the two materials are free of grain-boundary films. Two triple-junction phases were found and characterized to be rhombohedral Fe2B103 and orthorhombic Ti3B4. In addition, intra-granular precipitates, AlN, Mo2(C, B) and graphite, were identified and found to have coherent relationships with the boron carbide matrix. Micron-scale inclusions were also observed and most of them were determined to be graphite. The formation mechanisms of the secondary phases and their possible influence on mechanical properties are also discussed.
M Qu - One of the best experts on this subject based on the ideXlab platform.
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study on terminal effects of dense fragment cluster impact on Armor Plate part i analytical model
International Journal of Impact Engineering, 2005Co-Authors: L Qian, M Qu, G FengAbstract:The phenomena and the test results of dense fragment cluster impacting Armor Plate are briefly summarized. The test results indicate that the impulse and the rate of energy deposition on the target and the impacting duration of the fragment cluster are the most important factors, which induces the multi-fragment effects, i.e. synergistic effects, in the impacting process. Meanwhile, they are the characteristic parameters that distinguish the cumulative effects from the additive effects. The analytical methods are employed to investigate the cumulative effects and additive effects caused by the dense fragment cluster. Based on the analysis of the terminal effect of a single fragment, the extrusion-shear damage model of the target impacted by the fragment cluster is developed, and two criteria for the occurrence of the cumulative effect are given and applied to the test analysis. The dimensionless characteristic parameter of the fragment-cluster/target-Plate system is also derived.
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study on terminal effects of dense fragment cluster impact on Armor Plate part ii numerical simulations
International Journal of Impact Engineering, 2004Co-Authors: L Qian, M QuAbstract:In the paper of analytic modelling, i.e. Part I of this project, the phenomena and the test results of dense fragment cluster impacting Armor Plate are introduced. The analytical method is used to investigate the cumulative and additive effects. The extrusion-shear damage model of the target impacted by the fragment cluser is developed, and two criteria of the cumulative effect are proposed. This article describes numerical study of the problem in order to examine the analytical model and to study the target damage pattern. The numerical simulations of multi-fragment impact reproduce the experimental phenomena of fragment cluster penetrating into a target Plate. It shows that the cumulative and additive damage phenomena can be identified by the fragment density and the fragment hit-time interval. Meanwhile, the fragment density is more sensitive than the hit-time interval to the target damage pattern.
Catherine L Peichel - One of the best experts on this subject based on the ideXlab platform.
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Reverse evolution of Armor Plates in the threespine stickleback.
Current Biology, 2008Co-Authors: Jun Kitano, Daniel I. Bolnick, David A. Beauchamp, Michael M. Mazur, Seiichi Mori, Takanori Nakano, Catherine L PeichelAbstract:Summary Faced with sudden environmental changes, animals must either adapt to novel environments or go extinct. Thus, study of the mechanisms underlying rapid adaptation is crucial not only for the understanding of natural evolutionary processes but also for the understanding of human-induced evolutionary change, which is an increasingly important problem [1–8]. In the present study, we demonstrate that the frequency of completely Plated threespine stickleback fish ( Gasterosteus aculeatus ) has increased in an urban freshwater lake (Lake Washington, Seattle, Washington) within the last 40 years. This is a dramatic example of "reverse evolution," [9] because the general evolutionary trajectory is toward Armor-Plate reduction in freshwater sticklebacks [10]. On the basis of our genetic studies and simulations, we propose that the most likely cause of reverse evolution is increased selection for the completely Plated morph, which we suggest could result from higher levels of trout predation after a sudden increase in water transparency during the early 1970s. Rapid evolution was facilitated by the existence of standing allelic variation in Ectodysplasin ( Eda ), the gene that underlies the major Plate-morph locus [11]. The Lake Washington stickleback thus provides a novel example of reverse evolution, which is probably caused by a change in allele frequency at the major Plate locus in response to a changing predation regime.
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the genetic architecture of parallel Armor Plate reduction in threespine sticklebacks
PLOS Biology, 2004Co-Authors: Pamela F Colosimo, Catherine L Peichel, Kirsten S Nereng, Benjamin K Blackman, Michael D Shapiro, Dolph Schluter, David M. KingsleyAbstract:How many genetic changes control the evolution of new traits in natural populations? Are the same genetic changes seen in cases of parallel evolution? Despite long-standing interest in these questions, they have been difficult to address, particularly in vertebrates. We have analyzed the genetic basis of natural variation in three different aspects of the skeletal Armor of threespine sticklebacks (Gasterosteus aculeatus): the pattern, number, and size of the bony lateral Plates. A few chromosomal regions can account for variation in all three aspects of the lateral Plates, with one major locus contributing to most of the variation in lateral Plate pattern and number. Genetic mapping and allelic complementation experiments show that the same major locus is responsible for the parallel evolution of Armor Plate reduction in two widely separated populations. These results suggest that a small number of genetic changes can produce major skeletal alterations in natural populations and that the same major locus is used repeatedly when similar traits evolve in different locations.
