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941.
The type of Salvia dorrii is shown to represent the Great Basin phase of the species (currently called subsp. argentea ) rather than the Mojave Desert expression as implied by Epling and others. The Mojave Desert phase is hereby renamed S. dorrii var. pilosa (A. Gray) Strachan & Reveal. 相似文献
942.
Selenium is critical in livestock nutrition; forage can be either potentially deficient or toxic in this element. Selenium is accumulated in excessive amounts by a relatively few species of plants. Several of these plants, termed indicator species, occur in the western Great Basin; however, selenium toxicity is not a problem in Nevada for domestic livestock. The detection of marginal dietary deficiencies of selenium is of much greater economic importance to the livestock industry than an excess of this element. Selenium occurs as a trace element in the composition of various minerals. Selenium levels are very low in volcanic rocks of recent origin. Accumulations of this element require concentration through secondary dispersion and subsequent sedimentation. Therefore, excesses of selenium are usually associated with siltstone, sandstone, or other sedimentary rocks. Selenium is usually found in soils as selenate, a water-soluble mineral. The selenium concentration of plants is directly related to the selenate concentration in soil. In soils low in selenate, the ability of plants to accumulate selenium is similar. In soils with high levels of selenate, indicator species accumulate 10 times as much selenium as other species. The foliage of most indicator plants is generally avoided by grazing animals. Deficiencies in dietary selenium are associated with the occurrence of white muscle disease, retained placentas, and general unthriftiness of animals. Insufficient dietary selenium can be overcome through injection, intraluminal pellets, or supplementation with salt mixtures. 相似文献
943.
James R. Henderson 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2010,41(1):1-8
The Copenhagen interpretation of quantum mechanics is the dominant view of the theory among working physicists, if not philosophers. There are, however, several strains of Copenhagenism extant, each largely accepting Born's assessment of the wave function as the most complete possible specification of a system and the notion of collapse as a completely random event. This paper outlines three of these sub-interpretations, typing them by what the author of each names as the trigger of quantum-mechanical collapse. Visions of the theory from von Neumann, Heisenberg, and Wheeler offer different mechanisms to break the continuous, deterministic, superposition-laden quantum chain and yield discrete, probabilistic, classical results in response to von Neumann's catastrophe of infinite regress. 相似文献
944.
Vegetation and soils inside and outside an abandoned sheep corral on degraded subalpine range of the Wasatch Plateau were studied to determine the influence of approximately 37 years' use of the corral on soil and plant development. Vegetal and surface cover were estimated. Herbage, litter, and soils were sampled inside and outside the corral and analyzed for C org , N, P, and S. Soil pH, bulk density, and C0 3 -C also were measured. Storage (mass/unit area) of C org , N, P, and S was determined for each component. Yield and vegetal composition were significantly affected inside the corral boundary. Herbage yield was 2.2 times greater, litter mass 16 times greater, foliar cover of grasses 2 times greater, and forb cover 70% lower inside than outside the corral. Cover of meadow barley ( Hordeum brachyantherum ), a component of the predisturbance vegetation of the Wasatch Plateau, was nearly 12 times greater inside than outside the corral. These and other vegetal and cover differences reflect inside-outside differences in concentration, storage, and availability of soil C org , N, P, and S. Concentrations of C org and total and available N, P, and S were greater in the surface 5 cm of soil inside the corral. Available P inside the corral was much higher in all soil layers. Because of bulk density differences, storage was greater inside the corral only for C org and N at 0-5 cm and for P at 5-15 cm. Lower soil pH inside the corral appears related to soil P distribution and C0 3 -C storage. Results suggest a need to reexamine earlier conclusions that tall forbs are the climax dominants of the Wasatch summer range. 相似文献
945.
Kevin M. O Neill William P. Kemp Catherine Seibert Marni G. Rolston James A. Bess T. Keith Philips 《西北部美国博物学家》2011,61(2)
We conducted a 2-year survey, using sweep sampling and family-level taxon identification, of the predatory and parasitoid insects on grassland sites in the Gallatin Valley of southwestern Montana. The 25 sites were divided into 4 habitat classes: 2 native habitat types ( Stipa comata/Bouteloua gracilis and Festuca idahoensis/Agropyron spicatum ) and 2 that had been reseeded with either crested wheatgrass ( Agropyron cristatum ) or smooth brome ( Bromus inermis ). Our major goal was to make quantitative comparisons of the abundance of insects among native and reseeded habitats. Of 51 families in 5 insect orders identified, 7 Hymenoptera (Encyrtidae, Braconidae, Ichneumonidae, Pteromalidae, Eulophidae, Scelionidae, and Torymidae), 3 Hemiptera (Lygaeidae, Nabidae, and Reduviidae), 1 Coleoptera (Coccinellidae), and 1 Diptera (Asilidae) comprised 90% of the natural enemies sampled. Ordination analyses provided no strong evidence that the 4 habitat classes contained distinct overall natural enemy communities. However, contiguous native and reseeded sites usually had relatively different overall natural enemy assemblages, suggesting that vegetation was often a more important correlate of community composition than was close spatial proximity of sites. Furthermore, several common families exhibited differential abundances across habitat classes in one or both years. For example, in 1989, Eulophidae, Pteromalidae, and Torymidae were more abundant on native Festuca/Agropyron sites, whereas Encyrtidae and Nabidae were more abundant on Festuca/Agropyron sites reseeded with Bromus inermis . Although analyses of insect assemblages classified to the family level provide somewhat limited information on functional ecological differences among habitats, they allow one to survey a broad array of taxa to identify focal groups for future conservation and land management studies. 相似文献
946.
947.
Houlston RS Cheadle J Dobbins SE Tenesa A Jones AM Howarth K Spain SL Broderick P Domingo E Farrington S Prendergast JG Pittman AM Theodoratou E Smith CG Olver B Walther A Barnetson RA Churchman M Jaeger EE Penegar S Barclay E Martin L Gorman M Mager R Johnstone E Midgley R Niittymäki I Tuupanen S Colley J Idziaszczyk S;COGENT Consortium Thomas HJ Lucassen AM Evans DG Maher ER;CORGI Consortium;COIN Collaborative Group;COINB Collaborative Group Maughan T Dimas A Dermitzakis E Cazier JB 《Nature genetics》2010,42(11):973-977
Genome-wide association studies (GWAS) have identified ten loci harboring common variants that influence risk of developing colorectal cancer (CRC). To enhance the power to identify additional CRC risk loci, we conducted a meta-analysis of three GWAS from the UK which included a total of 3,334 affected individuals (cases) and 4,628 controls followed by multiple validation analyses including a total of 18,095 cases and 20,197 controls. We identified associations at four new CRC risk loci: 1q41 (rs6691170, odds ratio (OR) = 1.06, P = 9.55 × 10?1? and rs6687758, OR = 1.09, P = 2.27 × 10??, 3q26.2 (rs10936599, OR = 0.93, P = 3.39 × 10??), 12q13.13 (rs11169552, OR = 0.92, P = 1.89 × 10?1? and rs7136702, OR = 1.06, P = 4.02 × 10??) and 20q13.33 (rs4925386, OR = 0.93, P = 1.89 × 10?1?). In addition to identifying new CRC risk loci, this analysis provides evidence that additional CRC-associated variants of similar effect size remain to be discovered. 相似文献
948.
Drake JA Bird C Nemesh J Thomas DJ Newton-Cheh C Reymond A Excoffier L Attar H Antonarakis SE Dermitzakis ET Hirschhorn JN 《Nature genetics》2006,38(2):223-227
Noncoding genetic variants are likely to influence human biology and disease, but recognizing functional noncoding variants is difficult. Approximately 3% of noncoding sequence is conserved among distantly related mammals, suggesting that these evolutionarily conserved noncoding regions (CNCs) are selectively constrained and contain functional variation. However, CNCs could also merely represent regions with lower local mutation rates. Here we address this issue and show that CNCs are selectively constrained in humans by analyzing HapMap genotype data. Specifically, new (derived) alleles of SNPs within CNCs are rarer than new alleles in nonconserved regions (P = 3 x 10(-18)), indicating that evolutionary pressure has suppressed CNC-derived allele frequencies. Intronic CNCs and CNCs near genes show greater allele frequency shifts, with magnitudes comparable to those for missense variants. Thus, conserved noncoding variants are more likely to be functional. Allele frequency distributions highlight selectively constrained genomic regions that should be intensively surveyed for functionally important variation. 相似文献
949.
A naturally occurring epigenetic mutation in a gene encoding an SBP-box transcription factor inhibits tomato fruit ripening 总被引:26,自引:0,他引:26
Manning K Tör M Poole M Hong Y Thompson AJ King GJ Giovannoni JJ Seymour GB 《Nature genetics》2006,38(8):948-952
A major component in the regulatory network controlling fruit ripening is likely to be the gene at the tomato Colorless non-ripening (Cnr) locus. The Cnr mutation results in colorless fruits with a substantial loss of cell-to-cell adhesion. The nature of the mutation and the identity of the Cnr gene were previously unknown. Using positional cloning and virus-induced gene silencing, here we demonstrate that an SBP-box (SQUAMOSA promoter binding protein-like) gene resides at the Cnr locus. Furthermore, the Cnr phenotype results from a spontaneous epigenetic change in the SBP-box promoter. The discovery that Cnr is an epimutation was unexpected, as very few spontaneous epimutations have been described in plants. This study demonstrates that an SBP-box gene is critical for normal ripening and highlights the likely importance of epialleles in plant development and the generation of natural variation. 相似文献
950.