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121.
本文对更一般的结构模型给出了参数的一种常用的仪器变量估计近似分布方差的一种算法.并且给出了未知真值x服从指数分布的例子.此算法对生物科学中统计规律的探讨有一定的应用价值. 相似文献
122.
Does freshwater macroinvertebrate diversity along a pH‐gradient reflect adaptation to low pH? 总被引:1,自引:0,他引:1
1. The impacts of anthropogenic surface water acidification are much better known than those of natural acidity. Recent studies have indicated biodiversity is not degraded and species composition unaltered in naturally acidic compared to circumneutral watercourses.
2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.
3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.
4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.
5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups. 相似文献
2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.
3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.
4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.
5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups. 相似文献
123.
A probabilistic graphical model is proposed in order to detect the coevolution between different sites in biological sequences. The model extends the continuous-time Markov process of sequence substitution for single nucleic or amino acids and imposes general constraints regarding simultaneous changes on the substitution rate matrix. Given a multiple sequence alignment for each molecule of interest and a phylogenetic tree, the model can predict potential interactions within or between nucleic acids and proteins. Initial validation of the model is carried out using tRNA and 16S rRNA sequence data. The model accurately identifies the secondary interactions of tRNA as well as several known tertiary interactions. In addition, results on 16S rRNA data indicate this general and simple coevolutionary model outperforms several other parametric and nonparametric methods in predicting secondary interactions. Furthermore, the majority of the putative predictions exhibit either direct contact or proximity of the nucleotide pairs in the 3-dimensional structure of the Thermus thermophilus ribosomal small subunit. The results on RNA data suggest a general model of coevolution might be applied to other types of interactions between protein, DNA, and RNA molecules. 相似文献
124.
Chrysophyte scale assemblages were analyzed in the surface sediments (0–1 cm) of 146 lakes sampled in the U.S. Environmental Protection Agency's (EPA) Environmental Monitoring and Assessment Program–Surface Waters (EMAP-SW) in the northeastern U.S.A. Chrysophyte data from the EMAP lakes were combined with a previous study of 71 Adirondack PIRLA (Paleoecological Investigation of Recent Lake Acidification) lakes and collectively analyzed to examine the indicator potential of scaled chrysophytes in the northeastern U.S.A. with respect to several environmental variables. Canonical correspondence analysis (CCA) was used to determine which environmental variables influenced the distributions of species. Forward selection and Monte Carlo permutation tests showed that 51% of the variance in the chrysophyte assemblages was related to pH. The other six significant variables (conductivity, chloride, total phosphorus [TP], elevation, lake depth, and watershed area) contributed an additional 31% of the total (82%) variance explained by the seven forward-selected variables. Similar to previous studies, many taxa showed distinct distribution patterns with respect to pH. Partial and constrained CCAs indicated that, although all seven variables explained significant proportions of variation in the species data, a reliable inference model could be developed only for lake-water pH. The strength of this model ( R 2 = 0.78, RMSEboot = 0.47 of a pH unit) is comparable to a recently constructed diatom-based model for the EMAP lakes. The use of both models in paleolimnological and biomonitoring studies would be advantageous because they would provide two independent lines of evidence of environmental change. 相似文献
125.
Objective: To use longitudinal profiling of plasma adipokines to distinguish diabetogenic vs. non‐diabetogenic obesity syndrome in two new mouse models of polygenic obesity. Research Methods and Procedures: Male mice of the NONcNZO5 strain develop a polygenic obesity syndrome uncomplicated by diabetes, whereas NONcNZO10 males develop a comparable polygenic obesity that precipitates type 2 diabetes. A multiplex immunoassay for simultaneous measurement of insulin and a panel of mouse adipokines (leptin, resistin, adiponectin, interleukin‐6, tumor necrosis factor α, macrophage chemoattractant protein‐1, plasminogen activator inhibitor‐1) were used to profile longitudinal changes in these strains between 4 and 16 weeks of age that might distinguish the non‐diabetogenic vs. diabetogenic obesity (diabesity). Results: Both strains became adipose, with NONcNZO5 males attaining a higher mean body weight with a higher percentage fat content. Weight gain in NONcNZO5 was accompanied by a transient peak in plasma insulin (PI) at 8 weeks followed by a decline into normal range, with normoglycemia maintained throughout. In contrast, NONcNZO10 showed no early PI secretory response because both body weight and plasma glucose increased between 4 and 8 weeks. Only after 12 weeks, with hyperglycemia established, was a delayed PI secretory response observed. Neither plasma leptin nor adiponectin concentrations significantly differentiated the two syndromes over time. However, repeated measures ANOVA showed that NONcNZO10 males maintained significantly higher plasma concentrations of two adipokines, resistin and plasminogen activator inhibitor‐1, and the pro‐inflammatory cytokine/adipokine macrophage chemoattractant protein‐1. Discussion: Longitudinal profiling of PI and adipokines in two new mouse models developing moderate obesity demonstrated that specific marker signatures differentiated a non‐diabetogenic obesity from a diabetogenic obesity. 相似文献
126.
Mareuil F Sizun C Perez J Schoenauer M Lallemand JY Bontems F 《European biophysics journal : EBJ》2007,37(1):95-104
Most proteins comprise several domains and/or participate in functional complexes. Owing to ongoing structural genomic projects,
it is likely that it will soon be possible to predict, with reasonable accuracy, the conserved regions of most structural
domains. Under these circumstances, it will be important to have methods, based on simple-to-acquire experimental data, that
allow to build and refine structures of multi-domain proteins or of protein complexes from homology models of the individual
domains/proteins. It has been recently shown that small angle X-ray scattering (SAXS) and NMR residual dipolar coupling (RDC)
data can be combined to determine the architecture of such objects when the X-ray structures of the domains are known and
can be considered as rigid objects. We developed a simple genetic algorithm to achieve the same goal, but by using homology
models of the domains considered as deformable objects. We applied it to two model systems, an S1KH bi-domain of the NusA
protein and the γS-crystallin protein. Despite its simplicity our algorithm is able to generate good solutions when driven
by SAXS and RDC data. 相似文献
127.
Masaya Shimazaki Takehiro Sasaki Kouki Hikosaka Tohru Nakashizuka 《Global Change Biology》2011,17(11):3431-3438
Many studies have reported shifts in the altitudinal ranges of plant species in response to recent global warming. However, most studies of tree species have been conducted on a small scale and have focused on tree line ecotones by examining tree rings and age structure on account of the long life spans of the trees. To examine the impact of climate change on forest dynamics at a regional scale, we investigated differences in the population density and canopy height of a Japanese subalpine coniferous species, Abies mariesii, between 1967 and 2003 by analysis of high‐resolution aerial photographs of the Hakkoda Mountains, Honshu, Japan. In 712 plots within the photographs we analyzed which environmental variables (including elevation, aspect, wetness, and distance from moorlands) account for these changes. The population density of A. mariesii decreased below 1000 m a.s.l. and increased above 1300 m a.s.l. It also increased around moorlands, which may provide refugia at low elevations. The rate of increase in canopy height was lowest on the southeastern slopes and on the periphery of the moorlands. The distinct changes in the population density of A. mariesii at its distribution limits probably reflect the responses of the population to climatic changes during three decades. Areas surrounding the moorlands may offer refugia in spite of the poor growing conditions there. 相似文献
128.
在过去的100年里,动物模型的研究已在人类疫苗的发展中起到至关重要的作用。动物模型的使用不仅有助于疫苗从基本研究转到临床应用,而且动物模型通常能够预测疫苗实用的潜能,从而帮助疫苗的生产商预测财政风险。由于每种动物模型都有其自身的优缺点,选择一种合适的动物模型可促进疫苗研发的顺利进行。 相似文献
129.
Robin E. Russell J. Andrew Royle Richard Desimone Michael K. Schwartz Victoria L. Edwards Kristy P. Pilgrim Kevin S. Mckelvey 《The Journal of wildlife management》2012,76(8):1551-1561
Mountain lions (Puma concolor) are often difficult to monitor because of their low capture probabilities, extensive movements, and large territories. Methods for estimating the abundance of this species are needed to assess population status, determine harvest levels, evaluate the impacts of management actions on populations, and derive conservation and management strategies. Traditional mark–recapture methods do not explicitly account for differences in individual capture probabilities due to the spatial distribution of individuals in relation to survey effort (or trap locations). However, recent advances in the analysis of capture–recapture data have produced methods estimating abundance and density of animals from spatially explicit capture–recapture data that account for heterogeneity in capture probabilities due to the spatial organization of individuals and traps. We adapt recently developed spatial capture–recapture models to estimate density and abundance of mountain lions in western Montana. Volunteers and state agency personnel collected mountain lion DNA samples in portions of the Blackfoot drainage (7,908 km2) in west-central Montana using 2 methods: snow back-tracking mountain lion tracks to collect hair samples and biopsy darting treed mountain lions to obtain tissue samples. Overall, we recorded 72 individual capture events, including captures both with and without tissue sample collection and hair samples resulting in the identification of 50 individual mountain lions (30 females, 19 males, and 1 unknown sex individual). We estimated lion densities from 8 models containing effects of distance, sex, and survey effort on detection probability. Our population density estimates ranged from a minimum of 3.7 mountain lions/100 km2 (95% CI 2.3–5.7) under the distance only model (including only an effect of distance on detection probability) to 6.7 (95% CI 3.1–11.0) under the full model (including effects of distance, sex, survey effort, and distance × sex on detection probability). These numbers translate to a total estimate of 293 mountain lions (95% CI 182–451) to 529 (95% CI 245–870) within the Blackfoot drainage. Results from the distance model are similar to previous estimates of 3.6 mountain lions/100 km2 for the study area; however, results from all other models indicated greater numbers of mountain lions. Our results indicate that unstructured spatial sampling combined with spatial capture–recapture analysis can be an effective method for estimating large carnivore densities. Published 2012. This article is a U.S. Government work and is in the public domain in the USA. 相似文献
130.
Jesse D Riordan Luke J Drury Ryan P Smith Benjamin T Brett Laura M Rogers Todd E Scheetz Adam J Dupuy 《BMC genomics》2014,15(1)