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111.
Majid Iravani Martin Schütz Peter J. Edwards Anita C. Risch Christoph Scheidegger Helene H. Wagner 《Basic and Applied Ecology》2011,12(6):505-515
Free-ranging large herbivores can influence vegetation dynamics through seed dispersal within and among habitats. We investigated the content of germinable seeds in the dung (endozoochory) of red deer (Cervus elaphus L.), the most ubiquitous wild ungulate throughout the European Alps, and compared the results with the species composition of the vegetation type in which the dung was dropped. The study was conducted in the subalpine zone of the Swiss National Park and included the three most important vegetation types for red deer: (i) intensively grazed short-grass vegetation, (ii) less intensively grazed tall-grass vegetation, and (iii) adjacent conifer forest understory vegetation. Seeds of 47 species, mostly from small-seeded herbaceous species, were recorded in dung samples with three species accounting for 65% of germinated seeds. Our results confirmed the hypotheses that (H1) small-seeded species were more likely to occur in red deer dung than larger-seeded species, though seed size was unrelated to seed density, (H2) red deer dung contained mostly seeds from short-grass vegetation, with seed species composition in dung collected from any vegetation type being most similar to species composition of relevés from short-grass vegetation, and (H3) seeds were less likely to be dispersed between vegetation types than within vegetation types, with dung dropped in short-grass vegetation having a different species composition and containing over twice as many seeds as dung dropped in the other two vegetation types. These results collectively support the hypothesis that red deer endozoochory contributes to maintaining short-grass vegetation, the favoured grazing sites of hinds in the Swiss National Park, by increasing propagule pressure of seeds from herbaceous forage species adapted to endozoochory relative to other species and especially those from later stages of secondary succession. 相似文献
112.
Soil seed banks are an important source of new individuals for many plant populations and contribute to future genetic variability. In general, the size and persistence of soil seed banks is predicted to be greater where growth occurs in unpredictable pulses, where opportunities for disturbance‐related recruitment are frequent and where the probability of recruitment failure is high. In savanna ecosystems, characterized by disturbance from fire and unpredictable water availability, soil seed banks should be relatively important sources of recruitment. However, the few studies conducted in savannas are inconclusive about the importance of soil seed banks and, more specifically, how seed banks should change across environmental gradients. We determined the number of viable seeds in the soil seed bank across savanna‐grasslands in the Serengeti, an ecosystem characterized by frequent fire and seasonal drought. Soils were exposed to a combination of smoke and heat, cues which may be required to break seed dormancy in such ecosystems. Our a priori expectation was to observe large seed banks in regions characterized by seasonal drought and comparatively smaller seed banks in regions of higher moisture availability and high fire frequencies. In contrast to our hypothesis, seed germination increased strongly with precipitation and fire frequency. In addition, there was a significant interaction effect between fire and rainfall: low rainfall sites with frequent fire had greater seed germination than low rainfall sites with low fire frequency. Moreover, in laboratory experiments, heat had a negative, smoke a positive effect on final seed germination numbers. Together, these findings suggest that fire may be a key factor in driving herbaceous seed bank dynamics in tropical savannas. 相似文献
113.
Marc?A. Coram Qing Duan Thomas?J. Hoffmann Timothy Thornton Joshua?W. Knowles Nicholas?A. Johnson Heather?M. Ochs-Balcom Timothy?A. Donlon Lisa?W. Martin Charles?B. Eaton Jennifer?G. Robinson Neil?J. Risch Xiaofeng Zhu Charles Kooperberg Yun Li Alex?P. Reiner Hua Tang 《American journal of human genetics》2013,92(6):904-916
Blood lipid concentrations are heritable risk factors associated with atherosclerosis and cardiovascular diseases. Lipid traits exhibit considerable variation among populations of distinct ancestral origin as well as between individuals within a population. We performed association analyses to identify genetic loci influencing lipid concentrations in African American and Hispanic American women in the Women’s Health Initiative SNP Health Association Resource. We validated one African-specific high-density lipoprotein cholesterol locus at CD36 as well as 14 known lipid loci that have been previously implicated in studies of European populations. Moreover, we demonstrate striking similarities in genetic architecture (loci influencing the trait, direction and magnitude of genetic effects, and proportions of phenotypic variation explained) of lipid traits across populations. In particular, we found that a disproportionate fraction of lipid variation in African Americans and Hispanic Americans can be attributed to genomic loci exhibiting statistical evidence of association in Europeans, even though the precise genes and variants remain unknown. At the same time, we found substantial allelic heterogeneity within shared loci, characterized both by population-specific rare variants and variants shared among multiple populations that occur at disparate frequencies. The allelic heterogeneity emphasizes the importance of including diverse populations in future genetic association studies of complex traits such as lipids; furthermore, the overlap in lipid loci across populations of diverse ancestral origin argues that additional knowledge can be gleaned from multiple populations. 相似文献
114.
Carbon dioxide fluxes in a spatially and temporally heterogeneous temperate grassland 总被引:3,自引:0,他引:3
Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability
in soil processes, and plant biomass and composition in grasslands. However, it is unclear how this variation in plant and
soil properties affects carbon dioxide (CO2) fluxes. The aim of this study is to explore the effect of grazing, topographic position, and seasonal variation in soil
moisture and temperature on plant assimilation, shoot and soil respiration, and net ecosystem CO2 exchange (NEE). Carbon dioxide fluxes, vegetation, and environmental variables were measured once a month inside and outside
long-term ungulate exclosures in hilltop (dry) to slope bottom (mesic) grassland throughout the 2004 growing season in Yellowstone
National Park. There was no difference in vegetation properties and CO2 fluxes between the grazed and the ungrazed sites. The spatial and temporal variability in CO2 fluxes were related to differences in aboveground biomass and total shoot nitrogen content, which were both related to variability
in soil moisture. All sites were CO2 sinks (NEE>0) for all our measurments taken throughout the growing season; but CO2 fluxes were four- to fivefold higher at sites supporting the most aboveground biomass located at slope bottoms, compared
to the sites with low biomass located at hilltops or slopes. The dry sites assimilated more CO2 per gram aboveground biomass and stored proportionally more of the gross-assimilated CO2 in the soil, compared to wet sites. These results indicate large spatio-temporal variability of CO2 fluxes and suggest factors that control the variability in Yellowstone National Park. 相似文献
115.
Genetic analysis of breast cancer in the cancer and steroid hormone study. 总被引:47,自引:28,他引:47 下载免费PDF全文
The familial risk of breast cancer is investigated in a large population-based, case-control study conducted by the Centers for Disease Control. The data set is based on 4,730 histologically confirmed breast cancer cases aged 20 to 54 years and on 4,688 controls who were frequency matched to cases on the basis of both geographic region and 5-year categories of age, and it includes family histories, obtained through interviews of cases and controls, of breast cancer in mothers and sisters. Segregation analysis and goodness-of-fit tests of genetic models provide evidence for the existence of a rare autosomal dominant allele (q = .0033) leading to increased susceptibility to breast cancer. The effect of genotype on the risk of breast cancer is shown to be a function of a woman's age. Although, compared with noncarriers, carriers of the allele appear to be at greater risk at all ages, the ratio of age-specific risks is greatest at young ages and declines steadily thereafter. The proportion of cases predicted to carry the allele is highest (36%) among cases aged 20-29 years. This proportion gradually decreases to 1% among cases aged 80 years or older. The cumulative lifetime risk of breast cancer for women who carry the susceptibility allele is predicted to be high, approximately 92%, while the cumulative lifetime risk for noncarriers is estimated to be approximately 10%. 相似文献
116.
Jeffrey L. Waugh Jeremy Celver Meenakshi Sharma Robert L. Dufresne Dimitra Terzi S. Craig Risch William G. Fairbrother Rachael L. Neve John P. Kane Mary J. Malloy Clive R. Pullinger Harvest F. Gu Christos Tsatsanis Steven P. Hamilton Stephen J. Gold Venetia Zachariou Abraham Kovoor 《PloS one》2011,6(11)
117.
The fitness‐related consequences of egg size, independent of the influences of parental quality, are poorly understood in altricial birds. Not only can egg size and parental quality influence growth and survival, but each could influence the development of condition‐dependent plumage coloration in offspring. The Eastern Bluebird Sialia sialis is an altricial, multi‐brooded, cavity‐nesting passerine in which juveniles display dichromatic UV‐blue plumage. Previous research suggests that plumage coloration acts as a signal of individual quality among juvenile and adult Eastern Bluebirds. Here, we separate the effects of egg size and parental quality (defined by egg size laid) on nestling growth and plumage ornamentation by exchanging clutches of large eggs with clutches of small eggs. Nestlings were significantly larger immediately post‐hatching when hatched from a large egg, but to maintain a larger size, nestlings needed to have hatched from a large egg and to have been reared by high‐quality parents. Nestlings were brighter when reared by high‐quality parents and this relationship was strongest later in the breeding season. Nestlings exhibited greater UV chroma if hatched early in the season, but UV chroma was not significantly affected by egg size or parental quality. These findings demonstrate varying influences of both egg size and parental quality on offspring growth and plumage ornamentation but suggest that quality of post‐hatching investment is more influential than pre‐hatching investment. 相似文献
118.
Albert Rosenberger Stefanie Friedrichs Christopher I. Amos Paul Brennan Gordon Fehringer Joachim Heinrich Rayjean J. Hung Thomas Muley Martina Müller-Nurasyid Angela Risch Heike Bickeb?ller 《PloS one》2015,10(10)
Introduction
Gene-set analysis (GSA) methods are used as complementary approaches to genome-wide association studies (GWASs). The single marker association estimates of a predefined set of genes are either contrasted with those of all remaining genes or with a null non-associated background. To pool the p-values from several GSAs, it is important to take into account the concordance of the observed patterns resulting from single marker association point estimates across any given gene set. Here we propose an enhanced version of Fisher’s inverse χ2-method META-GSA, however weighting each study to account for imperfect correlation between association patterns.Simulation and Power
We investigated the performance of META-GSA by simulating GWASs with 500 cases and 500 controls at 100 diallelic markers in 20 different scenarios, simulating different relative risks between 1 and 1.5 in gene sets of 10 genes. Wilcoxon’s rank sum test was applied as GSA for each study. We found that META-GSA has greater power to discover truly associated gene sets than simple pooling of the p-values, by e.g. 59% versus 37%, when the true relative risk for 5 of 10 genes was assume to be 1.5. Under the null hypothesis of no difference in the true association pattern between the gene set of interest and the set of remaining genes, the results of both approaches are almost uncorrelated. We recommend not relying on p-values alone when combining the results of independent GSAs.Application
We applied META-GSA to pool the results of four case-control GWASs of lung cancer risk (Central European Study and Toronto/Lunenfeld-Tanenbaum Research Institute Study; German Lung Cancer Study and MD Anderson Cancer Center Study), which had already been analyzed separately with four different GSA methods (EASE; SLAT, mSUMSTAT and GenGen). This application revealed the pathway GO0015291 “transmembrane transporter activity” as significantly enriched with associated genes (GSA-method: EASE, p = 0.0315 corrected for multiple testing). Similar results were found for GO0015464 “acetylcholine receptor activity” but only when not corrected for multiple testing (all GSA-methods applied; p≈0.02). 相似文献119.
120.
Piper cenocladium is a common understory species in the wet primary forested areas of Costa Rica. The plant possesses a petiole chamber which is usually occupied by the ant Pheidole bicornis. The plant/ant relationship is unique in that the ant must be present for meaningful numbers of ant-food bodies to be differentiated. The food body is a lipid storing, single cell developed from one adaxial petiole epidermal cell. Cellular aspects of this differentiation process are described with particular reference to nucleolar ultrastructure. 相似文献