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Plant–pollinator interactions are essential for the functioning of terrestrial ecosystems, but are increasingly affected by global change. The risks to such mutualistic interactions from increasing temperature and more frequent extreme climatic events such as drought or advanced snow melt are assumed to depend on network specialization, species richness, local climate and associated parameters such as the amplitude of extreme events. Even though elevational gradients provide valuable model systems for climate change and are accompanied by changes in species richness, responses of plant–pollinator networks to climatic extreme events under different environmental and biotic conditions are currently unknown. Here, we show that elevational climatic gradients, species richness and experimentally simulated extreme events interactively change the structure of mutualistic networks in alpine grasslands. We found that the degree of specialization in plant–pollinator networks (H2′) decreased with elevation. Nonetheless, network specialization increased after advanced snow melt at high elevations, whereas changes in network specialization after drought were most pronounced at sites with low species richness. Thus, changes in network specialization after extreme climatic events depended on climatic context and were buffered by high species richness. In our experiment, only generalized plant–pollinator networks changed in their degree of specialization after climatic extreme events. This indicates that contrary to our assumptions, network generalization may not always foster stability of mutualistic interaction networks. 相似文献
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Ecological networks, nestedness and sampling effort 总被引：5，自引：0，他引：5
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Generalization of pollination systems is widely accepted by ecologists in the studies of plant–pollinator interaction networks at the community level, but the degree of generalization of pollination networks remains largely unknown at the individual pollinator level. Using potential legitimate pollinators that were constantly visiting flowers in two alpine meadow communities, we analyzed the differences in the pollination network structure between the pollinator individual level and species level. The results showed that compared to the pollinator species‐based networks, the linkage density, interaction diversity, interaction evenness, the average plant linkage level, and interaction diversity increased, but connectance, degree of nestedness, the average of pollinator linkage level, and interaction diversity decreased in the pollinator individual‐based networks, indicating that pollinator individuals had a narrower food niche than their counterpart species. Pollination networks at the pollinator individual level were more specialized at the network level (H′2) and the plant species node level (d′) than at the pollinator species‐level networks, reducing the chance of underestimating levels of specialization in pollination systems. The results emphasize that research into pollinator individual‐based pollination networks will improve our understanding of the pollination networks at the pollinator species level and the coevolution of flowering plants and pollinators. 相似文献
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Thomas W. H. Aspin Kieran Khamis Thomas J. Matthews Alexander M. Milner Matthew J. O&#x;Callaghan Mark Trimmer Guy Woodward Mark E. Ledger 《Global Change Biology》2019,25(1):230-244
Functional traits are increasingly being used to predict extinction risks and range shifts under long‐term climate change scenarios, but have rarely been used to study vulnerability to extreme climatic events, such as supraseasonal droughts. In streams, drought intensification can cross thresholds of habitat loss, where marginal changes in environmental conditions trigger disproportionate biotic responses. However, these thresholds have been studied only from a structural perspective, and the existence of functional nonlinearity remains unknown. We explored trends in invertebrate community functional traits along a gradient of drought intensity, simulated over 18 months, using mesocosms analogous to lowland headwater streams. We modelled the responses of 16 traits based on a priori predictions of trait filtering by drought, and also examined the responses of trait profile groups (TPGs) identified via hierarchical cluster analysis. As responses to drought intensification were both linear and nonlinear, generalized additive models (GAMs) were chosen to model response curves, with the slopes of fitted splines used to detect functional thresholds during drought. Drought triggered significant responses in 12 (75%) of the a priori‐selected traits. Behavioural traits describing movement (dispersal, locomotion) and diet were sensitive to moderate‐intensity drought, as channels fragmented into isolated pools. By comparison, morphological and physiological traits showed little response until surface water was lost, at which point we observed sudden shifts in body size, respiration mode and thermal tolerance. Responses varied widely among TPGs, ranging from population collapses of non‐aerial dispersers as channels fragmented to irruptions of small, eurythermic dietary generalists upon extreme dewatering. Our study demonstrates for the first time that relatively small changes in drought intensity can trigger disproportionately large functional shifts in stream communities, suggesting that traits‐based approaches could be particularly useful for diagnosing catastrophic ecological responses to global change. 相似文献
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Antony N. Waigwa Brian Njoroge Mwangi Gituru R. Wahiti Fred Omengo Yadong Zhou Qingfeng Wang 《Journal of Plant Ecology》2020,13(6):785
环境能一定程度上影响和改变植物的形态结构和生理生化。本文旨在拟研究热带东非高山不同海拔梯度下两 种代表植物Dendrosenecio keniensis和Lobelia gregoriana的形态结构和生理生化的变化。我们沿海拔梯度在海拔3500 m至4300 m的范围内 建立了90个10 m × 10 m的样方,使用1 km × 1 km网格单元在ArcGis 10.5 中栅格化研究区域并获取每个样方的气候数据,包括年平均气温、 年平均降水量、年总辐射量、水汽压,同时获取了每个样方的地形变量,包括坡向、坡度和阴影等。我们收集了每个样方两种植物的形态性状,包括株高、叶面积、叶厚、叶干重、比叶面积,以及叶化学计量性状,包括氮、碳、磷的含量,同时收集了样方的土壤有机碳、 土壤全氮、土壤有机氮和土壤磷数据。我们将海拔高度设为解释变量,对两种植物的形态性状和叶片化学计量性状进行线性回归分析,同时,在海拔梯度上对叶片形态和化学计量性状与气候、土壤和地形变量进行了相关分析。我们的研究发现,D. keniensis 有羊毛状的短柔毛叶, 而L. gregoriana则有粘液填充的肉质和蜡质的角质层叶子,以避免冻害。这两个物种都呈现出了降低的代谢率,表现在叶片磷含量较低。我 们的研究结果还表明,形态和叶片化学计量的变化是由气候、土壤和地形变量共同决定的,这些变量随肯尼亚山海拔的变化而变 化。我们推测,沿海拔梯度两种植物的形态和叶片化学计量性状的变异是对恶劣环境条件的适应。 相似文献
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Xiao-Jian Zhou Jean-Pierre Sommadossi 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1997,691(2):948
A rapid, sensitive and specific high-performance liquid chromatographic (HPLC) assay was developed and validated for the measurement of (−)-2′-deoxy-3′-thiacytidine (3TC) in human serum. The method included precipitation of serum proteins by trichloroacetic acid (20%, w/v) treatment followed by centrifugation. The resulting supernatant was directly injected and 3TC was isocratically chromatographed on a reversed-phase C18 column using a mixture of phosphate buffer and methanol (88.3:11.7, v/v) and monitored at 280 nm. The limit of quantitation was 20 ng/ml using 100 μl of serum. The standard curve was linear within the range of 20–10 000 ng/ml. Replicate analysis of three quality control samples (40–1500 ng/ml) led to satisfactory intra- and itner-assay precision (coefficient of variation from 3.0 to 12.9%) and accuracy (deviation from −6.3 to 9.7%). Moreover, sample treatment processes including human immunodeficiency virus (HIV) heat-inactivation, exposure at room temperature and freezing-thawing cycles did not influence the stability of the analyte. This assay was successfully applied to the determination of 3TC serum levels in HIV-infected patients. In addition, preliminary results indicated that this procedure may also be extended to the measurement of 3TC in human plasma and urine. 相似文献
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Yong‐Gui Gao Min Yao Ayuko Okada Isao Tanaka 《Acta Crystallographica. Section F, Structural Biology Communications》2006,62(12):1196-1200
Bacterial and archaeal 2′‐5′ RNA ligases, members of the 2H phosphoesterase superfamily, catalyze the linkage of the 5′ and 3′ exons via a 2′‐5′‐phosphodiester bond during tRNA‐precursor splicing. The crystal structure of the 2′‐5′ RNA ligase PH0099 from Pyrococcus horikoshii OT3 was solved at 1.94 Å resolution (PDB code 1vgj ). The molecule has a bilobal α+β arrangement with two antiparallel β‐sheets constituting a V‐shaped active‐site cleft, as found in other members of the 2H phosphoesterase superfamily. The present structure was significantly different from that determined previously at 2.4 Å resolution (PDB code 1vdx ) in the active‐site cleft; the entrance to the cleft is wider and the active site is easily accessible to the substrate (RNA precursor) in our structure. Structural comparison with the 2′‐5′ RNA ligase from Thermus thermophilus HB8 also revealed differences in the RNA precursor‐binding region. The structural differences in the active‐site residues (tetrapeptide motifs H‐X‐T/S‐X) between the members of the 2H phosphoesterase superfamily are discussed. 相似文献
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Clyde A. Smith Marta Toth Monolekha Bhattacharya Hilary Frase Sergei B. Vakulenko 《Acta Crystallographica. Section D, Structural Biology》2014,70(6):1561-1571
The bifunctional acetyltransferase(6′)‐Ie‐phosphotransferase(2′′)‐Ia [AAC(6′)‐Ie‐APH(2′′)‐Ia] is the most important aminoglycoside‐resistance enzyme in Gram‐positive bacteria, conferring resistance to almost all known aminoglycoside antibiotics in clinical use. Owing to its importance, this enzyme has been the focus of intensive research since its isolation in the mid‐1980s but, despite much effort, structural details of AAC(6′)‐Ie‐APH(2′′)‐Ia have remained elusive. The structure of the Mg2GDP complex of the APH(2′′)‐Ia domain of the bifunctional enzyme has now been determined at 2.3 Å resolution. The structure of APH(2′′)‐Ia is reminiscent of the structures of other aminoglycoside phosphotransferases, having a two‐domain architecture with the nucleotide‐binding site located at the junction of the two domains. Unlike the previously characterized APH(2′′)‐IIa and APH(2′′)‐IVa enzymes, which are capable of utilizing both ATP and GTP as the phosphate donors, APH(2′′)‐Ia uses GTP exclusively in the phosphorylation of the aminoglycoside antibiotics, and in this regard closely resembles the GTP‐dependent APH(2′′)‐IIIa enzyme. In APH(2′′)‐Ia this GTP selectivity is governed by the presence of a `gatekeeper' residue, Tyr100, the side chain of which projects into the active site and effectively blocks access to the adenine‐binding template. Mutation of this tyrosine residue to a less bulky phenylalanine provides better access for ATP to the NTP‐binding template and converts APH(2′′)‐Ia into a dual‐specificity enzyme. 相似文献
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Christopher L. Kilner;Alyssa A. Carrell;Daniel J. Wieczynski;Samantha Votzke;Katrina DeWitt;Andrea Yammine;Jonathan Shaw;Dale A. Pelletier;David J. Weston;Jean P. Gibert; 《Global Change Biology》2024,30(3):e17203
Microbes affect the global carbon cycle that influences climate change and are in turn influenced by environmental change. Here, we use data from a long-term whole-ecosystem warming experiment at a boreal peatland to answer how temperature and CO2 jointly influence communities of abundant, diverse, yet poorly understood, non-fungi microbial Eukaryotes (protists). These microbes influence ecosystem function directly through photosynthesis and respiration, and indirectly, through predation on decomposers (bacteria and fungi). Using a combination of high-throughput fluid imaging and 18S amplicon sequencing, we report large climate-induced, community-wide shifts in the community functional composition of these microbes (size, shape, and metabolism) that could alter overall function in peatlands. Importantly, we demonstrate a taxonomic convergence but a functional divergence in response to warming and elevated CO2 with most environmental responses being contingent on organismal size: warming effects on functional composition are reversed by elevated CO2 and amplified in larger microbes but not smaller ones. These findings show how the interactive effects of warming and rising CO2 levels could alter the structure and function of peatland microbial food webs—a fragile ecosystem that stores upwards of 25% of all terrestrial carbon and is increasingly threatened by human exploitation. 相似文献
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Rupa Walanj Paul Young Heather M. Baker Edward N. Baker Peter Metcalf Joseph W. Chow Stephen Lerner Sergei Vakulenko Clyde A. Smith 《Acta Crystallographica. Section F, Structural Biology Communications》2005,61(4):410-413
Bacterial resistance to the aminoglycoside antibiotics is primarily the result of deactivation of the drugs. Three families of enzymes are responsible for this activity, with one such family being the aminoglycoside phosphotransferases (APHs). The gene encoding one of these enzymes, APH(2′′)‐Ib, has been cloned and the protein (comprising 299 amino‐acid residues) expressed in Escherichia coli, purified and crystallized in the presence of 16%(w/v) PEG 3350 and gentamicin. The crystals belong to the monoclinic space group P21, with approximate unit‐cell parameters a = 79.7, b = 58.8, c = 81.4 Å, β = 98.4°, and preliminary X‐ray diffraction analysis is consistent with the presence of two molecules in the asymmetric unit. Synchrotron diffraction data to approximately 2.65 Å resolution were collected from a native APH(2′′)‐Ib crystal at beamline BL9‐2 at SSRL (Stanford, CA, USA). Selenium‐substituted crystals have also been produced and structure determination is proceeding. 相似文献
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Clyde A. Smith Marta Toth Thomas M. Weiss Hilary Frase Sergei B. Vakulenko 《Acta Crystallographica. Section D, Structural Biology》2014,70(10):2754-2764
Broad‐spectrum resistance to aminoglycoside antibiotics in clinically important Gram‐positive staphylococcal and enterococcal pathogens is primarily conferred by the bifunctional enzyme AAC(6′)‐Ie‐APH(2′′)‐Ia. This enzyme possesses an N‐terminal coenzyme A‐dependent acetyltransferase domain [AAC(6′)‐Ie] and a C‐terminal GTP‐dependent phosphotransferase domain [APH(2′′)‐Ia], and together they produce resistance to almost all known aminoglycosides in clinical use. Despite considerable effort over the last two or more decades, structural details of AAC(6′)‐Ie‐APH(2′′)‐Ia have remained elusive. In a recent breakthrough, the structure of the isolated C‐terminal APH(2′′)‐Ia enzyme was determined as the binary Mg2GDP complex. Here, the high‐resolution structure of the N‐terminal AAC(6′)‐Ie enzyme is reported as a ternary kanamycin/coenzyme A abortive complex. The structure of the full‐length bifunctional enzyme has subsequently been elucidated based upon small‐angle X‐ray scattering data using the two crystallographic models. The AAC(6′)‐Ie enzyme is joined to APH(2′′)‐Ia by a short, predominantly rigid linker at the N‐terminal end of a long α‐helix. This α‐helix is in turn intrinsically associated with the N‐terminus of APH(2′′)‐Ia. This structural arrangement supports earlier observations that the presence of the intact α‐helix is essential to the activity of both functionalities of the full‐length AAC(6′)‐Ie‐APH(2′′)‐Ia enzyme. 相似文献
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Mountains are among the most powerful natural gradients for testing ecological and evolutionary responses of biota to environmental influences because differences in climate and plant structure occur over short spatial scales. We describe the spatiotemporal distribution patterns and drives of fruit‐feeding butterfly diversity in the mountainous region of Serra do Cipó, Minas Gerais, Brazil. Seven elevations from 822 to 1,388 m a.s.l. were selected for evaluating the effects of abiotic factors and vegetation characteristics on butterfly diversity. A total of 44 fruit‐feeding butterfly species were recorded in a two‐year study. Species richness (local and regional) of fruit‐feeding butterflies decreased with increasing elevation. The interaction between temperature or humidity and precipitation influenced the abundance and β‐diversity of butterflies in the elevation gradient, whereas β‐diversity decreased with increasing plant richness. Butterfly richness (local and regional) and β‐diversity varied with the sampling period, with fewer species in July (2012 and 2013), the dry period, as expected for Neotropical insects. β‐Diversity in space and time was due to species replacement (turnover), indicating that butterfly composition differs throughout the mountain and over time. In summary, climate and plant richness largely influence butterfly diversity in the elevational gradient. Climatic changes in conjunction with increasing anthropic impacts on mountainous regions of southeast Brazil will likely influence the community of mountaintop butterflies in the Espinhaço Mountain Range. Abstract in Portuguese is available with online material. 相似文献
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It is known that mitochondrial DNA (mtDNA) replication is independent of the cell cycle. Even in post-mitotic cells in which nuclear DNA replication has ceased, mtDNA is believed to still be replicating. Here, we investigated the turnover rate of mtDNA in primary rat hepatocytes, which are quiescent cells. Southwestern blot analysis using 5-bromo-2'-deoxyuridine (BrdU) was employed to estimate the activity of full-length mtDNA replication and to determine efficient doses of replication inhibitors. Southern blot analysis showed that a two-day treatment with 20mM 2',3'-dideoxycytidine and 0.2mug/ml ethidium bromide caused a 37% reduction in the amount of mtDNA, indicating that the hepatocytes had a considerably high rate of turnover of mtDNA. Further, pulse-chase analysis using Southwestern analysis showed that the amount of newly synthesized mtDNA labeled with BrdU declined to 60% of the basal level within two days. Because the rate of reduction of the new mtDNA was very similar to the overall turnover rate described above, it appears that degrading mtDNA molecules were randomly chosen. Thus, we demonstrated that there is highly active and random turnover of mtDNA in hepatocytes. 相似文献
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Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snow melt but may not change the last frost‐free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant–pollinator interactions have rarely been explored. We examined the direct and pollinator‐mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (?1 to ?5°C) frost events in early spring in plants in situ. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species‐specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Furthermore, frost reduced aboveground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species‐specific direct and pollinator‐mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change. 相似文献
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M. Arshad Siddiqui Haolun Jin Colleen A. Evans Marika P. Dimarco H. L. Allan Tse Tarek S. Mansour 《Chirality》1994,6(2):156-160
Chemoselective reduction of one isomer of the 1-menthylester of 1,3-oxathiolan-5-one-2-carboxylic acid produces a mixture of four lactol diastereomers from which the title compound was isolated after acylation. The isomeric purity and absolute stereochemistry were determined by spectroscopic methods, chiral HPLC techniques, and conversion to (?)-2′-deoxy-3′-thiacytidine (Lamivudine, 3TCTM). © 1994 Wiley-Liss, Inc. 相似文献