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51.
Timing and abundance as key mechanisms affecting trophic interactions in variable environments 总被引:4,自引:0,他引:4
Joël M. Durant Dag Ø. Hjermann Tycho Anker-Nilssen Grégory Beaugrand Atle Mysterud Nathalie Pettorelli Nils Chr. Stenseth 《Ecology letters》2005,8(9):952-958
Climatic changes are disrupting otherwise tight trophic interactions between predator and prey. Most of the earlier studies have primarily focused on the temporal dimension of the relationship in the framework of the match–mismatch hypothesis. This hypothesis predicts that predator's recruitment will be high if the peak of the prey availability temporally matches the most energy‐demanding period of the predators breeding phenology. However, the match–mismatch hypothesis ignores the level of food abundance while this can compensate small mismatches. Using a novel time‐series model explicitly quantifying both the timing and the abundance component for trophic relationships, we here show that timing and abundance of food affect recruitment differently in a marine (cod/zooplankton), a marine–terrestrial (puffin/herring) and a terrestrial (sheep/vegetation) ecosystem. The quantification of the combined effect of abundance and timing of prey on predator dynamics enables us to come closer to the mechanisms by which environment variability may affect ecological systems. 相似文献
52.
53.
Gut microflora is now considered as a key organ involved in host energy homeostasis. Recent data suggest that the alterations of the gut bacteria ecosystem could contribute to the development of metabolic disorders such as type 2 diabetes and obesity. First, gut microflora may increase energy efficiency of non digested food via the fermentation, thus providing more energy to the host. Secondly, fatty acids flux and storage in the adipose tissue is under the control of the fasting-induced adipocyte factor FIAF, which expression depends on gut microflora. Third, high-fat diet feeding changes gut bacteria profile, leading to a drop in bifidobacteria content, which correlates with a higher LPS plasma levels, thereby participating to the onset of inflammation, insulin resistance and type 2 diabetes associated with obesity. Changing gut microflora composition could be a useful tool to prevent or to treat high-fat/low fibres diet-induced metabolic syndrome. double dagger. 相似文献
54.
Lafont E Dupont R Andrieu-Abadie N Okazaki T Schulze-Osthoff K Levade T Benoist H Ségui B 《Biochimica et biophysica acta》2012,1821(4):684-693
Ceramide, a biologically active sphingolipid in cell death signaling, accumulates upon CD95L treatment, concomitantly to apoptosis induction in Jurkat leukemia T cells. Herein, we show that ceramide did not increase in caspase-8 and -10-doubly deficient Jurkat cells in response to CD95L, indicating that apical caspases are essential for CD95L-triggered ceramide formation. Jurkat cells are typically defined as type 2 cells, which require the activation of the mitochondrial pathway for efficient apoptosis induction in response to CD95L. Caspase-9-deficient Jurkat cells significantly resisted CD95L-induced apoptosis, despite ceramide accumulation. Knock-down of sphingomyelin synthase 1, which metabolizes ceramide to sphingomyelin, enhanced (i) CD95L-triggered ceramide production, (ii) cytochrome c release from the mitochondria and (iii) caspase-9 activation. Exogenous ceramide-induced caspase-3 activation and apoptosis were impaired in caspase-9-deficient Jurkat cells. Conversely, caspase-9 re-expression in caspase-9-deficient Jurkat cells restored caspase-3 activation and apoptosis upon exogenous ceramide treatment. Collectively, our data provide genetic evidence that CD95L-triggered endogenous ceramide increase in Jurkat leukemia T cells (i) is not a mere consequence of cell death and occurs mainly in a caspase-9-independent manner, (ii) is likely involved in the pro-apoptotic mitochondrial pathway leading to caspase-9 activation. 相似文献
55.
Pei Y Hancock PJ Zhang H Bartz R Cherrin C Innocent N Pomerantz CJ Seitzer J Koser ML Abrams MT Xu Y Kuklin NA Burke PA Sachs AB Sepp-Lorenzino L Barnett SF 《RNA (New York, N.Y.)》2010,16(12):2553-2563
Effective small interfering RNA (siRNA)-mediated therapeutics require the siRNA to be delivered into the cellular RNA-induced silencing complex (RISC). Quantitative information of this essential delivery step is currently inferred from the efficacy of gene silencing and siRNA uptake in the tissue. Here we report an approach to directly quantify siRNA in the RISC in rodents and monkey. This is achieved by specific immunoprecipitation of the RISC from tissue lysates and quantification of small RNAs in the immunoprecipitates by stem-loop PCR. The method, expected to be independent of delivery vehicle and target, is label-free, and the throughput is acceptable for preclinical animal studies. We characterized a lipid-formulated siRNA by integrating these approaches and obtained a quantitative perspective on siRNA tissue accumulation, RISC loading, and gene silencing. The described methodologies have utility for the study of silencing mechanism, the development of siRNA therapeutics, and clinical trial design. 相似文献
56.
Nathalie Baghdassarian Régine Catallo Mohamed A. Mahly Patrick Ffrench Florence Chizat Paul A. Bryon Martine Ffrench 《Experimental cell research》1998,240(2):263
In order to analyze dexamethasone effects on peripheral blood lymphocyte proliferation, we defined various experimental conditions: dexamethasone introduced (i) at the time of phytohemagglutinin stimulation, (ii) 48 h after the beginning of phytohemagglutinin stimulation, and (iii) on unstimulated lymphocytes. In stimulated lymphocytes, we observed an early G1 accumulation (P< 0.005), a delayed increase in the duration of S-phase (P< 0.03), and a consequent increase in cell-cycle duration. The expression of several cyclins, cyclin-dependent kinases (CDKs), and CDK inhibitors (CKIs) was modified. Cyclin D3, CDK4, and CDK6 involved in G1-phase control were significantly decreased under dexamethasone treatment whatever the level of stimulation of lymphocytes (stimulated or unstimulated PBL). Cyclin E and CDK2, acting in G1/S-phase transition and S-phase regulation, decreased in stimulated lymphocytes before any modification of S-phase (P< 0.002). The expression of CKIs, mainly of p27Kip1, appeared to vary with the degree of cell stimulation: a decrease was observed on treated unstimulated lymphocytes, while p27Kip1increased in dexamethasone-treated cells during stimulation. Our results indicate sequential modifications of the cell-cycle regulation by dexamethasone starting with an action on G1 followed by S-phase control modifications. The protein analysis pinpoints the major complexes concerned: CDK4 and CDK6/cyclin D are mainly involved in G1-phase modifications, while CDK2 and its partner, cyclin E, might be specifically involved in the lengthening of S-phase. The variations observed for p27Kip1might amplify the functional effects of dexamethasone on kinasic complexes. 相似文献
57.
Anne Lorrain Heidi Pethybridge Nicolas Cassar Aurore Receveur Valrie Allain Nathalie Bodin Laurent Bopp C. Anela Choy Leanne Duffy Brian Fry Nicolas Goi Brittany S. Graham Alistair J. Hobday John M. Logan Frederic Mnard Christophe E. Menkes Robert J. Olson Dan E. Pagendam David Point Andrew T. Revill Christopher J. Somes Jock W. Young 《Global Change Biology》2020,26(2):458-470
Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open‐ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13C values of 0.8‰–2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel‐derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13C‐rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota. 相似文献
58.
Jiban C. Deb Stuart Phinn Nathalie Butt Clive A. McAlpine 《Ecology and evolution》2017,7(7):2238-2248
Two ecologically and economically important, and threatened Dipterocarp trees Sal (Shorea robusta) and Garjan (Dipterocarpus turbinatus) form mono‐specific canopies in dry deciduous, moist deciduous, evergreen, and semievergreen forests across South Asia and continental parts of Southeast Asia. They provide valuable timber and play an important role in the economy of many Asian countries. However, both Dipterocarp trees are threatened by continuing forest clearing, habitat alteration, and global climate change. While climatic regimes in the Asian tropics are changing, research on climate change‐driven shifts in the distribution of tropical Asian trees is limited. We applied a bioclimatic modeling approach to these two Dipterocarp trees Sal and Garjan. We used presence‐only records for the tree species, five bioclimatic variables, and selected two climatic scenarios (RCP4.5: an optimistic scenario and RCP8.5: a pessimistic scenario) and three global climate models (GCMs) to encompass the full range of variation in the models. We modeled climate space suitability for both species, projected to 2070, using a climate envelope modeling tool “MaxEnt” (the maximum entropy algorithm). Annual precipitation was the key bioclimatic variable in all GCMs for explaining the current and future distributions of Sal and Garjan (Sal: 49.97 ± 1.33; Garjan: 37.63 ± 1.19). Our models predict that suitable climate space for Sal will decline by 24% and 34% (the mean of the three GCMs) by 2070 under RCP4.5 and RCP8.5, respectively. In contrast, the consequences of imminent climate change appear less severe for Garjan, with a decline of 17% and 27% under RCP4.5 and RCP8.5, respectively. The findings of this study can be used to set conservation guidelines for Sal and Garjan by identifying vulnerable habitats in the region. In addition, the natural habitats of Sal and Garjan can be categorized as low to high risk under changing climates where artificial regeneration should be undertaken for forest restoration. 相似文献
59.
Moreau D Burstin J Aubert G Huguet T Ben C Prosperi JM Salon C Munier-Jolain N 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2012,124(4):755-768
Medicago truncatula is used as a model plant for exploring the genetic and molecular determinants of nitrogen (N) nutrition in legumes. In this
study, our aim was to detect quantitative trait loci (QTL) controlling plant N nutrition using a simple framework of carbon/N
plant functioning stemming from crop physiology. This framework was based on efficiency variables which delineated the plant’s
efficiency to take up and process carbon and N resources. A recombinant inbred line population (LR4) was grown in a glasshouse
experiment under two contrasting nitrate concentrations. At low nitrate, symbiotic N2 fixation was the main N source for plant growth and a QTL with a large effect located on linkage group (LG) 8 affected all
the traits. Significantly, efficiency variables were necessary both to precisely localize a second QTL on LG5 and to detect
a third QTL involved in epistatic interactions on LG2. At high nitrate, nitrate assimilation was the main N source and a larger
number of QTL with weaker effects were identified compared to low nitrate. Only two QTL were common to both nitrate treatments:
a QTL of belowground biomass located at the bottom of LG3 and another one on LG6 related to three different variables (leaf
area, specific N uptake and aboveground:belowground biomass ratio). Possible functions of several candidate genes underlying
QTL of efficiency variables could be proposed. Altogether, our results provided new insights into the genetic control of N
nutrition in M. truncatula. For instance, a novel result for M. truncatula was identification of two epistatic interactions in controlling plant N2 fixation. As such this study showed the value of a simple conceptual framework based on efficiency variables for studying
genetic determinants of complex traits and particularly epistatic interactions. 相似文献
60.
Élodie Breton Christian Goetz Jacqueline Kintz Nathalie Accart Gaëlle Aubertin Bernard Grellier Philippe Erbs Ronald Rooke André Constantinesco Philippe Choquet 《Comptes rendus biologies》2010,333(3):220-225