排序方式: 共有122条查询结果,搜索用时 31 毫秒
1.
Richard Meitern Elin Sild Mari-Ann Lind Marju M?nniste Tuul Sepp Ulvi Karu Peeter H?rak 《PloS one》2013,8(6)
Assessment of costs accompanying activation of immune system and related neuroendocrine pathways is essential for understanding the selective forces operating on these systems. Here we attempted to detect such costs in terms of disruption to redox balance and interference between different immune system components in captive wild-caught greenfinches (Carduelis chloris). Study birds were subjected to an endotoxin-induced inflammatory challenge and temporary exposure to a psychological stressor (an image of a predator) in a 2*2 factorial experiment. Injection of bacterial endotoxin resulted in up-regulation of two markers of antioxidant protection – erythrocyte glutathione, and plasma oxygen radical absorbance (OXY). These findings suggest that inflammatory responses alter redox homeostasis. However, no effect on markers of oxidative damage to proteins or DNA in erythrocytes could be detected. We found no evidence that the endotoxin injection interfered with antibody production against Brucella abortus antigen or the intensity of chronic coccidiosis. The hypothesis of within-immune system trade-offs as a cost of immunity was thus not supported in our model system. We showed for the first time that administration of endotoxin can reduce the level of corticosterone deposited into feathers. This finding suggests a down-regulation of the corticosterone secretion cascade due to an endotoxin-induced immune response, a phenomenon that has not been reported previously. Exposure to the predator image did not affect any of the measured physiological parameters. 相似文献
2.
Peeter Tulviste 《Journal of Russian & East European Psychology》2013,51(3-4):231-251
AbstractThis article discusses the performance of adults who did and did not attend school in experiments involving the definition of concepts, the finding of word-pair similarities, classification, and language objectivation. Most of the differences described correspond to the differences between every day and scientific concepts identified by L.S. Vygotsky. The existing data are insufficient to determine whether all the qualitative differences listed by Vygotsky exist between units of verbal thinking in those who did and did not attend school. In some cases, the thinking of people who did not attend school exhibits features that, according to Vygotsky, should emerge only in school with the assimilation of scientific knowledge (language objectivation and the “super-empirical” connections between concepts). 相似文献
3.
Cremona Fabien Laas Alo Hanson Paul C. Sepp Margot Nõges Peeter Nõges Tiina 《Ecosystems》2019,22(4):805-817
Ecosystems - We assessed the allochthonous organic carbon (OC) budgets for thirteen hemiboreal lakes using a simple equilibrium model coupled with a Bayesian framework for estimating parameter... 相似文献
4.
This study explored the spatiotemporal dynamics of the bacterioplankton community composition in the Gulf of Finland (easternmost sub-basin of the Baltic Sea) based on phylogenetic analysis of 16S rDNA sequences acquired from community samples via pyrosequencing. Investigations of bacterioplankton in hydrographically complex systems provide good insight into the strategies by which microbes deal with spatiotemporal hydrographic gradients, as demonstrated by our research. Many ribotypes were closely affiliated with sequences isolated from environments with similar steep physiochemical gradients and/or seasonal changes, including seasonally anoxic estuaries. Hence, one of the main conclusions of this study is that marine ecosystems where oxygen and salinity gradients co-occur can be considered a habitat for a cosmopolitan metacommunity consisting of specialized groups occupying niches universal to such environments throughout the world. These niches revolve around functional capabilities to utilize different electron receptors and donors (including trace metal and single carbon compounds). On the other hand, temporal shifts in the bacterioplankton community composition at the surface layer were mainly connected to the seasonal succession of phytoplankton and the inflow of freshwater species. We also conclude that many relatively abundant populations are indigenous and well-established in the area. 相似文献
5.
Performance of 18 DFT functionals (B1B95, B3LYP, B3PW91, B97D, BHandHLYP, BMK, CAM-B3LYP, HSEh1PBE, M06-L, mPW1PW91, O3LYP, OLYP, OPBE, PBE1PBE, tHCTHhyb, TPSSh, wB97xD, VSXC) in combinations with six basis sets (cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, aug-cc-pVTZ, IGLO-II, and IGLO-III) and three methods for calculating magnetic shieldings (GIAO, CSGT, IGAIM) was tested for predicting 1H and 13C chemical shifts for 25 organic compounds, for altogether 86 H and 88 C atoms. Proton shifts varied between 1.03 ppm to 12.00 ppm and carbon shifts between 7.87 ppm to 209.28 ppm. It was found that the best method for calculating 13C shifts is PBE1PBE/aug-cc-pVDZ with CSGT or IGAIM approaches (mae?=?1.66 ppm), for 1H the best results were obtained with HSEh1PBE, mPW1PW91, PBE1PBE, CAM-B3LYP, and B3PW91 functionals with cc-pVTZ basis set and with CSGT or IGAIM approaches (mae?=?0.28 ppm). We found that often larger basis sets do not give better results for chemical shifts. The best basis sets for calculating 1H and 13C chemical shifts were cc-pVTZ and aug-cc-pVDZ, respectively. CSGT and IGAIM NMR approaches can perform really well and are in most cases better than popular GIAO approach. 相似文献
6.
We studied the formation of dissolved silicon loads from rivers to lakes, the development of diatoms in lakes and the role of climatic forcing on the silicon cycle in three river-lake systems in Sweden, Estonia and Northern Germany. We found coherent seasonality in the silicon loads of the two northern rivers, which was probably caused by the common snow-type hydrology of the catchments as distinct from the rain-type hydrology of the catchment, further south. The similarity among lakes in the dynamics of the Si-related variables studied resulted from similarities in mean lake depth and mixing type rather than the climatic regime. Among the variables measured at the three sites, river water discharge responded most coherently to climatic forcing as synchronized by the North Atlantic Oscillation winter index (NAOw). Water discharge and Si load were strongly linked variables and showed coherent patterns among the river systems. We found significant season-specific correlations of the NAOw with either the biomass or the share of diatoms in each lake, but no coherent pattern among the lakes. Our results indicate that processes driven by water discharge are more coherent across regions than in-lake processes. 相似文献
7.
Luciana Mastrantuono Angelo G. Solimini Peeter Nõges Marcello Bazzanti 《Hydrobiologia》2008,599(1):143-152
Sampling benthic communities usually requires intensive field and lab work which is generally performed by skilled staff. In algal dominated communities, like those on the shores of the Azores, biotope characterization studies focused on the more conspicuous algae categories, thus reducing the skills required for species identification. The present study compares in situ quadrat quantifications done by a skilled reader, with computer based quadrat quantifications using digital photographic records of the same areas read in situ, accomplished by skilled and non-skilled readers. The study was conducted inter- and subtidally at various shore heights/depths. Quantification of algal coverage, both in situ and computer based, used the point to point method with quadrats of 0.25 m × 0.25 m for the intertidal, and 0.50 m × 0.50 m for the subtidal surveys, both subdivided into 36 intersection points. Significant differences were found between in situ readings and computer based readings of photographic records conducted both by experienced and inexperienced readers. Biotopes identified using in situ data and image based data differ both for the subtidal and intertidal. 相似文献
8.
In the 1990s a sharp decrease in nitrogen loading occurred in Estonian rivers, bringing about a reduction of the nitrogen-to-phosphorus ratio (N:P ratio) in the large shallow lakes, Peipsi (3,555 km2, mean depth 7.1 m) and Võrtsjärv (270 km2, 2.8 m). The average mass ratio of total nitrogen (TN) and total phosphorus (TP) in Võrtsjärv (45) was about twice as high as that in Peipsi (22). In Peipsi, the N2-fixing Gloeotrichia echinulata, Aphanizomenon flos-aquae and Anabaena species prevailed in the summer phytoplankton, while in Võrtsjärv the dominant cyanobacteria were Limnothrix planktonica, L. redekei and Planktolyngbya limnetica, which cannot fix N2; the main N2-fixing taxa Aphanizomenon skujae and Anabaena sp. seldom gained dominance. In May–October the critical TN:TP mass ratio, below which N2-fixing cyanobacteria (Nfix) achieved high biomasses, was ~40 in Võrtsjärv and ~30 in Peipsi. The percentages of both total cyanobacteria (CY) and Nfix (CY% and Nfix%) in Peipsi achieved their maximum values at an N:P mass ratio at or below 20 for both TN:TP and Nmin:SRP. In Võrtsjärv, the TN:TP supporting a high Nfix% was between 30 and 40 and the Nmin:SRP supporting this high percentage was in the same range as that in Peipsi (<20), though the maximum Nfix% values in Võrtsjärv (69%) were much lower than in Peipsi (96%). The Nmin:SRP ratio explained 77% of the variability in Nfix% in May–October. The temperature dependence of Nfix% approximated to the maximum function type, with an upper limiting value at a certain water temperature, and this was most distinct in May–October. The critical TN:TP ratios obtained from our study (roughly 30 for Peipsi and 40 for Võrtsjärv) are much higher than the Redfield N:P mass ratio routinely considered (7). Our results represent valuable guidelines for creating effective management strategies for large shallow lakes. They provide a basis for stressing the urgent need to decrease phosphorus loading and to keep the in-lake P concentration low, and not to implement nitrogen reduction measures without a simultaneous decrease of phosphorus concentration. 相似文献
9.
How feather colour reflects its carotenoid content 总被引:10,自引:1,他引:9
10.
Small-bodied cladocerans and cyclopoid copepods are becoming increasingly dominant over large crustacean zooplankton in eutrophic waters where they often coexist with cyanobacterial blooms. However, relatively little is known about their algal diet preferences. We studied grazing selectivity of small crustaceans (the cyclopoid copepods Mesocyclops leuckarti, Thermocyclops oithonoides, Cyclops kolensis, and the cladocerans Daphnia cucullata, Chydorus sphaericus, Bosmina spp.) by liquid chromatographic analyses of phytoplankton marker pigments in the shallow, highly eutrophic Lake Võrtsjärv (Estonia) during a seasonal cycle. Copepods (mainly C. kolensis) preferably consumed cryptophytes (identified by the marker pigment alloxanthin in gut contents) during colder periods, while they preferred small non-filamentous diatoms and green algae (identified mainly by diatoxanthin and lutein, respectively) from May to September. All studied cladoceran species showed highest selectivity towards colonial cyanobacteria (identified by canthaxanthin). For small C. sphaericus, commonly occuring in the pelagic zone of eutrophic lakes, colonial cyanobacteria can be their major food source, supporting their coexistence with cyanobacterial blooms. Pigments characteristic of filamentous cyanobacteria and diatoms (zeaxanthin and fucoxanthin, respectively), algae dominating in Võrtsjärv, were also found in the grazers’ diet but were generally avoided by the crustaceans commonly dominating the zooplankton assemblage. Together these results suggest that the co-occurring small-bodied cyclopoid and cladoceran species have markedly different algal diets and that the cladocera represent the main trophic link transferring cyanobacterial carbon to the food web in a highly eutrophic lake. 相似文献