排序方式: 共有48条查询结果,搜索用时 0 毫秒
1.
We investigated the population dynamics of Copidodiaptomus numidicus (Copepoda: Calanoida) and Thermocyclops dybowskii (Copepoda: Cyclopoida) in Castelo-do-Bode Reservoir (Portugal). Both species in the reservoir were regulated mainly by food availability during the summers of 1993 and 1994. C. numidicus was always more abundant than T. dybowskii in the reservoir. C. numidicus produced two generations during the sampling period of both years whereas T. dybowskii produced two and three generations in 1993 and 1994, respectively. Because of high temperatures and low rainfall in 1994, the reservoir was more eutrophic than in 1993. Higher clutch size and a higher percentage of ovigerous females suggest that both species were benefiting from better feeding conditions in 1994. Despite this, population growth was reduced in 1994 relatively to 1993. Vertebrate predation and predation by copepods seem to have been minor factors in explaining this decline. However, the presence of Mesostoma sp. in the reservoir may have contributed to the reduction of both copepod populations during specific periods in 1994 although the calanoid was more affected than the cyclopoid by this predation. 相似文献
2.
3.
Influence of drought on algal biofilms and meiofaunal assemblages of temperate reservoirs and rivers
Maria-José Caramujo Carlos Rafael B. Mendes Paulo Cartaxana Vanda Brotas Maria-José Boavida 《Hydrobiologia》2008,598(1):77-94
The role of hydrological droughts in shaping meiofauna abundance through alterations in biofilm biomass and composition was
investigated. In January 2005, continental Portugal was under a moderate to severe drought resulting from a 40% to 60% decrease
in rainfall during the previous 12 months relative to the long-term average (1961–1990). Reservoir capacity was reduced by
30–50% relative to average values and the width of streams was reduced by 20–80% in the Zêzere River Basin (central Portugal).
Algal biomass and algal class composition of biofilms was assessed through quantification of algal pigments in three reservoir
and six river locations. During drought, habitat alterations are expected to be sharp in rivers while, in the absence of water
quality deterioration, the habitat characteristics of reservoirs are expected to remain fairly unaffected. Chlorophylls and
carotenoid pigments were extracted from biofilm samples and analysed using high performance liquid chromatography (HPLC).
In the winter of 2003, during the period of average rainfall, biofilm biomass did not exceed 5 μg chlorophyll a cm−2 at any location. River biofilm biomass was roughly half of that measured in the reservoirs. In the winter of 2005 (drought),
biofilm biomass increased by more than 5-fold in river locations and remained low or decreased in the reservoirs. Algal biofilms
were either dominated by Bacillariophyceae or by Chlorophyceae regardless of the existence of drought. The relative contribution
of Bacillariophyceae to total biofilm biomass was higher during the drought than under average hydrological conditions. The
abundance of harpacticoids, cladocerans and ostracods was favoured by the drought only in the reservoirs where an increase
in diatom proportion in biofilms was observed. The increase in the abundance of cyclopoid copepods, turbellarians, nematodes
and chironomids in rivers during the drought could be explained by algal class composition and biomass of biofilms and environmental
variables (organic matter sediment content, phosphorus availability content and sediment granulometry). The hydrological drought
appears to regulate meiofauna abundance only in river locations, possibly through the promotion of the growth of biofilms
and the availability of organic matter deposited in rivers during the drought.
Handling editor: D. Ryder 相似文献
4.
The highly dynamic CRISPR1 system of Streptococcus agalactiae controls the diversity of its mobilome
MJ Lopez-Sanchez E Sauvage V Da Cunha D Clermont E Ratsima Hariniaina B Gonzalez-Zorn C Poyart I Rosinski-Chupin P Glaser 《Molecular microbiology》2012,85(6):1057-1071
Clustered regularly interspaced short palindromic repeats (CRISPR) confer immunity against mobile genetic elements (MGEs) in prokaryotes. Streptococcus agalactiae, a leading cause of neonatal infections contains in its genome two CRISPR/Cas systems. We show that type 1‐C CRISPR2 is present in few strains but type 2‐A CRISPR1 is ubiquitous. Comparative sequence analysis of the CRISPR1 spacer content of 351 S. agalactiae strains revealed that it is extremely diverse due to the acquisition of new spacers, spacer duplications and spacer deletions that witness the dynamics of this system. The spacer content profile mirrors the S. agalactiae population structure. Transfer of a conjugative transposon targeted by CRISPR1 selected for spacer rearrangements, suggesting that deletions and duplications pre‐exist in the population. The comparison of protospacers located within MGE or the core genome and protospacer‐associated motif‐shuffling demonstrated that the GG motif is sufficient to discriminate self and non‐self and for spacer selection and integration. Strikingly more than 40% of the 949 different CRISPR1 spacers identified target MGEs found in S. agalactiae genomes. We thus propose that the S. agalactiae type II‐A CRISPR1/Cas system modulates the cohabitation of the species with its mobilome, as such contributing to the diversity of MGEs in the population. 相似文献
5.
Daphnia hyalina is a cladoceran present throughthe whole year except for late summer in Maranhão,a meso-eutrophic reservoir in central Portugal. Apartfrom the influence of food, both vertebrate andinvertebrate predation pressures seem to have aneffect on D. hyalina population dynamics.Enclosure experiments were designed to assess therelative importance of both types of predation. Afterthe summer crash, D. hyalina reached highernumbers in the fishless enclosures than in the lakedespite of high predation pressure upon juveniles byAcanthocyclops robustus. Fish predation upon thelargest individuals, especially large egg bearingfemales, was responsible for the lower fertility ofthe open water population when compared with theenclosure population. In the enclosures an increase intail spine length was observed. The longer tail spineprobably offered protection from copepod predation,allowing at least some of the juveniles to coexistwith their potential predator and reach the adultstage, less susceptible to copepod predation. 相似文献
6.
Cátia Ramalhete Joseph Molnár Silva Mulhovo Virgílio E. Rosário Maria-José U. Ferreira 《Bioorganic & medicinal chemistry》2009,17(19):6942-6951
The novel cucurbitacins, balsaminagenin A and B (1–2) and balsaminoside A (3) and the know cucurbitacin karavelagenin C (4), together with five new mono or diacylated derivatives (5–9) of karavelagenin C were evaluated for multidrug resistance reversing activity on human MDR1 gene transfected mouse lymphoma cells. Compounds 2–6 exhibited a strong activity compared with that of the positive control, verapamil. Structure–activity relationships are discussed. Moreover, in the checkerboard model of combination chemotherapy, the interaction between doxorubicin and compounds 2–5 synergistically enhanced the effect of the anticancer drug. Compounds 1–4 were isolated from the aerial parts of Momordica balsamina L. The structures of the compounds were established on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC and NOESY). 相似文献
7.
Environmental factors determining the structure of rotifer communities in a river-shed reservoir 总被引:2,自引:0,他引:2
This study was designed to find out which environmental factors (temperature, oxygen concentration and food resources) are more important in steering the rotifers vertical distribution and community structure in an oligo-changing to-mesotrophic reservoir. It was observed that, despite the influence of temperature and oxygen content of the water, biotic factors especially the food availability and changes in trophic state were crucial in shaping the vertical distribution and species composition of rotifers in Meimoa Reservoir, located in Tagus River in Portugal. 相似文献
8.
9.
10.
Mouriès LP Almeida MJ Milet C Berland S Lopez E 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》2002,132(1):217-229
In vivo and in vitro studies provide strong evidence of the osteogenic activity of nacre obtained from Pinctada maxima. The in vitro studies indicate that diffusible factors from nacre are involved in cell stimulation. The water-soluble matrix (WSM) was extracted from nacre by a non-decalcifying process, and four fractions (SE(1)-SE(4)) were separated by SE-HPLC. Those fractions were tested in vitro on MRC5 fibroblasts. Alkaline phosphatase (ALP) activity was measured as a marker of osteoblastic differentiation. The anti-apoptotic protein Bcl-2 was also immunodetected in cultured osteoblasts from rat calvaria. WSM and fraction SE(4) increased ALP activity. BMP-2 had the same effect on the cells as WSM and SE(4). WSM greatly increased the amount of Bcl-2 in the cytoplasm and nucleus of osteoblasts. These in vitro studies support our initial hypothesis that nacre organic matrix (WSM) of a bivalve mollusk contains signal-molecules that can stimulate the osteogenic pathway in mammalian cells that are targets for bone induction. 相似文献