Stable isotopes reveal niche segregation between native and non-native Hoplias in a Neotropical floodplain     

Gustavo H. Zaia Alves  Vivian M. Cionek  Gislaine I. Manetta  Laryssa H. R. Pazianoto  Evanilde Benedito 《Ecology of Freshwater Fish》2020,29(4):602-610

We investigated whether isotopic niche partitioning could mediate the coexistence between native (Hoplias sp. B) and non-native (Hoplias mbigua) trahira in a Neotropical floodplain. We hypothesised that during the dry season both species inhabit isolated sites (i.e. lakes) and thus rely on distinct food resources to sustain their coexistence. We found evidence of trophic segregation among native and non-native freshwater fish in the Upper Paraná River, Brazil. Even though both species rely on the same primary littoral carbon sources and present similar trophic diversity, trophic segregation was attained through larger niche amplitude and smaller isotopic niche width for the non-native fish. Three decades after initial invasion, non-native Hoplias have distinct foraging behaviour and do not compete for trophic resources with native trahira; this is likely due to morpho-anatomical differences. Limited morphological similarity between these congeneric species might be the strongest factor contributing to their coexistence in the Paraná River floodplain during the dry season.  相似文献   

Oceanographic basis of the global surface distribution of Prochlorococcus ecotypes     

Bouman HA  Ulloa O  Scanlan DJ  Zwirglmaier K  Li WK  Platt T  Stuart V  Barlow R  Leth O  Clementson L  Lutz V  Fukasawa M  Watanabe S  Sathyendranath S 《Science (New York, N.Y.)》2006,312(5775):918-921

By using data collected during a continuous circumnavigation of the Southern Hemisphere, we observed clear patterns in the population-genetic structure of Prochlorococcus, the most abundant photosynthetic organism on Earth, between and within the three Southern Subtropical Gyres. The same mechanisms that were previously invoked to account for the vertical distribution of ecotypes at local scales accounted for the global (horizontal) patterns we observed. Basin-scale and seasonal variations in the structure and strength of vertical stratification provide a basis for understanding large-scale horizontal distribution in genetic and physiological traits of Prochlorococcus, and perhaps of marine microbial communities in general.  相似文献   

Leucine-tRNA initiates at CUG start codons for protein synthesis and presentation by MHC class I   总被引：1，自引：0，他引：1  

Starck SR  Jiang V  Pavon-Eternod M  Prasad S  McCarthy B  Pan T  Shastri N 《Science (New York, N.Y.)》2012,336(6089):1719-1723

Effective immune surveillance by cytotoxic T cells requires newly synthesized polypeptides for presentation by major histocompatibility complex (MHC) class I molecules. These polypeptides are produced not only from conventional AUG-initiated, but also from cryptic non-AUG-initiated, reading frames by distinct translational mechanisms. Biochemical analysis of ribosomal initiation complexes at CUG versus AUG initiation codons revealed that cells use an elongator leucine-bound transfer RNA (Leu-tRNA) to initiate translation at cryptic CUG start codons. CUG/Leu-tRNA initiation was independent of the canonical initiator tRNA (AUG/Met-tRNA(i)(Met)) pathway but required expression of eukaryotic initiation factor 2A. Thus, a tRNA-based translation initiation mechanism allows non-AUG-initiated protein synthesis and supplies peptides for presentation by MHC class I molecules.  相似文献   

Diversity of Enterococcus cecorum from chickens     

Boerlin P  Nicholson V  Brash M  Slavic D  Boyen F  Sanei B  Butaye P 《Veterinary microbiology》2012,157(3-4):405-411

Enterococcus cecorum is a normal inhabitant of the intestine of birds and other vertebrates. It has recently emerged in Canada and other countries as an important cause of arthritis and osteomyelitis in chickens. The objectives of this study were to assess if this emergence was caused by a particular clone of E. cecorum and to assess the antimicrobial susceptibility of this organism. One hundred and thirteen E. cecorum isolates from infections in Canadian chickens (cases) and from the ceca of control chickens from Canada and Belgium were examined. Isolates were identified using biochemical tests and, for a number of them, identification was confirmed by partial 16S rRNA gene sequencing. Case and control isolates were typed by pulsed-field gel electrophoresis and tested for antimicrobial susceptibility using the broth microdilution method. Cecal isolates from control birds were genetically very diverse but the vast majority of those from cases belonged to a single major clonal lineage. Reduced susceptibility was widespread for tetracycline, bacitracin, and erythromycin. Isolates from cases were generally less susceptible to antimicrobial agents than isolates from control birds.  相似文献   

Anatomical location of arterial and venous lines significantly affects motor performance in rats     

Alan A. ARTRU  Matthew BOYKO  Benjamin F. GRUENBAUM  Michael DUBILET  Akiva LEIBOWITZ  Yoram SHAPIRA  Vivian I. TEICHBERG  Alexander ZLOTNIK 《Animal Science Journal》2012,83(9):656-662

Several motor‐function scales have been developed to assess neurological function in animal models of stroke, subarachnoid hemorrhage and closed head injury. We hypothesize that the location of arterial and venous catheters, even in the absence of brain injury, may impact rats' motor performance. Our study examined the effect of catheter location, rate of infection and the time required for catheter placement. We further describe an original technique of tail artery cannulation without exposure of the artery. Sixty‐one rats were anesthetized and randomly assigned to one of seven groups, including no catheter, tail artery or artery + vein catheters, or femoral artery or artery + vein catheters. A neurological severity score (NSS) was determined at 1 h, 24 h and 48 h after surgical preparation or catheter placement. NSS at 1 h after placement of unilateral and bilateral femoral catheters was higher than the NSS observed at 1 h after placement of tail arterial and venous catheters (P < 0.01). The NSS also was higher at 24 h in the bilateral femoral catheter groups as compared with the tail catheter groups (P < 0.05). There were no differences in the NSS observed between the groups that had tail catheters and the sham group at 1 h, 24 h or 48 h. Infection rate at the site of catheter placement and the time required for catheter placement was also higher in the femoral catheter groups (P < 0.001). Thus, we propose that the line location may bias a study's results and lead to deceptive interpretations of neurological assessment following rat head injury. Compared to femoral vessels, tail blood vessels are preferable locations for lines placement.  相似文献   

Portraits of science. Logic, learning, and experimental medicine     

Nutton V 《Science (New York, N.Y.)》2002,295(5556):800-801

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Effects of Modulated Differential Scanning Calorimetry (MDSC) Variables on Thermodynamic and Kinetic Characteristics During Gelatinization of Waxy Rice Starch     

Vivian M.-F. Lai  Cheng-Yi Lii 《Cereal Chemistry》1999,76(4):519-525

The total, reversing, and nonreversing thermal properties during gelatinization of waxy rice starch (starch-to-water ratio = 1:2, w/w) were examined by modulated differential scanning calorimetry (MDSC). The effect of MDSC operating variables (i.e., the amplitude and frequency of temperature modulation and the underlying heating rate) on these thermal properties was determined by response surface methodology (RSM) and statistical analysis. The frequency of temperature modulation and the underlying heating rate significantly influenced the gelatinization temperatures and enthalpy changes in total and nonreversing endotherms. In addition, the combination of 0.025Hz and 4–8°C/min with a properly low degree of oscillation was suitable for characterization of starch gelatinization by MDSC. The enthalpy changes in the reversing (thermodynamic) endotherms increased, but those in the nonreversing (kinetic) endotherms decreased with increasing periods (i.e., decreasing frequencies) and underlying heating rates. However, the total enthalpy changes were only slightly influenced by the MDSC variables studied. In addition, the activation energies for the total and nonreversing events were 281.8–417.3 and 386.3–739.7 kJ/mol, respectively, depending on the MDSC conditions. From the compensation relationship between the activation energy and frequency factor, we concluded that the total and nonreversing endotherms were linked to the same single transition.  相似文献   

A state-space approach to stand growth modelling of European beech     

Thomas Nord-Larsen  Vivian K. Johannsen 《Annals of Forest Science》2007,64(4):365-374

Static models of forest growth, such as yield tables or cumulative growth functions, generally fail to recognize that forest stands are dynamic systems, subject to changes in growth dynamics due to silvicultural interventions or natural dynamics. Based on experimental data, covering a wide range of initial spacings and thinning practises, we developed a dynamic stand growth model of European beech in Denmark. The model entailed three equations for predicting dominant height growth, basal area growth, and mortality. The signs of the parameter estimates generally corroborated the anticipated growth paths of dominant height and basal area. Although statistical tests indicated significant systematic deviations between observed and predicted values, the deviations were small and of little practical importance. Cross validation procedures indicated that the model may be applied across a wide range of growth conditions and thinning practises without significant loss of precision.  相似文献   

An analysis of the leaching of chloride tracer applied to pipe-drained plots using a coupled unsaturated-saturated zone model of solute transport     

A.J.A. Vinten  B. Vivian  M.H. Redman 《Soil Use and Management》1991,7(2):103-109

Abstract. The modelling of leaching of nitrate and other solutes in artificially drained soils is complicated by the need to consider both unsaturated and saturated components of the system. This work is an attempt to couple together an unsaturated zone transport model (Addiscott & Whitmore, 1991) with a steady state travel- time model (Ernst, 1973) for the saturated zone. The model was tested using chloride leaching data from eight hydrologically isolated plots on a pipe-drained clay loam soil. Approaches to parameter estimation are discussed. Results were variable, for on some plots saturated zone travel time could be virtually neglected, whereas on other plots this component was apparently important.  相似文献   

Specific Oligonucleotide Primers for the Rapid Identification and Detection of the Agent of Tomato Pith Necrosis, Pseudomonas corrugata, by PCR Amplification: Evidence for two Distinct Genomic Groups     

Vittoria Catara  Dawn Arnold  Gabriella Cirvilleri  Alan Vivian 《European journal of plant pathology / European Foundation for Plant Pathology》2000,106(8):753-762

Unique DNA bands from strains representative of two groups of Pseudomonas corrugata, as shown by amplification of their genomic DNA by polymerase chain reaction using short random sequence oligonucleotide primers (RAPD-PCR), were isolated, cloned and sequenced. Two pairs of specific primer sequences, based on the ends of the cloned unique DNA bands from strains IPVCT10.3 and IPVCT8.1, were used in multiplex PCR with a range of P. corrugata strains. All strains produced one of the two specific bands, 1100bp (from the IPVCT10.3-based primers) and 600bp (from the IPVCT8.1-based primers), representing groups designated I and II, respectively. The primers were also tested on a wider range of Pseudomonas species, including the closely-related fluorescent Pseudomonas genomospecies FP1, FP2 and FP3: none of these bacteria produced any bands following amplification by PCR with these primers. The primer sets detected P. corrugata in tomato pith necrosis-infected plants providing a useful tool for rapid identification and epidemiological studies.  相似文献