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961.
Birds often engage in nest defence against predators to improve breeding success, but defence efficiency requires the capability to assess the threat level posed by potential predators. For species with low breeding-site tenacity, which may encounter varying occurrence and density of predators in different areas, threat recognition could be compromised due to naivety, and so predator recognition may focus on broad key features to diminish the risk of misidentification. We experimentally tested this hypothesis by recording behavioural reactions of the nomadic wood warbler Phylloscopus sibilatrix to objects reflecting various levels of threat: least weasel and Eurasian jay taxidermy mounts, an inanimate object and an empty display mount. To assess actual nest predators, we used remote cameras to record predation events at wood warbler nests. As in other studies in Western Europe, Eurasian jay was found to be the main nest predator, with occasional predation by least weasel. The reaction of adult warblers to the models was generally to remain silent and on nests during the incubation stage presumably due to the need to maintain efficient nest camouflage and concealment. During the nestling stage, behavioural responses of adult warblers, calling and suspended feeding of young, showed the strongest effects from the jay taxidermy mount, moderate to the weasel and weakest to the inanimate object and empty mount. As the reaction of wood warblers reflected the degree of genuine threat posed by the predators depicted by the models, we conclude that predator recognition may be present in this species. 相似文献
962.
Lynnath E. Beckley Geremy Cliff Malcolm J. Smale Leonard J.V. Compagno 《Environmental Biology of Fishes》1997,50(3):343-348
Available information on whale shark strandings around the coast of South Africa during the period 1984–1995 was collated.
Stranded animals ranged in size from 3–11 m TL, most were immature and the sex ratio was even. Aerial observations and sightings
by divers indicate that whale sharks are most abundant in South African waters during the austral summer and autumn months.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
963.
Malcolm G. Keeping 《Journal of Insect Behavior》1997,10(2):265-278
Colonies ofBelonogaster petiolata in Gauteng (South Africa) produced reproductive offspring (gynes and males) in late January and early February of each nesting
season; their appearance was associated with a decline in worker and brood numbers. Brood decline could commence in the presence
of a dominant, reproductively active queen, and loss or removal of the queen was not followed directly by cessation of nest
growth and brood care. An older worker usually took over the α-position in queenless colonies. Several factors appear to contribute
to brood decline and, ultimately, termination of the colony cycle in this species. These include (1) cessation of the supply
of solid food to colonies (and particularly their larvae) during the reproductive phase, (2) a decrease in the worker/larva
ratio during the latter phase due to the progressive loss of workers, (3) increasing number of gynes and males, and (4) an
adult priority over food reception from foragers. 相似文献
964.
965.
Derepressed Hyphal Growth and Reduced Virulence in a VH1
Family-related Protein Phosphatase Mutant of the Human Pathogen
Candida albicans 总被引:3,自引:0,他引:3
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Csilla Csank Constantin Makris Sylvain Meloche Klaus Schrppel Martin Rllinghoff Daniel Dignard David
Y. Thomas Malcolm Whiteway 《Molecular biology of the cell》1997,8(12):2539-2551
Mitogen-activated protein (MAP) kinases are pivotal components of eukaryotic signaling cascades. Phosphorylation of tyrosine and threonine residues activates MAP kinases, but either dual-specificity or monospecificity phosphatases can inactivate them. The Candida albicans CPP1 gene, a structural member of the VH1 family of dual- specificity phosphatases, was previously cloned by its ability to block the pheromone response MAP kinase cascade in Saccharomyces cerevisiae. Cpp1p inactivated mammalian MAP kinases in vitro and acted as a tyrosine-specific enzyme. In C. albicans a MAP kinase cascade can trigger the transition from the budding yeast form to a more invasive filamentous form. Disruption of the CPP1 gene in C. albicans derepressed the yeast to hyphal transition at ambient temperatures, on solid surfaces. A hyphal growth rate defect under physiological conditions in vitro was also observed and could explain a reduction in virulence associated with reduced fungal burden in the kidneys seen in a systemic mouse model. A hyper-hyphal pathway may thus have some detrimental effects on C. albicans cells. Disruption of the MAP kinase homologue CEK1 suppressed the morphological effects of the CPP1 disruption in C. albicans. The results presented here demonstrate the biological importance of a tyrosine phosphatase in cell-fate decisions and virulence in C. albicans. 相似文献
966.
Carina Van Der Veen Keri L. H. Carpenter Susan E. Taylor Julie A. McDonald Malcolm J. Mitchinson 《Free radical research》1997,27(5):459-476
The present study shows that copper oxidation of LDL is a tightly-ordered process which can be finely controlled by appropriate selection of duration of oxidation and of concentrations of LDL and copper. Oxidation of LDL (0.1-2.0 mg LDL protein/ml) was carried out by copper catalysis (in the ratio of 2.5 μM Cu2+ to 0.1 mg LDL protein/ml) in phosphate-buffered saline, and was monitored by agarose gel electro-phoresis, gas chromatography (GC), anion exchange fast protein liquid chromatography (FPLC), fluorescence spectroscopy and dynamic light scattering. Analysis of the data showed strong cross correlations between many of the parameters of oxidation. Oxidation was more rapid for lower concentrations than for higher concentrations of LDL, despite the same ratio of copper to LDL being employed. Chemical kinetics analysis of the GC data suggested that 7β-hydroxycholesterol formation occurred as a first order (or pseudo first order) consecutive reaction to the oxidation of linoleate. The first order rate constants for decomposition of lioleate and production of 7β-hydroxycholesterol correlated closely with the theoretically-calculated times between collision of LDL particles. LDL particle diameter, measured by dynamic light scattering, increased by ca. 50% over 24 h oxidation, suggesting unfolding of apo B-100.
Prolonged oxidation of LDL at low concentration suggested that the radical chain reaction was able to propagate, albeit slowly, on cholesterol after all the polyunsaturated fatty acid was consumed. For higher concentrations of LDL, prolonged oxidation resulted in partial aggregation. These findings are applicable to preparing oxidised LDL with different degrees of oxidation, under controlled conditions, for studying its biological properties. 相似文献
Prolonged oxidation of LDL at low concentration suggested that the radical chain reaction was able to propagate, albeit slowly, on cholesterol after all the polyunsaturated fatty acid was consumed. For higher concentrations of LDL, prolonged oxidation resulted in partial aggregation. These findings are applicable to preparing oxidised LDL with different degrees of oxidation, under controlled conditions, for studying its biological properties. 相似文献
967.
A series of binary T-DNA vectors (pBECKS) has been created for use in theAgrobacterium-mediated genetic transformation of plants. The pBECKS series has corrected the undesirable features of the popular pBIN19
vector; the deleterious mutation within the coding sequence ofnptII has been amended and the cloning sites are now adjacent to the right border repeat in order to reduce the possibility of
producing truncated sequences of novel genes within transformants. One set of vectors incorporates various combiantions of
the marker genesgusA,C1/Lc,nptII,hph, andbar, for pursuit of early and stable transformation events. A set of constructs which contain deleted T-DNA borders in various
combinations and display predictably altered efficacies for gene transfer has also been created. A modular set of vectors
has been designed to facilitate the insertion and transfer of novel gene sequences by providing anptII-linked plant expression cassette orlacZ-multiple cloning site. A range of antibiotic resistance genes has been incorporated into the non-T-DNA part of the vectors
in order to facilitate their selection across the range ofAgrobacterium virulence strains. 相似文献
968.
A rapid, efficient, routine system has been established forAgrobacterium tumefaciens-mediated production of hundreds of fertile transgenic plants from commercially important rice cultivars, including an indica
cultivar, Pusa Basmati 1. Calli induced from embryos of mature rice seeds were cocultivated withA. tumefaciens strain LBA4404 carrying the plasmid pTOK233, then exposed to hygromycin selection followed by an efficient regeneration system.
Based on the total number of calli co-cultivated, the transformation frequencies of independent transgenic rice plants including
cultivars Pusa Basmati 1, E-yi 105, E-wan 5 and Zhong-shu-wan-geng, were 13.5, 13.0, 9.1, and 9.3%, respectively. T1 seeds
were harvested within 7–8 mo of initiation of mature embryo cultures. Data from Southern hybridization analysis proved that
foreign genes on T-DNA were stably integrated into the rice genome at low copy/site numbers. Mendelian inheritance of the
transgenes was confirmed in T1 progeny. 相似文献
969.
Michael A. Rex Ron J. Etter Alisabet J. Clain Malcolm S. Hill 《Evolution; international journal of organic evolution》1999,53(4):1298-1301
The shift to smaller body size in marine invertebrates at the deep-sea threshold and size-depth clines within the deep-sea ecosystem are global biogeographic phenomena that remain poorly understood. We present the first standardized measurements of larval and adult size among ecologically and phylogenetically similar species across a broad and continuous depth range, using the largest family of deep-sea gastropods (the Turridae). Size at all life stages increases significantly with depth from the upper bathyal region to the abyssal plain. These consistent clines may result from selection favoring larger size at greater depths because of its metabolic and competitive advantages. The unusually small size of deep-sea mollusks, in general, may represent an independent evolutionary process that favors invasion by inshore taxa composed of small organisms. 相似文献
970.
Upland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol?1) and elevated (700 μmol mol?1) CO2 in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO2 alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO2 was 35% that of uninfected, control plants, while at elevated CO2, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO2 supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO2. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO2. There were significant CO2 and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO2] (A/Ci curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO2 had significantly lower CO2 saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO2‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO2, but had no impact on photosynthesis of hosts grown at ambient CO2. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO2 had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO2. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO2 or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO2 concentrations. These results demonstrate that elevated CO2 concentrations can alleviate the impact of infection with Striga on the growth of C3 hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO2. 相似文献