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Results for “exploitation competition”

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PubMed1998

Sex and the evolution of intrahost competition in RNA virus phi6.

Sex allows beneficial mutations that occur in separate lineages to be fixed in the same genome. For this reason, the Fisher-Muller model predicts that adaptation to the environment is more rapid in a large sexual population than in an equally large asexual population. Sexual reproduction occurs in populations of the RNA virus phi6 when multiple bacteriophages coinfect the same host cell. Here, we tested the model's predictions by determining whether sex favors more rapid adaptation of phi6 to a bacterial host, Pseudomonas phaseolicola. Replicate populations of phi6 were allowed to evolve in either the presence or absence of sex for 250 generations. All experimental populations showed a significant increase in fitness relative to the ancestor, but sex did not increase the rate of adaptation. Rather, we found that the sexual and asexual treatments also differ because intense intrahost competition between viruses occurs during coinfection. Results showed that the derived sexual viruses were selectively favored only when coinfection is common, indicating that within-host competition detracts from the ability of viruses to exploit the host. Thus, sex was not advantageous because the cost created by intrahost competition was too strong. Our findings indicate that high levels of coinfection exceed an optimum where sex may be beneficial to populations of phi6, and suggest that genetic conflicts can evolve in RNA viruses.

Adaptation, Physiological↗

PubMed1980

Antigen induced modulation by shed lymphocyte membrane gangliosides.

A unique regulatory mechanism has been proposed for ganglioside which functions to immune responses to temporarily restrain B lymphocytes of all specificities and at various levels of differentiation. Utilizing antigen competition protocols, experiments was designed to exploit and extend the antigen induction properties of this modulation. Spleen cell cultures were prepared from TNP-BGG primed mice. In vitro stimulation of the cultures with ovalbumin (OVA) followed 24 hours later by addition of TNP-BGG resulted in only one weak TNP hemolytic plaque responses when compared to control cultures which did not receive OVA. OVA induced competitive effects were absorbed by anti-Thy-1 or anti-ganglioside. Glycolipids could be extracted from the culture media supernatants of experimental and control groups as a ganglioside fraction containing Thy-1 determinants. These molecules, when formulated into liposomes, produced the same modulatory effect as that of media from the competitive culture group. These results support and extend the proposal that glycolipids released by antigen stimulated T cells provide unrestricted modulation of B cells to prevent overload during T cell maturation. This regulatory mechanism prevents direct antigen binding and prepares B cell receptivity for further stimuli which orchestrate their terminal differentiation into plasma cells.

Animals↗

PubMed1995

The myth of masochism.

The personality disorder called "Masochism," which traditionally has been regarded as a preference for and pursuit of suffering is dynamically misconceived. There presently is no fundamental agreement on a diagnostic category for this personality disorder. There are aspects of what is called masochism, such as sexual arousal associated with pain, which have not been considered in this study. I feel that the essential nature of the pain in those designated as masochists is low self-esteem and that it develops in a childhood context of inadequate loving nurturance. I strongly believe that low self-esteem evolves from and is maintained by the competitive social milieu and a resultant personal functioning, which is diffusely competitive. The competitive activity is often associated unawarely with cynicism (Bonime, 1989). The gratification of victory substitutes for the gratifications of intimacy and growth, but is relatively brief, and although it produces some self acceptance, it is never enough to overcome the basic low feeling about oneself. Here was Marjorie, a woman who had miserably low self-esteem as a child, as low as being "just a crack in the door." As an adult, as shown in her dream, she felt like a woman full of shit that comes out involuntarily. She struggled to keep from being exposed as such and ached with humiliation or inwardly--and sometimes openly--raged when some distasteful quality or inadequacy showed or threatened to show. This pained person strove to overcome her sense of inadequacy as a person. She overcame it by succeeding in outdoing others according to her private, competitive standards. Her criteria of value were success in evoking signs of approval and sustaining herself while suffering, while "taking it." Her highest value was being able to take it, to suffer intensely without breaking. She was cynical and never sensed for long that she was genuinely regarded as an acceptable human being. She didn't believe in the existence of any genuine caring. She dreamt of an ecstatic evening dining, dancing, and having wonderful sex with "Bill" who she felt was an exceptional man. Later in the dream, she expected the same ecstasy the following evening with him. However, he said to her they couldn't go on because she was cruel. Almost always the prospect of an enjoyable situation "scared" her because it required her to abandon her protective cynicism, which made her a defeatable, exploitable target for the cynicism and competitiveness of others.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2002

Oscillatory neuronal synchronization in primary visual cortex as a correlate of stimulus selection.

Spike and local field potential activity were recorded simultaneously from multiple sites in primary visual cortex of strabismic cats, while monocular stimulation alternated with dichoptic stimulation, inducing interocular rivalry. During interocular rivalry, there is competition between the two nonfusible stimuli presented to the two eyes, and only one stimulus is selected at any time. We biased this competition in three different ways: (1) we exploited the condition that in strabismic cats there is often one dominant eye that is selected for most of the time. (2) We presented the two stimuli with a temporal offset, which biases competition in favor of the newly appearing stimulus. (3) We presented the two stimuli with highly different contrasts, which biases competition in favor of the stimulus with higher contrast. Whenever competition was biased in favor of the stimulus activating the recorded neurons, gamma-frequency synchronization of the respective responses was enhanced, and vice versa. Firing rates showed some differences between stimulation conditions. However, when present, these changes were inversely related to a competitive advantage of the respective stimulus. We hypothesize that enhanced gamma-frequency synchronization in primary visual cortex is a correlate of stimulus selection. Synchronization is likely to be translated into firing rate changes at later processing stages.

Action Potentials↗

PubMed1992

Heparin binding to human plasma low-density lipoproteins: dependence on heparin sulfation degree and chain length.

Binding between low-density lipoproteins (LDL) and fluorescein-labeled heparin was studied quantitatively with a modified form of a published procedure [Cardin, A. D., Randall, C. I., Hirose, N., & Jackson, R. L. (1987) Biochemistry 26, 5513-5518], using fluorescence anisotropy titrations. Assumption of binding site equivalence satisfactorily interpreted experimental data. Accordingly, the apparent total capacity, n, and the average dissociation constant, Kd, were estimated as n approximately 24 disaccharides per LDL particle and Kd approximately 4 microM in 0.05 M HEPES/0.1 M NaCl, pH 7.4, 22 degrees C. Competition experiments with unlabeled heparins were exploited for the quantitative study of Kd as a function of heparin chain length and sulfation degree (ns = sulfate groups per disaccharide). The former parameter was investigated with a series of bovine lung heparin fractions with Mw ranging from 1,800 to 21,000 and constant sulfation degree (ns = 2.8 +/- 0.1). A series of physically fractionated or chemically modified heparins having 1.2 less than ns less than 3.5 were used to explore the dependence on sulfation degree. LDL affinity was found to increase with increasing both ns and Mw: an empirical Mw-1.6 dependence represented very well the chain length data set; a linear dependence was observed for log Kd as a function of ns, after appropriate allowance was made for chain length differences among samples. This regularity confirmed that LDL-heparin binding is mainly driven by electrostatic forces.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein B-100↗

PubMed1983

Fluorescence stopped flow analysis of the interaction of virginiamycin components and erythromycin with bacterial ribosomes.

The kinetics of the interaction between the 50 S subunits (R) of bacterial ribosomes and the antibiotics virginiamycin S (VS), virginiamycin M (VM), and erythromycin have been studied by stopped flow fluorimetric analysis, based on the enhancement of VS fluorescence upon its binding to the 50 S ribosomal subunit. Virginiamycin components M and S exhibit a synergistic effect in vivo, which is characterized in vitro by a 5- to 10-fold increase of the affinity of ribosomes for VS, and by the loss of the ability of erythromycin to displace VS subsequent to the conformational change (from R to R*) produced by transient contact of ribosomes with VM. Our kinetic studies show that the VM-induced increase of the ribosomal affinity for VS (K*VS = 25 X 10(6) M-1 instead of KVS = 5.5 X 10(6) M-1) is due to a decrease of the dissociation rate constant (k*-VS = 0.008 s-1 instead of 0.04 s-1). The association rate constant remains practically the same (k+VS approximately k*+VS = 2.8 X 10(5) M-1 s-1), irrespective of the presence of VM. VS and erythromycin bind competitively to ribosomes. This effect has been exploited to determine the dissociation rate constant of VS directly by displacement experiments from VS . 50 S complexes, and the association rate constant of erythromycin (k+Ery = 3.2 X 10(5) M-1 S-1) on the basis of competition experiments for binding of free erythromycin and VS to ribosomes. By making use of the change in competition behavior of erythromycin and VS, after interaction of ribosomes with VM, the conformational change induced by VM has been explored. Within the experimentally available concentration region, the catalytic effect of VM has been shown to be coupled to its binding kinetics, and the association rate constant of VM has been determined (k+VM = 1.4 X 10(4) M-1 S-1). Evidence is presented for a low affinity binding of erythromycin (K*Ery approximately 3.3 X 10(4) M-1) to ribosomes altered by contact with VM. A model involving a sequence of 5 reactions has been proposed to explain the replacement of ribosome-bound erythromycin by VS upon contact of 50 S subunits with VM.

Erythromycin↗

PubMed1985

Homogeneous colorimetric enzyme inhibition immunoassay for cortisol in human serum with Fab anti-glucose 6-phosphate dehydrogenase as a label modulator.

The Fab fragment of rabbit IgG antibody to bacterial glucose 6-phosphate dehydrogenase covalently linked to the cortisol retained the capacity to inhibit the enzyme completely. In optimal conditions the antibody to cortisol effectively bound the cortisol residues of the cortisol-Fab conjugate, making it incapable of inhibiting the enzyme. The enzyme modulatory properties of the cortisol-Fab conjugate were exploited to set up a direct competitive homogeneous enzyme immunoassay for cortisol in human serum. The procedure involved the use of the auxiliary enzyme diaphorase, specific for NADH, which converts the nitro blue tetrazolium salt to a colored formazan. The procedure detects modulated glucose 6-phosphate dehydrogenase activity by a single-point measurement without serum interference. The assay working range was between 20 and 640 micrograms/1 of cortisol and used 50 microliters of sample.

Antibody Specificity↗

PubMed2002

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions.

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.

Journal Article↗

PubMed2000

Multiple benefits of multiple mating in guppies.

The rewards of promiscuity for males are undisputed. But why should a female mate promiscuously, particularly when her partners offer no resources other than sperm and increase her chances of succumbing to predation or disease? This question has been hotly debated but at present remains largely unresolved [Jennions, M. D. & Petrie, M. (2000) Biol. Rev. 75, 21-64]. One possibility is that females exploit postcopulatory mechanisms, such as sperm competition, to increase both the quality and quantity of their offspring. In this paper, we use the Trinidadian guppy, a species with a resource-free mating system, to test the hypothesis that females gain multiple benefits from multiple mating. Our results indicate that multiply mated females secure substantive advantages: They have shorter gestation times and larger broods, and they produce offspring with better developed schooling abilities and escape responses than their singly mated counterparts.

Animals↗

PubMed1991

Interfaces of the yeast killer phenomenon.

A new prophylactic and therapeutic antimicrobial strategy based on a specific physiological target that is effectively used by killer yeasts in their natural ecological competition is theorized. The natural system exploited is the yeast killer phenomenon previously adopted as an epidemiological marker for intraspecific differentiation of opportunistic yeasts, hyphomycetes, and bacteria. Pathogenic microorganisms (Candida albicans) may be susceptible to the activity of yeast killer toxins due to the presence of specific cell wall receptors. On the basis of the idiotypic network, we report that antiidiotypic antibodies, produced against a monoclonal antibody bearing the receptor-like idiotype, are in vivo protecting animals immunized through idiotypic vaccination and in vitro mimicking the antimicrobial activity of yeast killer toxins, thus acting as antibiotics.

Adsorption↗

PubMed2007

Resolving the tragedy of the commons: the feedback between intraspecific conflict and population density.

Competition and conflict among individuals can favour exploitative strategies that undermine the common good. Theory suggests that this can lead to a tragedy of the commons and ultimately population extinction, a phenomenon known as evolutionary suicide. Here, I present a model of the evolutionary tragedy of the commons that explicitly considers the population dynamics where individuals invest in individually costly competitive traits. In the simplest form, this supports the notion that selection for high levels of conflict can cause evolutionary suicide. However, as competition comes with survival and fecundity costs, a feedback between the investment in competition and population density can act to reduce the level of conflict and prevent the population from going extinct. This suggests that the interaction between population ecology and the evolution of competition and conflict among individuals may be an important mechanism in resolving the level of competition and conflict among individuals.

Biological Evolution↗

PubMed2003

A highly sensitive flow-through amperometric immunosensor based on the Peroxidase chip and enzyme-channeling principle.

A concept based on the Peroxidase-chip (P-chip), antibody co-immobilization, competitive and enzyme-channeling principle was exploited to develop an integrated flow-through amperometric biosensor for detection of environmental pollutants such as s-triazine herbicides. In this concept, recombinant peroxidase is immobilized on the gold electrode (P-chip) in such a way that direct electron transfer is achieved. The recognition and quantitation the target analyte is realized through the competition between the simazine-glucose oxidase (GOD) conjugate and free simazine for the binding sites of the monoclonal antibody co-immobilized with peroxidase on the gold electrode. The arrangement allows to generate a specific signal in the presence of glucose through the channeling of H2O2 produced by GOD conjugate bound to the antibody. The immunosensor exhibited 50% signal decrease (IC50 value) at approximately 0.02 microg l(-1). A concentration of 0.1 ng l(-1) gave a signal clearly distinguishable from the blank whereas the ELISA using the same antibody had a typical detection limit of about 1 microg l(-1), which is four orders of magnitude higher compared to the presented biosensor system. The results demonstrated that gene engineering biomolecules, in this case recombinant peroxidase, might be attractive reagents for the development of electrochemical immunosensors.

Biosensing Techniques↗

PubMed2003

Spatial dynamics in model plant communities: what do we really know?

A variety of models have shown that spatial dynamics and small-scale endogenous heterogeneity (e.g., forest gaps or local resource depletion zones) can change the rate and outcome of competition in communities of plants or other sessile organisms. However, the theory appears complicated and hard to connect to real systems. We synthesize results from three different kinds of models: interacting particle systems, moment equations for spatial point processes, and metapopulation or patch models. Studies using all three frameworks agree that spatial dynamics need not enhance coexistence nor slow down dynamics; their effects depend on the underlying competitive interactions in the community. When similar species would coexist in a nonspatial habitat, endogenous spatial structure inhibits coexistence and slows dynamics. When a dominant species disperses poorly and the weaker species has higher fecundity or better dispersal, competition-colonization trade-offs enhance coexistence. Even when species have equal dispersal and per-generation fecundity, spatial successional niches where the weaker and faster-growing species can rapidly exploit ephemeral local resources can enhance coexistence. When interspecific competition is strong, spatial dynamics reduce founder control at large scales and short dispersal becomes advantageous. We describe a series of empirical tests to detect and distinguish among the suggested scenarios.

Ecosystem↗

PubMed2003

New concepts and tools in imaging for the study of neurodegenerative disease.

Existing technologies permit the detection of changes in neurotransmitter and/or neuroreceptor expression. This may be useful for diagnosis, for monitoring disease progression, and for assessing the pathogenesis of complications associated with long-term treatment. Although the binding of [11C]raclopride to D2 receptors is subject to competition from endogenous dopamine, this can be exploited to estimate changes in synaptic levels of dopamine. Assessment of processes downstream to the receptor will require the development of new approaches.

Carbon Radioisotopes↗

PubMed2002

Photobleaching fluorescence resonance energy transfer reveals ligand-induced oligomer formation of human somatostatin receptor subtypes.

The existence of dimers and higher oligomers of G-protein-coupled receptors (GPCRs) has been frequently reported using strategies based on coimmunoprecipitation or Western blot assays. These methods rely on highly artificial systems with overexpressed receptors, resulting in conflicting observations on the question of whether GPCR dimers are preformed or are formed in response to agonist treatment. Fluorescence resonance energy transfer (FRET) microscopy is a superior and less perturbing technique which can be performed on selected cell regions, e.g., plasma membrane of intact cells with a sensitivity high enough to allow study under physiological levels of receptor expression. Here we describe the application of photobleaching (pb) FRET microscopy for investigating ligand-dependent oligomerization of somatostatin receptors. Procedures for the introduction of suitable donor-acceptor fluorophores in a given GPCR are described. The competitive nature of FRET and photobleaching is exploited to enable the indirect measurement of FRET via its effect on donor photobleaching lifetimes on a pixel-by-pixel basis. The method allows enhanced resolution between 10 and 100A and represents a sensitive and specific biophysical tool for characterizing the assembly and regulation of GPCR oligomers on the cell surface.

Animals↗

PubMed1990

Localization of an antiviral site on the pregnancy recognition hormone, ovine trophoblast protein 1.

Ovine trophoblast protein 1 (oTP-1) is the interferon alpha (IFN-alpha) variant with potent antiviral activity and low toxicity that is responsible for maternal recognition of pregnancy in sheep. To examine the structure/function basis for the potent antiviral activity of oTP-1, we have exploited the direct approach of synthetic peptide competition with oTP-1 for receptor, using N-terminal oTP-1-(1-37) and C-terminal oTP-1-(139-172) peptides. These peptides possess structures similar to those predicted for the intact molecule on the basis of circular dichroism. oTP-1-(1-37) at 1.5 mM specifically blocked oTP-1 antiviral activity without affecting the antiviral activity of natural ovine IFN-alpha, recombinant bovine IFN-alpha, and recombinant human IFN-alpha. At concentrations as low as 0.15 mM, oTP-1-(139-172) blocked the antiviral activity of oTP-1, as well as that of natural ovine IFN-alpha, recombinant bovine IFN-alpha, and recombinant human IFN-alpha, but not recombinant bovine interferon gamma. Further, binding of radiolabeled oTP-1 to endometrial membrane preparations could be effectively inhibited by polyclonal anti-C-terminal and anti-N-terminal antisera, with the anti-C-terminal antiserum being the more effective inhibitor. Consistent with peptide and antiserum functional data, oTP-1 and recombinant bovine IFN-alpha are predicted to possess similar C-terminal structure but different N-terminal structure by composite surface profile predictions. The findings suggest that the C-terminal regions of IFN-alpha s bind to a common site on the IFN-alpha receptor while the N-terminal region binds to a site unique for the particular IFN-alpha.

Amino Acid Sequence↗

PubMed1994

The process of managerial control in quality improvement initiatives.

The fundamental intent of strategic management is to position an organization with in its market to exploit organizational competencies and strengths to gain competitive advantage. Competitive advantage may be achieved through such strategies as low cost, high quality, or unique services or products. For health care organizations accredited by the Joint Commission on Accreditation of Healthcare Organizations, continually improving both processes and outcomes of organizational performance--quality improvement--in all operational areas of the organization is a mandated strategy. Defining and measuring quality and controlling the quality improvement strategy remain problematic. The article discusses the nature and processes of managerial control, some potential measures of quality, and related information needs.

Data Collection↗

PubMed2002

Comparison and validation of novel pyrogen tests based on the human fever reaction.

The absence of pyrogens (fever-inducing contamination) in injectable drugs is a crucial safety control because pyrogens can pose a life-threatening risk to the patient. The field of applications for pyrogen-testing is expanding and becoming more diverse due to innovative high-tech products such as medical devices, cellular therapies and species-specific agents (e.g. recombinant proteins). The overall aim of the consortium is to develop, evaluate and validate a method based on the human fever reaction to replace the rabbit pyrogen test and the Limulus assay. The network brings together the six most prominent test systems developed recently in Europe for trans-national comparison and subsequent validation of the most promising models. This pre-competitive development will initiate further applications and exploitations for new fields of pyrogen testing such as cellular therapies, medical devices and pyrogen pollution control in the work place. A method for introduction into the European Pharmacopoeia will be developed as a replacement for the rabbit pyrogen test for end-product control.

Animal Use Alternatives↗