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PubMed1980

Competition trait anxiety, state anxiety, and performance.

This study tested predictions about social facilitation using a competitive (evaluation) vs non-competitive setting. In addition, subjects who exhibited low, moderate, or high anxiety concerning competition were selected to determine the relation of anxiety to social facilitation. The design was 2 (competition/no competition) X 3 (competition trait anxiety), with state anxiety and performance as the major dependent variables. In a significant main effect of anxiety about competition subjects high in competitive anxiety displayed higher levels of state anxiety than subjects moderate or low in anxiety about competition. Performance differences were non-significant although means were as predicted.

Achievement↗
PubMed1978

Achievement motivation and competition: perceptions and responses.

This study investigated the influence of achievement motivation (Nach) on how individuals perceive an evaluative competition situation, whether they prefer to perform in this type of setting, and whether they seek the inherent appraisal information regarding their motoric competence. Specifically, perceived threat to self esteem was examined as indicated by state anxiety responses and measured by the Competitive Short Form of the Spielberger State Anxiety Inventory. State anxiety was assessed at rest, while performing a motor task alone in a nonevaluative setting, and during competition against an equal ability opponent. Situation perference and information seeking behavior were assessed at the conclusion of the closely paced competition. Subjects were asked whether they had perferred performing in the noncompetition or competition situation and were given the opportunity to select the relative ability level of a future opponent. As predicted, the major findings indicated that high Nach males experienced less threat during competition than low Nach males. Further, more high than low Nach individuals perferred the competition situation to the noncompetition situation and sought the evaluative ability information to a greater extent by choosing opponents of equal or greater relative ability for a future hypothetical competition.

Achievement↗
PubMed1997

Relationship between market competition and the activities and attitudes of medical school faculty.

CONTEXT: Growth in health care market competition and the concomitant increasing dependence of academic health centers on clinical revenues may require medical school faculty to increase patient care activity, perhaps at the expense of research and teaching. However, the relationship between health care market competitiveness and the activities and attitudes of medical school faculty has not been established. OBJECTIVE: To examine the relationship between market competitiveness and the activities and attitudes of medical school faculty members. DESIGN: Mailed survey of 3394 life-science faculty in the 50 universities that received the most funding from the National Institutes of Health in 1993. SETTING: Medical schools in research-intensive universities. PARTICIPANTS: A total of 2167 faculty responded to the survey (response rate, 64%). We analyzed the responses of 1671 medical school research faculty located in markets of differing health care competitiveness, ranging from least competitive (stage 1) to most competitive (stage 4) markets. MAIN OUTCOME MEASURES: The number of publications in refereed journals in the last 3 years, the average number of hours per week of teaching contact, whether faculty in clinical departments had patient care responsibilities, and measures of departmental community, cooperation, and conflict. RESULTS: Clinical researchers in stage 1 and 2 markets published more scientific articles than those in stage 3 markets (14.5 vs 12.6, P=.04) or in stage 4 markets (14.5 vs 12.0, P=.03). Among 96 young faculty (professional age-<10 years) in clinical departments, 11 (44%) of those in stage 1 and 2 markets had patient care duties compared with 32 (56.1%) of young faculty members in stage 3 markets (P=.04) and 12 (85.7%) of those in stage 4 markets (P=.01). The percentage of senior faculty in clinical departments (n=691) with patient care responsibilities did not differ significantly by market stage. Compared with faculty in less competitive markets, faculty in stage 4 markets perceived lower levels of departmental cooperation and higher levels of conflict. CONCLUSIONS: Increased competitiveness of health care markets seems to hinder the capacity of academic health centers to conduct clinical research and to foster the careers of young clinical faculty.

Academic Medical Centers↗
PubMed1997

Factors affecting internal mammary artery graft survival: how is competitive flow from a patent native coronary vessel a risk factor?

Recent studies have suggested that competitive flow is an important factor in early internal mammary artery (IMA) graft failure. Flow competition from minimally diseased native coronary vessels has been implicated in the failure of IMA grafts, but does not seem to affect saphenous vein grafts (SVG). The objective of this study was to determine the effects of competitive flow on SVG and IMA grafts and to compare the patterns of flow dynamics and pressure on proximal and distal grafts to the left anterior descending (LAD) artery; factors that may be involved in graft failure. Twelve mongrel dogs underwent coronary artery bypass grafting using IMAs and a SVG to an open LAD artery. The right IMA (PIMA) and the SVG were anastomosed in the proximal LAD and the left IMA (DIMA) was anastomosed at a more distal location. The procedure was performed through a left thoracotomy, using an "off pump" technique. Graft flows were measured isolated and in competition. The IMAs and SVG provided flow levels similar to the native LAD when each one was the sole inflow to the LAD. During competitive flow conditions, total and diastolic SVG flows were reduced 54.4 and 50.5%, respectively (P < 0.05). Total and diastolic PIMA and DIMA flows were reduced more drastically (68.6-73.3 and 69.5-68.1%, respectively; P < 0.05). The DIMA had better preservation of diastolic flow compared to PIMA. A delay in the pressure wave was noted in the isolated IMAs, but not in the SVG. This pattern of flow disappeared during competition due to the large, systolic retrograde flow up the IMA grafts. In conclusion, IMAs compared to the SVG are longer and narrower conduits with lower levels of flow during competition. Low levels of flow and oscillating flow (retrograde/ antegrade) may be poorly tolerated by the IMA endothelium and may be factorial to graft failure. These data suggest that a more distal placement of the IMA graft may be protective to the arterial graft under competitive flow conditions.

Animals↗
PubMed1997

Community structure and the interplay between interspecific infection and competition.

Our motivation is the need to understand how two different interactions between species-shared infection and interspecific competition-combine to determine community structure. We introduce a proto-typical model of two hosts sharing a pathogen and also competing directly. We discuss forces of infection, forces of competition and invasion criteria and their relevance to long-term outcomes and community structure. To understand their interplay, we consider first purely competitive and second purely infective interactions. We then investigate our full model to establish how the two forces combine and how the combination and related invasion criteria determine community structure. The forces of infection and competition do not merely add; there is a synergetic resistance to invasion. Using generalised invasion criteria and subsidiary conditions for the feasibility and stability of uninfected coexistence, we classify long-term outcomes. We distinguish two main routes to three-species coexistence. In the first, two host species, each of which would not alone support the pathogen, support it jointly if interspecific competition is relatively weak, interspecific infection strong. In the second, at least one host species would alone support the pathogen and both are invadable by the other, but subsidiary conditions yield two cases. In one, infected coexistence results when the two hosts would coexist stably purely competitively and at sufficiently high densities to support the pathogen jointly. Thus coexistence is promoted by weak interspecific competition but there is a tension between weak interspecific infection favouring invadability and strong interspecific infection promoting pathogen survival. In the other, infected coexistence results when the two hosts would not coexist in the absence of the pathogen. This pathogen-mediated host coexistence is expected where there is strong intraspecific infection (lowering densities) and weak interspecific infection (favouring invadibility) as necessary. Results are compared with previous work and apparent competition and resource- and transmission-mediated coexistence are discussed.

Animals↗
PubMed2000

Effects of sediment type and intra- and interspecific competition on growth rate of the marine snails Hydrobia ulvae and Hydrobia ventrosa.

The combined effects of sediment grain size and intra- and interspecific competition on growth rate of Hydrobia ulvae and H. ventrosa were investigated in a 2-month laboratory experiment. Individuals of H. ulvae grew faster than H. ventrosa at all competition intensities. Growth rate did not differ between fine- and coarse-grained sediments in any of the species. This suggests that other factors than the sediment quality cause the often observed size differences between Hydrobia snails from these sediment types in nature. Competition from 1.6 to 1.9 times larger competitors affected growth of the smaller target snails. Competition between the species was asymmetrical and, in both species, per capita effect of competition was stronger from H. ulvae than from H. ventrosa, regardless of sediment type. From growth, Lotka-Volterra competition coefficients were estimated to 0.2 from H. ventrosa on H. ulvae and 1.8 from H. ulvae on H. ventrosa. Since competition between the species seems to be independent of sediment grain size, the shift in numerical dominance in nature, from H. ulvae on coarse-grained sediment to H. ventrosa on fine-grained, could not be explained with different competitive ability in different environments.

Journal Article↗
PubMed2006

CD8 T cell competition for dendritic cells in vivo is an early event in activation.

T cell responses against an antigen are often focused on a small fraction of potentially immunogenic determinants, a phenomenon known as immunodominance. Immunodominance can be established at several stages of antigen presentation, including antigen processing, binding of peptides to MHC, and competition between T cells for dendritic cells (DCs). The mechanism of this T cell competition is unclear, but may include competition for physical access to DCs, competition for limiting soluble DC-derived factors, or a suppressive effect of one T cell population on the other(s). To model DC-specific T cell competition, normal mice were injected with one or two T cell receptor transgenic CD8 T cell populations, each with high affinity for different peptides presented by different class I MHC complexes. These mice were immunized with DCs pulsed with peptides that are recognized by the transferred T cells. Competition was detectable when both T cell populations were transferred and their target peptides were present on the same DCs. The competition resulted in fewer cells entering the response, but had no effect on the level of activation of the cells that did respond. The effect was evident very early in the response, and in fact the competing T cells needed to be present in the first 5 h of the response for competition to occur. Thus, some aspect of DCs other than peptide/MHC complexes is limiting in the earliest stages of the CD8 T cell response. These results have implications for the design of multivalent vaccines.

Animals↗
PubMed2006

Sperm competition enhances functional capacity of mammalian spermatozoa.

When females mate promiscuously, sperm from rival males compete within the female reproductive tract to fertilize ova. Sperm competition is a powerful selective force that has shaped sexual behavior, sperm production, and sperm morphology. However, nothing is known about the influence of sperm competition on fertilization-related processes, because it has been assumed that sperm competition only involves a race to reach the site of fertilization. We compared four closely related rodent species with different levels of sperm competition to examine whether there are differences in the proportion of spermatozoa that become ready to interact with the ovum ("capacitated") and in the proportion of spermatozoa that experience the acrosome reaction in response to a natural stimulant. Our results show that differences between species in levels of sperm competition were associated with the proportion of spermatozoa that undergo capacitation and with the proportion of spermatozoa that respond to progesterone, an ovum-associated signal. Sperm competition thus favors a larger population of spermatozoa that are competent to fertilize, and spermatozoa that are more sensitive to the signals emitted by the ovum and that may penetrate the ova vestments more rapidly. These results suggest that, contrary to previous assumptions, competition between spermatozoa from rival males continues at the site of fertilization. These findings may have further evolutionary implications because the enhanced competitiveness of spermatozoa during fertilization may increase the risk of polyspermy to females. This could lead to antagonistic coevolution between the sexes and may contribute to the explanation of the rapid divergence observed in fertilization-related traits.

Acrosome↗
PubMed1971

Further studies of antigenic competition. 3. A model to account for the phenomenon based on a deficiency of cell-to-cell interaction in immune lymphoid cell populations.

A striking correlation between the capacity of an antigen to nonspecifically suppress humoral immune responses of subsequently administered antigens which are non-cross-reacting, i.e. to manifest antigenic competition and produce enlargement of spleen size through cell proliferation, was found. Increase in spleen size was always accompanied by a drop in the normal proportion of thymus-derived cells to non-thymus-derived cells. Various means of altering the immune response to the initial antigen, and hence, the capacity of that antigen to suppress in a model of antigenic competition were performed and correlated with changes in spleen size and in the proportion of theta-positive cells in the spleen. In all instances, when the experimental condition reduced or abolished antigenic competition, the increase in spleen size and reduction in the proportion of theta-positive cells in the spleen was reduced or abolished. Furthermore, under conditions in which the suppressive capacity of the initial antigen was unaltered, the increase in spleen size and reduction in theta-proportion occurred normally. Finally, the better the suppression in a model of antigenic competition, the greater the increase in spleen size and reduction in the proportion of theta-positive cells. On the basis of these observations, it appears that there is a relationship between spleen enlargement through clonally restricted cell proliferation and the expression of antigenic competition; one cannot have the latter without the former. It is postulated that the immunological lesion associated with antigenic competition resides at the level of interference with cell interaction between thymus-derived antigen-reactive cells and marrow-derived antibody-forming cells. This occurs as a result of a relative "diluting out" of cells of both populations carrying antigenic specificity differing from the one(s) which induced the dilution effect in the first place. The net effect of this is to decrease the chance of a "hit" or interaction between a marrow-derived and thymus-derived cell of the same specificities. This mechanism, which is compatible with theories of clonal selection, and which in fact is dependent upon them, supports the view that the term "antigenic competition" is a misnomer; there is no competition by the antigens for anything. The term "antigen-induced suppression" is suggested as a more suitable alternative.

Animals↗
PubMed2005

Sperm competition, mating rate and the evolution of testis and ejaculate sizes: a population model.

There are various ways to estimate ejaculate expenditure. Ejaculate size or sperm number (s) is an absolute number of units of ejaculate. Relative ejaculate expenditure (E) is the expenditure on the ejaculate as the proportion of the total expenditure on all aspects of the mating, including finding and acquiring a female, and so on. Relative testis size or gonadosomatic index (sigma) is testes mass divided by body mass; it is assumed to reflect the product of mating rate (M) and ejaculate mass (s). In a new model, where mating rate, sperm competition and sperm allocation interact, and where the female's inter-clutch interval is assumed to be independent of s or M, we show that sigma is directly proportional to the mean E for a species; across species sigma and E increase monotonically with sperm competition. However, the relation between s and sperm competition across species depends on the range of sperm competition (low risk or high intensity): s increases with sperm competition at low risk levels, but decreases with sperm competition at high intensity levels. This situation arises because s alpha E/M; both E and M increase with sperm competition, but E increases differently with sperm competition in its two ranges.

Animals↗
PubMed2001

Sperm competition experiments between lines of crickets producing different sperm lengths.

Sperm numbers can be important determinants of fertilization success in sperm competition. However, the importance of variation in sperm size is less well understood. Sperm size varies significantly both between and within species and comparative studies have suggested that some of this variance can be explained by sperm competition. In this study we examine whether variation in sperm length has consequences for fertilization precedence using controlled sperm competition experiments in the field cricket Gryllus bimaculatus. This species is an ideal model for such investigations because the mechanism of sperm competition generates complete mixing of different males' spermatozoa in the female (thereby allowing individual sperm to express their own competitive abilities). We successfully bred lines of crickets, the males of which produced short, medium and long sperm types with narrow and non-overlapping distributions. Males of different lines were then sequentially mated with control females in order to create two-male sperm competitions. The paternity outcomes of these competitions were measured after matings using an irradiated male technique (with a full reciprocal design that controls for natural fertility and any irradiation effects on gamete competitiveness) over a 12 day oviposition period. However, having successfully bred diverging sperm length lines and competing males that differed in sperm length, we found no evidence that a male's sperm size explained any of the variation in their relative fertilization success. Males from lines producing longer sperm showed no fertilization advantage over males producing shorter sperm across 97 double matings. There was also no advantage for males producing a sperm length close to the population mean over those competitors whose sperm length had been selectively diverged across 63 matings.

Animals↗
PubMed2003

Sperm competition and the evolution of gamete morphology in frogs.

Despite detailed knowledge of the ultrastructure of spermatozoa, there is a paucity of information on the selective pressures that influence sperm form and function. Theoretical models for both internal and external fertilizers predict that sperm competition could favour the evolution of longer sperm. Empirical tests of the external-fertilization model have been restricted to just one group, the fishes, and these tests have proved equivocal. We investigated how sperm competition affects sperm morphology in externally fertilizing myobatrachid frogs. We also examined selection acting on egg size, and covariation between sperm and egg morphology. Species were ranked according to probability of group spawning and hence risk of sperm competition. Body size, testis size and oviposition environment may also influence gamete traits and were included in our analyses. After controlling for phylogenetic relationships between the species examined, we found that an increased risk of sperm competition was associated with increased sperm head and tail lengths. Path analysis showed that sperm competition had its greatest direct effect on sperm tail length, as might be expected under selection resulting from competitive fertilization. Sperm competition did not influence egg size. Oviposition location had a strong influence on egg size and a weak influence on sperm length, with terrestrial spawners having larger gametes than aquatic spawners. Our analysis revealed significant correlated evolution between egg morphology and sperm morphology. These data provide a conclusive demonstration that sperm competition selects for increased sperm length in frogs, and evidence for evolutionary covariance between aspects of male and female gamete morphology.

Animals↗
PubMed2005

Does egg competition occur in marine broadcast-spawners?

When the availability of sperm limits female reproductive success, competition for sperm, may be an important broker of sexual selection. This is because sperm limitation can increase the variance in female reproductive success, resulting in strong selection on females to compete for limited fertilization opportunities. Sperm limitation is probably common in broadcast-spawning marine invertebrates, making these excellent candidates for investigating scramble competition between broods of eggs and its consequences for female reproductive success. Here, we report our findings from a series of experiments that investigate egg competition in the sessile, broadcast-spawning polychaete Galeolaria caespitosa. We initially tested whether the order in which eggs encounter sperm affects their fertilization success at two ecologically relevant current regimes. We used a split-clutch-split--ejaculate technique to compare the fertilization success of eggs from individual females that had either first access (competition-free treatment) or second access (egg competition treatment) to a batch of sperm. We found that fertilization success depended on the order in which eggs accessed sperm; eggs that were assigned to the competition-free treatment exhibited significantly higher fertilization rates than those assigned to the egg competition treatment at both current speeds. In subsequent experiments we found that prior exposure of sperm to eggs significantly reduced both the quantity and quality of sperm available to fertilize a second clutch of eggs, resulting in reductions in fertilization success at high and low sperm concentrations. These findings suggest that female traits that increase the likelihood of sperm-egg interactions (e.g. egg size) will respond to selection imposed by egg competition.

Animals↗
PubMed2005

Above-ground space sequestration determines competitive success in juvenile beech and spruce trees.

A 2-yr phytotron study was conducted to investigate the intra- and inter-specific competitive behaviour of juvenile beech (Fagus sylvatica) and spruce (Picea abies). Competitiveness was analysed by quantifying the resource budgets that occur along structures and within occupied space of relevance for competitive interaction. Ambient and elevated CO(2) and ozone (O(3)) regimes were applied throughout two growing seasons as stressors for provoking changes in resource budgets, growth and allocation to facilitate the competition analysis. The hypothesis tested was that the ability to sequester space at low structural cost will determine the competitive success. Spruce was a stronger competitor than beech, as displayed by its higher above-ground biomass increments in mixed culture compared with monoculture. A crucial factor in the competitive success of spruce was its ability to enlarge crown volume at low structural costs, supporting the hypothesis. Interspecific competition with spruce resulted in a size-independent readjustment of above-ground allocation in beech (reduced leaf : shoot biomass ratio). The efficient use of resources for above-ground space sequestration proved to be a parameter that quantitatively reflects competitiveness.

Carbon↗
PubMed1998

A competitive enzyme-linked immunosorbent assay for measuring the levels of serum antibody to Haemophilus influenzae type b.

A competitive ELISA method is described for the measurement of total antibodies to the capsular polysaccharide of Haemophilus influenzae type b (HibCPS) in human sera. The competitive method showed an excellent correlation to the radioantigen binding assay (RABA, or Farr assay) and improved correlation of sera with low titers with respect to the more conventional noncompetitive method. Overestimation of samples in the low concentration range was no longer observed with the competitive ELISA method. The free HibCPS competition allowed us to eliminate the day-to-day background variation typical of some sera; thus, only values representing the true anti-HibCPS response were determined. The use of precoated microplates, which could be stored up to 8 months, greatly improved the speed of the procedure. An overall correlation coefficient of 0. 9660 was found when 407 serum samples with a wide variety of anti-HibCPS antibody levels were tested with the competitive ELISA and RABA. The regression line was very close to the ideal line, with a slope of 1.0045 and an intercept of -0.1996. A subset of 96 serum samples representative of all pre- and postimmunization samples was used to compare the competitive ELISA with a previously described ELISA method. The competitive method performed in two laboratories in different countries showed a better correlation with the RABA. The correlation factors were 0.9770 and 0.9816, respectively, while a factor of 0.9547 was found with the previously described noncompetitive procedure, which was better for this method than previously reported (r = 0.917). Therefore, the competitive ELISA is proposed for the assay of anti-HibCPS titers in sera from vaccinated subjects.

Adult↗
PubMed1993

Scanning and competition between AGs are involved in 3' splice site selection in mammalian introns.

In mammalian intron splicing, the mechanism by which the 3' splice site AG is accurately and efficiently identified has remained unresolved. We have previously proposed that the 3' splice site in mammalian introns is located by a scanning mechanism for the first AG downstream of the branch point-polypyrimidine tract. We now present experiments that lend further support to this model while identifying conditions under which competition can occur between adjacent AGs. The data show that the 3' splice site is identified as the first AG downstream from the branch point by a mechanism that has all the characteristics expected of a 5'-to-3' scanning process that starts from the branch point rather than the pyrimidine tract. Failure to recognize the proximal AG may arise, however, from extreme proximity to the branch point or sequestration within a hairpin. Once an AG has been encountered, the spliceosome can still see a limited stretch of downstream RNA within which an AG more competitive than the proximal one may be selected. Proximity to the branch point is a major determinant of competition, although steric effects render an AG less competitive in close proximity (approximately 12 nucleotides). In addition, the nucleotide preceding the AG has a striking influence upon competition between closely spaced AGs. The order of competitiveness, CAG congruent to UAG > AAG > GAG, is similar to the nucleotide preference at this position in wild-type 3' splice sites. Thus, 3' splice site selection displays properties of both a scanning process and competition between AGs based on immediate sequence context. This refined scanning model, incorporating elements of competition, is the simplest interpretation that is consistent with all of the available data.

Animals↗
PubMed2006

Neighborhood analyses of canopy tree competition along environmental gradients in New England forests.

We use permanent-plot data from the USDA Forest Service's Forest Inventory and Analysis (FIA) program for an analysis of the effects of competition on tree growth along environmental gradients for the 14 most abundant tree species in forests of northern New England, USA. Our analysis estimates actual growth for each individual tree of a given species as a function of average potential diameter growth modified by three sets of scalars that quantify the effects on growth of (1) initial target tree size (dbh), (2) local environmental conditions, and (3) crowding by neighboring trees. Potential growth of seven of the 14 species varied along at least one of the two environmental axes identified by an ordination of relative abundance of species in plots. The relative abundances of a number of species were significantly displaced from sites where they showed maximum potential growth. In all of these cases, abundance was displaced to the more resource-poor end of the environmental gradient (either low fertility or low moisture). The pattern was most pronounced among early successional species, whereas late-successional species reached their greatest abundance on sites where they also showed the highest growth in the absence of competition. The analysis also provides empirical estimates of the strength of intraspecific and interspecific competitive effects of neighbors. For all but one of the species, our results led us to reject the hypothesis that all species of competitors have equivalent effects on a target species. Most of the individual pairwise interactions were strongly asymmetric. There was a clear competitive hierarchy among the four most shade-tolerant species, and a separate competitive hierarchy among the shade-intolerant species. Our results suggest that timber yield following selective logging will vary dramatically depending on the configuration of the residual canopy, because of interspecific variation in the magnitude of both the competitive effects of different species of neighbors and the competitive responses of different species of target trees to neighbors. The matrix of competition coefficients suggests that there may be clear benefits in managing for specific mixtures of species within local neighborhoods within stands.

Ecosystem↗
PubMed2000

[Individual tree growth-competition model in mixed plantation of manchurian ash and dahurian larch].

Based on distance-dependent competition models and neighborhood interference models, the competition index components and competition effect coefficients were used to quantify the spatial competition among trees in the mixed plantation of ash(Fraxinus mandshurica) and larch(Larix gmelini). Taking each component of competition index as independent variables and the yearly volume growth as dependent variable, the competition-growth model was established with good regression result. The study provided a new approach to deal with the further improvement of spatial competition models and the plant competition-growth relationship ecological study.

Ecosystem↗