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PubMed2006

Cooperation and the scale of competition in humans.

Explaining cooperation is one of the greatest challenges for evolutionary biology. It is particularly a problem in species such as humans, where there is cooperation between nonrelatives. Numerous possible solutions have been suggested for the problem of cooperation between nonrelatives, including punishment, policing, and various forms of reciprocity. Here, we suggest that local competition for resources can pose a problem for these hypotheses, analogous to how it can select against cooperation between relatives. We extend the prisoner's dilemma (PD) game to show that local competition between interacting individuals can reduce selection for cooperation between nonrelatives. This is because, with local competition, fitness is relative to social partners, and cooperation benefits social partners. We then test whether nonrelated humans adjust their level of cooperation facultatively in response to the scale of competition when playing the PD for cash prizes. As predicted, we found that individuals were less likely to cooperate when competition was relatively local. Cooperation between humans will therefore be most likely when repeated interactions take place on a local scale between small numbers of people, and competition for resources takes place on a more global scale among large numbers of people.

Competitive Behavior↗
PubMed2006

Animal cognition: know your enemy.

Food-storing corvids are able to remember which individual saw them store food, and take preventive action that is tailored to that particular competitor's knowledge. This raises the question of whether abilities like 'theory of mind' have arisen independently more than once in evolution.

Animals↗
PubMed2006

Ecology of microbial invasions: amplification allows virus carriers to invade more rapidly when rare.

Locally adapted residents present a formidable barrier to invasion . One solution for invaders is to kill residents . Here, we explore the comparative ecological dynamics of two distinct microbial mechanisms of killing competitors, via the release of chemicals (e.g., bacteriocins ) and via the release of parasites (e.g., temperate phage ). We compared the short-term population dynamics of susceptible E. coli K12 and isogenic carriers of phage varphi80 in experimental cultures to that anticipated by mathematical models using independently derived experimental parameters. Whereas phages are a direct burden to their carriers because of probabilistic host lysis, by killing competitor bacteria they can indirectly benefit bacterial kin made immune by carrying isogenic phage. This is similar to previously described bacteriocin-mediated effects. However, unlike chemical killing, viable phage trigger an epidemic among susceptible competitors, which become factories producing more phage. Amplification makes phage carriers able to invade well-mixed susceptibles even faster when rare, whereas chemical killers can only win in a well-mixed environment when sufficiently abundant. We demonstrate that for plausible parameters, the release of chemical toxins is superior as a resident strategy to repel invasions, whereas the release of temperate phage is superior as a strategy of invasion.

Bacteriocins↗
PubMed2006

Male chimpanzees prefer mating with old females.

Cross-cultural studies indicate that women's sexual attractiveness generally peaks before motherhood and declines with age. Cues of female youth are thought to be attractive because humans maintain long-term pair bonds, making reproductive value (i.e. future reproductive potential) particularly important to males. Menopause is believed to exaggerate this preference for youth by limiting women's future fertility. This theory predicts that in species lacking long-term pair bonds and menopause, males should not exhibit a preference for young mates. We tested this prediction by studying male preferences in our closest living relative, the chimpanzee (Pan troglodytes). We show that despite their promiscuous mating system, chimpanzee males, like humans, prefer some females over others. However, in contrast to humans, chimpanzee males prefer older, not younger, females. These data robustly discriminate patterns of male mate choice between humans and chimpanzees. Given that the human lineage evolved from a chimpanzee-like ancestor, they indicate that male preference for youth is a derived human feature, likely adapted from a tendency to form unusually long term mating bonds.

Age Factors↗
PubMed2006

Queen-queen competition by precocious male production in multiqueen ant colonies.

Arriving earlier in the breeding area than his rivals may be beneficial for a male when females mate only once or during a short time span. The timing of a male's entrance is usually determined by the male himself, e.g., through returning early from his winter quarters or through accelerated larval development . Here, we document a surprisingly simple way of "first come, first served" in a species with local mate competition. In multiqueen colonies of a Cardiocondyla ant, mother queens make sure that their own sons are the first to monopolize mating with a large harem of female sexuals by producing extremely long-lived males early in colony life. Whereas queens in newly founded single-queen colonies started to produce male and female sexuals only several weeks after the eclosion of their first worker offspring, queens in multiqueen colonies precociously reared sons long before the first female sexuals and even before the emergence of their first workers. These early males killed all later emerging males in the nest and mated with all female sexuals subsequently produced. Our data document that the patterns of growth and productivity of insect colonies are surprisingly flexible and can be turned upside down under appropriate selection pressures.

Animals↗
PubMed2006

Digital cows grazing on digital grounds.

Picture a pasture open to all (...) As a rational being, each herdsman seeks to maximize his gain. Explicitly or implicitly, more or less consciously, he asks, "What is the utility to me of adding one more animal to the herd?" This utility has one negative and one positive component. 1) The positive component is a function of the increment of one animal. Since the herdsman receives all the proceeds from the sale of the additional animal, the positive utility is nearly +1. 2) The negative component is a function of the additional overgrazing created by one more animal. Since, however, the effects of overgrazing are shared by all the herdsmen, the negative utility for any particular decision-making herdsman is only a fraction of -1. Adding together the component partial utilities, the rational herdsman concludes that the only sensible course for him to pursue is to add another animal to the herd. And another; and another...

Altruism↗
PubMed2004

Does interspecific competition alter effects of early season ozone exposure on plants from wet grasslands? Results of a three-year experiment in open-top chambers.

Chronic effects of ozone on wet grassland species early in the growing season might be altered by interspecific competition. Individual plants of Holcus lanatus, Lychnis flos-cuculi, Molinia caerulea and Plantago lanceolata were grown in monocultures and in mixed cultures with Agrostis capillaris. Mesocosms were exposed to charcoal-filtered air plus 25 nl l(-1) ozone (CF+25), non-filtered air (NF), non-filtered air plus 25 nl l(-1) ozone (NF+25) and non-filtered air plus 50 nl l(-1) ozone (NF+50) early in the growing seasons of 2000 through 2002. Ozone-enhanced senescence and visible foliar injury were recorded on some of the target plants in the first year only. Ozone effects on biomass production were minimal and plant response to ozone did not differ between monocultures and mixed cultures. After three years, above-ground biomass of the plants in mixed culture compared to monocultures was three times greater for H. lanatus and two to four times smaller for the other species.

Air Pollutants↗
PubMed2005

Arm coordination symmetry and breathing effect in front crawl.

This study analysed the relationships among arm coordination symmetry, motor laterality and breathing laterality during a 100-m front crawl, as a function of expertise. Ten elite swimmers (G1), 10 mid-level swimmers (G2), and 8 non-expert swimmers (G3) composed three skill groups, which were distinguished by velocity, stroke rate, stroke length, breathing frequency (BF) and the mean number of strokes between two breaths - the stroke breath (SB) - over a 100-m front crawl. Four stroke phases were identified by video analysis (catch, pull, push and recovery) and the index of coordination (IdC) measured the lag time between the propulsive phases of the two arms. The three modes of coordination are catch-up (IdC<0%), opposition (IdC=0%) and superposition (IdC>0%). The IdC was established as the mean of IdC1 and IdC2, which measured the lag time between the propulsive phases of the left and right arms, respectively. The coordination symmetry was analysed by comparing IdC1 and IdC2, and the breathing effect was studied by distinguishing IdC1 (and IdC2) with and without breathing. Motor laterality was determined by an adaptation of the Edinburgh Handedness Inventory. Breathing laterality was determined by a questionnaire and observation during the 100-m trial. Most of the front crawl swimmers showed asymmetric arm coordination, with propulsive discontinuity on one side and propulsive superposition on the other. This asymmetry was most often related to breathing laterality (a preferential breathing side for a unilateral breathing pattern) and motor laterality (arm dominance), with different profiles noted. More than the breathing laterality itself, the breathing actions of the non-expert swimmers amplified their asymmetric coordination on the breathing side. Conversely, the elite swimmers, who had higher and more stable spatial-temporal parameters (velocity and stroke lengths), a high coordination value (IdC) and lower breathing frequency (BF), managed their race better than the less proficient swimmers and their asymmetric arm coordination was not disturbed by breathing actions. By determining the dominant arm and the preferential breathing side, the coach can obtain a swimmer profile that allows both coach and swimmer to better understand and respond to excessive coordination asymmetry.

Acceleration↗
PubMed2005

Parasites grow larger in faster growing fish hosts.

Parasites depend on host-derived energy for growth and development, and so are potentially affected by the host's ability to acquire nutrients under competitive foraging scenarios. Although parasites might be expected to grow faster in hosts that are better at acquiring nutrients from natural ecosystems, it is also possible that the most competitive hosts are better at countering infections, if they have an improved immune response or are able to limit the availability of nutrients to parasites. I first quantified the ability of uninfected three-spined sticklebacks Gasterosteus aculeatus to compete in groups for sequentially-presented food items, and then exposed either the best or worst competitors to infective stages of the cestode Schistocephalus solidus. Fish were subsequently raised in their original groups, under competitive feeding regimes, for 96 days, after which fish and parasite growth was determined. Unexpectedly, pre-exposure host competitive ability had no effect on susceptibility to infection, or on post-infection growth rate. Furthermore, despite a 120-fold variation in parasite mass at the end of the study, pre-infection competitive ability was not related to parasite growth. The closest predictor of parasite mass was body size-corrected host growth rate, indicating that the fastest growing fish developed the largest parasites. Faster growing hosts therefore apparently provide ideal environments for growing parasites. This finding has important implications for ecology and aquaculture.

Animals↗
PubMed2006

Heterogeneous interspecific interactions in a host-parasite system.

Macroparasites of vertebrates usually occur in multi-species communities, producing infections whose outcome in individual hosts or host populations may depend on the dynamics of interactions amongst the different component species. Within a single co-infection, competition can occur between conspecific and heterospecific parasite individuals, either directly or via the host's physiological and immune responses. We studied a natural single-host, multi-parasite model infection system (polystomes in the anuran Xenopus laevis victorianus) in which the parasite species show total interspecific competitive exclusion as adults in host individuals. Multi-species infection experiments indicated that competitive outcomes were dependent on infection species composition and strongly influenced by the intraspecific genetic identity of the interacting organisms. Our results also demonstrate the special importance of temporal heterogeneity (the sequence of infection by different species) in competition and co-existence between parasite species and predict that developmental plasticity in inferior competitors, and the induction of species-specific host resistance, will partition the within-host-individual habitat over time. We emphasise that such local (within-host) context-dependent processes are likely to be a fundamental determinant of population dynamics in multi-species parasite assemblages.

Animals↗
PubMed2005

Individual flight styles in ski jumping: results obtained during Olympic Games competitions.

From the physics point of view, the jump length in ski jumping depends on: the in-run velocity v(0), the velocity perpendicular to the ramp v(p0) due to the athlete's jumping force, the lift and drag forces acting during take-off and during the flight, and the weight of the athlete and his equipment. The aerodynamic forces are a function of the flight position and of the equipment features. They are a predominant performance factor and can largely be influenced by the athlete. The field study conducted during the Olympic Games competitions 2002 at Park City (elevation: 2000 m) showed an impressive ability of the Olympic medallists to reproduce their flight style and remarkable differences between different athletes have been found. The aerodynamic forces are proportional to the air density. Elite athletes are able to adapt their flight style to thin air conditions in order to maximise jump length and to keep the flight stable. The effects of flight position variations on the performance have been analysed by means of a computer model which is based on the equations of motion and on wind tunnel data corresponding to the flight positions found in the field. Athletes have to solve extremely difficult optimisation problems within fractions of a second. The computer simulation can be used as a reliable starting point for the improvement of training methods and gives an insight into the "implicit" knowledge of physics that the ski jumping athlete must have available for a good performance.

Air Movements↗
PubMed2006

Is economy of competitive cyclists affected by the anterior-posterior foot position on the pedal?

The primary purpose of this investigation was to test the hypothesis that cycling economy, as measured by rate of oxygen consumption (VO(2)) in healthy, young, competitive cyclists pedaling at a constant workrate, increases (i.e. VO(2) decreases) when the attachment point of the foot to the pedal is moved posteriorly on the foot. The VO(2) of 11 competitive cyclists (age 26.8+/-8.9 years) was evaluated on three separate days with three anterior-posterior attachment points of the foot to the pedal (forward=traditional; rear=cleat halfway between the head of the first metatarsal and the posterior end of the calcaneous; and mid=halfway between the rear and forward positions) on each day. With a randomly selected foot position, VO(2) was measured as each cyclist pedaled at steady state with a cadence of 90 rpm and with a power output corresponding to approximately 90% of their ventilatory threshold (VT) (mean power output 203.3+/-20.8 W). After heart rate returned to baseline, VO(2) was measured again as the subject pedaled with a different anterior-posterior foot position, followed by another rest period and then VO(2) was measured at the final foot position. The key finding of this investigation was that VO(2) was not affected by the anterior-posterior foot position either for the group (p=0.311) or for any individual subject (p>or=0.156). The VO(2) for the group was 2705+/-324, 2696+/-337, and 2747+/-297 ml/min for the forward, mid, and rear foot positions, respectively. The practical implication of these findings is that adjusting the anterior-posterior foot position on the pedal does not affect cycling economy in competitive cyclists pedaling at a steady-state power output eliciting approximately 90% of VT.

Adult↗
PubMedDate not supplied

Two coexisting lines of the endoparasitoid Venturia canescens show differences in reproductive success under conspecific superparasitism.

In a laboratory colony of the endoparasitic wasp Venturia canescens Grav. (Hymenoptera: Ichneumonidae), two genetically distinct lines (RP, RM) appear to coexist sympatrically. The two lines display pronounced differences in ovarian morphology, parasitism behaviour and number of offspring produced under competing superparasitism. Since V. canescens is a solitary endoparasitoid, larvae inside superparasitised hosts must compete for host possession. We examined the outcome of conspecific superparasitism between the wasp lines with different time intervals between ovipositions. The results showed that the competitive abilities of the two lines were not symmetrical. Further, the RM-line won a significantly higher fraction (around 60%) of the overall contests. Dissection of parasitoid larvae from their hosts indicated that most contests between competing larvae had occurred within the first 24 h of the eggs hatching, suggesting the advantage of the RM-line relates to physical combat. It was previously thought that the coexistence of the two lines was exclusively due to maternal effects. The results of this study indicate for the first time that these differences are based on phenotypic variations in both the larval offspring and the mother.

Age Factors↗
PubMed2006

The role of juvenile hormone in competition and cooperation by burying beetles.

Few studies have addressed the physiological mechanisms that modulate aggression in insects. In some social insects, there is a correlation of JH and aggression in colony defense and in the establishment of dominance, but only a few studies demonstrate a causal relationship. Burying beetles aggressively defend a breeding resource, a carcass, and juvenile hormone (JH) hemolymph titers increase rapidly upon the discovery of a carcass. In this study, I show that treatment with the JH analog, methoprene, in the absence of a carcass increases the probability of injuries from aggressive interactions, but treatment to one member of a pair of competing Nicrophorus orbicollis females does not increase the probability that she will win control of the resource. In addition, higher JH levels are not associated with greater competitive ability in communally breeding Nicrophorus tomentosus females. Treatment of one female N. tomentosus does not increase her share of the communal brood. Methoprene seems to make a less competitive female more persistent and less willing to concede, which, although maintaining her share of reproduction, results in her exclusion from the brood chamber.

Aggression↗