Assessment strategy and the evolution of fighting behaviour.

Zoology Department, Liverpool University, Liverpool, L69 3BX, England
Journal of Theoretical Biology (Impact Factor: 2.3). 10/1974; 47(1):223-43. DOI: 10.1016/0022-5193(74)90111-8
Source: PubMed

ABSTRACT The view is examined that the adaptive value of conventional aspects of fighting behaviour is for assessment of relative RHP (resource holding power) of the combatants. Outcomes of aggressive disputes should be decided by each individual's fitness budget available for expenditure during a fight (determined by the fitness difference between adoption of alternative strategies, escalation or withdrawal without escalation) and on the rate of expenditure of the fitness budget if escalation occurs (determined by the RHPs of the combatants). Thus response thresholds for alternative strategies (“assessments”) will be determined by natural selection on a basis of which opponent is likely to expend its fitness budget first, should escalation occur. This “loser” should retreat (before escalation) and the winner should stay in possession of the resource. Many aggressive decisions depend on whether one is a resource holder, or an attacker. Assuming the RHP of the combatants to be equal, there are many instances of fitness pay-off imbalances between holder and attacker which should weight the dispute outcome in favour of one or other opponent by allowing it a greater expendable fitness budget. Usually the weighting favours the holder; the attacker therefore needs a correspondingly higher RHP before it may be expected to win. This is not invariably the case, and much observed data fits the predictions of this sort of model. If assessments are perfect and budget expenditure rates exactly predictable, then there would never seem to be any case for escalation. Escalation can be explained in terms of injury inflictions (expenditures) occurring as discrete events; i.e. as “bouts” won or lost during fighting. Assessment can give only a probabilistic prediction of the outcome of a bout. A simple model is developed to investigate escalation situations. Each combatant assesses relative RHP; this correlates with an absolute probability of winning the next bout (cabs). The stake played for is infliction of loss of RHP and is determined by the fitness budgets of the opponents. (Each individual plays for the withdrawal of its opponent.) This defines a critical probability of winning (ccrit) for each combatant, above which escalation is the favourable strategy (cabs > ccrit) and below which withdrawal is favourable (cabs < ccrit). Escalation should occur only where cabs-ccrit is positive for both combatants. This model gives predictions compatible with the observations, indicating that RHP loss alone can be adequate to explain withdrawal: escalation behaviour. Withdrawal tendency will be increased by low searching costs. Escalations should be restricted to closely matched RHP opponents if RHP disparity is the major imbalance. Outside the “escalation range” of a given individual, the higher RHP individual wins and the lower one loses (i.e. it should withdraw after conventional display). RHP disparity and holder: attacker imbalance should both interact to shape the observed pattern, though their relative importances will depend on species and situation. In some instances selection may favour immediate withdrawal from an occupied territory even without assessment of RHP.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In several animal species, aggressive experience influences the characteristics and outcomes of subsequent conflicts, such that winners are more likely to win again (the winner effect) and losers more likely to lose again (the loser effect). We tested the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae), as a model system to evaluate the role of the winner and loser effects in male-male territorial contests. Further, we conducted experiments to test if winning and losing probabilities are affected only by the outcome of the previous contests, or whether the fighting experience itself is sufficient to induce an effect. Both winners and losers of two consecutive encounters displayed higher intensity of aggression and fought longer in subsequent contests. In both cases, they achieved higher fighting success than naïve males. The enhanced fighting performance of both winners and losers was stimulated by merely experiencing a contest, not necessarily by the relative outcome of previous fights. Overall, this study highlights the fact that previous victories and defeats both enhance aggressive behaviour in olive fruit flies, allowing them to achieve higher fighting success in subsequent contests against inexperienced males.
    Scientific Reports 03/2015; 5. DOI:10.1038/srep09347 · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: During agonistic interactions, decisions about contest persistence can be informed by assessment of one's own energy or time expenditure (self-assessment), one's own expenditure combined with opponent inflicted costs (cumulative assessment), or through information exchange with an opponent (mutual assessment). Females and males can be expected to exhibit different strategies for contest resolution due to contrasting energetic requirements and resource valuation. We examined the assessment strategies crayfish employ during same-sex and mixed-sex fights. Two individuals interacted for 15 min, and fight duration and times spent at various intensity levels were quantified. Results indicated that both sexes employ a self-assessment strategy during same-sex fights. Evidence for assessment during mixed-sex fights was notably weaker, suggesting the resolution of mixed-sex fights involves different behavioural elements and/or sources of information. In species where mixed-sex fights are common year-round, the lack of common rules can lead to greater energy expenditure for both sexes.
    Behaviour 02/2015; 152(5). DOI:10.1163/1568539X-00003265 · 1.40 Impact Factor
  • Behaviour 07/2010; 147(8):979-992. DOI:10.1163/000579510X499434 · 1.40 Impact Factor

Full-text (2 Sources)

Available from
Sep 10, 2014