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Skilful fighting encompasses an individual's ability not only to perform agonistic behaviours accurately and efficiently, but also to choose the most appropriate behaviour or tactic from its repertoire based on the information available. The efficacy of different tactics may depend both on the behaviour of the opponent and on the individual's internal state, for example a specific behaviour may become less effective over time as fatigue sets in. Furthermore, because fights are dynamic interactions, the ability to choose the appropriate tactic will require rapid information processing and may thus be constrained by an individual's cognitive ability. Here, we conducted a three-phase experiment to investigate the effects of reduced performance capacity induced by exposure to hypoxia and decision-making speed on skilful fighting in the European hermit crab, Pagurus bernhardus. During fights attackers attempt to elicit an eviction either by rapping on the defender's shell or by rocking the defender's shell back and forth. By analysing the effect of exposure to hypoxia and decision-making speed on the relative use of these tactics, we show that contrary to our prediction, neither performance capacity nor decision-making speed alone predicted the type of behaviour performed. Rather, these two traits interacted to determine the amount of effort (raps and rocks) attackers needed to exert to elicit an eviction. Furthermore, we show that while neither performance capacity nor decision-making speed predicted skill when fights were analysed as a whole, the effects of these variables became apparent when analysing the change in accuracy as fights progressed, likely due to the accumulating effects of fatigue. • The performance of agonistic behaviours varies in terms of vigour and skill. • Vigour is linked to energetic status, but the underpinnings of skill are unknown. • We explore the effects of performance capacity and decision-making speed on skill. • We measure two aspects of skill, accuracy and appropriateness (choice of tactics). • We find that performance capacity and decision-making speed impact skill over time. [ABSTRACT FROM AUTHOR]

Understanding the determinants of fighting ability (or resource-holding potential, RHP) is key to elucidating the evolution of aggressive behaviour, as current tests of contest theory rely on realistic proxies for overall RHP. Traditionally, RHP is considered equivalent to body size but it is increasingly clear that a wider range of morphological and physiological traits contribute to fighting ability. In situations analogous to contests, such as courtship displays in animals and competitive sport in humans, the role of skill has long been appreciated but this component has been neglected in analyses of animal fights. Here, we investigated two spatial components of skill, accuracy and precision, during shell fights in hermit crabs, where an attacker repeatedly strikes (raps) its shell against that of a defender. By analysing the points of impact of these strikes, we found that attackers that rapped with coarse-scale accuracy were more likely to win the fight, indicating that the ability to target a 'sweet spot' on the defender's shell is an important determinant of contest success. Furthermore, we found that this element of skill correlated with temporal performance (vigour). Taken together these results show that spatial skill is an RHP component. Moreover, in contrast to the traditional assumption that fighting ability is equivalent to body size, RHP is actually underpinned by a suite of interlinked traits including performance capacities, morphology and skill. • Fighting often involves the repeated performance of agonistic behaviours. • Individuals may vary in how skilfully they perform such behaviours. • We investigate the link between spatial skill and fighting success in hermit crabs. • We find that winners perform rapping behaviour more skilfully than losers. • Our results indicate that skill is tightly correlated with other fighting traits. [ABSTRACT FROM AUTHOR]