Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework

• Published in: Animal behaviour Vol. 108; pp. 183 - 191
• Main Authors: Camerlink, Irene, Turner, Simon P., Farish, Marianne, Arnott, Gareth
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.10.2015; Harcourt Brace Jovanovich Ltd
• Subjects: aggression; Animal behavior; assessment; contest; Game theory; Hogs; personality; Physiology; pig; resource-holding potential; Sus scrofa; assessment; contest; aggression; personality; resource-holding potential; pig
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2015.07.032

Understanding animal contests has benefited greatly from employing the concept of fighting ability, termed resource-holding potential (RHP), with body size/weight typically used as a proxy. However, victory does not always go to the larger/heavier contestant and the existing RHP approach thereby fails to accurately predict contest outcome. Aggressiveness, typically studied as a personality trait, might explain part of this discrepancy. We investigated whether aggressiveness forms a component of RHP, examining effects on contest outcome, duration and phases, plus physiological measures of costs (lactate and glucose). Furthermore, using the correct theoretical framework, we provide the first study to investigate whether individuals gather and use information on aggressiveness as part of an assessment strategy. Pigs, Sus scrofa, were assessed for aggressiveness in resident–intruder tests whereby attack latency reflects aggressiveness. Contests were then staged between size-matched animals diverging in aggressiveness. Individuals with a short attack latency in the resident–intruder test almost always initiated the first bite and fight in the subsequent contest. However, aggressiveness had no direct effect on contest outcome, whereas bite initiation did lead to winning in contests without an escalated fight. This indirect effect suggests that aggressiveness is not a component of RHP, but rather reflects a signal of intent. Winner and loser aggressiveness did not affect contest duration or its separate phases, suggesting aggressiveness is not part of an assessment strategy. A greater asymmetry in aggressiveness prolonged contest duration and the duration of displaying, which is in a direction contrary to assessment models based on morphological traits. Blood lactate and glucose increased with contest duration and peaked during escalated fights, highlighting the utility of physiological measures as proxies for fight cost. Integrating personality traits into the study of contest behaviour, as illustrated here, will enhance our understanding of the subtleties of agonistic interactions. •The personality trait aggressiveness was studied as a component of fighting ability.•Between size-matched pigs more aggressive individuals were not more likely to win.•Aggressiveness did not affect fighting ability but did alter contest behaviour.•Aggressiveness may form an honest signal of intent but dishonest signal of ability.•There was no evidence that aggressiveness was part of an assessment strategy.