Fighting ability, decision rules and animal personalities in beadlet anemone (Actinia equina) contests

When competing for resources such as food, space or mates, animals often engage in intraspecific contests. Contestants may have the ability to gather and assess information about their own fighting ability (resource holding potential or RHP) or that of their opponent and there are several game-theoretical assessment models that describe the decision rules during contests. RHP may be influenced by a number of factors such as body size or mass, weaponry, experience or energetic reserves. The sedentary cnidarian Actinia equina (L.) uses specialised tentacles called acrorhagi, which contain nematocysts capable of inducing necrosis, to attack intruding conspecific competitors for space by inflicting acrorhagial peels on them. In this study I investigated the effects of body size (dry weight), weapon size (nematocyst length) and the number of peels inflicted on the outcome and duration of staged, pairwise encounters in A. equina. Additionally, contest dynamics were assessed. These results were used to evaluate three main types of assessment models: self-assessment, cumulative assessment and mutual assessment. In a second experiment I investigated whether A. equina exhibits consistent behavioural between-individual differences across time and/or situations (often termed ‘personalities’) and whether these differences affect contest success by examining startle responses. My results show that different factors influence RHP depending on whether or not attacks occurred during contests: dry weight when neither individual inflicted acrorhagial peels, nematocyst length when only one individual inflicted peels and the number of peels inflicted when both individuals inflicted peels. Contests shared certain features of the cumulative assessment model, regardless of the occurrence of acrorhagial peels. Additionally, support for the presence of consistent behavioural differences (and therefore ‘personalities’) in A. equina was found but these differences did not seem to influence RHP. This study represents the first attempt at investigating the decision rules underlying contests in sedentary animals and I suggest that the differences in the factors that influence RHP may be a feature of other contests that involve injuriesFaculty of Science & Technolog