Boldness and asymmetric contests: role- and outcome-dependent effects of fighting in hermit crabs

Consistent between-individual differences in behavior have been demonstrated in an array of species from diverse taxa, and variation in boldness may be associated with variation in aggressiveness. However, little is known about how boldness is linked with the ability to win fights (resource holding potential) or about how the experience of fighting may alter subsequent boldness. Animal contests often involve role asymmetries, where the 2 opponents fight in different ways. Here, we investigate boldness before and after fighting in attacking and defending hermit crabs during contests over the ownership of gastropod shells. Although prefight boldness did not influence the chance of winning for attackers, successful defenders had longer startle responses (less bold) than those that gave up. Postfight changes in boldness also differed between roles. For defenders, there was a significant decline in consistency of startle responses after fighting, coupled with outcome-dependent plasticity in mean boldness. Furthermore, postfight boldness in defenders varied with the intensity of agonistic behavior inflicted on them by attackers. In contrast, boldness in attackers was stable across the before- and after-fighting situations. Links between internal state and agonistic behavior are known to vary between roles in asymmetric contests. It now appears that similar role-specific links are present between aggression and animal personality.