The logical polyp: assessments and decisions during contests in the beadlet anemone Actinia equina

Abstract

Contest behavior, where individuals compete directly against one another for access to limited resources, is widespread across animal taxa. In many cases, contests are settled though the use of noninjurious behavior such as agonistic signals and even fights that involve weapons are often resolved through processes of assessment and strategic decision making. Here, we determine the role of these “decision rules” during staged contests in a simple animal, the beadlet sea anemone Actinia equina using a recently suggested approach of analyzing 1) traits linked to resource holding potential (RHP), 2) relationships between RHP and contest duration, and 3) contest dynamics. Depending on the activities used in the encounter, RHP, is linked to overall body size, the size of stinging nematocyst weapons, or by the ability to land blows on the opponent. Furthermore, changes in the intensity of aggression as the contest progresses indicate the use of 2 distinct types of self-assessment-based decision rules, which differ according to whether weapons are used in the contest. Therefore, these fights in animals that lack a centralized nervous system appear to involve the use of logical decision rules similar to those observed in contests in animals that are often assumed to be more “complex” in their behavior. Indeed, anemones appear to use different sources of information about incurred costs, depending on the intensity of the contest.