Shelled shut-ins: A conditional escape task demonstrates perceptual awareness in hermit crabs

Sentience is an increasingly popular topic in animal welfare and behaviour research. However, studying sentience can be difficult and contentious. As sentience has frequently been associated with ‘feelings’ and ‘subjective states’ not directly accessible to human observers, an alternative approach is to investigate awareness in animals. Frameworks of awareness have been developed for experimental examination of cognitive capacities that might underpin ‘feelings’, both as affective states and subjective experiences. Using a framework of four hierarchically arranged levels of awareness (i.e., perceptual, cognitive, assessment, and executive), we assess awareness of an intertidal crustacean, the common hermit crab Pagurus bernhardus. Inspired by recent work on cognitive abilities and task-solving in terrestrial hermit crabs, we designed a series of four experiments to test the ability of P. bernhardus to solve a simple conditional task: if the crab changes its shell, then it can escape confinement. Crabs were exposed to different levels of confinement, including complete confinement, confinement requiring shell changes for escape, confinement requiring no shell changes for escape, and no confinement. In addition to testing crabs in the absence of external motivation (Experiment 1), to ensure that individuals were motivated to escape, we tested crab responses in the presence of food (Experiment 2), an additional shell (Experiment 3), and under hypoxic conditions (Experiment 4). Crabs were more likely to escape confinement if they did not have to change shells. Sequence analysis of the behaviour patterns of crabs suggests that they are not tactically assessing different components of their confinement to aid in task solving. Combined, these experiments suggest that P. bernhardus displays perceptual awareness without evidence of insight or forward planning.