Unruly octopuses are the rule: Octopus vulgaris use multiple and individually variable strategies in an episodic-like memory task

The evolution of complex cognition can be explained by different hypotheses, mutually non-exclusive: the social intelligence hypothesis, the ecological intelligence hypothesis and the predator-prey interaction hypothesis. Episodic-like memory can be used as a proxy to study complex cognition. This ability has mainly been studied through experimental tasks where subjects have to remember what they ate, where and when or in which context. Seemingly quite common in mammals and corvids, episodic-like memory abilities have been observed in only one invertebrate species: the common cuttlefish, a cephalopod mollusc. To explore if this ability is common to all cephalopods or if it has emerged to face specific constraints, we conducted an episodic-like memory task with seven Octopus vulgaris. Only one individual learnt the replenishing rates during the training and subsequently showed episodic-like memory abilities, whereas the other individuals favoured simpler foraging strategies, such as avoidance of familiarity and alternation, use of win-stay strategy and risk-sensitivity. A high variability in the use of these strategies was observed between and within individuals throughout the training. Since octopuses seem to live under lighter environmental pressure than cuttlefish, they may not need to rely on episodic-like memory abilities to optimize foraging as cuttlefish do. These results highlight the differences in the use of complex cognitive abilities between cuttlefish and octopuses, which might be linked with different environmental, predatory and social constraints. Summary statementWhen trained in an episodic-like memory task, common octopuses favour individually variable foraging strategies rather than keeping track of time to solve the task as cuttlefish do.