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

Abstract

Episodic-like memory has mainly been studied through experimental tasks in which subjects have to remember what they ate, where and when or in which context. Seemingly quite common in mammals and corvids, episodic-like memory ability has also been demonstrated in the common cuttlefish, a cephalopod mollusc. To explore whether this ability is common to all cephalopods or whether it has emerged to face specific ecological constraints, we conducted an episodic-like memory task with seven Octopus vulgaris. Only one individual learnt the replenishing rates during training and subsequently showed episodic-like memory ability, whereas the other individuals favoured simpler foraging strategies, such as avoidance of familiarity and alternation, use of a win-stay strategy and risk sensitivity. A high variability in the use of these strategies was observed between and within individuals throughout training. As octopuses seem to live under lighter environmental pressure than cuttlefish, they may not need to rely on episodic-like memory ability 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 to different environmental and predatory constraints.