Can cuttlefish learn by observing others?

Observational learning is the ability to learn through observing others' behavior. The benefit of observational learning is apparent in that individuals can save time and energy without trial-and-error, thus enhance the chance of survival and reproduction. Cephalopods (octopus, squid, and cuttlefish) have the most sophisticated central nervous system among invertebrates, and it is conceivable that cephalopods can develop some forms of cognition. Although it has been suggested that octopuses have the capacity of observational learning, a previous study indicates that cuttlefish do not improve their predation tactics by observing conspecifics. Given that the danger avoidance is important for animals' survival, we sought to reevaluate whether cuttlefish show some form of observational learning or observational conditioning under threatening conditions. Cuttlefish (Sepia pharaonis) were divided into three groups: the Experiencer group, the Observer group, and the Control group. In the training phase, a toy submarine was remotely controlled to expel the cuttlefish from its initially preferred place to establish the threat-place association in the Experiencer group. In the Observer group, the threat-place association was established by expelling a conspecific demonstrator at the observer's initially preferred place while the observer watched the whole process from behind a transparent divider. In the Control group, the observer watched a conspecific and a static toy submarine without actual threat. In the testing phase, the choice of safe place in the absence of threat was used to probe the learning/conditioning of cuttlefish. In the Experiencer group, we found that animals chose the safe place more often than their initially preferred place after training, an indication of the association learning/conditioning. However, in the Observer group, only a subset of animals showed this threat-place association by observation, while the place preference was unchanged in the Control group. These results indicate that most cuttlefish did not learn by observing others, but individual differences exist, and some cuttlefish may have the potential of observational learning/conditioning within their cognitive capacities.