Octopuses are intriguing creatures expressing what appear to be emotions and reactions to their environment with eye catching colour changes. However, finding out how these cephalopods respond to their environment is easier said than done. Movies of animals would seem to offer the best alternative for studying an individual's behaviour, as they are controllable (you can repeatedly show the same behaviour to many animals and track their responses) and they move realistically, unlike pictures, which are static and unrealistic. However octopus vision is relatively sophisticated, so previous attempts to get the cephalopods to interact with movies failed, probably because the TV images were not realistic enough for the animals on old-fashioned TVs. Renata Pronk and her colleagues from Macquarie University, Australia, realised that the recent development of liquid crystal high definition television (HDTV) could overcome this problem, so they decided to test out the gloomy octopus's reactions to HDTV (p. 1035).

Teaming up with David Wilson to build a high definition video system where she could fine-tune the quality of the movies, Pronk filmed a tasty crab, another gloomy octopus and an intriguing jar ready to play the movies to other gloomy octopuses in an aquarium. Collecting wild octopuses from Sydney Harbour, Pronk and Robert Harcourt returned to the Sydney Institute of Marine Science to show the videos to the animals, but at first the animals didn't respond. Refilming the images at 50 frames s−1 and programming the system to refresh every line on the screen simultaneously – to maintain smooth edges on the moving images – Pronk replayed a movie of a crab walking to an octopus and waited to see whether it would react.

Amazingly it did. ‘The octopus jetted towards the screen and tried to catch the crab and eat it. I thought, this is great, I've finally gotten the reaction I was hoping for!’ says Pronk.

Having succeeded in finding movies that were convincing enough that the octopuses recognised the images and reacted, Pronk decided to find out whether the animals could be said to have a personality. ‘Personality can be defined as behavioural differences between individuals that are consistent over time and across ecologically important contexts,’ explains Pronk. So would a shy octopus always be a wallflower and aggressive animals remain assertive?

Showing the octopuses a movie of a crab on one day to see if the animal would try to catch it and repeating the show on several occasions over a period of days, Pronk found that the octopuses' responses were consistent on a particular day. However, reshowing the movies some time later often produced different reactions. For example, an octopus would be very excited on one day, but less enthusiastic on another occasion. And when she tried to get the animals riled up with movies of another octopus or pique their interest with an object that they hadn't seen before (the jar) octopuses that responded eagerly one day were equally as likely to show little or no interest the next.

The octopuses seemed to demonstrate personalities, but they were not consistent over a period of time. ‘We term this “episodic personality” because over the course of the experiment their personality traits would change in response to the same stimuli,’ says Pronk.

Having succeeded in convincing octopuses to respond to movies and found that their personalities vary over time, Pronk is keen to find out more about other octopus behaviours, including their communication, learning and social interactions, using her octopus-convincing movie system.

D. R.
Video playback demonstrates episodic personality in the gloomy octopus
J. Exp. Biol.