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Octopuses make for discerning TV viewers: it seems they prefer high-definition to traditional cathode ray images (CRT). What鈥檚 more, the first study using video to trick octopuses, finds that they may be the Jekyll and Hydes of the oceans: aggressive one day, shrinking violets the next.

鈥淧eople have been trying for over a decade to get proper behavioural responses from octopuses and other cephalopods using videos,鈥� says , an octopus researcher at the Marine Resources Center, Woods Hole, Massachusetts, who was not involved in the study. 鈥淏ut this is the first time anyone has managed it.鈥�

Gloomy octopuses (Octopus tetricus) reacted to films shown on liquid crystal high definition television (HDTV) as if they were seeing the real thing, according to a new study by Renata Pronk at Macquarie University in Sydney, Australia, and colleagues. 鈥淭hey lunge forwards to attack crabs and back off from other octopuses, much as they do in the wild,鈥� says Hanlon.

Surprisingly, an octopus that was bold, aggressive and exploratory on one day was just as likely to be shy, submissive and stationary the next. 鈥淭his suggests that the gloomy octopus does not have personality,鈥� writes Pronk in the new study.

No personality

By 鈥減ersonality鈥�, researchers mean consistency in behaviour. You might expect an individual to respond to crabs, other octopuses, jars, for example, by being consistently bold, shy or aggressive.

In contrast, the octopuses in Pronk鈥檚 study were more moody than gloomy. The team captured 31 gloomy octopuses in Sydney harbour and showed them a set of 3-minute videos displayed on a screen at the front of their tank. The videos were filmed at 50 frames per second and featured a crab (their prey), another gloomy octopus, a jar and a water-filled aquarium.

Previous attempts to get octopuses to respond to videos failed, probably because they used CRT, which displays footage at a rate of 24 frames per second 鈥� too slowly for their sophisticated eyes. 鈥淭he images that they see on CRT screens are incomplete and probably incoherent,鈥� says Hanlon.

To Pronk鈥檚 surprise, the octopuses behaved as if animals in the film were real. They lunged forwards at crabs using jet propulsion, often striking the front of the aquarium. But when they saw films of other octopuses, which they avoid in the wild, they cowered behind a terracotta pot placed in the aquarium.

Octopuses that reacted to one film aggressively tended to respond to all films on a particular day in the same way. But over longer periods of time, any trace of 鈥減ersonality鈥� or consistency evaporated. They might react aggressively one day, but much less so on another day. 鈥淚t鈥檚 a bit of a surprise,鈥� says Hanlon. Other cephalopods, such as the dumpling squid, display consistent personalities for most of their lives.

Huge brains

This lack of consistent behaviour may be related to octopuses鈥檚 huge brain size, relative to other cephalopods. Big brains may 鈥渁fford octopuses considerable behavioural flexibility that allows them to change their behaviour adaptively over time,鈥� write the researchers.

Lack of personality may not necessarily be a bad thing. They live in dynamic environments (shallow coastal waters and reefs) and 鈥渢hese conditions may select for behavioural flexibility as individuals could then optimise their behaviour in a variety of typical environmental conditions鈥�. For example, behaving shyly may be an octopus鈥檚 best response when it is threatened by a predator, but behaving boldly may be the best behaviour when foraging.

Hormones may drive short-term changes in the octopuses鈥� behaviour from day to day, the authors also speculate.

The new video technology used in the experiment could help to settle several long-standing debates, says Hanlon. 鈥淔or example, scientists have debated since 1992 whether or not an octopus can learn behaviours simply by watching each other,鈥� he says. 鈥淭his technology will open many doors.鈥�

Journal reference: , DOI: 10.1242/jeb.040675