Most species of shallow water octopuses appear to be pretty solitary animals. They live in dens and venture out from them to hunt or find mates; defending these dens and getting busy are the only social interaction that many species of octopuses are observed to have in the wild. I like to think of them as the curmudgeons of the reef environment, keeping to themselves because that’s just the way they like it.
It might surprise us, then, to learn that Elena Tricarico and her coworkers, working out of the Stazione Zoologica in Naples, just published a paper arguing the octopuses (of the species Octopus vulgaris), can recognize other individual octopuses. While it’s clear that this ability might be important to more social cephalopods (like squids, which form schools), what good could it do for a species with such a hermit-like existence?
It turns out that keeping to one’s self in an area where there are lots of other organisms around requires some social skills – you have to know a little about the folks around you and what behavior to expect from them. For example, if you see the same animal patrolling an adjacent territory each day, it doesn’t do much good to make a huge fuss over it all the time. If you have your territory, and she has hers, it behooves you both to be able to recognize each other so that you don’t waste time and energy chasing off somebody who isn’t actually going to cause you any problems (this is called the “dear enemy” effect.) On the other hand, if a wandering octopus comes through looking for a good nesting site, it would be useful to be able to tell that he’s a stranger so that you could drive him away and keep him from taking over your territory. Thinking about it in these terms, it makes sense that the ability to recognize other octopuses could be a useful ability to have.
To test whether octopuses could do this, Tricarico and coworkers divided up their experimental octopuses into two groups; in one group, pairs of octopuses were housed with a clear divider between them, so that they could see their partner, while in the other group the octopuses had an opaque divider. After letting the octopuses either see or not see each other for 3 days, they watched how these pairs interacted with each other when they were put into the same test tank for 15 minutes. It turns out that pairs that had seen each other before avoided each other more, touched each other less, and spent a longer time ignoring each other when they were placed in the same tank than pairs that had been separated by the opaque divider.
This alone isn’t enough evidence to conclude that octopuses can recognize other individual octopuses – after all, the pairs that could see each other might just be getting used to being around any octopus. To test whether the octopuses had learned to recognize their specific partner or just gotten used to the presence of other octopuses, the researchers did one more test – they put the octopuses back in the test tank, but this time, they put some of them in with the familiar octopus they had been seeing throughout the experiment, and some of them in with an octopus they had never seen before. What they saw was this: when octopuses were placed with another octopus that they were familiar with, they touched each other less, avoided each other more, and their interactions were shorter than when they were placed with unfamiliar octopuses. It looked as if the octopuses had learned to recognize their partner, and responded differently to them than to a strange octopus.
Like all good experiments, this one begs plenty of questions: can octopuses tell who individuals are, or do they just categorize other octopuses as familiar or unfamiliar? Does their ability to discriminate other individuals imply some sort of social cognition, and of what sort (I’d argue that it suggests only very basic social cognitive skills, but opens the door for more investigation,) and, finally, do I need to worry that someday, the octopuses will learn to recognize ME?
Thanks for reading! I’d like to point out that I took the title of this post directly from the paper it discusses; it was such a good title that I couldn’t think of anything more fitting.
Elena Tricarico, Luciana Borrelli, Francesca Gherardi, Graziano Fiorito (2011). I Know My Neighbour: Individual Recognition in Octopus vulgaris PLOS One : 10.1371/journal.pone.0018710