When one octopus meets another octopus, the leggy animal remembers the acquaintance for at least a day, a new study indicates.
Recognizing a fellow member of your species is called individual recognition. Mammals, like humans, birds and even fish, are capable of what is known as true individual recognition in which we not only know we've met this other individual, we also recognize this individual by associating specific traits with him or her.
It also appears that some invertebrates, animals without backbones, including wasps and crabs, are capable of a degree of individual recognition. Now octopuses have joined this club. [Watch an octopus meet its neigbhor]
Clever cephalopods
A study that paired 48 octopuses has shown they are capable of a less-specific form of individual recognition. They know if another octopus is familiar or unfamiliar. To figure if the animals actually recognize the other individual, scientists would first need to know what cues, such as color or scent, the octopuses are using, and those remain unknown, according to Elena Tricarico, the lead researcher and a postdoctoral researcher at the Universita` degli Studi di Firenze in Italy.
One thing is clear: Octopuses are smart. They can learn tricks, like opening a jar, by observing other octopuses, and they have individual personalities. Tricarico's octopuses became so familiar with their feeding schedule that when she arrives in the morning, they "ask" for food by stretching arms up to the surface of the water toward her.
Most octopuses are considered asocial, solitary animals; however, there are some clues indicating they may be capable of individual recognition: They communicate with one another using color patterns on their bodies, and, even though they are territorial, octopuses occupying neighboring dens co-exist relatively peacefully, suggesting they can recognize their neighbors and do not see them as threats.
Avoiding your partner
When octopuses first encounter one another, they touch each other with their suction-cup covered arms. But after getting acquainted, they prefer to stay away; the researchers used these behaviors to tell if the animals recognized each other.
The researchers kept the pairs of octopuses in tanks designed so some pairs could see each other while others had their view blocked. (Octopuses have well-developed eyes.) The pairs were later placed together and allowed to interact for 15 minutes each day for three days. On the fourth day, half of the pairs were swapped so they received new partners. (The other half kept the same partners.) Their interactions were observed again for 15 minutes.
Overall, they found that octopuses that had seen or encountered each other for at least a day earlier avoided one another. And those meeting for the first time touched more often. The unfamiliar octopuses were also more likely to shoot ink, a sign they felt threatened, she said.
It's still not entirely clear how the octopuses recognized each other. Although sight appears to play a part, smell or even touch could also be important, she said.
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