Most people have heard that octopuses are smart. But how smart are we talking about, and how did they get that way independent of vertebrates? Cephalopoda, which includes octopuses, squid, cuttlefish, and nautiluses, is highly a specialized and advanced class of invertebrates dating back to the late Cambrian. These animals share the same phylum, Mollusca, with slugs and snails, clams, and other “lower” organisms. So what made them so different? All but the nautilus have completely lost their shells, and in cuttlefish, it is reduced to a small internal structure called the cuttlebone – you know, that thing people give parrots and rodents to chew on as a supplement. This has given the group a ridiculous amount of flexibility (both literally and figuratively) to hunt, explore, manipulate, and perform complex behaviors not seen in other mollusks.
We will explore the reasons behind the development of intelligence and the extent to which we understand it in these amazing animals by looking at the North Pacific giant octopus (Enteroctopus dofleini). This cephalopod, also called the giant Pacific octopus, is the largest of its kind in the world. Only the giant and colossal squid can contend with it in a battle of size. The largest specimens can reach up to 30 feet from arm tip to arm tip and weigh several hundred pounds. Despite its large size, this octopus is generally considered to be a curious, gentle giant. That is, unless you’re a tasty crab. Unfortunately, a long lived octopus will only get to be 5 years old. If an animal has such a short life, why and how is it so intelligent?
Photo Credit: Drew Collins
There are several hypotheses as to the rapid evolution of intelligence in cephalopods. One idea is that coleoids, the taxon that includes all shell-less cephalopods, evolved side by side with teleosts, or bony fish, during the Jurassic. Teleost fish during this period, all of which possessed complex vertebrate behavior, were undergoing rapid diversification and occupying countless environmental niches. In response, the coleoids developed intelligence of their own in order to survive in a quickly changing environment filled with new pressures from these vertebrate predators and prey. These cephalopods had to be able to learn, remember, interpret and predict the behaviors and actions of the bony fish to survive. Their positions within the trophic web (food chain) and their life habits created a demanding existence, making higher cognition a necessity.
Giant Pacific octopuses typically use one den for several weeks at a time in the wild. After a foraging outing, they are able to remember where they are in the environment in relationship to their home, and travel back quickly, often jetting over the sea floor. This shows that they have a sense of self as separate from their surroundings and can understand where they are positioned in space. Cognition like this is typical of vertebrates, but cephalopods are the only group of invertebrates that display this advanced form of spatial navigation and problem solving. Not only are they able to return to a den site with ease after hunting, giant Pacific octopuses will not visit the same foraging area consecutively. Behavior such as this demonstrates that these animals have an awareness of how they themselves have impacted the environment in which they live (removed prey from it) in the past, and modify their hunting strategies accordingly. Thus, the octopuses are able to remember where they were and what took place. The navigational abilities of octopuses are still not well understood, but they do use many tactile cues, such as following the contours of the sea floor to relocate a den. Their excellent vision helps them navigate in clear, shallow waters and allows them to use jet propulsion as a movement option.
It is not surprising that the giant Pacific octopus is able to navigate and live successfully in such a complicated environment when you consider that cephalopods have the largest brain to body ratio of any invertebrate. This ratio is comparable to that of mammals and birds. Octopuses are strange in that their arms are radially symmetrical, yet they have bilateral brains. Half of the arms are controlled by one half of the brain and half are controlled by the other. Because of this, octopuses often display “handedness” like humans do. The front pair of tentacles is the pair mainly used for manipulation of objects and the environment, and octopuses can show favoritism towards the left or right tentacle, depending on the individual. Three fifths of the octopus nervous system is concentrated in these arms. The arm and sucker control is highly complex and very precise, allowing possibly the widest range of motion seen in any animal. Such freedom of motion allows these cephalopods to explore their environment in ways that other species would not be capable of. With this exploration comes lots of learning.
Exploration through sight and touch is everything to an octopus. When something novel is presented, such as a new environment, it will proceed to gather as much information as it can through these senses, building a mental map and gaining an understanding of how things work. As familiarity is established, the octopus’ exploratory behavior will decline, and more time will be spent resting and hiding, suggesting that the animal remembers what it learned and has no need for continued exploration. This is seen often in tanks when an octopus is brought in from the wild or a different aquarium. After the territory and sense of safety is established, the octopus has a tendency to display very play-like behavior when given a novel object. One such study, performed at Washington’s very own Seattle Aquarium, presented eight giant Pacific octopuses with a toy (an empty pill bottle with a float in it) and observed their behavior over ten trials. Two of the octopuses took the bottle with a stretched out arm and held it in place before jetting water to make it float to the other side of the tank. They waited until the slow current returned the bottle to them and then repeated the process over 20 times. Other studies with the common octopus (Octopus vulgaris) also described play behavior. When given a choice of clam prey, empty shells, and plastic blocks, the octopuses ignored the shells, ate the clams, and often manipulated the blocks for quite some time. They were seen passing a single block from arm to arm, pulling it around with them when they moved, and bringing it back and forth from the center of their bodies. Octopuses are solitary and do not need to play to learn about their place in a social group, and the play-behavior displayed is not restricted to a specific environment as it would be in a vertebrate (like the safety of a family group). Also unlike vertebrates, play occurs equally throughout the lifespan, though it is infrequent.
Ramsey the octopus from Plymouth’s National Marine Aquarium with a soccer ball
Wild and captive giant Pacific octopuses are also capable of human recognition, among their many other astounding abilities. Another study done at the Seattle Aquarium collected eight octopuses from Neah Bay in Washington and Seaside, Oregon. The animals were transported to the Seattle Aquarium and placed in separate tanks. Three researchers, dressed identically, interacted with the octopuses over ten days with a two day break in the middle. The interactions were done in a non-predictable order. One tester fed the octopus while the other “mildly irritated” it by gently touching it with a bristly stick for 30 seconds. A range of behaviors from these interactions was catalogued. At the end of the experimentation period, each researcher looked into the octopuses’ tanks and recorded their reactions. The order of researchers was reversed for each octopus and presentations were ten minutes apart. When the irritator appeared, octopuses overwhelmingly reacted with responses consistent with their irritation trials, such as displaying a dark Eyebar or jetting water at the observer. Likewise, the octopuses’ behavior toward feeders reflected that of the feeding trials. This just adds to the already impressive array of cognitive abilities in these amazing animals.
Eyebar on Octopus vulgaris. Photo Credit: Lawrence Tulissi
If I haven’t already convinced you that giant Pacific octopuses and other cephalopods are fascinating creatures, then you have no sense of wonder and should reevaluate your life. To top everything off, here is one more thing to impress you. I could list more, but then I would be writing this article forever!
Octopuses have personalities too! Yet another study conducted at the Seattle Aquarium demonstrated that giant Pacific octopuses vary across three dimensions: Activity, Reactivity, and Avoidance. For comparison, the standard temperament dimensions established for humans are Activity, Emotionality, and Sociability. As mentioned before, octopuses are solitary animals, so it is not realistic to measure variance in the Sociability or Emotionality dimensions. Because of this, the researchers designated Reactivity and Avoidance as the analogues. The results from the study showed that variance in octopus behavior accounted for by these three dimensions was 45%. To give you an idea of how amazing this is, compare that to 43% of the individual variance explained by Sanson et al.’s nine factors for human babies. In addition, much of this variance was across the Approach and Activity dimensions. It is not known why octopuses display so much difference between individuals, but it may again be due to their ever changing and demanding environments and evolutionary competition with teleost fish. There are many adaptive reasons for this variance and octopuses are highly intelligent, learning animals that are shaped by life experiences. It is no wonder that each octopus has its own way of behaving and thinking about the world.
Cephalopods like the giant Pacific octopus can teach us so much about the minds of invertebrate animals and the heights to which intelligence can rise. We really know very little about how other animals perceive the world and solve the problems that they are faced with throughout their lives. Learning about cephalopods opens a door to other mollusks and in turn other invertebrates. Intelligence is something that fascinates us because we consider it to be a key factor of what makes us “different” from other animals. Animals such as the giant Pacific octopus may make us question what really sets us apart as we discover more about them.
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