Signs of Fall 13: Octopuses Lead the Way!

Common octopus. Photo by A. Kok. Wikimedia Commons

(Click on the following link to listen to an audio version of this blog … Octopuses lead the way

Octopuses (Phylum Mollusca, Class Cephalopoda) are acknowledged to be extremely intelligent. Intelligence in animals is measured in many ways, but high on the list of criteria for a high powered brain is the ability to escape from enclosures and entrapments, the ability to solve problems and puzzles, the ability to find food and avoid being someone else’s food, and the ability to learn and remember. In all of these categories, octopuses score extremely high on animal intelligence scales. Many lists of “most  intelligent animals” put octopuses among the ten most intelligent animals in all of Nature! They are more intelligent than dogs or cats, but slightly less intelligent than chimpanzees, orangutans, elephants or dolphins! They are, without question, the most intelligent, invertebrate organisms in existence!

Octopuses are active predators that live in marine habitats that are loaded both with complex places for potential prey to hide and also an abundance of other, often larger, predators that would love to dine on some fresh octopus! The evolution of the octopus’ intelligence has undoubtedly been linked to its ability to find food and to avoid becoming food for someone else. Further, the evolution of their remarkable brains has followed very independent and very different pathways from the evolution of mammalian brains.

AI octopus. Photo by M. Ong Public Domain

For example, in mammals the brain is a single organ well stuffed with highly interconnected neurons. In octopuses, there is one central brain but also eight auxiliary brains that are each associated with one of the octopus’s tentacles. Muscular control of the tentacles is independently accomplished by these “auxiliary” brains while sensory analysis, memory, learning, homeostasis and overall body control  is a function of the larger, central brain.

On average, octopuses have a total of 500 million neurons in their nine brains. This is about the same number of neurons that are found in the brain of a dog (humans, just for comparison, have 100 billion highly interconnected neurons in their brains (200 times more neurons that the average octopus or average dog)!). About two-thirds of the octopus neurons are in the central brain while the rest are divided up between their auxiliary, tentacular brains.

There is, though, another feature of brain neurons that is remarkably well developed in octopuses: the types and sophistications of the cell surface proteins that functionally knit the brain’s neurons together! The genes that encode for these vital, cell surface proteins are called the “protocadherin” genes. In mammals, 70 of these protocadherin genes have been identified and 53 of these are found in humans. In a typical invertebrate there are only 16 or 17 of these protocadherin genes. In octopuses, though, there are 168 protocadherin genes! The neurons in each of an octopus’s nine brains are knitted together by these cell surface proteins in remarkably complex ways!

Recent research has demonstrated that octopuses experience sleep cycles that seem to include dream states. Other research has shown that diurnally active octopuses have larger and more complex visual cortexes than deep ocean or nocturnal octopuses and that octopuses that rely on vision for prey detection and capture have larger vertical (i.e “memory”) brain lobes. Some of these diurnally active octopuses also are able to exert the force of their intellect on other organisms around them! There are detailed descriptions of octopuses organizing gangs of fish around them and, then, by controlling the activity of these fish through food rewards and also physical intimidation, use them to help the octopus find prey.

“Day octopus” (Octopus cyanea). Photo by P.W Jackson Wikimedia Commons

In a paper recently published in the journal Nature, Ecology and Evolution (September 23, 2024) scientists from the Max Planck Institute of Animal Behavior in Germany observed multispecies groups of fish in the Red Sea working with the typically solitary octopus Octopus cyanea (also called the “day octopus”) to form what they referred to as “hunting packs.” The fish, most typically species of goatfish (including the barbed goat fish (Parupereus macronemus) and the yellow and blue goatfish (P. cyclostomas), fanned out in front of the hunting octopus and churn up sediment and explore crevices as they searched for prey.  The octopus controlled the direction of the pack’s movement by crawling toward the most active flurry of behavior in the scouting fish. As the octopus moved, the hunting pack constantly reformed around her.

When the goatfish identified a prey-rich crevice, the octopus would squeeze itself into the crevice and often linger there for quite a while as she fed. Occasionally, some of the prey species would escape from the octopus only to find themselves surrounded by hungry goatfish. The resulting feeding frenzy, then, illustrates a distinct mutualistic symbiosis between the octopus and the goatfish.

Day octopuses also hunt on their own without an accompanying goatfish posse. As solo hunters, though, they are forced to visit many more crevices and have a much lower rate of successful prey encounter and capture.

Blaktip grouper. Photo by . Wikimedia Commons

There are some other fish species that trail behind and move in and out of the octopus-led hunting pack. In this Red Seas study, two of these lurking fish were species of grouper (the lyretail grouper (Variola louti) and the blacktip grouper (Epinephelus fascialus). These groupers normally hunt their prey by stalking them in the open waters (primarily the lyretail) or by hiding and ambushing passing fish (primarily the blacktip). When these groupers encounter an octopus-led hunting pack, though, their behaviors change.  When some prey is found by the pack or roiled up out of a crevice by the hunting octopus, the groupers dart in and attempt to snatch it away. The octopus, though, keeps track of the fish in the hunting pack and will violently flick one its tentacles and slam it into one of the non-pack fish if it gets too close to the pack’s prey. In this study, the blacktip groupers were most often the fish species “punched” by the day octopuses. Since the groupers do not contribute to the hunting effectiveness of the pack, they are rewarded with bruises instead of food!

Giant Pacific octopus. Photo by N. Lea, NOAA/R. Public Domain

Dr. Eduardo Sampaio, the lead scientist in this study, described the role of the octopus’s in these hunting packs to that of a chief executive. He further described the goatfish to be the equivalent of a company’s research and development team.

“You can be a leader by pushing forward and expanding boundaries and taking the group to new places,” Dr. Sampaio said. “Or you can be the leader in terms of being the decider. The octopus lets other animals study the marketplace and then chooses the company’s direction.”

An octopus CEO, or an octopus mob boss? Or something in between? Take your pick and watch out for flying tentacles!