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The Octopus: More Complex than a Simple Mollusk Should Be

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The octopus continues to surprise researchers. Its amazing body, eyes, and behavior seem far too complex for a soft-bodied invertebrate. Yet we are told that these animals (pl. octopuses), along with their fellow cephalopods the squid and cuttlefish, are descendants of clams and snails. Wondrous as those mollusks are in their own right, they lack tentacles with suckers, camera eyes, and the behavioral complexity of the octopus.

Recently, Israeli scientists studied the crawling behavior of Octopus vulgaris. In Current Biology, they describe how video studies revealed the strategy for the complex task. The words “surprising” and “unique” stand out as challenges to evolution, as do all the references to control systems.

To cope with the exceptional computational complexity that is involved in the control of its hyper-redundant arms, the octopus has adopted unique motor control strategies in which the central brain activates rather autonomous motor programs in the elaborated peripheral nervous system of the arms. How octopuses coordinate their eight long and flexible arms in locomotion is still unknown. Here, we present the first detailed kinematic analysis of octopus arm coordination in crawling. The results are surprising in several respects: (1) despite its bilaterally symmetrical body, the octopus can crawl in any direction relative to its body orientation; (2) body and crawling orientation are monotonically and independently controlled; and (3) contrasting known animal locomotion, octopus crawling lacks any apparent rhythmical patterns in limb coordination, suggesting a unique non-rhythmical output of the octopus central controller. [Emphasis added.]

The researchers identified a strategy the octopus uses for moving in a certain direction: push, then elongate. The octopus can send this “autonomous motor program” to any one of its eight arms, regardless of the animal’s orientation.

We show that this uncommon maneuverability is derived from the radial symmetry of the arms around the body and the simple pushing-by-elongation mechanism by which the arms create the crawling thrust. These two together enable a mechanism whereby the central controller chooses in a moment-to-moment fashion which arms to recruit for pushing the body in an instantaneous direction.

Sounds simple enough, until you look at the details. The octopus apparently understands Newton’s law of action-reaction. It has to push the arm on the opposite side of the direction it wants to go. It has to constantly monitor and adjust for changes in texture of the surface, currents, and other variables. And this “motor control strategy” appears to be unique in the animal kingdom; how did that arise from mollusk ancestors?

Nevertheless, some reporters emphasized how “simple” the strategy is. Live Science quoted one of the authors as saying, “It’s a very simple solution to a very complicated problem.” BBC News, similarly, quoted co-author Guy Levy, “[It has] found a very simple solution to a potentially complicated problem — it just has to pick which arm to recruit.” Science said, “Because octopus legs are evenly spaced around the body, choosing a direction is as simple as choosing which legs to stretch: to move right, elongate the legs on the left; to move forward, elongate the legs in the back.” What could be simpler?

To find out, try building a robot that can do this. Researchers at SMART (Singapore-MIT Alliance for Research and Technology) are happy just to have imitated one octopus trick: efficient jet propulsion. The video at PhysOrg shows their creation darting off in a straight line when a balloon-like sac rapidly deflates. This looks like something a kid could make for the backyard swimming pool or bathtub. The deflation step is the easy part. How do you make an autonomous robot repeatedly inflate and aim itself? And how do you put eight flexible arms on it that a central brain can direct, allowing it to move in any direction over any surface?

A more sophisticated octopus robot announced by Waseda University has four arms and four tank-like tread wheels. It’s pretty impressive, but look at all the wires, servos, and hydraulic pistons on the big, heavy contraption. It may help clear debris in the Fukushima nuclear plant, but it’s not going to dart off in the water without a lot more design work.

Octopuses are also fascinating for their adaptability to a wide range of habitats. Some live in shallow water tide pools; others survive in abyssal depths and near hydrothermal vents. Live Science shows a species that lives in freezing Antarctic waters, surviving thanks to “blue blood.” A copper-containing pigment protein in its blood allows it to transport oxygen efficiently to its tissues in spite of the frigid conditions.

The rapid color-change trickery of the octopus and other cephalopods is another marvel that engineers are trying to master. Of special note is the “mimic octopus” of Indonesia. See Louise Gentle’s description and video at The Conversation. This species looks like it’s having fun!

This octopus was discovered in 1998 off the coast of an Indonesian island, and is perhaps the greatest shape-shifter of all. Similar to the cuttlefish, it is capable of mimicking its background environment by changing the colour and texture of its skin. However, impressively, it is the only animal able to mimic a diverse range of species — at least 13 have been recorded so far — including lion fish, sea snakes, jellyfish and sea anemones.

Could the engineers at SMART and Waseda University match that? “The mimic octopus has remarkable dexterity, being capable of changing its colour, behaviour, shape and texture, and can alter its mimickry according to the circumstances.” Watch how fast it turns black and shapes itself into a tent to scare off a crab, then transforms itself into a dull-colored halibut and a complex lionfish.

As we observed last year, the octopus even has control programs and mechanisms to prevent its semi-autonomous arms from tying themselves in knots. All the parts must match and act in concert for these complex functions.

Our findings suggest that the soft molluscan body has affected in an embodied way the emergence of the adaptive motor behavior of the octopus.

We’ve heard of “embodied organization” before. It’s a useful concept in robotics, but for evolutionary theory, it is vacuous, leaving unexplained the origin of all the parts that need to work synergistically for function.

Clearly the octopus is an extremely well-designed animal for its marine environment. The word “elegant” is often used of its graceful movements. Does Darwinism offer any understanding of how a snail or clam transmogrified into an octopus? As usual, we see nothing but “proof by assertion.” It just evolved. End of story.

“Octopuses use unique locomotion strategies that are different from those found in other animals,” says Binyamin Hochner of The Hebrew University of Jerusalem. “This is most likely due to their soft molluscan body that led to the evolution of ‘strange’ morphology, enabling efficient locomotion control without a rigid skeleton. (Cell Press)

It’s likely that octopuses developed their unique way of moving because, unlike their clam cousins, they don’t have protective outer shells, the researchers said. In fact, the octopus is thought to have evolved from a snail-like ancestor whose foot evolved into eight long and slender arms, giving the animals enormous flexibility. Octopuses also developed excellent vision, a large brain and camouflage capabilities, making them adept hunters. (Live Science)

Victoria Gill at the BBC News omitted any evolutionary imagineering. The original paper in Current Biology, incidentally, had almost nothing to say about evolution: just one quick reference in the last sentence:

Our results also support the embodied-organization concept of adaptive behaviors (in the general sense, not only in octopuses) as they show the marvelously reciprocal interaction between the control system, the physical properties of the body, and the morphology, an interaction that leads to an evolutionary successful adaptation of the emerging behavior to the ecological niche.

This juxtaposition of design concepts with evolution is awkward. From the numerous references to motor control, autonomous programs, biomechanics, and similar terms in the paper, it’s evident that design thinking did the heavy lifting in advancing what we understand about the octopus. Looking at each complex, elegant creature in the biosphere with design in mind is the key to understanding, motivation, and application.

Image credit: Harrieta171 (File:Knossos frise pieuvre.JPG) [Public domain], via Wikimedia Commons.

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