These brains are comprised of million neurons and capable of problem-solving and memorization and even predicting important soccer games. The octopus nervous system differs from ours in a key way: million peripheral neurons extend through their tentacle arms and facilitate movement. So, when an octopus arm gets chopped off by accident or in a fight with a predator, it remains active for about an hour—instinctively grasping and holding anything it touches.
Because of their autonomy, the researchers saw amputated octopus arms as a way to try to answer questions about how these cannibalistic animals recognize their own attached and unattached arms from potential food. The researchers began by humanely amputating an arm from common octopuses Octopus vulgaris in their lab. The researchers put an octopus and different objects—amputated arms, skinned arms, fish, shrimp, and petri dishes partially covered in octopus skin—in a tank and watched what happened.
Amputated arms never attached to themselves or grasped the arms of the live octopus in the tank, instead avoiding its former neighboring suckers. The severed arms, however, did latch on to skinned octopus arms and the plastic part of petri dishes. The researchers measured the force applied to each object and found that the arms never applied grasping force to skin.
So whatever signal prevented sucker attachment reflexes, it had to be coming from the skin. The forces applied by the severed arms to petri dishes with octopus slime were 10 times less than a regular petri dish and 20 times less than a petri dish with fish slime. The top of an octopus's sucker known as the acetabular protuberance was much stiffer than the rest of the sucker.
It withstood 3. This lesser elasticity is likely crucial for the local generation of the low-pressure that makes the adhesion possible. Under pressure, both tissues became stiffer, which also helps insure a good hold once the octopus sucker has made contact with a surface. The artificial materials, on the other hand or arm , by in large did not vary their elasticity under different pressures.
Further study of these surfaces and their elasticity will likely help us develop more effective soft-bodied robots. For instance, the stiffer upper section of the octopus sucker has considerably more connective tissue. And although they don't yet know for sure why, researchers hypothesize that this might help the animal "store elastic energy to generate attachment for long periods of time without muscle contractions"—a huge energy saver.
Until then, however, the amazing cephalopod sucker continues to be quite the engineering sticking point. Hat tip to Lucas Laursen for spotting this gripping study. To learn more about the octopus's suckers and the rest of its bizarre body, check out my new book Octopus! Illustration courtesy of Ivan Phillipsen. The views expressed are those of the author s and are not necessarily those of Scientific American.
Katherine Harmon Courage is an award-winning freelance journalist, editor, and author based in Colorado. Follow Katherine Harmon Courage on Twitter. Already a subscriber?
Sign in. Some test subjects were water-soluble, like salts, sugars, amino acids; others do not dissolve well and are not typically considered of interest by aquatic animals. Surprisingly, only the poorly soluble molecules activated the receptors. Researchers then went back to the octopuses in their lab to see whether they too responded to those molecules by putting those same extracts on the floors of their tanks. They found the only odorants the octopuses receptors responded to were a non-dissolving class of naturally occurring chemicals known as terpenoid molecules.
While the study provides a molecular explanation for this aquatic touch-taste sensation in octopuses through their chemotactile receptors, the researchers suggest further study is needed, given that a great number of unknown natural compounds could also stimulate these receptors to mediate complex behaviors.
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