Keeping two arms and two legs coordinated is not always easy. Octopuses not only have twice as many limbs to wield, but their arms behave as if they have minds of their own.
New research suggests that the task of motor control could be simplified by attaching to a preferred arm to catch prey.
Using California two-spot octopuses (bimaculoid octopus), the researchers tested the response of invertebrates to crabs and shrimp that fell into their tanks. The octopuses were hidden inside burrows, with one eye looking out. Hundreds of video clips revealed how octopuses constantly used the second arm from the middle, on the side where their watchful eye was, to catch their prey. When necessary, neighboring weapons were also used.
“Although all eight arms share a general anatomy and are considered equipotential, such use of the arms for specific actions could reflect subtle evolutionary adaptations,” the researchers write in their published paper.
Crabs and shrimp move differently and at different speeds, causing the octopuses to use different methods of attack for each. For example, a cat-like motion led by the second arm was used for crabs, which scuttle much slower than flitting shrimp..
For the faster, more evasive shrimp, the octopuses steered more slowly with the second arm, possibly incorporating subtle movements that help camouflage arm movements.
“The octopus is known to mimic during foraging, and we speculate that it swings its arms close to the shrimp to habituate the shrimp’s antennae and the sensory hairs of the uropods, reducing the likelihood that it will escape with a tail strike.” , the researchers write.
Once contact was made, neighboring arms (numbered one and three) were used to secure helpless prey.
The consistency of the second arm’s attack was somewhat surprising, given that octopuses often look anything but coordinated, but the researchers say it likely has to do with their field of vision (as previous studies have suggested).
“As each octopus eye covers about 180 degrees with virtually no intersection and shows limited eye movement and no head movement, octopuses likely prefer to target in the middle rather than at the edge of their field. view,” he writes. the researchers.
Seconds count when it comes to catching food in the wild, of course, and it seems that by simplifying the catching process and using multiple arms, octopuses can maximize their chances of getting some food.
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The next step for biologists would be to analyze how the activity of neurons is related to such precise motor movements. Scientists don’t think the octopus’s central nervous system is necessarily involved in recruiting additional arms to capture prey; instead, it is likely to be more of a reflex action.
Having a better understanding of the mechanics behind this arm coordination could also help in the development of soft robots, the researchers say, especially those that go to work underwater.
“Octopuses are extremely strong,” says biologist and study author Trevor Wardill of the University of Minnesota. “For them, grabbing and opening a door is trivial, given their dexterity.”
“If we can learn from octopuses, then we can apply that to make an underwater vehicle or soft robot application.”
The research has been published in current biology.