For an octopus, almost any arm will do.
New research published Thursday shows that octopuses have the ability to use any of their eight limbs to perform tasks like reaching, tiptoeing or grasping.
“These animals are incredible multitaskers, so they’re able to perform multiple actions on one arm and on multiple arms at the same time,” said Kendra Buresch, a research biologist at the Marine Biological Laboratory in Woods Hole, Massachusetts, and an author of the study. “Some other animals have different specializations for different parts of their body, whereas the octopus is really adapted to being able to use any of their arms in basically any situation.”
The findings, which were published in the journal Scientific Reports on Thursday, reveal new details on how the famously flexible creatures coordinate some of the most complex movements in the animal kingdom. Further research could help scientists understand how the animals evolved such neurologically complex motor skills.
The work could also help build robots for medical applications or to examine hard-to-reach areas. Octopuses are increasingly used as inspiration for soft robots, and this new inventory of arm movements could give engineers new insights, the study authors said.
The researchers found that each arm could perform a full range of motions. Octopuses favored using their front arms (about 60% to 40%) over their back arms. They used their front arms more often to explore and their back arms for movement. The cephalopods didn’t show a preference between their right and left arms.
To understand the animals’ movements, researchers from Florida Atlantic University and the Marine Biological Laboratory reviewed footage of wild octopuses roaming the seafloor, analyzing them frame by frame like a football coach might break down a complicated play.
First, the researchers collected one-minute videos of 25 wild octopuses that were filmed in Spain, South Florida, the Cayman Islands and elsewhere from 2007 to 2015. Divers filmed the creatures as they explored or moved through reefs, seagrasses and the sandy ocean floor.
The researchers evaluated each video frame by frame, to create a play-by-play of specific arm motions like tucking, lowering or rolling — as the animal performed different behaviors, like standing or moving a rock.
They broke down how the animals bent, retracted or extended different portions of an individual limb, from the base near the head all the way to the tip of each arm.
Each minute of video took hours to analyze, Buresch said. All in all, the researchers cataloged 3,907 arm actions that required 6,871 arm deformations.
The inventory of the animals’ arm movement could help researchers better understand the neural connections that allow octopuses to coordinate their arms to work in different combinations and to receive feedback from the environment.
Octopuses have a complex and poorly understood nervous system, with nerves that run down each of their eight arms. Suckers on each arm give the animals a sense of touch, but also have chemoreceptors that allow them to essentially taste by touch.
“If I’m an octopus, I’m using my arms to run over surfaces, stick them in holes in the seafloor, looking in crevices in coral heads or rocky ledges and feeling around in there, but mostly tasting around in there to see what’s happening,” Buresch said.
Octopuses have a decentralized nervous system with more neurons in their arms than in their central brain, Buresch said.
“We’re all sort of starting to piece together the different parts of the puzzle that explain, How does this bizarre nervous system work?”
