Octopuses can crawl in any direction relative to the body orientation, says a team of marine biologists headed by Dr Binyamin Hochner of the Hebrew University of Jerusalem, Israel.
An octopus at the USC Wrigley Marine Science Center on Catalina Island. Image credit: University of Southern California.
Octopuses are fast learners, have large brains, and are among the most developed invertebrates. With eight arms and no rigid skeleton, they perform many tasks like crawling, swimming, mating and hunting.
And unlike most animals – who are restricted in their movements by a rigid skeleton which helps in determining the position of their limbs – octopuses have limitless flexibility.
But because they have no such rigid structure, it was believed that they have only limited control over their eight flexible limbs.
However, Dr Hochner and his colleagues have shown otherwise. Their study, reported in the journal Current Biology, is the first to systematically attempt to explain how the octopuses coordinate their eight arms during locomotion.
“The orientation of its body and crawling direction are independently controlled, and its crawling lacks any apparent rhythmical patterns in limb coordination,” the scientists explained.
They show that this uncommon maneuverability of octopuses is derived from the radial symmetry of their arms around the body and the simple mechanism by which the arms create the crawling thrust: pushing-by-elongation.
“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.”
The octopus needs only to choose which arms to activate in order to determine the direction of locomotion.
According to the team, the findings lend support to what’s known as the Embodied Organization concept.
In the traditional view, motor-control strategies are devised to fit the body. But under this concept, the control and the body evolve together in lockstep within the context of the environment with which those bodies interact.
“This concept, which is borrowed from robotics, argues that the optimal behavior of an autonomous robot or an animal is achieved as a result of the optimization of the reciprocal and dynamical interactions between the brain, body, and the constantly changing environment, thus leading to optimal adaptation of the system, as a whole, to its ecological niche,” said study first author Dr Guy Levy of the Hebrew University of Jerusalem.
“Another important virtue of this type of organization is that every level, including the physical properties and the morphology, contribute to the control of the emerging behavior – and not only the brain, as we tend to think.”
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Guy Levy et al. Arm Coordination in Octopus Crawling Involves Unique Motor Control Strategies. Current Biology, published online April 16, 2015; doi: 10.1016/j.cub.2015.02.064
