May 16, 2014
Special Chemical In Skin Keeps Octopus Arms From Entangling
Brett Smith for redOrbit.com - Your Universe Online
With eight long arms covered on one side with prey-grabbing suckers – octopi appear to be very susceptible to getting themselves tangled up in knots.
However, a chemical generated by an octopus' skin prevents this problem from happening by temporarily preventing its suckers from sticking, according to a new study in the journal Current Biology.
"We were surprised that nobody before us had noticed this very robust and easy-to-detect phenomena," said study author Guy Levy, an octopus specialist at The Hebrew University of Jerusalem. "We were entirely surprised by the brilliant and simple solution of the octopus to this potentially very complicated problem."
The study team has been researching the motor control system of octopi for years and also recently found that the animals don’t exactly know what their arms are doing sometimes.
"Our motor control system is based on a rather fixed representation of the motor and sensory systems in the brain in a formant of maps that have body part coordinates," said study author Binyamin Hochner, a principal investigator in the octopus group.
He added that the human motor control system is set up this way because of the limits placed on our movement by our skeletal system – limits that octopi don’t adhere to.
"It is hard to envisage similar mechanisms to function in the octopus brain because its very long and flexible arms have an infinite number of degrees of freedom," Hochner said. "Therefore, using such maps would have been tremendously difficult for the octopus, and maybe even impossible."
Knowing that octopi don’t know what their arms are doing, the research team wondered why they don’t tie themselves in knots.
To answer that question, the study team watched the actions of amputated octopus arms, which continue to be dynamic for an hour after separation. The team saw that the arms could not grab octopus skin, but would grab a skinned octopus arm. The amputated arms also didn't grab Petri dishes enclosed in octopus skin, either, and they grabbed dishes coated with octopus skin extract with significantly less pressure than they otherwise would.
[ Watch the Video: Octopus Doesn’t Treat Its Own Amputated Arm As Food ]
"The results so far show, and for the first time, that the skin of the octopus prevents octopus arms from attaching to each other or to themselves in a reflexive manner," the researchers wrote in their report. "The drastic reduction in the response to the skin crude extract suggests that a specific chemical signal in the skin mediates the inhibition of sucker grabbing."
The researchers also found that octopi can override this mechanism when it suits them – as they have been observed grabbing the amputated arm of another octopus.
[ Watch the Video: Octopus Treats Other’s Amputated Arm As Food ]
The study team said they will now focus on identifying the exact compound behind this mechanism and speculated that their work could be used in robotics design.
"Soft robots have advantages [in] that they can reshape their body," co-author Nir Nesher said. "This is especially advantageous in unfamiliar environments with many obstacles that can be bypassed only by flexible manipulators, such as the internal human body environment."
"We hope and believe that this mechanism will find expression in such new classes of robots and their control systems," Hochner added.