Life on Earth doesn’t get much more alien than octopuses. These hyper-intelligent animals roam the oceans (and sometimes land) slinking around with eight sucker-lined limbs that have seen them complete puzzles, mimic other animals, and expertly camouflage themselves using shells and coconuts. New research published in the journal Cell has uncovered a further skill of octopuses: they have finally identified the cell that enables these bizarre animals to taste their environment using their arms.
The unique talent improves the octopuses’ foraging success by relaying information about the environment and picking up telltale signs that a snack is lurking nearby. It's been suspected by scientists for a long time that octopuses could use their arms in this way, but until now nobody had looked at the suckers that line them at a molecular level.
This new research took a closer look at the nervous system in octopus arms by first identifying which cells in the suckers appear to be feeling and tasting objects. They then isolated and cloned these receptors and inserted them into frog eggs and in human cell lines. This part sounds loopy, but by popping the receptors into a context where such a cell never exists the researchers essentially formed closed vessels for the study of the touch/taste receptors.
The frog-human-octo-vessels were then exposed to flavors an octopus might come across in the ocean, including water-soluble treats like salt and others that don’t dissolve in water so well. Their findings revealed it was the latter of these that activated the receptors, so they tried the same test on living octopuses and found they too responded to the non-dissolving chemicals.
The research, while limited in the chemicals it exposed the octopuses to, was able to determine that it was indeed the sensors coating the suction cups that enable these animals to taste with their arms. They have named the touchy-feely-tasty sensors “chemotactile receptors,” bringing to mind a disturbing image of octopuses rolling around on eight big tongues. While a harrowing image, the clever adaptation means that octopuses are able to constantly assess what they are touching and reliably recognize if it’s prey.
"We think because the molecules do not solubilize well, they could, for instance, be found on the surface of octopuses' prey and [whatever the animals touch]," said Nicholas Bellono, the study's senior author, in a statement. "So, when the octopus touches a rock versus a crab, now its arm knows, 'OK, I'm touching a crab [because] I know there's not only touch but there's also this sort of taste.'
"We think that this is important because it could facilitate complexity in what the octopus senses and also how it can process a range of signals using its semi-autonomous arm nervous system to produce complex behaviors.”
As if octopuses' arms didn’t already seem weird enough, they’re known to operate largely independently of the central brain as two-thirds of these animals' neurons are located in their arms. This means that if an arm gets cut off, it can still reach for, taste, and grasp objects. Imagine minding your own business looking for some eggs to fertilize and you get scooped up by a semi-autonomous, decapitated octopus arm-tongue.
I think that’s enough science for today.