New research reveals a previously unknown type of nerve cell found in octopus arms that allows their suckers to taste anything they touch, reports Katherine J. Wu for the New York Times.
The fact that octopus suckers can taste the world around them has been known for some time, but in the new paper, published this week in the journal Cell, researchers finally uncover some of the complex biology underlying one of this cephalopod’s many superpowers.
These specialized cells, which are not found in other animals, allow the arms to do things like distinguish food from other objects they may encounter as they probe blind crevices in the octopus’ underwater habitat, reports Jonathan Lambert for Science News. This skill comes in handy because each of the soft-bodied cephalopod’s eight arms can call its own shots, with a cluster of nerve cells capable of directing the appendage’s movements without needing to wait for instructions from the brain.
So when an octopus hunts, the arms can search nooks and crannies almost autonomously, tasting what’s inside with their suckers and swiftly capturing prey like crabs, snails and fish while discarding everything else without any need to take a closer look.
“There was a huge gap in knowledge of how octopus [arms] actually collect information about their environment,” Tamar Gutnick, a neurobiologist who studies octopuses at Hebrew University of Jerusalem who was not involved in the study, tells Science News. “We’ve known that [octopuses] taste by touch, but knowing it and understanding how it’s actually working is a very different thing.”
To figure out how octopus suckers accomplish this complex task the researchers took a closer look at the suckers of California two-spot octopuses (Octopus bimaculoides) in the lab. Under a microscope, the researchers found structures that looked like sensory cells on the surface of the suckers, per Science News. When the team isolated and tested these cells, they found there were two types.
One type was sensitive to touch and similar to cells seen in other animals. But the other cell type was something altogether new, featuring receptor proteins that responded to chemical stimuli like fish extract.
If humans were octopuses, it might feel like having eight long tongues covered in suckers, Lena van Giesen, an evolutionary biologist at Harvard University and the study’s lead author, tells the Times. “Or maybe it feels totally different, we just don’t know.”
To learn more about how these taste-sensitive sucker cells worked van Giesen and her colleagues conducted genetic experiments that revealed a broad palette of these receptor proteins covering the newly discovered taste cells. Each protein receptor is tuned to respond to a different chemical in the environment, providing the octopus with a wealth of sensory information about anything they lay a sucker on.
With the help of these cells the octopuses create “a very detailed taste map of what they’re touching,” Rebecca Tarvin, a biologist at the University of California, Berkeley, who penned a commentary about the new paper but was not involved in the research itself, tells the Times. “They don’t even need to see it. They’re just responding to attractive and aversive compounds.”
Part of what may make the octopus’ ability to taste its environment with its arms so useful is that not all chemicals dissolve well in seawater. Put simply, this means there are things that are hard to smell but simple to taste. The experiments carried out by the researchers suggest that octopus suckers are capable of tasting at least one class of these less-soluble compounds, called terpenoids.
Next, the team is trying to identify the full range of tastes these nerve cells are capable of detecting, according to Science News, as well as whether they always send the same signals. For example: Would the taste of a crab elicit the same signal if the octopus isn’t hungry?