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Octopuses, with their eight sucker-covered tentacles, can taste objects simply by touching them. A team of researchers has finally figured out how these cephalopods are able to accomplish this extraordinary trick.
Octopus is a wonder of the biological world. They are super smart, excellent problem solvers, and even a little mischievous. These cephalopods have no choice but to be intelligent, as they are forced to grow on their own soon after birth. They even respond to MDMA in a way that resembles how humans react to this pro-social drug.
Their tentacles, scattered with hundreds of suckers, are an important part of their success, as octopuses can literally taste objects by simply touching them. This ability can be very useful when an octopus has to reach deep into a dark crevice while searching for food or scouring the seafloor. The ocean is full of evil and noxious creatures, hence the ability to discern a authentic the meal of something more harmful is clearly beneficial.
An octopus looking at a cup of coffee. (Image: Lena van Giesen)
“The strategies they have developed to solve problems in their environment are unique to them and this inspires great interest from both scientists and non-scientists,” Peter Kilian, a co-author of the new study and a biologist from Bellono Lab’s Harvard University said in a statement from Harvard. “People are attracted to octopuses and other cephalopods because they are very different from most other animals.”
Despite this fascination, our understanding of the chemical and molecular basis of their tactile-gustatory capacity is sorely lacking. The new research, published today in Cell, marks an important step in this direction.
Nicholas Bellono, the study’s senior author and a molecular biologist at Harvard, and his colleagues kicked off the project by confirming the tactile-gustatory ability in octopuses. They did this with a California two-spotted octopus (Octopus bimaculoides), which in laboratory tests exhibited different behaviors when its suckers touched prey than something less appetizing.
While writing an accompanying paper on Leading Edge for Cell, Rebecca Tarvin, a biologist at the University of California, Berkeley, took a step back to marvel at this ability and what it means to scientists.
“While many never know what it’s like to be a bat, or an octopus for that matter, defining the molecular mechanisms these animals use to explore their environment will help our imaginations,” wrote Tarvin, who is not affiliated with the new. study. “Such important discoveries should also fuel our curiosity about what else remains hidden.”
Indeed, with the affirmation of the sense of touch-taste, the next step for scientists was to do exactly that: study suckers at the molecular level. Their search for the unique sensory cells involved in the process led them to discover a distinct population of cells located at the tips of the suckers. These newly detected sensors are now referred to as ‘chemotactile receptors’, as the team believes they are responsible for tactile-taste ability.
As the team demonstrated in subsequent tests, these sensors reacted to molecules that don’t dissolve well in water. Because the molecules do not solubilize well, “they could, for example, be found on the surface of octopus prey and [whatever the animals touch]”Bellono said in the Harvard statement.” So when the octopus touches a rock against a crab, now his arm knows, ‘OK, I’m touching a crab. [because] I know that there is not only touch, but also this kind of taste. “
The team also found a second cell type – a population of mechanosensory cells – inside the suckers. These cells convert mechanical stimulation into signals that the brain can understand as touch, among other senses.
As the authors explain, octopus chemotactile receptors are capable of both detecting and discriminating between different chemical signals. The chemically sensitive receptors form discrete ion channel complexes that can pick up specific signals and then transmit electrical signals to the octopus’ nervous system, which are interpreted as taste.
This is important “because it could facilitate the complexity in what the octopus perceives and also how it can process a series of signals using its semi-autonomic arm nervous system to produce complex behaviors,” Bellono said.
Importantly, this unique signal filtering system is made possible by the octopus’ distributed nervous system, in which the tentacles can function independently of the brain. About two-thirds of octopus neurons are in their tentacles, which is why a severed arm can still attempt to reach out and grab something. Disturbing, but true.
“These results demonstrate that the peripherally distributed octopus nervous system is a key site for signal processing and highlight how molecular and anatomical features synergistically evolve to adapt to an animal’s environmental context,” the authors wrote in the study.
The new research has also shown that octopus receptors are sensitive to terpenoids, a chemical warning shot produced by many marine animals when threatened. In nature, an octopus that suddenly tastes terpenoids may retreat, as it is a potential sign of poisonous prey.
“The impressive array of … experiments carried out by [the authors] demonstrate that through these two cell types, suckers produce finely tuned electrical signals that likely allow discrimination between fixed and moving objects and between attractive and aversive substances, ”Tarvin wrote.
The authors suspect that terpenoids are one of many other unknown compounds capable of stimulating octopus’ chemotactile receptors and recommend future research in this area. Furthermore, they would like to know if other cephalopods, such as squid and cuttlefish, have similar tactile abilities.
“Overall, the findings are an exciting leap in the description of the octopus’ chemo-tactile sensory system and will generate many new questions about the neurobiology, evolutionary ecology and behavior of these intriguing animals,” according to Tarvin.
Indeed, the new study will interest evolutionary biologists, who must now understand how the ability to touch and taste first emerged. As a possible clue, it could be a classic case of shape-matching function, where the octopus body plane eventually led to this ability. But the reverse might also be true, with the skill of tactile taste ultimately leading to lengthy exploratory appendages. Or maybe it was a combination of the two. Fortunately, this is not my problem to solve and I can let the scientists understand everything.
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