How octopuses taste with their arms


Cephalopods — the group that includes octopuses and squids — have long fascinated neuroscientists because their brains and sensory systems are unlike those found in any other animals. Octopuses, for instance, have more neurons in their arms than in their central brain: a structure that allows each arm to function independently as if it has its own brain3. And researchers have long known that the hundreds of suckers on each arm can both feel the environment and taste it4.

Molecular biologist Nicholas Bellono at Harvard University in Cambridge, Massachusetts, and his group were studying the California two-spot octopus (Octopus bimaculoides) when they came across a distinctive structure on the surface of the animal’s tentacle cells. Bellono suspected that this structure acted as a receptor for chemicals in the octopus’s environment. He contacted neurobiologist Ryan Hibbs at the University of California San Diego, who studies receptors that are architecturally similar to the octopus structures found by Bellono’s team: both types consist of five barrel-like proteins clustered to form a hollow tube.

When the researchers looked at the octopus genome, they found 26 genes for these barrel-shaped proteins, which could be shuffled to create millions of distinct five-part combinations that detect various tastes1. The researchers found that the octopus receptors tend to bind to ‘greasy’ molecules that don’t dissolve in water, suggesting that they are optimized for detecting chemicals on surfaces such as a fish’s skin, the sea floor or the octopus’s own eggs.

The authors think that having a wide variety of molecules in the suckers could allow an octopus to quickly determine what it is tasting, without having to send this information to the brain for processing. . . .

Analysing the squid and octopus genomes showed that the receptors had evolved independently after squid and octopus ancestors diverged around 300 million years ago, acquiring new properties over time. The need for different types of receptors makes sense: squids float in the water, see their prey and shoot out tentacles to capture it, meaning that their suckers don’t taste a fish until they touch it. But for octopuses, which tend to sit on the sea floor and feel their way around for prey, having a variety of sensitive tentacle suckers is crucial.