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Harvard researchers found that octopi use a family of specialized cells called chemotactile receptors to “taste” using their sense of touch when employing their arms.

In a study published last week in Cell, the team, led by Molecular and Cellular Biology Professor Nicholas Bellono, showed that octopi use these receptors to sense whether or not a nearby object is poorly soluble in water. When an octopus touches a poorly soluble material, the receptors in its arms interpret it as potential prey, thereby activating the octopus’ sense of taste.

“The octopus seems to detect these poorly soluble molecules which couldn't travel well through water and be sensed at a distance, so it really has to insert its arm to the area where that molecule is present, because the gradient can be quite local,” Bellono said.

Bellono said the team had to first identify which of the cells located in the nervous system of octopus arms were responsible for sensing taste by touch. The researchers then exposed those cells to molecules from different octopus prey to understand what stimuli they responded to.

“For chemicals it’s much more challenging, because we don't know what the octopus cares about,” Bellono said. “And so what we did was, we ended up making extracts from its prey. So we would take ground-up prey and then separate some molecular weight, and then apply this extract – which is full of lots and lots of molecules – to the cells and ask if they do anything.”

While the biomechanical function of the octopus arms’ suction cups has been studied for decades, the molecular makeup and mechanisms of these arms is not well-understood, according to the study. Bellono said his team’s work could shed light on whether other cephalopods have similar sensors that can taste by touch, which could provide insight on the evolution of related creatures over time.

“Could it be that in other cephalopods, they're using similar receptors for distinct purposes, because the octopus explores with its arms and the sea floor, but the squid is in the open ocean and detecting greater distances and capturing with its chemicals which it extends out to grab prey?” Bellono said. “And so it could be a really nice system to ask about evolutionary adaptation.”

The team will expand on this research by investigating whether cephalopods such as cuttlefish and squid possess similar chemotactile receptors. The researchers will also experiment with other natural materials to further understand what stimulates the receptors, according to Bellono.

“We're trying to sample around natural products to see, what do the receptors detect? What do the animals detect? And then use those molecules as tools to understand how the receptors have evolved to suit that animal, detecting these ecologically relevant molecules,” Bellono said.

—Staff writer Ethan Lee can be reached at ethan.lee@thecrimson.com.