Cuttlefish are full of personality, as behavioral ecologist Alexandra Schnell found out while researching the cephalopod's potential to display self-control. One test subject, named Franklin, was so impatient, she would shoot water at Schnell until dinner time. Other cuttlefish were better at waiting, and they were rewarded for it.
While working at the Marine Biological Laboratory in Woods Hole, Massachusetts, Schnell tested six juvenile cuttlefishes’ ability to delay gratification to get their favorite meal. The experiments showed some cuttlefish could resist a less-preferred piece of food for between 50 and 130 seconds if they knew that they would be rewarded with something better, Sarah Keartes reports for Hakai magazine.
A follow-up test showed that the most patient cuttlefish were also better at learning than the impatient ones. The results of the study appear in the March 3 issue of the Proceedings of the Royal Society B.
"Self-control is thought to be the cornerstone of intelligence, as it is an important prerequisite for complex decision-making and planning for the future," says Schnell, who now works at the University of Cambridge, to Yasemin Saplakoglu at Live Science. "Why cuttlefish evolved the ability to exert self-control is a bit of a mystery.”
The new study used a modified version of the “marshmallow test,” which was first used about 50 years ago in a psychology study at Stanford University, to test the animals' self restraint. During the original marshmallow test, psychologist Walter Mischel presented children between age four and six with one marshmallow. He told them that if they waited 15 minutes and didn’t eat it, he would give them a second marshmallow.
A long-term follow-up study showed that the children who waited for the second marshmallow had more success later in life. Mischel cautioned against overgeneralizing the results, and another study published in 2018 that controlled for the kids’ socioeconomic background showed a much weaker correlation between patience and later success, Jennifer Ouellette reports for Ars Technica.
The cuttlefish version of the experiment looked a lot different. The researchers worked with six cuttlefish under nine months old and presented them with seafood instead of sweets. (Preliminary experiments showed that cuttlefishes’ favorite food is live grass shrimp, while raw prawns are so-so and Asian shore crab is nearly unacceptable.)
Since the researchers couldn’t explain to the cuttlefish that they would need to wait for their shrimp, they trained them to recognize certain shapes that indicated when a food item would become available.
The symbols were pasted on transparent drawers so that the cuttlefish could see the food that was stored inside. One drawer, labeled with a circle to mean “immediate,” held raw king prawn. Another drawer, labeled with a triangle to mean “delayed,” held live grass shrimp.
During a control experiment, square labels meant “never.”
“If their self-control is flexible and I hadn’t just trained them to wait in any context, you would expect the cuttlefish to take the immediate reward [in the control], even if it’s their second preference,” says Schnell to Hakai magazine, and that’s what they did. That showed the researchers that cuttlefish wouldn’t reject the prawns if it was the only food available.
In the experimental trials, the cuttlefish didn’t jump on the prawns if the live grass shrimp were labeled with a triangle—many waited for the shrimp drawer to open up. Each time the cuttlefish showed it could wait, the researchers tacked another ten seconds on to the next round of waiting before releasing the shrimp. The longest that a cuttlefish waited was 130 seconds.
Schnell tells Live Science that the cuttlefish usually sat at the bottom of the tank and looked at the two food items while they waited, but sometimes, they would turn away from the king prawn "as if to distract themselves from the temptation of the immediate reward."
In past studies, humans, chimpanzees, parrots and dogs also tried to distract themselves while waiting for a reward.
Not every species can use self-control, but most of the animals that can share another trait in common: long, social lives. Cuttlefish, on the other hand, are solitary creatures that don’t form relationships even with mates or young. The fact that cuttlefish are so different than the other species is part of what makes the new research exciting.
“We don’t know if living in a social group is important for complex cognition unless we also show those abilities are lacking in less social species,” says Oakland University comparative psychologist Jennifer Vonk, who wasn’t involved with the new study, to Hakai magazine. “There’s still so much room to understand more.”
Future studies could puzzle out the evolutionary benefit of patience in cuttlefish. One hypothesis is that it might have to do with hunting strategy, Schnell writes for the Conversation. Since cuttlefish lose their camouflage when they spring for prey, they might learn to wait until the optimal meal swims past.