Cuttlefish show self-control, pass 'marshmallow test'

A cuttlefish (Sepia officinalis) in the water.
(Image credit: Shutterstock)

Cuttlefish can pass the "marshmallow test" — the famous psychological test of self-control. 

In this case, the cephalopods were willing to forgo meals when they knew that waiting meant they would be rewarded with more delicious treats, according to a new study. That makes them the first known invertebrates to show the ability to exert self-control.

The common cuttlefish (Sepia officinalis) — relatives of squids and octopuses — are sneaky hunters and impressive camouflagers, with the ability to quickly disappear into any environment. They are also scarily smart; studies previously showed that they have a good memory, can learn the value of different types of prey and can use past experience to help them predict where to find food.

But prior to this study, it was unclear whether these creatures could also delay gratification.

Related: Cuttlefish cuties: photos of color-changing cephalopods

"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," said lead author Alex Schnell, a research associate in the Department of Psychology at the University of Cambridge. Not all animals share this trait, and it was previously thought that the ones that do, such as great apes, corvids and parrots, have long and social lives. 

To see if a cephalopod should join the ranks, Schnell and her team adapted the famous "marshmallow test" so that it appealed to cuttlefish. In the 1960s, Walter Mischel led an experiment at Stanford University to test how much self-control children have when presented with a preferred treat such as a marshmallow (or other treats such as cookies and pretzels) and two options: either eat the one marshmallow now or wait for 15 to 20 minutes and get rewarded with two marshmallows.

In the current study, Schnell's team swapped out marshmallows for seafood munchies, after figuring out what six individual 9-month-old (not yet fully adult) cuttlefish preferred to eat. It turned out, all of them preferred live grass shrimp the most, followed by king prawn, with the Asian shore crab coming in last of the three. 

They then set up a two-chamber apparatus with transparent sliding drawers. Behind one drawer, they placed a preferred meal (such as live grass shrimp) and behind the other, they placed a less preferred meal (such as Asian shore crab). The doors had symbols on them that indicated whether it would open with a delay (a triangle) or open immediately (a circle), which the cuttlefish learned to recognize. 

The drawer with the less preferred meal always opened to the cuttlefish immediately, but the other drawer opened after a delay. In the control condition, the door with the preferred snack didn't open at all (a square). When the cuttlefish approached one chamber, the researchers immediately removed the snack in the other.

One of the six 9-month old cuttlefish that participated in the experiment.

One of the six 9-month old cuttlefish that participated in the experiment. (Image credit: Alex Schnell)

A bit of a mystery

The cuttlefish indeed chose to delay gratification to score a more delicious meal if they knew the door would open after a delay; they were able to delay grabbing their snack for anywhere between 50 to 130 seconds. During this time, they generally sat at the bottom of the tank looking at the two rewards, Schnell told Live Science in an email. 

Sometimes, they would even turn away from the immediate (less preferred but currently available) option "as if to distract themselves from the temptation of the immediate reward," she said. This same distraction technique was previously observed in humans, chimpanzees, jays, parrots and dogs, she said.

"Why cuttlefish evolved the ability to exert self-control is a bit of a mystery," Schnell said. "This finding is an extreme example of convergent evolution because cuttlefish have significantly different evolutionary histories from the more commonly studied apes, corvids and parrots, and yet they share the same cognitive feature." (Convergent evolution occurs when different species evolve similar traits independently of one another.)

"Cuttlefish can tolerate delays to obtain the food of higher quality comparable to that of some large-brained vertebrates," the authors wrote in the study. Those include great apes, parrots and corvids. But the benefits of self-control for such social and long-lived animals "are obvious," Schnell said. 

If these animals resist temptation now, they may have better outcomes in the future and live a longer life. For example, these animals may wait for others to eat to strengthen social bonds or forego hunting and foraging to give themselves time to craft tools in order to optimize hunting and foraging in the future, she said. 

The benefits for cuttlefish are less obvious. "Cuttlefish are not long-lived, not social and do not manufacture or build tools," Schnell said. 

The researchers hypothesize that the cuttlefish evolved self-control as a byproduct of an unrelated trait: camouflage. To avoid being detected by predators, cuttlefish need to spend long periods of their day in hiding, taking only brief breaks to forage. "Thus, perhaps self-control evolved to optimize their foraging behavior and reduce their predator exposure," she added.

The researchers also tested whether the degree of self-control in cuttlefish was linked to higher intelligence, or in this case, the ability of the cuttlefish to learn. To do this, they trained the cuttlefish to associate the reward with various stimuli; cuttlefish that exerted more self-control (waited longer to get their food) had a better ability to learn, according to the findings. 

To link self-control to intelligence researchers need to study how the cuttlefish perform in other cognitive tests such as spatial memory and object permanence, which means an understanding that an object continues to exist regardless of whether you can see it, Schnell said. 

The findings were published Tuesday (March 2) in the journal Proceedings of the Royal Society B.

Originally published on Live Science.

Yasemin Saplakoglu
Staff Writer

Yasemin is a staff writer at Live Science, covering health, neuroscience and biology. Her work has appeared in Scientific American, Science and the San Jose Mercury News. She has a bachelor's degree in biomedical engineering from the University of Connecticut and a graduate certificate in science communication from the University of California, Santa Cruz.