So proud of the cuttlefish
- The Biophilia Effect
- Mar 22, 2021
- 5 min read
By Talia Chen
I don’t know if you’ve heard, but some cuttlefish recently passed a cognitive test meant for little kids *applause* and I’m incredibly proud of them. On March 3 of 2021, Cambridge University scientists published a study about the cognitive abilities of cuttlefish. They did a version of the marshmallow test, a test meant to test self control. The marshmallow test was popularized by Stanford psychologist Walter Mischel in the 70’s, and it consisted of putting a marshmallow in front of a kid and telling them that if they wait 15 more minutes before eating it, they can get another one. It was initially supposed to correlate childhood self control to life outcomes but later studies showed that it might not have been super accurate since Mischel didn’t control factors like socioeconomic background. Fun fact: I didn’t pass this test when I was a kid because I was a sucker.
This study is the first time scientists have demonstrated self-control in an invertebrate! Cuttlefish are smart, opportunistic eaters who can change the color/texture of their bodies for camouflage like octopuses, so it‘s probable that they use patience and intellect to wait for meals on the seafloor, especially since they have to choose when to break camouflage when hunting, which riskily exposes them to predators. Advanced self control is linked to better performance in cognitive tasks so “cuttlefish can tolerate delays to obtain food of higher quality comparable to that of some large-brained vertebrates” (Cuttlefish exert self control in a delayed gratification task). Generally, it is also possible that if a species leans to cooperation for survival, they could have better self control because they must overcome immediate gratification to help someone and receive a reciprocated favor later. However, cuttlefish are individualistic and have fast metabolism and a short lifespan of under 2 years. For them, the first explanation fits better because they must explore to hunt food, which requires advanced navigation and memory. Past studies have shown that cuttlefish can remember what-when-where components of encounters as well.
So this is how they did it. They used 6 sub-adult cuttlefish, each 9 months old and with no previous experiment experience. The scientists 3D printed an aquarium with two chambers on one side with plastic drawers and transparent sliding doors so the cuttlefish could see inside the chamber. The door with the full meal was put on a timer to set a delay in place. Each chamber had a detachable white plastic symbol so the cuttlefish could associate the shape with what was in the chamber. The opposing side of the aquarium had a triangular apex for the cuttlefish to settle in (aw) between both chambers. The immediate gratification chamber had a piece of king prawn shrimp and the delay chamber had a whole live grass shrimp. The cuttlefish were previously trained to use the doors and get the food. The scientists had the cuttlefish do one session of 6 trials a day, and varied which symbol represented which chamber, so for example, a triangle indicated a live shrimp for some cuttlefishes/some trials but for others, the triangle was used for the piece. They measured how long the cuttlefish took to approach a chamber and also how many times they striked the chamber with their two feeding tentacles (aw) trying to get the food. To ensure that the cuttlefish didn‘t just learn to wait in every run for more food, they trained them to go up and choose between the options. They tested increments of 10 seconds for the live shrimp chamber. The scientists tried using Asian shore crabs but it wasn’t a hit with the cuttlefish. They wouldn't approach it for a while, and some refused to eat it altogether. They ended up using live grass shrimp and a piece of raw king prawn, and the immediate option was always the less preferred one. They ran control rounds, like practice rounds, and then the experimental ones, so the cuttlefish would do 3 control trials then 3 experimental trials on each day. If the cuttlefish chose the delayed chamber and waited for all 3 experimental trials, the delay would be increased. If not, the cuttlefish would be retested at the same level of delay for 3 consecutive days. The maximum waiting time for each cuttlefish was the one recorded.
All the cuttlefish liked the live grass shrimp the best, followed by the raw king prawn and the Asian shore crab. The cuttlefish also modified their latency in response to increased delay. The maximum wait time for subjects was 50-130 seconds. Intuitively, the cuttlefish that withstood longer delays showed better learning performance. Their choosing to wait or not depended on the time delay, which is in line with studies on self control in mammals and birds. It becomes harder to wait when the time is longer. Some of these studies have been criticized because the choice is irrevocable so once they choose they can’t change their minds but for this study, the less preferred prey remained visible and accessible throughout the trial, so cuttlefish could have changed their minds and eaten the piece of prawn, they just didn’t want to. *Obviously, they were trained so that if they ate one they wouldn’t get the other, like the human version of the marshmallow challenge. In tests like this one, other animals like chimpanzees, dogs, and grey parrots have shown strategies for waiting such as looking away, closing their eyes, distracting themselves. The cuttlefish did the same, turning their bodies away from the immediate prey item to distract themselves. This wasn’t measured in the study because the aquarium had a partially opaque roof, so scientists couldn’t monitor that well. Further research is needed to draw a conclusion on how animals distract themselves from food.
Cuttlefish foraging behavior entails long, stationary periods of camouflage, so self control would be important in their evolution. However, further research would be needed to transfer this inference to octopuses/other cephalopods. It is very likely that octopuses do the same though. So, cuttlefish, like primates, corvids, and parrots can use past experiences a.k.a. win-stay-lose-shift situations where they stick to the rewarded response but shift when it doesn’t work anymore. They structure conditional rules that change in response to what they experience. The ability of self control is linked to the ability to plan for the future. The study adds that there are “comparable cognitive capacities between cuttlefish and more commonly studied mammals and birds with regard to self-control. Our results also provide the first evidence of a link between self-control and learning performance in a non-primate animal” (Cuttlefish exert self control in a delayed gratification task). If you were curious, there are no ethics regulations for research on cephalopods so no ethical approval was needed, but worry not because the study was designed to minimize stress on the cuttlefish and no noxious stimuli were used in any part.
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Written by Talia Chen
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