Enlarge /. A common squid, Sepia officinalis, in the Marine Resources Center of the Marine Biological Laboratory, Woods Hole, MA. A new study found that squid can delay gratification – a key trait of the famous "marshmallow test".
Certain species display a remarkable ability to delay gratification, particularly great apes, corvids, and parrots, while other species do not (such as rodents, chickens, and pigeons). Add the squid to the former category.
Scientists administered an adapted version of the Stanford Marshmallow Test to squid and found that the cephalopods could delay gratification – that is, wait a little for preferred prey rather than settle for less desirable prey. Squids also did better on a subsequent study test, according to a new article published in the journal Proceedings of the Royal Society B. It is the first time that such a link between self-control and intelligence has been found in a non-mammalian species.
As we previously reported, the late Walter Mischel's landmark behavioral study included 600 children between the ages of four and six, all of whom were selected from Stanford University's Bing Nursery School. He would give every child a marshmallow and give them the option to eat it right away if they wanted. But if they could wait 15 minutes, they'd get a second marshmallow as a reward. Then Mischel would leave the room and a hidden video camera would record what happened next.
Some kids ate the marshmallow right away. Others found a handy distraction: they covered their eyes, kicked the desk, or poked the marshmallow with their fingers. Some smelled it, licked it, or took tiny nibbles by the edges. About a third of the kids lasted long enough to earn a second marshmallow. A few years later, Mischel noticed a strong correlation between the success of some of these children later in life (better grades, higher self-confidence) and their ability to delay gratification in kindergarten. Mischel's follow-up study confirmed the correlation.
Mischel himself warned against over-interpreting the results, emphasizing that children who simply cannot stand this second marshmallow are not necessarily doomed to a life of failure. A more nuanced picture was provided by a study from 2018 in which the marshmallow test was repeated with preschool children. The same correlation was found between later performance and the ability to withstand temptation in preschool, but this correlation was much less significant after the researchers considered aspects such as family background, home environment, etc. And a German study from 2020 adapted the classic test setup with Oreos and vanilla biscuits for German and Kenyan school children. This study found that children are more likely to delay satisfaction when they are dependent on one another.
Other selected species have also shown the ability to retard gratification through "forward foraging". For example, monkeys and corvids respond to a variable and unpredictable food supply by not eating some food right away in preparation for a future shortage. Cambridge University biologist Alexandra Schnell, lead author of this latest study, wanted to investigate whether cuttlefish (Sepia officinalis, a relative of the squid and cuttlefish) can also show self-control during a fellowship at the Marine Biological Laboratory in Woods Hole, Massachusetts. Previous studies had shown that squid can optimize foraging behavior and memorize details about what, where, and when they come from previous feeds in order to adapt their strategy to changing prey conditions. But was this future-oriented foraging evidence of self-control?
To find out, Schnell and her team first conducted tests to determine the preferred prey for the six 9-month-old squids used in their experiments: live grass prawns, live Asian bank crabs, and pieces of raw king prawns. The squids turned out to be quite fussy eaters, least likely to favor the Asian bank crab. Some of the squids wouldn't eat the crabs at all. Between the two remaining prey animals, the squids showed a clear preference for the live grass prawns over the raw king prawns.
Enlarge /. Alexandra Schnell at the Cephalopod Mariculture Facility of the Marine Biological Laboratory in Woods Hole, Massachusetts.
For the experimental setup, the team printed a two-chamber device in 3D, which consisted of two black plastic drawers, each with a transparent sliding door so that the squid could see the contents. Each chamber was given its own removable, uniquely shaped symbol. The team placed the apparatus in an aquarium and then used PVC barriers at the other end of the tank to keep the squid an equal distance from both chambers.
Next, the squid went through a double training phase. In the first case, the cephalopods were placed in the aquarium and then provided with a single chamber, labeled with one of the visual symbols, to train subjects to associate this space with a certain level of accessibility for the prey. For example, a symbol was associated with instant access to the prey (instant gratification); another involved delayed release followed by access to the loot (delayed gratification); and a third was related to the inaccessibility of the prey (no satisfaction). In the third option, the squid would encounter a clear barrier keeping them away from the prey after the sliding door was opened after a short delay.
The second training phase included the selection of your choice. There were two unmarked chambers (no associated symbols) that were baited with the same type of prey. When the squid made a "choice" by approaching one of the chambers, the prey in the other chamber was immediately removed. Subjects also went through a pre-test phase to teach them that the delays in accessing prey would sequentially increase. In this pre-test, the delay time was between two seconds and 20 seconds, and each squid had to "choose" between an immediate and a delayed option.
For the actual experiment, the squid had to choose between two different prey animals: it could eat the raw king prawn immediately or delay the satisfaction for the preferred live grass prawns. (A control group of squid had to choose between immediate access to prey or no access at all.) Subjects could see either option for the duration of the trial and give up waiting at any time and eat the king prawn when they got tired keep an eye out for the grass prawns. The team also put the squid on a learning task to assess cognitive performance. The cephalopods first learned to associate a visual symbol with a specific prey reward, and then the researchers reversed the situation so that the same reward was associated with another symbol.
Enlarge /. Scheme of test conditions in the delay maintenance task: (a) control condition and (b) trial condition.
Alexandra K. Schnell et al., 2021
The results: "Squids in the present study were all able to wait up to 50-130 seconds for the better reward and tolerated delay, which is comparable to what we see in large-brained vertebrates like chimpanzees, crows and parrots," Schnell said . "The squids that learned both associations (with the food reward) the fastest were able to control themselves better."
Humans may have developed the ability to delay gratification in order to strengthen social bonds and thereby benefit the species as a whole. In monkeys, corvids and parrots, the evolutionary driver could be linked to the use of tools and the storage of food (caching behavior) as well as the strengthening of social bonds. But octopuses do not use tools or store food and are not a social species. Squids appear to have developed this link between self-control and cognitive performance through a completely different evolutionary path – an example of convergent evolution.
"Squids spend most of their time camouflaging, sitting and waiting, interrupted by short foraging periods," Schnell said of her working hypothesis of how the cephalopods might have developed this ability to control themselves. “They break camouflage when they forage, so they are exposed to any predator in the ocean that tries to eat them better quality waits for food. "
DOI: Procedure of the Royal Society B, 2021. 10.1098 / rspb.2020.3161 (Via DOIs).