Zipping through water like shimmering arrowheads, cuttlefish are swift, sure hunters — death on eight limbs and two waving tentacles for small creatures in their vicinity. They morph to match the landscape, shifting between a variety of hues and even textures, using tiny structures that expand and contract beneath their skin. They even seem to have depth perception, researchers using tiny 3-D vision glasses found, placing them apart from octopuses and squids. And their accuracy at striking prey is remarkable.
But for cuttlefish, these physical feats in pursuit of food are not the whole story. A new study published this month in the journal Royal Society Open Science shows that there is even more to cuttlefish cognition than scientists may have known.
The sea creatures appear to be capable of performing calculations that are more complicated than simply “more food is better.” Presented with a choice between one shrimp or two, they will actually choose the single shrimp when they have learned through experience that they are rewarded for this choice.
While the braininess of their octopus cousins gets a lot of attention, researchers who study animal cognition have uncovered surprising talents in cuttlefish over the years. For instance, the cephalopods will hunt fewer crabs during the day if they learn that shrimp, their preferred food, is predictably available during the night. That shows that they can think ahead.
Chuan-Chin Chiao, a biologist at National Tsing Hua University in Taiwan, and an author of the current paper alongside his colleague Tzu-Hsin Kuo, has found in the past that cuttlefish that are hungry will choose a bigger, harder-to-catch shrimp to attack, and those that are not will choose smaller, easier-to-catch ones.
But researchers have also found that animals do not always make decisions that seem logical at first glance. Like humans, whose behavior rarely fits economists’ visions of what an ideal, rational creature would do, animals respond to their environments using learned experiences.
In these new experiments, curious to see whether they could alter the value cuttlefish attach to a single shrimp, the researchers gave the cuttlefish the option of entering a chamber with one shrimp or a chamber with none. Each time they entered the chamber with a shrimp, the researchers gave them a smaller shrimp as a reward.
Then each cuttlefish took a second test. They could enter a chamber and chase after two shrimp. Or they could enter another chamber that had only one.
“You’d think they always choose the larger quantity,” Chiao said. But that was not what happened.
In the second round the cuttlefish chose one shrimp significantly more often than two. Cuttlefish that hadn’t had the training reliably picked two shrimp over one, demonstrating that those that chose the smaller number were anticipating the reward and operating differently than their fellows. Even waiting until an hour had passed since the initial training did not completely erase the new behavior.
The process of being rewarded for choosing one shrimp seems to have given that option an extra glow as far as cuttlefish are concerned, Chiao said. That suggests that they are not simply making basic responses to prey they come across — they’re remembering what has come before and using it to make a choice. Even if in this situation the behavior didn’t result in a bigger haul, it adds to the evidence that they are complex creatures, capable of using their brains in ways that may surprise us.