You and I both have the ability to travel back in time… at least in our minds. For example, I can remember that last Monday, I was at my desk, writing a post about stomachless animals. You too have a seemingly endless catalogue of the whats, wheres and whens of your life.
This ability to remember the what, where and when of our past experiences is known as “episodic memory”. The term was first coined in the 1970s by Canadian psychologist Endel Tulving, who thought that such memories depended on language and were unique to humans.
He was wrong. In 1998, Nicky Clayton from the University of Cambridge published the first of many seminal experiments with western scrub-jays, showing that they can remember where they had stored food and which hoards were freshest. In other words, these bird brains also have episodic-like memories. We say “episodic-like” since we can’t really know if the animals store their what-where-when information into single coherent memories in the way that we do. Still, it’s clear that the components are there.
Since then, the episodic-like memory club has grown to include the great apes, rats, hummingbirds, and pigeons. But these are all mammals and birds. Christelle Jozet-Alves from Normandie University wanted to know if the same skills existed in animals that are very different to these usual suspects. She turned to the common cuttlefish (Sepia officinalis).
Like octopuses and squid, cuttlefish are cephalopods—a group of animals known for their amazing colour-changing skin and sophisticated intelligence. Cuttlefish are separated from birds and mammals by almost a billion years of evolution. But Jozet-Alves, together with Clayton and Marion Bertin, has shown that they too can “keep track of what they have eaten, and where and how long ago they ate”.
They are also soft-bodied and nutritious, which puts them on the menu of virtually every major group of ocean predator. Cuttlefish deal with these manifold threats through camouflage, defensive ink, and just plain-old hiding. They spend more than 95 percent of their time hiding in safe places. When they do venture out to search for food, it pays them to be quick about it. “Cuttlefish live fast and die young. They live less than two years, but their size drastically increases between hatching and old age,” says Jozet-Alves. “They definitely need to be very efficient when foraging if they want to grow as fast as possible.”
First, the team trained three cuttlefish to approach a black-and-white symbol to get a morsel of food—either crab, which they were fine with, or shrimp, which they vastly preferred. The cuttlefish also learned that the shrimp supply took a while to refill. If they approached the symbols within 3 hours of their last meal, they got nothing.
Next, Jozet-Alves presented them with two of the same symbols at different positions in their tank. The cuttlefish randomly approached one of the symbols, and Jozet-Alves dropped shrimp in front of one, and crab in front of the other.
She tested them an hour later. At this time, it would have been pointless to approach the shrimp symbol, since it wouldn’t have replenished. And the cuttlefish knew that—they almost always approached the crab symbol the second time around. But if Jozet-Alves tested them three hours later, they almost always approached the shrimp symbol instead. They knew that their favourite morsel would have replenished and that it was worth trying for it.
Their behaviour shows that they remember what (shrimp or crab), where (which symbol was associated with which food) and when (the time since they last ate). Admittedly, the team only tested three individuals but all of them behaved in the same consistent way. Like scrub-jays, chimps and hummingbirds, they have episodic-like memory.
But cuttlefish, being invertebrates, are very distantly related to these other members of the club. The only other invertebrates with a hint of the same abilities are honeybees, and they were only trained to go to the same place at the same time every day. That’s not quite the same as encoding information about specific events. Still, it’s clear that contrary to Tulving’s claims, the ability to encode what, where and when isn’t a uniquely human trait. It’s probably not even a uniquely vertebrate one.
Jennifer Mather from the University of Lethbridge, who studies cephalopod smarts, isn’t surprised. Years ago, she noticed that octopuses are “win-switch foragers”. That is, if they find food somewhere, they don’t visit it for a few days. “This paper isn’t the first behavioral evidence of episodic-like memory in an invertebrate, but it’s certainly the first experimental evidence of this capacity,” she says. “It underlines the tremendous flexibility and cognitive capacity of these very interesting animals.”
Jozet-Alves agrees. “Everyone who had the chance to work with cuttlefish have seen how amazing and fascinating they are,” she says. “At the same time, working with them is a real challenge to your patience. They are so shy that just making a cuttlefish eat in front of you can take sometimes days or even weeks. But once a cuttlefish gives you its trust, you just enjoy working with them and totally forget the hours waiting that they move out of their shelter!”
Reference: Jozet-Alves, Bertin & Clayton. 2013. Evidence of episodic-like memory in cuttlefish. Current Biology http://dx.doi.org/10.1016/j.cub.2013.10.021
More on cuttlefish:
- Cuttlefish learn from watching potential prey even before they are born
- Cuttlefish tailor their defences to different predators
- How cuttlefish could “see” with their skin
- Cuttlefish woos female and dupes male with split-personality skin
- How dolphins prepare the perfect cuttlefish meal
- Will all camouflaged cuttlefish please raise their tentacles?