Predatory Sea Slug Learns What Not to Eat by Putting Everything in its Mouth

A certain predatory sea slug is a bit like a human toddler; it will put anything and everything in its mouth--whether it's good for it or not. Now, researchers have discovered that this sea slug learns from its mistakes, remembering to avoid dangerous prey in the future.

The slug, named Pleurobranchaea californica, is a deep-water species that can be found off the coast of California. Despite its ability to learn, it has a relatively simple neural circuitry and set of behaviors. A generalist feeder, it will try almost anything once. In fact, researchers have seen it try to gobble down stinging animals--rather like how a toddler will try to gobble down plastic keys. Yet one particular incident stuck out when it came to this species of sea slug.

"I had a Pleurobranchaea in a small aquarium that we were about to do a physiological experiment with, and my supplier from Monterey had just sent me these beautiful Spanish shawls," said Rhanor Gillette, the head researcher, in a news release. "So I said to the visitor, 'Would you like to see Pleurobranchaea eat another animal?"

Spanish shawls are colorful orange and purple sea slugs. They can move gracefully through the water, undulating in waves in order to escape predators. Yet this species also has another adaptation they use to deter predators. The animal possesses stinging cells in the orange outgrowths that cover its back.

Gillette ended up placing the Spanish shawl into the aquarium with the predatory sea slug. Unsurprisingly, the predator approached, smelled, and then bit into the Spanish shawl. In turn, the purple and orange sea slug stung the attacker who then quickly let go of the Spanish shawl and began its escape with an avoidance turn. The chewed-on Spanish shawl, in turn, fled with its "flamenco dance of escape."

Gillette wasn't quite done with the slugs, though. His curiosity piqued, he then placed the slugs together in the same aquarium again. Rather than trying to eat the colorful slug, though, Pleurobranchae immediately began its avoidance turn.

"I had never seen that before!" said Gillette in a news release. "We began testing them and found that they were learning the odor of the Spanish shawl very specifically and selectively."

Gillette decided to conduct a series of experiments to see if this behavior was typical for predatory slugs. They tested slugs that were both hungry and full and found that all of them that were "trained" in an encounter with a Spanish shawl later avoided the creature. Yet those that were ravenously hungry would still eat the other slug.

The findings show that the "simple" eating behaviors of Pleurobranchaea are actually far more complex than researchers first thought. In fact, it shows that the slug is capable of learning what things are good to eat and what things are better to avoid.

The findings are published in the Journal of Experimental Biology.