Put a cuttlefish on the spot — or, to be more exact, a series of spots — and it will disappear. These relatives of the squid and the octopus mimic the color and texture of their surroundings, camouflaging themselves to blend in with seaweed, sand or stone, which helps them escape predators.
But no one is quite sure how a cuttlefish brain takes what the eyes see and gets the muscles of the skin to copy it. Are they watching their own skin as it changes and tweaking it to fit the sand? Or what if getting the match doesn’t rely solely on eyesight — does a certain kind of speckling feel different to the animal than, say, stripes?
In an effort to answer this question, scientists have turned to high-resolution videos that can show what individual skin cells are up to as a cuttlefish changes color.
In a paper published in the journal Nature on Wednesday, researchers found that cuttlefish sampled a wide variety of different options while they worked to make a match between their skin and their surroundings. As they got closer and closer to a match, they repeatedly paused in their morphing, as if they were checking to see if this time, they’d gotten it right. The findings are a glimpse at what’s going on in a fundamentally different form of life as it does something that, to our eyes, seems almost magical.
To match their backgrounds, cuttlefish use an array of pigment-filled skin cells called chromatophores and raised structures called papillae. Cuttlefish contract myriad tiny muscles that open and close the chromatophores, like pixels on a screen, to get the right pattern of any surface they swim over.
An extensive body of research has established that cuttlefish can reach their final pattern in less than a second. It was possible, thought Gilles Laurent, a professor at the Max Planck Institute for Brain Research in Germany and an author of the new paper, that the cuttlefish sees an image, decides how it’s going to mimic it and then goes straight to a matching skin pattern. Dr. Laurent and his colleagues broke that fraction of a second down to observe which chromatophores were open and closed on the way to the final product.
For the study, the team presented 30 backgrounds printed on fabric to cuttlefish, unrolling the backgrounds on the floor of their tank. As the animals changed their color and pattern, the cameras were watching, and when the researchers analyzed the data, they saw that each cuttlefish was working through different patterns.
“What we observe is the animals move in an intermittent fashion slowly toward that end pattern, in segments of motion, interrupted by times when they stop and seem to be comparing themselves to the end goal they want to achieve,” Dr. Laurent said. “Eventually, when they reach something that satisfies them, they stop.”
The little pauses get longer as the cuttlefish gets closer to the end goal, he continued. Perhaps it gets harder for the cuttlefish to tell if its skin pattern requires additional changes.
“We believe they have some knowledge of the pattern they express at a given time,” he said. “How that is acquired, we don’t know.” It might be that they are using their eyes to check their coloration. But it could also be that the cuttlefish is aiming for a certain feeling in its skin. No one is sure of the answer.
What’s more, Dr. Laurent’s team noticed that when a cuttlefish encountered a background it had seen before, it did not go about matching it in exactly the same way. The cuttlefish took a different route to its final pattern each time.
That suggests that the animals are not learning a strategy for achieving a goal the way humans do when they learn to walk, or pick up objects, Dr. Laurent said. Instead, they are somehow born with the ability to paint what they see onto their skin using thousands of tiny muscle contractions.
“It’s so foreign to us, as a motor system, as a behavior, as an animal,” he said. “These are just amazing creatures.”
This system, honed through eons of evolution, may turn out to be quite complicated, or deceptively simple. Only more research will get scientists closer to understanding the experience of a cuttlefish as it flits over dappled sand, flexes its skin and disappears.
