Meet an eight-legged actor
If you think the Oscar nominees are good at pretending, wait till you hear what this octopus can do
At first, it's just a lump creeping across the sand. Then it speeds up. It flattens its body, pulling all eight arms in tight. Instead of jetting like an octopus, it moves its body in a wave. What is this thing? An octopus or a flatfish?
Several years ago, divers found this very strange octopus. It was the size of a child's bicycle tire and swam in the warm, tropical waters of Indonesia. It lived in a mucky area where few people had been scuba diving. Octopuses are famous for being able to change color and shape, but this one was special.
Divers said it could imitate a whole cast of other animals: flatfish, mantis shrimp, sea snakes, jellyfish, anemones, and even lionfish. They called it "the mimic octopus."
"When I first heard about the octopus," says Denis Tackett, an underwater photographer, "it sounded impossible. Then, "One day, I thought I had found a new type of mantis shrimp. I got closer and saw it was really the mimic octopus."
Divers showed scientists photos of the new octopus acting like other animals - many other animals. But figuring out the octopus's act was sometimes like looking for shapes in clouds. "Some people were getting really carried away," says Tom Tregenza, a biologist at the University of Leeds, in England. "We looked at photographs of the octopus and joked, 'This one is doing a double bed, and this one is doing a car stereo.' "
Scientists found it hard to believe that the octopus could look and act like so many other sea creatures. Some animals mimic other animals, but no creature imitates more than one. At least, that is what scientists used to think.
Why does one animal imitate another? Mimicry is a strategy some animals use to try to trick predators into leaving them alone. They do this by pretending to be a different animal - usually an animal the predator knows is dangerous or tastes bad.
For example, one particular beetle looks like a wasp. Birds don't like wasps because of their sting, so they won't often eat the tasty beetle because it looks and acts like a wasp. The beetle is the mimic, the wasp is the model, and the bird is the predator the mimic is trying to fool.
This strange new octopus raised many questions. Could it truly mimic many models? Was the mimic octopus nature's greatest actor?
Many divers were certain the octopus could mimic other sea creatures. Scientists needed a lot more than photographs to be convinced that the octopus was a true mimic, however. Two Australian biologists working with Dr. Tregenza traveled to Indonesia to see the octopus. So did American scientist Roger Hanlon. When the biologists saw the mimic octopus's home, they could guess why it might need to fool predators by pretending to be other animals.
Octopuses often live on reefs or rocky ocean bottoms, where there are plenty of hiding places. The mimic octopus lives on a plain of mud and sand. "There is nowhere to hide," Tregenza says. "You either tough it out on top, hoping a predator can't catch you, or you try to become so distasteful that if they do catch you, they can't eat you. Or you hide in the sand, which is what most animals do. But there is one other option: You're out, but you look like something else."
The mimic octopus's favorite model seems to be the flatfish. Dr. Hanlon and a team of volunteers videotaped the octopuses for six days. Divers went down in shifts from 4:30 a.m. until dark. "The octopus did the flatfish 800 times," Hanlon says. "It is beautiful mimicry. You think of how hard it is for that animal to flatten itself and get all eight arms to look like one body and wiggle the edges just like fins. It is a real work of art." (For a video, see Web links on facing page.)
Hanlon thinks the mimic octopus may imitate flatfish because the fish are very common and less likely to attract a predator than an octopus is. An octopus is "a soft, juicy hunk of protein that everything else out there wants to eat. So, you stay camouflaged when you are still or moving slowly. But what if you have to move faster? When they act like one of those flatfish, they don't look like an octopus anymore."
Tregenza's team claims that the mimic octopus can imitate at least three animals: flatfish, sea snakes, and lionfish. Hanlon says only flatfish mimicry has been proved conclusively, but that the octopus has more tricks. "When the octopus stops, it often gets into the exact shape and color of a sponge, a feather-duster worm, or a sea squirt," Hanlon says.
If the mimic octopus really can imitate these and other animals, the biologists will need hundreds more hours of videotape to prove it.
The mimic octopus does seem to be a wonderful actor, but one "player" in the drama is still missing. Animals don't evolve mimicry to impress divers, biologists, and readers of The Christian Science Monitor. What predator is the mimic octopus trying to fool?
"It would be nice to find the predator," Hanlon says. "We don't know who is preying on the octopus, so we have to guess. Who is watching all this? What did the mimicry evolve for?"
Scientists are also still guessing why the octopus mimics many different animals. Tregenza thinks that a predator faced with lots of mimicry is less likely to see through the octopus's deception.
The mimic octopus has enough tricks up its eight sleeves to keep predators - and biologists - watching its act for a long time.
A short video clip of the mimic octopus impersonating a flatfish can be viewed at: www.macdonaldproductions.com/preview.html
For more information on how squids and octopuses make their rapid color changes, go to: hermes.mbl.edu/services/MRC/adaptive.html
Biologist Roger Hanlon will be back in Indonesia next December, trying to solve the mystery of the mimic octopus. Interested volunteer divers should check out: www.coralreefalliance.org/travel/kungkunganbay.html
Around the coral reefs of the South Pacific, everybody loves the cleaner wrasse. The little striped fish grooms larger fish, picking off tiny parasites and dead scales. Instead of lunching on the cleaner wrasse, larger fish line up to get the wrasse's "beauty treatment."
Enter the sabre-toothed slime fish. It looks and acts like a cleaner wrasse - except it has two long sharp teeth. Instead of grooming the larger fish, the sabre-toothed slime fish swims up behind it, takes a big bite, and zips away.
We often use red, black, and yellow as warning colors. Think of fire alarms and "danger" signs. These are also nature's warning colors. The poisonous coral snake of the Southeastern United States has bright bands of red, black, and yellow that say "watch out!" The harmless king snake's similar color bands help it scare off predators, too.
If a toothy predator were chasing you, would you stick your head in a hole and wave your bottom around? Probably not, but that's what the comet fish does.
This small fish from the tropical Pacific is dark brown with tiny white dots, just like a common (and fierce) moray eel. The comet fish also has an "eye spot" near its tail that looks like the eye of a moray eel. When chased by a bigger fish, the comet fish dives headfirst into a hole and wiggles its "fake eel" fanny.
Imagine putting a tasty-looking chocolate in your mouth - and biting down on a bar of soap! That's how a bird feels when it tries to eat a lovely-looking, nasty-tasting monarch butterfly. Once a bird has tried a monarch, it stays away from the black-and-orange insect. The tasty (to a bird) viceroy is slightly smaller than the monarch, but mimics its beautiful colors. So when a bird sees a viceroy, it thinks "yuck!" not "yum!"
Imagine you could instantly turn your curly red hair and freckles to straight black hair and olive skin. An octopus does something like that. It can change its color.
An octopus's skin contains pinprick-size sacs of color. The color sacs come in red, brown, yellow, and black. Tiny muscles surround each color sac. If an octopus wants to turn red, it flexes the muscles surrounding only the red color sacs. When the red color sacs are open, the octopus looks bright red.
What if an octopus wants to look blue or green? It doesn't need color sacs for those colors. It has tiny plates in its skin that reflect the blue-green color of the water. When an octopus wants to look blue, it "turns on" its reflectors. Using its color sacs and reflecting plates in combination, an octopus can be blue-spotted, red-striped, or almost any other combination. An octopus in Tahiti was videotaped changing its "look" 177 times in an hour - three times a minute!