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Have Tentacles, Will Mimic

29 August 2001 7:00 pm
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Present arms. The octopus, resting (a), foraging (b), and closely resembling the poisonous banded sole (c and d), the lionfish (e and f), and a sea snake (g and h).

Researchers have discovered what they say is one of the most striking examples ever of mimicry in the animal world: an octopus that can change its appearance to look like several different poisonous animals in its environment.

Mimicry abounds in nature; harmless snakes look like dangerous coral snakes, for instance, and flies take on the yellow and black warning stripes of bees and hornets. Most octopuses, however, are much more demure. They specialize in camouflage, morphing their bodies and the texture and color of their skin to hide among rocks, algae, or coral.

So when marine photographers Roger Steene and Rudie Kuiter first told cephalopod biologist Mark Norman of the Melbourne Museum in Australia about a strange octopus off the coast of Sulawesi in Indonesia, Norman was astonished. Norman had helped discover 150 species of octopus, but none were like the one described by the duo. Later, Norman agreed to lead a diving trip, sponsored by the BBC and the Discovery Channel, to find the eight-legged wonder. The resulting show, "Octopus Hunter," aired last year, and a scientific account of the discovery appears in the 7 September Proceedings of the Royal Society of London B.

The striped octopus, not yet named, can spread its limbs wide and swim in open water to resemble the highly toxic lionfish. Or it can flatten its body and undulate along the bottom like a flatfish with poisonous spines. And when territorial damselfish nip at its flesh, the octopus withdraws six legs into the nearest hole and protrudes two boldly striped legs to imitate a venomous sea snake, one of the damselfish's worst enemies. That suggests the animal adapts its mimicry to counter the threat at hand, the team says. The repertoire of behaviors may even include other dangerous animals found in the region, including sand anemones, stingrays, and crocodile snake eels, Norman says.

The octopus badly needs its mimicry, says co-author Tom Tregenza of the University of Leeds, because unlike other octopus species, it forages by day over open sandy bottom in full view of its fish predators. "It's such an exposed habitat that camouflage just isn't good enough," Tregenza says.

Other researchers are fascinated, but still somewhat skeptical of the octopus' skills at impersonation. What's needed now are experiments to show how the octopus reacts to the sight of predators and how predators react to the mimicry, note butterfly mimicry experts James Mallet of University College London and Durrell Kapan of the University of Puerto Rico, Rio Piedras. "If these cases of mimicry hold up," Mallet says, "this is very unusual."

Related sites

Octopus imitating a sea snake
Primer on mimicry from James Mallet's home page
Some info on Mark Norman and Australian cephalopods
Popular article with photos of octopus mimicry

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