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Issue 469, 24 September 2001

Eight arms make for better impersonations

Researchers have discovered one of the most striking examples of mimicry in the animal world: an octopus which scares off predators by changing its appearance selectively to resemble poisonous animals.

Acting for survival - the octopus mimics a sea-snake (above left) and a poisonous banded sole (above right).

While mimicry is common in nature by harmless creatures hoping to be mistaken for their more dangerous counterparts, most octopuses alter their appearance to melt into the background, resembling rocks, coral or drifting plants. The mimic octopus is the first animal discovered by scientists which is able to choose selectively from a range of impersonations, and to respond appropriately to different predators.

Dr Tom Tregenza of the school of biology and colleagues from Australia were the first to document the mimic octopus, noticing their astounding behaviour during research dives in Indonesia.

When travelling at speed, the octopus draws all its arms into a leaf-shaped wedge and undulates its body, to resemble a type of sole common to the area. It can also swim above the sea floor, with arms clearly striped and trailing from the body, to resemble the poisonous lion-fish. When attacked by damsel fishes, the octopus threads six of its arms down a hole, and raises the other two in opposite directions, creating the appearance of the damsel fishes' main predator, the banded sea-snake.

Dr Tregenza explains: "The octopus is ideally suited to these kind of impersonations, as its lack of skeleton allows for flexible movement, and it has the ability to change the colour, pattern and shape of its skin. We also saw the octopus take on other forms that seemed to resemble sea-anemones and jellyfish. We need to do more research to find out about these fascinating creatures."

Click here for further information, and links to a movie of the sea-snake impersonation



 
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