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October 28, 2013 | By:  Sarah Jane Alger
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The Mimic Octopus: Master of Disguise

Different animal species have evolved a number of ways to hide in their environments. One of the most popular tactics is by camouflage, often by matching the background or by having patterns that break up the animal's outline (think: zebras and leopards). Others have evolved to resemble other species that are generally toxic or venomous, in a technique called mimicry. But a few amazing species have been recently discovered to have the ability to alter their mimicry to actively imitate a range of species, depending on their circumstances. The most remarkable of these is the mimic octopus, which shifts its shape and behavior to mimic a number of different species as fluidly as a real-life Mystique from the X-Men.

The mimic octopus was discovered in 1998 off the coast of Sulawesi, Indonesia. They live on the shallow sandy bottoms near river mouths, which are extremely exposed habitats with lots of predators. They spend much of their time looking out from their burrows and foraging along the sandy bottoms in mottled drab brown colors that blend with their surroundings. This camouflage technique does a good job hiding them from predators as long as they don't move too much. Animal vision is often fooled by colors and patterns that blend in with the surroundings... until the image moves. Our strong movement detection abilities will quickly bring a moving camouflaged animal into focus. So how could a soft-bodied animal safely move around an exposed and predator-rich environment?

The mimic octopus has a brilliant solution to this problem. When swimming in the open-water, they take on black and white bands and trail their arms behind them like the flared poisonous spines of a lion-fish. When moving rapidly from place to place, they turn the mottled brown of the sandy bottom, arrange their arms in a leaf-shape and undulate their bodies along the contours of the sand, swimming like a sole, a populous and poisonous flatfish in the area. And when attacked by small and fiercely territorial damselfish, they hide six of their arms in a hole and raise the other two in opposite directions, now with thick black and beige bands, appearing like a venomous banded sea-snake. And this isn't all. SCUBA divers report mimic octopuses resembling anenomes, jellyfish, mantis shrimp, feather stars, brittle stars, giant crabs, seahorses, crocodile snake eels, stingrays, and nudibranchs. These imitations have yet to be scientifically verified, but the potential is astounding!

These images from the Norman, 2001 article in Proc. R. Soc. Lond. B show many of the disguises of the mimic octopus. (a) shows a mimic octopus looking out of its burrow; (b) is a foraging mimic octopus with coloration to blend with the sand; (c) shows a mimic octopus as a sole and (d) is an actual sole; (e) shows a mimic octopus as a lion-fish and (f) is an actual lion-fish; and (g) shows a mimic octopus as a banded sea-snake and (h) is an actual banded sea-snake.

What is it about the mimic octopus that makes it so good at mimicking other species? For one thing, cephalopods like octopuses are well-known for their ability to change the color, pattern and texture of their skin to blend in with rocks, coral and plants. But unlike other cephalopods, octopuses do not have rigid skeletal elements, allowing their bodies much greater flexibility in the forms they imitate.

Despite these abilities common to many cephalopods, and octopuses in particular, this ability to change both physical appearance and behavior to switch back and forth among imitations of multiple species even when those species are not around is unique. In this species we see the evolutionary "perfect storm" in which a species with flexibility in their skin and body shape is consistently exposed to a predator-rich environment that contains toxic or venomous species such as soles, lion-fish and banded sea-snakes. This combination provides both the selective pressures and the opportunity to these otherwise vulnerable animals to evolve into the world's greatest masters of disguise!


Further reading:
Norman, M.D., Finn, J. and Tregenza, T. Dynamic mimicry in an Indo-Malayan octopus, Proc. R. Soc. Lond. B, 268, 1755-1758 (2001). DOI: 10.1098/rspb.2001.1708.

Hanlon, R.T., Conroy, L. and Forsythe, J.W. Mimicry and foraging behaviour of two tropical sand-flat octopus species off North Sulawesi, Indonesia, Biological Journal of the Linnean Society 93, 23-38. (2008). DOI: 10.1111/j.1095-8312.2007.00948.x.

Image Credits:
The Mystique photo was adapted from Mystique-xmen by Ken Fager at Flickr.

Figure 1 from the Norman, 2001 article in Proc. R. Soc. Lond. B

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