Mimic octopus - the cephalopod that can look like a fish

August 2010: The Indonesian mimic octopus can impersonate flatfish and sea snakes to dupe potential predators. By creatively configuring its limbs, adopting characteristic undulating movements and displaying conspicuous colour patterns, the octopus can successfully pass for a number of different creatures that share its habitat, several of which are toxic.

Now, scientists from the California Academy of Sciences and Conservation International Indonesia have conducted DNA analysis to determine how this remarkable adaptation evolved.

NO CHANGE: The mimic octopus before it uses one of its elaborate disguises

Like its relatives, the mimic octopus is capable of hiding from hungry predators by blending into its background. But this species often chooses to make itself more conspicuous to predators by mimicking flatfish, lionfish or sea snakes that display high-contrast colour patterns. This daredevil manoeuvre is thought to help the octopus confuse or scare away predators.

Because it is relatively rare for an animal to develop such a high-risk, conspicuous defence strategy, the authors of the recent study hoped to gain insight into the evolutionary forces that fuelled this behaviour by conducting genetic research on the mimic octopus and its relatives. They focused on the mimic's ability to flatten its arms and head and swim along the sea floor like a flatfish, while simultaneously exhibiting a bold, brown-and-white colour pattern.

Researchers discovered that the octopus's ancestors employed the bold colour displays as a secondary defence if camouflage failed. They then evolved to use the flatfish swimming technique and the long arms that facilitate this motion. Finally, the mimic octopus began displaying bold colour patterns while impersonating a flatfish during both daily forays away from its den and at rest. In evolutionary terms, this last step represents an extremely risky shift in defence strategy.

BOLD DEFENCE: The bright colours warn off predators

‘The close relatives of the mimic octopus use drab colours and camouflage quite successfully to hide from predators,' says Dr. Christine Huffard, Marine Conservation Priorities Advisor at Conservation International Indonesia. ‘Why does it draw attention to itself, and repeatedly abandon the camouflage abilities it inherited from its ancestors in favour of a bold new pattern? Somehow, through natural selection, being conspicuous has allowed the mimic octopus to survive and reproduce more successfully than some of its less showy ancestors, and eventually evolve into its own lineage.'

The researchers suggest several possibilities for why such a bold approach would be advantageous. It may fool predators into thinking the octopus is a toxic flatfish (such as the peacock sole or the zebra sole); it may obscure the octopus's outline against the black-and-white sandy bottoms; or it may serve as an honest warning sign of the mimic's unpalatable flesh.

FACING THE ENEMY: Scientists think the mimic octopus' disguises make predators do a life-saving double-take

‘While the mimic octopus's imitation of flatfish is far from perfect, it may be good enough to fool predators where it lives, in the world's centre of marine biodiversity,' says Dr. Healy Hamilton, Director of the Center of Applied Biodiversity Informatics at the California Academy of Sciences. ‘These octopuses can change their colour pattern to look similar to numerous toxic and non-toxic flatfishes in their area. In the time it takes a predator to do a double-take, the octopus may be able to get away.'

Discovered in 1998
Undescribed by scientists until 1998, much remains unknown about the mimic octopus.

‘This study reminds us that evolution does not have an endgame, but is a continuous process,' says Huffard. ‘These octopuses will continue evolving as long as we can protect them and their habitat from threats such as trawling, land reclamation, and run-off.'