New study into evolution of mimicry in octopuses

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Some octopuses deceive predators by mimicking flatfish and how this mimicry has evolved has been examined in a paper published in the most recent issue of the Biological Journal of the Linnean Society.

Flatfish swimming is a mode of locomotion in which the octopus mimics a swimming flatfish.  

It does so by positioning its tentacles to attain a flatfish shape, positioning both eyes prominently as in a flatfish, and swims with undulating movements of its tentacles to resemble the fin movements of flatfish.  

There is an advantage for the octopus in mimicking swimming flatfish, because this may confuse predators long enough for the octopus to escape.

Christine Huffard and coauthors studied the evolution of flatfish swimming in octopuses (particularly in the mimic octopus, Thaumoctopus mimicus) by reconstructing a molecular phylogeny of shallow-water octopuses using 1216 base pairs representing the sequences of two mitochondrial genes (16s rRNA and cytochrome oxidase I). 

By mapping characters on the resulting phylogeny, the authors hypothesised the sequence of events that led to the evolution of flatfish swimming in the mimic octopus: The ancestors of the mimic octopus first evolved the use of highly contrasting brown-and-white colour to be used in surprising predators when camouflage fails.  

Next, they evolved flatfish swimming and the long tentacles that facilitate this mode of locomotion.

Finally, the mimic octopus combined the presence of a bold colour pattern with flatfish swimming in order to deceive predators.

The authors also suggested possibilities on why the mimic octopus bears such a highly contrasting colour pattern.  

They posit three possibilities:

  • The colour may actually be useful as camouflage by breaking up the outline of the octopus;
  • It may serve as aposematic (warning) coloration to warn predators that the octopus is toxic;
  • It may have evolved to enable the octopus to mimic toxic flatfish (such as the peacock sole, Pardachirus pavoninus, or the zebra sole, Zebrias spp.).

"This study reminds us that evolution does not have an endgame, but is a continuous process," says Christine Huffard.

"These octopuses will continue evolving as long as we can protect them and their habitat from threats like trawling, land reclamation, and run-off."

For more information, see the paper: Huffard, CL, N Saarman, H Hamilton and WB Simison (2010) The evolution of conspicuous facultative mimicry in octopuses: an example of secondary adaptation? Biological Journal of the Linnean Society 101, pp. 68–77.