Octopus vulgaris reacting to a diver (predator).
The initial change from camouflaged to conspicuous takes only milliseconds due to direct neural control of the skin. Full expression of the threat display (right) is two seconds. Video frame rate is 30 frames per second. Watch the video clip.
Everyone here is familiar with the incredible ability of cephalopods to change their appearance, right? If you aren’t, review your cuttlefish anatomy and watch this video. A few frames from the video are shown on the right.
This is an amazing ability, and the question is how do they do it? Roger Hanlon has been spending years tinkering with cephalopods, trying to puzzle it out and come up with an explanation. There are a couple of things a master of disguise needs.
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A good visual system. To match the background, you need to be able to see the background at least as well as the predator trying to see you.
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Fast connections to the effector organs. Cephalopods have motor nerves that go straight from their brains to the chromatophore organs with no synaptic delays along the way.
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The hard part: cutaneous chromatophore organs that can change intensity and texture with a fair amount of spatial resolution. Cephalopods have tiny, discrete sacs of pigment scattered all over their body, each one ringed with muscles that can iris shut to conceal the pigment, or expand the sac to expose the pigment. There are also muscular papillae that work hydrostatically to change the texture of the skin from smooth to rough to spiny/spiky.
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An algorithm. A set of rules that translate a visual field into an effective skin pattern that hides the animal.
One of the minor surprises of this work is that that last item, the algorithm for generating camouflage, may not be that complex. By studying many camouflaged organisms, they’ve categorized camouflage techniques into just three different strategies.
