Oh yeah? You’re a cuttlefish fan? How many visual processing systems do they use to camouflage themselves?

The answer is two. Probably? Possibly?

Ok, so maybe it’s not a fair question. Apparently the most accepted answer is that they relied on a small handful of variations, without much room for judgement or finesse. The problem is, as the press release notes, cuttlefish seemed to have a lot more going on than would be needed for an “easy” answer like that.

A new study by City, University of London and others suggests that the European cuttlefish (sepia officinalis) may combine two distinct neural systems that process specific visual features from its local environment, and visual cues relating to its overall background environment, in order to create the body patterns it uses to camouflage itself on the sea floor.

This is in contrast to previous research suggesting that the cognitive (brain) processes involved are much simpler, in that the cuttlefish adopts one of only three major types of body patterns to visually merge with its background. However, that does not explain why the animal possesses about 30 different body pattern components it could use to achieve this.

I am by no means an expert on evolution, but in general, if I see some part of an organism that’s taking up energy without any apparent purpose, I assume that there is a purpose that I just don’t know about. That’s part of why I’m predisposed to believe the more complex system – it seems like a simpler answer overall.

The  study explored whether the cuttlefish uses a cognitive process that is triggered by specific, visual features in its environment and which warrants the number of body pattern components it possesses.

Like their cephalopod relatives the octopus and the squid, cuttlefish are masters at blending in with their environments, which is largely attributable to the way their brains are able to control how pigments in special cells called chromatophores on their skin are displayed across their bodies.

In the study, 15 European cuttlefish were independently acclimated to a small water tank in which they were randomly exposed to either a uniform, grey background, or one of seven backgrounds with detailed, patterned features (e.g., small black squares, small white squares, white stripes).  The animals’ camouflage responses to these visual cues were photographed with a camera, and then analysed to see which of the 30 body pattern components appeared activated across the sample of test subjects.

So 15 isn’t exactly a huge sample size, but as the researchers note, this is a preliminary study. Based on these results, the next step would be to get funding for a more rigorous investigation. This isn’t enough to give us a clear answer, but it does seem to create a compelling outline.

The analysis included a statistical technique called ‘principal component analysis’ (PCA) which searches for clusters of responses in the observed data and attempts to largely explain it with a reduced set of key characteristics of the data.

The results of the PCA found that a few key characteristics did not explain most of the variability in the experimental data, but which would have been expected if the cuttlefish were employing a cognitive system which was expressing only three body patterns. Instead, the findings were more in line with a system whereby the whole range of the animals’ body pattern components could be activated, but selectively and in limited numbers, in response to the patterned feature they had been visually exposed to in the water tank.

Whilst the study findings are preliminary, they are in line with a model in which European cuttlefish do employ a cognitive system that processes specific visual features of the environment,  and which is used in combination with a system which responds to the visual background overall. Furthermore, a model in which the visual feature system is implemented in a hierarchical fashion (i.e., when needed, to fine tune a basic response to the overall background), in order for the animal to create the myriad camouflage responses used on the sea floor.

Honestly, I hope I hear more about this soon. One of the novels I’ve got on the back burner would benefit a lot from a better understanding of how cuttlefish do what they do. Another reason I want to believe the more complex answer is that it would fit that story much better. I also think it helps explain why some cuttlefish are able to write poetry. On that note, I’ll leave you with an explanation of the current understanding from a few years ago:

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  1. Bruce says

    Whether for a cuttlefish or a chameleon, an interesting followup study might include putting an animal in a chamber where one half is checks and the other half is swirls. I think a simple three-component system would not function there, but I bet a lot of cephalopods would do fine. Anyone know of any data on this already? It seems like it would be an obvious goal for most researchers.

  2. txpiper says

    Mind-blowing complexity. Reminds me of this guy Lining up the rings on his tentacles so that they appear to be stripes is quite a trick.
    Natural selection acting on random mutations doesn’t really sound like an adequate explanation for how hyper-sophisticated systems like this could develop.

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