When your strategy to elude predators is to camouflage yourself to blend in with your surroundings, how do you accomplish this when you are colour-blind? It seems that cuttlefish, which are among the world's foremost artists in the medium of body camouflage, are unable to see colours. Despite this, they are able to colour-match their surroundings precisely enough to fool predators. This apparent paradox has been vexing scientists for years, so Chuan-Chin Chiao and his colleagues at the Marine Biological Laboratory in Woods Hole, USA, set out to use a novel imaging system in the hope that it would reveal potential clues as to how cuttlefish colour-match their surroundings. They also used the image data to create images of the cuttlefish as viewed through the eyes of potential predators.
Setting up cuttlefish in tanks with one of three natural substrates on the floor in order to get them to produce one of three distinct camouflage patterns, Chiao and his colleagues then used a hyperspectral imaging system to take pictures of the animal's bodies and the surrounding substrates. Hyperspectral imaging is a unique technique that provides much more spectral and spatial data than a regular digital photograph and produces a 3-D cube of data representing both the colours and their reflection spectra. Once a picture of the camouflaged cuttlefish had been taken, the team used known visual properties of several potential cuttlefish predators to convert the spectral data into a predator's eye view, which allowed them to analyse the colour-matching abilities of the cuttlefish from the predator's perspective.
The hyperspectral images of the cuttlefish revealed that the cuttlefish displayed colour and reflectance spectra similar to the background, with one notable exception: the majority of the reflectance spectra from the cuttlefish were in the infrared range, which was surprising as the natural substrates did not extend into the infrared spectrum. The biological importance of this curious finding is unknown at this time. Regardless, analysis of the spectral data revealed that the spectral properties of the skin of cuttlefish and those of three natural substrates were similar.
Modelling of the hyperspectral data to create images of the cuttlefish through the eyes of predators revealed that cuttlefish not only accurately match the background colour but also the surrounding pattern, rendering them invisible to predators. The question of how exactly they do this is still unclear, but the hyperspectral system may allow scientists to more accurately test the abilities of cuttlefish and analyse their responses to various backgrounds.
So, how do you successfully blend in with your surroundings when you are colour-blind? Previous work has shown that variables such as brightness, contrast and edging are essential to induce camouflage in animals. However, scientists have been limited by technology in their analysis of the minute details of the camouflage created by colour-blind animals. Hyperspectral imaging appears to allow detailed examination of the colour, the reflectance and the pattern of camouflage, bringing us one step closer to solving this vexing problem. Additionally, the system creates data that can generate pictures of the animals through the eyes of other animals. This allows scientists to potentially see prey as predators see them.
