Colorblindness in Cuttlefish

 

Studies have shown that cuttlefish are colorblind, which is somewhat surprising since they have the ability to adapt their coloration extremely well to their background (Mäthger et al., 2006). There are two main pieces of evidence that support the existence of colorblindness in cuttlefish. There is visual pigment evidence and behavioral evidence.

 

Visual pigment evidence:

In one study, researchers P.K. Brown and P.S. Brown were able to measure the spectral absorption of cuttlefish retinal extracts. They found that cuttlefish only have one visual pigment that has a maximum absorption (492 nm) (Brown and Brown 1958). This suggests that cuttlefish can only detect light waves that are at 492 nm, meaning they can't distinguish between waves of other lengths. If they can only discern one wavelength of light from others then it means they wouldn't be able to see color, like humans can. Furthermore, a study done by Marshall and Messenger showed that only one type of rhodopsin (visual pigments that are responsible for detection of color) is expressed in cuttlefish, and this type of rhodopsin had a maximum absorption at 492nm, which agrees with the Brown and Brown study (Marshall and Messenger, 1996).

Color Blindness
Night Camouflage
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Behavioral evidence:

Marshall and Messenger conducted another experiment in which they attempted to find evidence for colorblindness in cuttlefish by studying their behavior. They placed cuttlefish on gravel of differing colors. They had red and white gravel as one substrate and then blue and yellow as another substrate. The cuttlefish displayed a disruptive patterning on the red and white gravel, but a uniform patterning on the blue and yellow substrate. Since there is a high contrast between the red and white gravel, it makes sense that the cuttlefish would be able to detect this and display disruptive patterning. But the contrast between blue and yellow is much more subtle so they couldn't detect it, thinking the background was uniform (Marshall and Messenger, 1996). These findings support the hypothesis that cuttlefish are colorblind. If they could distinguish colors, then the cuttlefish in this experiment would have displayed the disruptive patterning in the blue and yellow gravel environment as well.

Futher Studies on Cuttlefish colorblindness

Mäthger et al. conducted an experiment to gain further evidence for the presence of colorblindness in cuttlefish. In one part of their overall study they conducted a similar experiment to the Marshall and Messenger experiment. They exposed European cuttlefish (Sepia officinalis) to a blue and yellow checkerboard, a black and white checkerboard, a solid blue background, and a solid yellow background (see Figure 9). They found that when placed on the blue and yellow checkerboard, the cuttlefish displayed a uniform pattern. Here, the cuttlefish think they are on a uniform background because the color intensities matched according to their visual system. This finding is consistent with the results of the Marshall and Messenger study. The cuttlefish also displayed a uniform patterning with the solid blue and solid yellow backgrounds, as expected. Lastly, they displayed a typical disruptive pattern with the black and white checkerboard pattern (Mäthger et al., 2006).

 

checkeredyellow/blue

Figure 9. Reproduced with permission from Dr. Mäthger. The different camouflage responses the cuttlefish displayed when placed on the 4 different backgrounds. A uniform pattern was displayed when they were placed on the yellow/blue checkerboard, the solid yellow substrate, and the solid blue substrate (Mäthger et al., 2006).

 

 

 

In another part of their experiment, Mäthger et al. conducted a "grey card" experiment. They made 16 green and gray checkerboards in which the contrast between the green and gray squares differed (they changed the shade of the grey sqaures and kept the green squares the same). They then exposed the cuttlefish to these 16 different backgrounds. The results for this experiment can be seen in Figure 10. The researchers concluded that cuttlefish are able to perceive background objects that differ in contrast of about 15% (Mäthger et al., 2006).

colorblindgraph

Figure 10 (adapted from Mäthger et. al, 2006). Average grade of cuttlefish disruptive pattern vs. checkerboard contrast. This graph shows that as the green and gray contrast of the checkerboard increased, the disruptive pattern exhibited by the cuttlefish became more intense. These results are consistent with the belief that cuttlefish are colorblind, since they depend primarily on contrast cues in the background rather than color. Thus it makes sense that the higher the contrast in the checkerboard, the stronger the display of disruptive patterning.

 

 

 

 

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