Natures wonders: Cuttlefish hide in plain ight (Introduction)

by David Turell @, Wednesday, March 23, 2016, 20:12 (1000 days ago) @ David Turell

They can change 40 items on their skin and blend into the background:

http://blogs.scientificamerican.com/not-bad-science/beyond-a-shadow-of-a-doubt-cuttlefi...

"Cuttlefish take on the appearance of their background, creating a very impressive camouflage. In doing so, they have to take in visual information from their surroundings and change their body colouration according to what they see. Therefore, by giving cuttlefish different types of background and seeing how they change their colouration, we can in theory determine how they may be perceiving the background in question.

"Cuttlefish have excellent vision: their eyes give them a 360 view of the background they're on. They use what they see to control 40 discrete visual features of their skin. For example, when on backgrounds with lots of objects like pebbles, cuttlefish produce a disruptive pattern on their skin.

"In particular, cuttlefish have a ‘white square' on their backs that they use in their camouflage. For example, when over pebbles of around the same size as their square, they change the colour of the square to match the colour of the pebbles (making it look like a pebble).

***

"The researchers found that the cuttlefish accentuated the 3-dimensional shading on the white squares of their backs when they were given a background of actual 3-dimensional hemispheres. This was as expected, given how cuttlefish behave when sitting on pebbles. However, the researchers also found that the cuttlefish did the same thing when they were given the background of 2-dimensional drawings of shaded circles. The researchers could tell that the cuttlefish were doing this in response to the shading, rather than just the contrast of black and white stimuli, because the cuttlefish did not shade their white squares in response to the black-and-white circle (bottom right image above). Instead, this image elicited a similar response to circles that were completely white (top left image).

"The cuttlefish were also sensitive to which direction light came from. For example, when the researchers illuminated the background such that light fell in the same direction as the gradient of the 2-D shaded circles (i.e. so that the light came towards the lighter side of the circle), the cuttlefish shaded their white squares to a greater extent.

"All evidence from this experiment, therefore, implies that cuttlefish perceive depth cues in a similar manner to us. There were some discrepancies between how the cuttlefish did certain things compared to how we might do it, likely due to the fact that they live under water where the lighting and shadow effects are less prominent than in air. However, cuttlefish live over a range of depths. At greater depths where there is more diffuse light, the depth cues on cuttlefish backs may be less important, but at shallower depths their ability to detect and reflect depth cues is likely critical in protecting them from predators."

Comment: If one cuttlefish developed this method he couldn't teach it to others because it is an internal metabolic trick. Learning to do it stepwise would result in lots of dead cuttlefish who are not disguised before they figure out the whole process. Saltation from God is one solution that makes sense. Any just-so stories?


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