How 3 broad classes of camouflage body patterns achieve visual deceit

January 16th, 2009 - 11:21 am ICT by ANI  

Washington, January 16 (ANI): A senior scientist at the Marine Biological Laboratory (MBL) has discovered three broad classes of camouflage body patterns by studying the cephalopods, which include squid, octopus, and cuttlefish. Roger Hanlon, who has spent 35 years studying animal camouflage, has also found how the three pattern classes termed uniform, mottled, and disruptive achieve several mechanisms of visual deceit.
“Cephalopods are the most changeable animal on earth for camouflage. There is no animal group that can equal it for speed or diversity of disguise. They have the widest range of patterns and they have the fastest change. Therefore, they are a good model to help unravel the general principles of camouflage,” the researcher says.
Hanlon is developing a mathematical description of camouflage patterns that can be used comparatively across the animal kingdom to better understand this biological phenomenon.
He and his colleagues have developed a software program that measures the degree of contrast and granularity (spatial scale) in the light and dark patches on the animal’’s body.
The researchers have revealed that the two metrics allow them to broadly sort all kinds of photographs of animal camouflage into the three classes of body patterns.
Uniform and mottle patterns are what most people recognize as camouflage, and these patterns function by resembling the background. However, such background matching is not so simple.
Hanlons study on cephalopods has revealed that there are few high-fidelity matches to the background, and that there are varying qualities of match in terms of colour, intensity, pattern or 3-dimensional texture of the skin.
He and his colleagues, however, say how to measure these in terms of visual perception by the predator is still a daunting task.
As regards disruptive coloration, the researcher say that these patterns tend to obscure the outline of the animal against certain backgrounds.
They say that a predator may easily detect the patter, but it will not recognise it as prey.
The researchers explain this with an example of a panda bear in a tree, whose large-scale black and white patches would appear to be disjunctive areas of shadow and bright light, rather than being recognized as animal skin, if viewed by looking up into the brightly lit sky.
Hanlons research marshals evidence that strongly supports the notion that disruptive coloration is a bona fide mechanism of camouflage.
He is now planning to quantify camouflage body patterns in fish.
“We hope that other investigators will pick up this technique to describe and quantify camouflage patterns in other animal groups. Visual predator-prey interactions are one of the most widespread phenomena known in natural selection. In terms of being an evolutionary force, camouflage is one of the great defences,” he says.
A research article on Hanlons work has been published in the journal Philosophical Transactions of the Royal Society B. (ANI)

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