Scientist unravels invisibility cloak of creatures

January 16th, 2009 - 6:21 pm ICT by IANS  

Washington, Jan 16 (IANS) Cuttlefish and chameleons could teach Harry Potter a thing or two about becoming invisible, either as predator or as prey.Roger Hanlon, senior scientist at the Marine Biological Laboratory (MBL), who has been studying animal camouflage for 35 years, discerned three distinct ‘invisibility patterns’ comprising uniform, mottled and disruptive.

“Camouflage is found throughout the animal kingdom, among big, small, wet, and dry animals, but it is probably one of the least-studied natural phenomena we know of,” Hanlon said.

“No one has successfully quantified, for instance, what is exactly meant by ‘background matching,’ which is when an animal visually blends into its environment,” Hanlon said.

Although Hanlon and colleagues have begun to compare camouflage tactics in many animals - large primates, amphibians, reptiles, fishes, insects - this week’s analysis focuses on the cephalopods, which include squid, octopus, and cuttlefish.

Remarkably, these soft-bellied mollusks are able to dynamically produce all three classes of camouflage body patterns.

“Cephalopods are the most changeable animal on earth for camouflage,” Hanlon said. “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.”

Hanlon is developing a mathematical description of camouflage patterns that can be used comparatively across the animal kingdom to better understand this biological phenomenon.

His team accordinglty 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.

These 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 recognise as camouflage. The patterns function by resembling the background. Such background matching is not so simple, however.

In cephalopods, there are few high-fidelity matches to the background. More commonly, there are varying qualities of match in terms of colour, intensity, pattern or 3-D texture of the skin. How to measure these in terms of visual perception by the predator is still a daunting task.

The patterns in the third class, disruptive coloration, tend to obscure the outline of the animal against certain backgrounds. While a predator might easily detect the pattern, it won’t recognise it as prey.

Disruptive coloration is a controversial camouflage mechanism among vision scientists. “It’s a counter-intuitive notion,” Hanlon said. An extreme example is a panda bear in a tree. If viewed by looking up into the brightly lit sky, the bear’s large-scale black and white patches may not be recognised as animal skin, but rather as disjunctive areas of shadow and bright light.

“Viewed against the right background, that body pattern is just an odd jigsaw puzzle. The pieces don’t connect into an animal,” Hanlon said, according to an MBL release.

These findings have been detailed in this week’s issue of Philosophical Transactions of the Royal Society B, entirely devoted to camouflage.

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