Although they have begun to compare camouflage tactics in many animals — large primates, amphibians, reptiles, fishes, insects — they are currently focusing 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 (termed uniform, mottled, and disruptive).
"Cephalopods are the most changeable animal on earth for camouflage," Hanlon says. "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."
Pictured are Octopus burryi clinging to a calcareous alga that is swinging in the surge. The mottle coloration of the octopus produces effective background matching to the algae. Photo taken at Saba, Netherlands Antilles. Photo Credit: Roger T. Hanlon
Hanlon is developing a mathematical description of camouflage patterns that can be used comparatively across the animal kingdom to better understand this biological phenomenon. To accomplish this, his team 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.
In cephalopods, there are few high-fidelity matches to the background. More commonly, there are varying qualities of match in terms of color, intensity, pattern or 3-dimensional 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 recognize it as prey. Disruptive coloration is a controversial camouflage mechanism among vision scientists. "It's a counterintuitive notion," Hanlon says. 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 recognized 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 says. His research marshals evidence that strongly supports the notion that disruptive coloration is a bona fide mechanism of camouflage.
As a next step, Hanlon and colleagues plan 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," he says.
"Visual predator-prey interactions are one of the most widespread phenomena known in natural selection," Hanlon says. "In terms of being an evolutionary force, camouflage is one of the great defenses."