Tuesday, February 19, 2008

In plain sight: Simple rules for complex camouflage

Fox and rabbitTo the most faithful readers of Jurisdynamics and BioLaw, I owe a small apology. The "life-dinner principle" outlined in Richard Dawkins & John R. Krebs, Arms Races Between and Within Species, 205:1161 Proc. Royal Soc'y London: Series B, Biol. Scis. 489-511 (1979) — the observation that "a lineage under strong selection may out-evolve a weakly selected one" — is a bedrock tenet of evolutionary biology. I had no business giving the life-dinner principle its Jurisdynamics Network debut on MoneyLaw. But I did. Now I will try to make amends.

A bedrock tenet of complexity theory — which after all is merely an extension of evolutionary biology — is that complex processes often emerge from relative simple constituent rules. Work by Roger Hanlon of Woods Hole strongly suggests that camouflage may arise from a very limited set of biological strategies for avoiding detection by predators.

Consider the cuttlefish. Along with squid and octopus, cuttlefish belong to the coleoid subclass of cephalopods. Distinct from their nautiloid relatives, and alone among all mollusks, coleoids lack a shell. No sooner than you can say ika kudasai or tako onegai-shimasu, coeloids can come to you as sushi, sashimi, or a deep-fried appetizer. In ecosystems larger than a Japanese restaurant, Coleoidea provide food for a wide range of predatory organisms. In other words, cuttlefish, squid, and octopus are bait.

Kings of Camouflage

Cephalopods, especially coleoids, are really cool. They are also exceptionally smart. Probably no other invertebrate taxon exhibits as much intelligence. In the sidebar, I've embedded videos previewing the forthcoming PBS/Nova program, Kings of Camouflage. The Nova VodCast, in particular, is available via YouTube.

Camouflage is singularly important to cuttlefish and its coleoid relatives because these organisms are virtually defenseless once they are seized by predators. They depend on deception and concealment as primary defenses.

A recent New York Times article explains Roger Hanlon's startling hypothesis that cuttlefish and other cephalopods, despite the complexity of their skin, are using mental shortcuts to generate a dazzling and seemingly endless array of camouflage patterns. “They don’t have time to analyze all this visual information,” he said.

Hanlon when he and his colleagues reviewed thousands of images of cuttlefish and tried to sort their patterns into categories. “It finally dawned on me there aren’t dozens of camouflage patterns,” he said. “I can squeeze them into three categories.”
  1. Uniform color. Cephalopods take on this camouflage to match a smooth-textured background.

  2. Mottled patterns. Mottling helps cephalopods hide in busier environments.

  3. Disruptive patterning. In this strategy, a cuttlefish creates large blocks of light and dark. These blocks disrupts the outlines of its body.
Even more remarkably, Hanlon's conclusions about cephalopod camouflage may apply throughout the animal kingdom. Cephalopods aren't the only organisms that use camouflage; they are outstanding for the speed with which they can change color and patterns. Among other animals, chameleons also shift between uniform, mottled, and disruptive strategies. But the spread of hormones across their skin is slower than in cuttlefish.

The availability of fact that cephalopods may need just three camouflage categories could mean that there are just a few basic ways to fool predators. Hanlon's laboratory has sorted thousands of pictures of other camouflaged animals and have assigned them to the same three categories:
  1. A frog's drab skin blends into the drab forest floor.

  2. A bird's mottled plumage matches a nearby leaf and branch pattern.

  3. The black and white patches on a giant panda are arguably a form of disruptive camouflage. Those black and white patches blend into the sunlight and shadows, or perhaps on a snowy landscape.
CuttlefishWhat Roger Hanlon's work with cuttlefish suggests is nothing short of a unified field theory of camouflage. It represents biology — and allied fields of thought such as complexity theory — working at the simplest and best level of scientific inquiry.


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