The working hypothesis here is that three basic types of camouflage might fool all visual systems. Meaning that every species deploys (at least) one of these three basic camo types, with species-specific elaborations on the chosen theme. But what is camouflage? We’ve pointed to a plausible evolutionary function: namely, the ability to fool other animals’ visual systems, making predation and evasion easier. While that might suggest what camouflage is for, it doesn’t tell us how that is accomplished in any particular animal. In order to answer that question, Hanlon and his team have extensively documented the camouflaging abilities of Cephalopoda, a class of the phylum Mollusca. Specifically these MBL scientists look at cuttlefish and octopuses, in the wild and in the lab.
Cuttlefish and octopuses are remarkably useful model organisms upon which to base studies of camouflage because of the remarkably dynamic nature of their camouflage abilities: they both change their camouflage depending on the background they’re against. This means that there must be a tight relationship between the visual system in these animals and their ability to manipulate their skin and body. Because of this fact, studying camouflage in these animals allows the scientist to study it as a visual phenomena from two directions: from the eye of the predator, whose visual system is fooled by this remarkable shifting, and from the eye of the prey, who has to extract relevant information from the environment and translate that into the complex body movements that alter the animal’s external appearance.
Hanlon and his lab’s extensive study of camouflaging animals suggests that most if not all camouflage is low-fidelity. That is, even in the most dynamic and skilled camouflaging animals, the task mostly isn’t achieved by becoming identical, or nearly so, to the background (hi-fidelity camo). Rather it appears as though good camouflage is an attempt to disguise the boundaries of a body by capitalizing on contrastive differences between patches of the coloration on the body and patches of coloration in the environment (low-fidelity camo). We’ve already seen how edge detection depends on the visual system’s exaggerating contrast between color fields (the Mach bands effect) in Hartline’s work. Camouflaging animals take advantage of this feature of visual perception by changing the color contrast of parts of their bodies against parts of the environment, thus hiding the location of the edges of their bodies. This can be seen in the first figure above, but perhaps the best way is to look at some of the videos produced about Hanlon’s lab. The New York Times’s science correspondent, Carl Zimmer, produced a video overview of Hanlon’s work that shows some of his best field and lab work. Additionally, Hanlon has a three part series of video web lectures with iBiology.org that explore all the details of this work and include man breathtaking filmed examples of dynamic camouflaging abilities.
Note: There is no science without a scientist, and so the author has attempted to maintain the essential truth of that—namely that at each stage of the scientific process there is a person looking at evidence and making judgments. However there is almost no personal biography, and much of the professional biography of each author has been abridged dramatically. In spite of this, the reader should keep in mind that each of these individuals were complicated people who share at least a job description. George Wald once said, “A scientist should be the happiest of men. Not that science isn't serious; but as everyone knows, being serious is one way of being happy, just as being gay is one way of being unhappy”. Each of these individuals had a scientific ethic, as well as a body of scientific work, and where possible, the author of each section has attempted to not forget the romanticism of the spirit of investigation, or the fact that many of these people were excited by a simple truth—after all, they were seeing things no one else had seen before. That majesty can be easy to forget if you are an outsider new to the complexities of visual physiology, but these scientists never forgot it.
Universalizing Photochemical Theories of Vision: Hecht, Wald, and the Marine Biological Laboratory
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Haldan Keffer Hartline, a Prize, and Two Accidents
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Roger Hanlon, Universal Camouflage, and Studying Vision at the MBL in the 21st Century
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