Concealing Coloration in Animalsby Judy Diamond, Alan B. Bond
The biological functions of coloration in animals are sometimes surprising. Color can attract mates, intimidate enemies, and distract predators. But color patterns can also conceal animals from detection. Concealing coloration is unusual because it is an adaptation not only to the visual features of the environment but also to the perceptual and cognitive
The biological functions of coloration in animals are sometimes surprising. Color can attract mates, intimidate enemies, and distract predators. But color patterns can also conceal animals from detection. Concealing coloration is unusual because it is an adaptation not only to the visual features of the environment but also to the perceptual and cognitive capabilities of other organisms. Judy Diamond and Alan Bond bring to light the many factors at work in the evolution of concealing coloration.
Animals that resemble twigs, tree bark, stones, and seaweed may appear to be perfect imitations, but no concealment strategy is without flaws. Amid the clutter of the natural world, predators search for minute, telltale clues that will reveal the identity of their prey. Predators have remarkable abilities to learn to discriminate the fake from the real. But prey have their own range of defensive tactics, evolving multiple appearances or the ability to change color at will. Drawing on modern experimental evidence of the functional significance of animal color strategies, Diamond and Bond offer striking illustrations of how the evolution of features in one organism can be driven by the psychology of others.
Concealing Coloration in Animals takes readers on a scientific adventure that explores creatures inside mats of floating seaweed, mice and lizards on desert rocks and sand, and rare parrots in the rainforest of New Zealand. Color photographs extensively document the mind-boggling array of deceptive strategies animals use to blend in, mislead, or vanish from view.
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Chapter 2: Mistaken Identity
Some of the most unusual animals in the ocean live just below the surface in gigantic, entangled mats of free-floating kelp, called sargassum. These creatures appear exactly like pieces of the intertwined stems, floating bladders, and fronds that make up their habitat. They look very little like their relatives from closer to shore. Drawn together by the convergence of ocean currents, this underwater forest covers a highly variable area, depending on time of year and prevailing winds. In some places, there are just scattered patches; in others the stuff is so thick it can slow sailing vessels. Patches of sargassum are found in the Indian Ocean and in the Western Pacific, but by far the largest one is in the North Atlantic. It is called the Sargasso Sea.
An early explorer of the Sargasso Sea was a young clergyman and botanist, Peter Osbeck. Aboard the merchant vessel, Prince Charles, Osbeck set sail from Sweden in 1750, bound for China and the East Indies. Osbeck was a disciple of Carl Linnaeus, the founder of biological classification, and his primary assignment was scientific exploration. Linnaeus had encouraged the young man to make the trip and had recommended him for the position. In return, Osbeck lavished attention on the natural history of the regions he passed through, bringing back numerous specimens of oriental plants and ultimately producing a detailed narrative of the voyage.
On the trip home, while his ship passed through the eastern edge of the Sargasso Sea, Osbeck eagerly trolled his nets through the mats of seaweed. He collected, among other exotic creatures, several specimens of the sargassum fish, a small and bizarrely colored member of the frogfish family. Osbeck was surprised to see that the fish’s whole body was covered with small leaf-like projections. He was, after all, a botanist, so he likened the projections to little sargassum leaves, and went on to speculate, “Perhaps Providence has clothed this fish with fulcra resembling leaves, that the fishes of prey might mistake it for sea-weed, and not entirely destroy the breed” (Osbeck, 1771, 113). Osbeck’s note on this unusual fish was one of the first published accounts of object resemblance, a form of protective coloration in which an animal adopts the detailed appearance of an inedible object.
Open-water predators such as dolphin fish and yellowtail amberjacks forage around the mats, and the sargassum fish’s resemblance to a wad of seaweed may help it to avoid detection. But sargassum fish have additional means of escape: Both their pectoral and their pelvic fins are shaped more like hands than paddles, allowing them to climb deep into the tangles of the mat. In addition, like all frogfishes, their gill openings are restricted to small circular holes just behind the pectoral fins. When under attack, they can rapidly expel water through these holes and zip away by jet propulsion.
Meet the Author
Judy Diamond is Professor and Curator at the University of Nebraska State Museum.
Alan B. Bond is Research Professor of Biological Sciences and Co-Director of the Center for Avian Cognition at the University of Nebraska–Lincoln.
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