Bernadette Barbier November 20, 2019 Fruit
The main mechanisms to create the resemblances described by Poulton – whether in nature or in military applications – are crypts, blending into the background so as to become hard to see (this covers both special and general resemblance); disruptive patterning, using color and pattern to break up the animal’s outline, which relates mainly to general resemblance; mime sis, resembling other objects of no special interest to the observer, which relates to special resemblance; counter shading, using graded color to create the illusion of flatness, which relates mainly to general resemblance; and counter illumination, producing light to match the background, notably in some species of squid.
When we see leaf-eating insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in winter, the red-grouse the colour of heather, and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger. Grouse, if not destroyed at some period of their lives, would increase in countless numbers; they are known to suffer largely from birds of prey; and hawks are guided by eyesight to their prey, so much so, that on parts of the Continent persons are warned not to keep white pigeons, as being the most liable to destruction. Hence I can see no reason to doubt that natural selection might be most effective in giving the proper colour to each kind of grouse, and in keeping that colour, when once acquired, true and constant.
While many animals are unable to synthesize carotene pigments to create red and yellow surfaces, the green and blue colors of bird feathers and insect carapaces are usually not produced by pigments at all, but by structural coloration. Structural coloration means the production of color by microscopically-structured surfaces fine enough to interfere with visible light, sometimes in combination with pigments: for example, peacock tail feathers are pigmented brown, but their structure makes them appear blue, turquoise and green. Structural coloration can produce the most brilliant colors, often iridescent. For example, the blue green gloss on the plumage of birds such as ducks, and the purple blue green red colors of many beetles and butterflies are created by structural coloration. Animals use several methods to produce structural color, as described in the table.
Edward Bagnall Poulton’s strongly Darwinian 1890 book The Colours of Animals, their meaning and use, especially considered in the case of insects argued the case for three aspects of animal coloration that are broadly accepted today but were controversial or wholly new at the time. It strongly supported Darwin’s theory of sexual selection, arguing that the obvious differences between male and female birds such as the Argus pheasant were selected by the females, pointing out that bright male plumage was found only in species ”which court by day” The book introduced the concept of frequency-dependent selection, as when edible mimics are less frequent than the distasteful models whose colors and patterns they copy. In the book, Poulton also coined the term antisemitism for warning coloration, which he identified in widely differing animal groups including mammals (such as the skunk), bees and wasps, beetles, and butterflies.
Abbott Handerson Thayer’s 1909 book Concealing-Coloration in the Animal Kingdom, completed by his son Gerald H. Thayer, argued correctly for the widespread use of crypts among animals, and in particular described and explained countershading for the first time. However, the Thayers spoilt their case by arguing that camouflage was the sole purpose of animal coloration, which led them to claim that even the brilliant pink plumage of the flamingo or the roseate spoonbill was cryptic—against the momentarily pink sky at dawn or dusk. As a result, the book was mocked by critics including Theodore Roosevelt as having ”pushed [the ”doctrine” of concealing coloration] to such a fantastic extreme and to include such wild absurdities as to call for the application of common sense thereto.
Warning coloration is effectively the ”opposite” of camouflage, and a special case of advertising. Its function is to make the animal, for example a wasp or a coral snake, highly conspicuous to potential predators, so that it is noticed, remembered, and then avoided. As Peter Forbes observes, ”Human warning signs employ the same colours – red, yellow, black, and white – that nature uses to advertise dangerous creatures.” Warning colors work by being associated by potential predators with something that makes the warning colored animal unpleasant or dangerous.
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