Vivien Colin November 28, 2019 Fruit
Selflessness is an important feature of some fruits of commerce. Commercial cultivars of bananas and pineapples are examples of seedless fruits. Some cultivars of citrus fruits (especially grapefruit, mandarin oranges, navel oranges), satsumas, table grapes, and watermelons are valued for their selflessness. In some species, selflessness is the result of parthenogenesis, where fruits set without fertilization. Parthenogenesis fruit set may or may not require pollination, but most seedless citrus fruits require a stimulus from pollination to produce fruit.
Many hundreds of fruits, including fleshy fruits (like apple, kiwifruit, mango, peach, pear, and watermelon) are commercially valuable as human food, eaten both fresh and as jams, marmalade and other preserves. Fruits are also used in manufactured foods (e.g., cakes, cookies, ice cream, muffins, or yogurt) or beverages, such as fruit juices (e.g., apple juice, grape juice, or orange juice) or alcoholic beverages (e.g., brandy, fruit beer, or wine). Fruits are also used for gift giving, e.g., in the form of Fruit Baskets and Fruit Bouquets.
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.
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.
Darwin explained such male-female differences in his theory of sexual selection in his book The Descent of Man. Once the females begin to select males according to any particular characteristic, such as a long tail or a colored crest, that characteristic is emphasized more and more in the males. Eventually all the males will have the characteristics that the females are sexually selecting for, as only those males can reproduce. This mechanism is powerful enough to create features that are strongly disadvantageous to the males in other ways. For example, some male birds of paradise have wing or tail streamers that are so long that they impede flight, while their brilliant colors may make the males more vulnerable to predators. In the extreme, sexual selection may drive species to extinction, as has been argued for the enormous horns of the male Irish elk, which may have made it difficult for mature males to move and feed.
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.
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