Bernadette Barbier November 20, 2019 Fruit
There are several separate reasons why animals have evolved colors. Camouflage enables an animal to remain hidden from view. Animals use color to advertise services such as cleaning to animals of other species; to signal their sexual status to other members of the same species; and in mimicry, taking advantage of the warning coloration of another species. Some animals use flashes of color to divert attacks by startling predators. Zebras may possibly use motion dazzle, confusing a predator’s attack by moving a bold pattern rapidly. Some animals are colored for physical protection, with pigments in the skin to protect against sunburn, while some frogs can lighten or darken their skin for temperature regulation. Finally, animals can be colored incidentally. For example, blood is red because the heme pigment needed to carry oxygen is red. Animals colored in these ways can have striking natural patterns.
Chromatophores are special pigment-containing cells that may change their size, but more often retain their original size but allow the pigment within them to become redistributed, thus varying the color and pattern of the animal. Chromatophores may respond to hormonal and or neurobal control mechanisms, but direst responses to stimulation by visible light, UV-radiation, temperature, pH-changes, chemicals, etc. have also been documented. The voluntary control of chromatophores is known as metachrosis. For example, cuttlefish and chameleons can rapidly change their appearance, both for camouflage and for signalling, as Aristotle first noted over 2000 years ago
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.
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.
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.
Countershading was first described by the American artist Abbott Handerson Thayer, a pioneer in the theory of animal coloration. Thayer observed that whereas a painter takes a flat canvas and uses colored paint to create the illusion of solidity by painting in shadows, animals such as deer are often darkest on their backs, becoming lighter towards the belly, creating (as zoologist Hugh Cott observed) the illusion of flatness, and against a matching background, of invisibility. Thayer’s observation ”Animals are painted by Nature, darkest on those parts which tend to be most lighted by the sky’s light, and vice versa” is called Thayer’s Law.
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