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Lecture 10

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BIOL 225
Ian Ferguson

 Batesian mimicry, where an edible species resembles a distasteful or dangerous species. This is most common in insects such as butterflies. A familiar example is the resemblance of harmless hoverflies (which have no sting) to bees.  Müllerian mimicry, where two or more distasteful or dangerous animal species resemble each other. This is most common among insects such as wasps and bees (hymenoptera). Batesian mimicry was first described by pioneering naturalist Henry W. Bates. When an edible prey animal comes to resemble, even slightly, a distasteful animal, natural selection favours those individuals that even very slightly better resemble the distasteful species. This is because even a small degree of protection reduces predation and increases the chance that an individual mimic will survive and reproduce. For example, many species of hoverfly are coloured black and yellow like bees, and are in consequence avoided by birds (and people). Müllerian mimicry was first described by pioneering naturalist Fritz Müller. When a distasteful animal comes to resemble a more common distasteful animal, natural selection favours individuals that even very slightly better resemble the target. For example, many species of stinging wasp and bee are similarly coloured black and yellow. Müller's explanation of the mechanism for this was one of the first uses of mathematics in biology. He argued that a predator, such as a young bird, must attack at least one insect, say a wasp, to learn that the black and yellow colours mean a stinging insect. If bees were differently coloured, the young bird would have to attack one of them also. But when bees and wasps resemble each other, the young bird need only attack one from the whole group to learn to avoid all of them. So, fewer bees are attacked if they mimic wasps; the same applies to wasps that mimic bees. The result is mutual resemblance for mutual protection. Colour is often used in startling 'deimatic' displays that have evolved to scare off predators. These combine bright colours and patterns such as eyespots with threatening behaviour. For example, the Mediterranean mantis, Iris oratoria, rears up, and spreads out and waves its long front legs, to make itself look as big and alarming as possible. The Colombian four eyed frog, Pleurodema brachyops inflates itself with air and raises its hind parts to appear as large as possible. Deimatic displays are often combined with chemical defences such as the poison glands of frogs like P. brachyops or the bitter taste of moths in the family Arctiidae, in which case the coloration is also genuinely aposematic. Many insects, includ
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