ANSC 420 Lecture Notes - Lecture 10: Colombian Four-Eyed Frog, Deimatic Behaviour, Iris Oratoria
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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, including the peacock butterfly (Inachis io) use a combination of coloration
strategies for survival. The underside, presented when the insect is resting in vegetation with
wings closed, is cryptic, being a leaf mimic. But if disturbed by a predator, the butterfly flashes
its wings, displaying the conspicuous eyespots, and startling the predator to hesitate, increasing
the butterfly's chances of escape. Since the eyespots do not resemble any particular animal, the
startle coloration and behaviour are not exactly mimicry.
Butterflies with eyespots often survive predator attack for another reason also: birds typically
attack the eyespots, not the body (see illustration).
Many noctuid moths, such as the large red underwing, Catocala nupta which are highly cryptic
when at rest, display a startlingly bright flash of colours – combinations of red, yellow, orange,
pink, black, and white – when disturbed. Similarly, some orthopterans such as grasshoppers are
cryptic at rest, but flash bright wing colours including blue if disturbed. The moths then rapidly