Evolutionary reasons for animal coloration Animal coloration

1 evolutionary reasons animal coloration

1.1 camouflage
1.2 signalling

1.2.1 advertising services
1.2.2 sexual selection
1.2.3 warning


1.3 mimicry
1.4 distraction

1.4.1 startle
1.4.2 motion dazzle


1.5 physical protection
1.6 temperature regulation
1.7 incidental coloration

evolutionary reasons animal coloration
camouflage

one of pioneers of research animal coloration, edward bagnall poulton classified forms of protective coloration, in way still helpful. described: protective resemblance; aggressive resemblance; adventitious protection; , variable protective resemblance. these covered in turn below.

a camouflaged orange oak leaf butterfly, kallima inachus (centre) displays protective resemblance

protective resemblance used prey avoid predation. includes special protective resemblance, called mimesis, whole animal looks other object, example when caterpillar resembles twig or bird dropping. in general protective resemblance, called crypsis, animal s texture blends background, example when moth s colour , pattern blend in tree bark.

a flower mantis, hymenopus coronatus, displays special aggressive resemblance

aggressive resemblance used predators or parasites. in special aggressive resemblance, animal looks else, luring prey or host approach, example when flower mantis resembles particular kind of flower, such orchid. in general aggressive resemblance, predator or parasite blends in background, example when leopard hard see in long grass.

for adventitious protection, animal uses materials such twigs, sand, or pieces of shell conceal outline, example when caddis fly larva builds decorated case, or when decorator crab decorates seaweed, sponges , stones.

in variable protective resemblance, animal such chameleon, flatfish, squid or octopus changes skin pattern , colour using special chromatophore cells resemble whatever background resting on (as signalling).

the main mechanisms create resemblances described poulton – whether in nature or in military applications – crypsis, blending background become hard see (this covers both special , general resemblance); disruptive patterning, using colour , pattern break animal s outline, relates general resemblance; mimesis, resembling other objects of no special interest observer, relates special resemblance; countershading, using graded colour create illusion of flatness, relates general resemblance; , counterillumination, producing light match background, notably in species of squid.

countershading first described american artist abbott handerson thayer, pioneer in theory of animal coloration. thayer observed whereas painter takes flat canvas , uses coloured paint create illusion of solidity painting in shadows, animals such deer darkest on backs, becoming lighter towards belly, creating (as zoologist hugh cott observed) illusion of flatness, , against matching background, of invisibility. thayer s observation animals painted nature, darkest on parts tend lighted sky s light, , vice versa called thayer s law.

signalling

colour used signalling in animals diverse birds , shrimps. signalling encompasses @ least 3 purposes:

advertising, signal capability or service other animals, whether within species or not
sexual selection, members of 1 sex choose mate suitably coloured members of other sex, driving development of such colours
warning, signal animal harmful, example can sting, poisonous or bitter-tasting. warning signals may mimicked truthfully or untruthfully.

advertising services

cleaner wrasse signals cleaning services big eye squirrelfish

advertising coloration can signal services animal offers other animals. these may of same species, in sexual selection, or of different species, in cleaning symbiosis. signals, combine colour , movement, may understood many different species; example, cleaning stations of banded coral shrimp stenopus hispidus visited different species of fish, , reptiles such hawksbill sea turtles.

sexual selection

male goldie s bird of paradise displays female

darwin observed males of species, such birds of paradise, different females.

darwin explained such male-female differences in theory of sexual selection in book descent of man. once females begin select males according particular characteristic, such long tail or coloured crest, characteristic emphasized more , more in males. males have characteristics females sexually selecting for, males can reproduce. mechanism powerful enough create features disadvantageous males in other ways. example, male birds of paradise have wing or tail streamers long impede flight, while brilliant colours may make males more vulnerable predators. in extreme, sexual selection may drive species extinction, has been argued enormous horns of male irish elk, may have made difficult mature males move , feed.

different forms of sexual selection possible, including rivalry among males, , selection of females males.

warning

a venomous coral snake uses bright colours warn off potential predators.

warning coloration (aposematism) opposite of camouflage, , special case of advertising. function make animal, example wasp or coral snake, highly conspicuous potential predators, noticed, remembered, , avoided. peter forbes observes, human warning signs employ same colours – red, yellow, black, , white – nature uses advertise dangerous creatures. warning colours work being associated potential predators makes warning coloured animal unpleasant or dangerous. can achieved in several ways, being combination of:

the black , yellow warning colours of cinnabar moth caterpillar, tyria jacobaeae, instinctively avoided birds.



distasteful, example caterpillars, pupae , adults of cinnabar moth, monarch , variable checkerspot butterfly have bitter-tasting chemicals in blood. 1 monarch contains more enough digitalis-like toxin kill cat, while monarch extract makes starlings vomit.
foul-smelling, example skunk can eject liquid long-lasting , powerful odour
aggressive , able defend itself, example honey badgers.
venomous, example wasp can deliver painful sting, while snakes viper or coral snake can deliver fatal bite.

warning coloration can succeed either through inborn behaviour (instinct) on part of potential predators, or through learned avoidance. either can lead various forms of mimicry. experiments show avoidance learned in birds, mammals, lizards, , amphibians, birds such great tits have inborn avoidance of colours , patterns such black , yellow stripes.

mimicry


hawk-cuckoo resembles predatory shikra, giving cuckoo time lay egg in songbird s nest unnoticed

mimicry means 1 species of animal resembles species closely enough deceive predators. evolve, mimicked species must have warning coloration, because appearing bitter-tasting or dangerous gives natural selection work on. once species has slight, chance, resemblance warning coloured species, natural selection can drive colours , patterns towards more perfect mimicry. there numerous possible mechanisms, of far best known are:

batesian mimicry, edible species resembles distasteful or dangerous species. common in insects such butterflies. familiar example resemblance of harmless hoverflies (which have no sting) bees.
müllerian mimicry, 2 or more distasteful or dangerous animal species resemble each other. common among insects such wasps , bees (hymenoptera).

batesian mimicry first described pioneering naturalist henry w. bates. when edible prey animal comes resemble, slightly, distasteful animal, natural selection favours individuals better resemble distasteful species. because small degree of protection reduces predation , increases chance individual mimic survive , reproduce. example, many species of hoverfly coloured black , yellow bees, , in consequence avoided birds (and people).

müllerian mimicry first described pioneering naturalist fritz müller. when distasteful animal comes resemble more common distasteful animal, natural selection favours individuals better resemble target. example, many species of stinging wasp , bee coloured black , yellow. müller s explanation of mechanism 1 of first uses of mathematics in biology. argued predator, such young bird, must attack @ least 1 insect, wasp, learn black , yellow colours mean stinging insect. if bees differently coloured, young bird have attack 1 of them also. when bees , wasps resemble each other, young bird need attack 1 whole group learn avoid of them. so, fewer bees attacked if mimic wasps; same applies wasps mimic bees. result mutual resemblance mutual protection.

distraction

a praying mantis in deimatic or threat pose displays conspicuous patches of colour startle potential predators. not warning coloration insect palatable.


startle

some animals such many moths, mantises , grasshoppers, have repertory of threatening or startling behaviour, such displaying conspicuous eyespots or patches of bright , contrasting colours, scare off or momentarily distract predator. gives prey animal opportunity escape. behaviour deimatic (startling) rather aposematic these insects palatable predators, warning colours bluff, not honest signal.

motion dazzle

some prey animals such zebra marked high-contrast patterns possibly confuse predators, such lions, during chase. bold stripes of herd of running zebra have been claimed make difficult predators estimate prey s speed , direction accurately, or identify individual animals, giving prey improved chance of escape. since dazzle patterns (such zebra s stripes) make animals harder catch when moving, easier detect when stationary, there evolutionary trade-off between dazzle , camouflage. theory zebra s stripes provide protection flies , biting insects.

physical protection

many animals have dark pigments such melanin in skin, eyes , fur protect against sunburn (damage living tissues caused ultraviolet light).

temperature regulation

this frog changes skin colour control temperature.

some frogs such bokermannohyla alvarengai, basks in sunlight, lighten skin colour when hot (and darkens when cold), making skin reflect more heat , avoid overheating.

incidental coloration

the olm s blood makes appear pink.

some animals coloured purely incidentally because blood contains pigments. example, amphibians olm live in caves may largely colourless colour has no function in environment, show red because of haem pigment in red blood cells, needed carry oxygen. have little orange coloured riboflavin in skin. human albinos , people fair skin have similar colour same reason.