Mechanisms of colour production in animals Animal coloration

1 mechanisms of colour production in animals

1.1 coloration pigments
1.2 variable coloration chromatophores
1.3 structural coloration
1.4 bioluminescence

mechanisms of colour production in animals

side of zebrafish shows how chromatophores (dark spots) respond 24 hours in dark (above) or light (below).

animal coloration may result of combination of pigments, chromatophores, structural coloration , bioluminescence.

coloration pigments


the red pigment in flamingo s plumage comes diet of shrimps, microscopic algae.

pigments coloured chemicals (such melanin) in animal tissues. example, arctic fox has white coat in winter (containing little pigment), , brown coat in summer (containing more pigment), example of seasonal camouflage (a polyphenism). many animals, including mammals, birds, , amphibians, unable synthesize of pigments colour fur or feathers, other brown or black melanins give many mammals earth tones. example, bright yellow of american goldfinch, startling orange of juvenile red-spotted newt, deep red of cardinal , pink of flamingo produced carotenoid pigments synthesized plants. in case of flamingo, bird eats pink shrimps, unable synthesize carotenoids. shrimps derive body colour microscopic red algae, plants able create own pigments, including both carotenoids , (green) chlorophyll. animals eat green plants not become green, however, chlorophyll not survive digestion.

variable coloration chromatophores



fish , frog melanophores cells can change colour dispersing or aggregating pigment-containing bodies.

chromatophores special pigment-containing cells may change size, more retain theiroriginal size allow pigment within them become redistributed, varying colour , pattern of animal. chromatophores may respond hormonal and/or neurobal control mechanisms, direst responses stimulation visible light, uv-radiation, temperature, ph-changes, chemicals, etc. have been documented. voluntary control of chromatophores known metachrosis. example, cuttlefish , chameleons can rapidly change appearance, both camouflage , signalling, aristotle first noted on 2000 years ago:

the octopus ... seeks prey changing colour render colour of stones adjacent it; when alarmed.

squid chromatophores appear black, brown, reddish , pink areas in micrograph.

when cephalopod molluscs squid , cuttlefish find against light background, contract many of chromatophores, concentrating pigment smaller area, resulting in pattern of tiny, dense, spaced dots, appearing light. when enter darker environment, allow chromatophores expand, creating pattern of larger dark spots, , making bodies appear dark. amphibians such frogs have 3 kinds of star-shaped chromatophore cells in separate layers of skin. top layer contains xanthophores orange, red, or yellow pigments; middle layer contains iridophores silvery light-reflecting pigment; while bottom layer contains melanophores dark melanin.

structural coloration

the brilliant iridescent colours of peacock s tail feathers created structural coloration.



butterfly wing @ different magnifications reveals microstructured chitin acting diffraction grating.

while many animals unable synthesize carotenoid pigments create red , yellow surfaces, green , blue colours of bird feathers , insect carapaces not produced pigments @ all, structural coloration. structural coloration means production of colour microscopically-structured surfaces fine enough interfere visible light, in combination pigments: example, peacock tail feathers pigmented brown, structure makes them appear blue, turquoise , green. structural coloration can produce brilliant colours, iridescent. example, blue/green gloss on plumage of birds such ducks, , purple/blue/green/red colours of many beetles , butterflies created structural coloration. animals use several methods produce structural colour, described in table.

bioluminescence

a euplokamis comb jelly bioluminescent.

bioluminescence production of light, such photophores of marine animals, , tails of glow-worms , fireflies. bioluminescence, other forms of metabolism, releases energy derived chemical energy of food. pigment, luciferin catalysed enzyme luciferase react oxygen, releasing light. comb jellies such euplokamis bioluminescent, creating blue , green light, when stressed; when disturbed, secrete ink luminesces in same colours. since comb jellies not sensitive light, bioluminescence unlikely used signal other members of same species (e.g. attract mates or repel rivals); more likely, light helps distract predators or parasites. species of squid have light-producing organs (photophores) scattered on undersides create sparkling glow. provides counter-illumination camouflage, preventing animal appearing dark shape when seen below. angler fish of deep sea, dark hunt sight, contain symbiotic bacteria in bait on fishing rods . these emit light attract prey.