Examine individual changes

'[[File:Watasenia scintillans (rotated).jpg|thumb|350px|''[[Watasenia scintillans]]'', the sparkling enope squid, uses [[bioluminescence]] to illuminate its underside to match the brightness of the sea surface above]] {{Camouflage}} '''Counter-illumination''' is a method of [[camouflage]] in which an animal (or possibly a military vehicle) produces light to match an illuminated background, such as the ocean surface or sky. It differs from [[countershading]] which uses only pigment, such as a vehicle's paint or the melanin in an animal's skin, to paint out the appearance of shadows. By adding the right amount of light through [[bioluminescence]] or electronically controlled lamps, counter-illumination can at best exactly match the brightness of the background, making for more effective camouflage than countershading can provide. Since counter-illumination allows the intensity of the generated light to be adjusted, camouflage can be [[active camouflage|actively]] adapted to varying lighting conditions and backgrounds. Counter-illumination is one of the dominant methods of [[Aquatic camouflage|camouflage in marine organisms]], along with transparency and silvering. All three methods make animals in open water resemble their environment. == Principle == Among marine organisms, counter-illumination [[camouflage]] occurs where [[bioluminescent]] light from an [[organism]]'s ventral surface<ref name="bioluminesence1977">Young. R.E, Roper. C.F.E. 1977. Intensity Regulation of Bioluminesence during Countershading in Living midwater animals. Science, New Series. Vol 191,4231: 1046-1048.</ref> is matched to the light radiating from the environment. The [[bioluminescence]] is used to obscure the organism's silhouette produced by the down-welling light.<ref name="Jones 2004: p.1151">Jones(2004): p.1151</ref> Some midwater [[cephalopod]]s, [[Decapoda|decapod]] [[crustacean]]s, and [[fish]]es utilize this form of camouflage.<ref name="Jones 2004: Young 1977">Jones(2004): Young 1977, as cited by Jones et al. 2004</ref> The bioluminescence used for Counter-illumination can be either [[autogenic]] (produced by the animal itself) or bacteriogenic (produced by [[bacteria]]l [[Symbiosis|symbionts]]).<ref>(Jones et al. 2004)</ref> The luminescent bacterium is often ''[[Vibrio ficheri]]''.<ref>Jones. B.W, Nishiguchi. M.K. 2004. Counterillumination in the Hawaiian bobtail squid, Euprymna scolpes Berry (Mollusca: Cephalopoda). Marine Biology. 144:1151-1155.</ref> Reducing the organism's silhouette is primarily an [[Antipredator adaptation|anti-predator defence]] for mesopelagic organisms. The reduction of the silhouette from highly directional down-welling light is important as there is no refuge in the mesopelagic, and predation occurs from below.<ref>Young. R.E, Roper. C.F.E. 1976. Bioluminescent countershading in Midwater Animals from living Squid. Science, New Series. Vol 191,4231: 1046-1048.</ref><ref name="bioluminesence1977"/><ref>{{cite web|url=http://www.bbc.co.uk/nature/blueplanet/infobursts/counter_illumination_bg.shtml |title=Science & Nature - Sea Life - Ocean info - Counter-illumination |publisher=BBC |date=2004-03-11 |accessdate=2012-10-03}}</ref> == Examples of the strategy == Many species in the [[mesopelagic]] areas of the ocean utilize this alternative to [[counter shading|countershading]]. For these marine species, counter-illumination best serves them when ambient light levels are low, leaving the diffuse down-welling light from above as the only light source.<ref name="Jones 2004: p.1151">Jones(2004): p.1151</ref> At night, nocturnal organisms match the [[wavelength]] and [[Brightness|light intensity]] of their bioluminescence to that of the down-welling moonlight and direct it downward as they swim, to help them remain unnoticed by any observers below.<ref name="Guerrero-Ferreira 2009: p.307">Guerrero-Ferreira(2009): p.307</ref> This strategy has been shown to significantly reduce predation among individuals employing it over those not employing it in the fish species ''[[Midshipman fish|Porichthys notatus]]'', the plainfin midshipman.<ref name="Jones 2004: Harper 1999">Jones(2004): Harper 1999, as cited by Jones et al. 2004</ref> Besides its effectiveness as a predator avoidance mechanism, counter-illumination also serves as an essential tool to predators themselves. Some shark species, such as the deepwater ''[[Etmopterus spinax]]'', use counter-illumination to remain hidden from their prey.<ref name="Claes 2010: p.28">Claeus(2010): p.28</ref> another example would be the Bobtail squid, which also uses counter-illumination as a means of predation.<ref>Jones. B.W, Nishiguchi. M.K. 2004. Counterillumination in the [[Hawaiian bobtail squid]], Euprymna scolpes Berry (Mollusca: Cephalopoda). Marine Biology. 144:1151-1155.</ref> Other well-studied examples include the [[cookiecutter shark]], the [[marine hatchetfish]], and the [[Hawaiian bobtail squid]].<ref name="Jones 2004: p.1154">Jones(2004): p.1154</ref> More than 10% of shark species may be bioluminescent, though some such as the [[lantern shark]]s may use the light for signalling as well as for camouflage.<ref>{{cite web | url=http://www.bbc.co.uk/nature/17812363 | title=Tiny sharks provide glowing clue | publisher=BBC | date=26 April 2012 | accessdate=12 February 2013 | author=Davies, Ella}}</ref> == Military applications == [[File:Principle of Yehudi Lights with Avenger head-on view.jpg|thumb|[[Yehudi Lights]] on [[Grumman TBM Avenger]] raised the average brightness of the plane from a dark shape to the same as the sky.]] Counter-illumination has rarely been used for military purposes. "[[Diffused lighting camouflage]]", in which light was projected on to the sides of ships to match the faint glow of the night sky, was trialled by Canada's National Research Council during World War II. The Canadian concept was trialled in American aircraft including [[Consolidated B-24 Liberator|B-24 Liberators]] and [[Grumman TBM Avenger|TBM Avengers]] in the [[Yehudi lights]] project, using forward-pointing lamps automatically adjusted to match the brightness of the sky.<ref name="NavalMuseumQuebec">{{cite web | url=http://www.navy.forces.gc.ca/navres/NMQ_MNQ/researches_recherches/diffusedLighting_camouflageLumineux/index-eng.asp | title=Naval Museum of Quebec | publisher=Royal Canadian Navy | work=Diffused Lighting and its use in the Chaleur Bay | accessdate=January 19, 2012}}</ref> [[Active camouflage]] could in theory exploit counterillumination in both the [[visible light|visible]] and other parts of the [[electromagnetic spectrum]]. [[BAE Systems]]'s ''[[Adaptiv]]'' prototypes the use of [[infrared]] camouflage technology with about 1000 rapidly heated and cooled panels to cover the sides of an [[armoured vehicle]], providing [[crypsis]] by matching the background, or [[mimicry|mimesis]] by depicting an object such as a car when viewed in infrared.<ref>{{cite web | url=http://www.bbc.co.uk/news/technology-14788009 | title=BBC News Technology | publisher=BBC | work=Tanks test infrared invisibility cloak | date=5 September 2011 | accessdate=13 June 2012}}</ref><ref name=Adaptiv-Cloak>{{cite web | url=http://www.baesystems.com/magazine/BAES_019786/adaptiv--a-cloak-of-invisibility | title=Adaptiv-A Cloak of Invisibility | publisher=BAE Systems |year=2011 | accessdate=13 June 2012}}</ref> == Footnotes == {{Reflist|32em}} == References == *{{cite journal |author=Claes, Julien M., Dag L. Aksnes & Jérôme Mallefet |year=2010 |title=Phantom hunter of the fjords: camouflage by counterillumination in a shark (''Etmopterus spinax'') |journal=[[Journal of Experimental Marine Biology and Ecology]] |volume=388 |issue=1–2 |pages=28–32 |doi=10.1016/j.jembe.2010.03.009 |url=http://www.bio.uib.no/modelling/papers/Claes_2010_Phantom_hunter.pdf |format=PDF}} *{{cite journal |author=Guerrero-Ferreira, R. C. & M. K. Nishiguchi |year=2009 |title=Ultrastructure of light organs of loliginid squids and their bacterial symbionts: a novel model system for the study of marine symbioses |journal=[[Vie et Milieu]] |volume=59 |issue=3–4 |pages=307–313 |issn=0240-8759}} *{{cite journal |author=Jones, B. W. & M. K. Nishiguchi |year=2004 |title=Counterillumination in the hawaiian bobtail squid, ''Euprymna scolopes'' Berry (Mollusca : Cephalopoda) |journal=[[Marine Biology (journal)|Marine Biology]] |volume=144 |issue=6 |pages=1151–1155 |doi=10.1007/s00227-003-1285-3 |url=http://www.medmicro.wisc.edu/labs/mcfall_ruby_papers/pdf/2004/Jones_Nishiguchi_2004_Biol.pdf |format=PDF}} == External links == * [http://www.scientificamerican.com/slideshow.cfm?id=bioluminescent-avatar Scientific American: 10 Bioluminescent Creatures] * [http://www.sciencemag.org/content/208/4449/1286.short Science Magazine: Bioluminescence in Mesopelagic Squid] * [http://www.pbs.org/wgbh/nova/sciencenow/0305/04-glow-07.html Nova: Science Now: Glowing in the Dark] (Squid ''Abralia veranyi'' belly lights) {{Navboxes |title = Articles related to Animal coloration |list = {{vision in animals|state=expanded}} }} [[Category:Antipredator adaptations]] [[Category:Deception]] [[Category:Camouflage]] [[it:Controilluminazione]]'