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Bioluminescence is the production and emission of light by a living organism. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms and terrestrial invertebrates. Some symbiotic organisms carried within larger organisms produce light.
Bioluminescence is a form of luminescence, or "cold light" emission by living organisms; less than 20% of the light generates thermal radiation. It should not be confused with iridescence, structural coloration, phosphorescence.
Bioluminescence is a form of chemiluminescence where light energy is released by a chemical reaction. Fireflies, anglerfish, and other creatures produce the chemicals luciferin (a pigment) and luciferase (an enzyme). The luciferin reacts with oxygen to create light. The luciferase acts as a catalyst to speed up the reaction, which is sometimes mediated by cofactors such as calcium ions or ATP. The chemical reaction can occur either inside or outside the cell. In bacteria, the expression of genes related to bioluminescence is controlled by an operon called the Lux operon.
Bioluminescence occurs widely among some groups of animals, especially in the open sea; in some fungi and bacteria; and in various terrestrial invertebrates including insects. Many, perhaps most deep-sea animals produce light. Most marine light-emission is in the blue and green light spectrum, the wavelengths that pass furthest through seawater. However, some loose-jawed fish emit red and infrared light, and the genus Tomopteris emits yellow light. Sometimes thousands of square miles of the ocean shine with the light of bioluminescent bacteria in the "Milky seas effect".
Non-marine bioluminescence is less widely distributed. The two best-known forms of land bioluminescence are fireflies and glow worms. Other insects, insect larvae, annelids, arachnids and even species of fungi have been noted to possess bioluminescent abilities. Some forms of bioluminescence are brighter (or exist only) at night, following a circadian rhythm.
Bioluminescence has several functions in different taxa.
In many animals of the deep sea, including several squid species, bacterial bioluminescence is used for counterillumination camouflage, in which the animal matches the overhead environmental light as seen from below. In these animals, photoreceptors control the illumination to match the brightness of the background. These light organs are usually separate from the tissue containing the bioluminescent bacteria. However, in one species, Euprymna scolopes, the bacteria are an integral component of the animal's light organ.
Bioluminescence is used as a lure to attract prey by several deep sea fish such as the anglerfish. A dangling appendage that extends from the head of the fish attracts small animals to within striking distance of the fish.
The cookiecutter shark uses bioluminescence to camouflage its underside, but a small patch near its pectoral fins remains dark, appearing as a small fish to large predatory fish like tuna and mackerel swimming beneath it. When such fish approach the lure, they are bitten by the shark.
Dinoflagellates may use bioluminescence for defence against predators. They shine when they detect a predator, possibly making the predator itself more vulnerable by attracting the attention of predators from higher trophic levels. A South American giant cockroach, Lucihormetica luckae, uses bioluminescence to mimic the toxic Pyrophorus beetle for defensive purposes.
In the marine environment, use of luminescence for mate attraction is well documented only in ostracods, small shrimplike crustaceans. Pheromones may be used for long-distance communication, with bioluminescence used at close range to enable mates to "home in".
Certain squid and small crustaceans use bioluminescent chemical mixtures or bacterial slurries in the same way as many squid use ink. A cloud of luminescent material is expelled, distracting or repelling a potential predator, while the animal escapes to safety.
Communication (quorum sensing) plays a role in the regulation of luminesence in many species of bacteria. Using small extracellularly secreted molecules, they turn on genes for light production only at high cell densities.
While most marine bioluminescence is green to blue, the Black Dragonfish produces a red glow. This adaptation allows the fish to see red-pigmented prey, which are normally invisible in the deep ocean environment where red light has been filtered out by the water column.
Bioluminescent organisms are a target for many areas of research. Luciferase systems are widely used in the field of genetic engineering as reporter genes. Luciferase systems have also been harnessed for biomedical research using bioluminescence imaging. Vibrio symbiosis with numerous marine invertebrates and fish, namely the Hawaiian Bobtail Squid (Euprymna scolopes), are key experimental models for bioluminescence.
The structures of photophores, the light producing organs in bioluminescent organisms, are being investigated by industrial designers. Engineered bioluminescence could perhaps one day be used to reduce the need for street lighting, or for decorative purposes.
In June 2013 the Glowing Plant project successfully raised nearly $500,000 on the crowd funding site Kickstarter to create a bioluminescent plant. The project's long term goal is the creation of trees that can be used for street lighting.
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|Wikisource has the text of the 1920 Encyclopedia Americana article Luminosity of Animals.|