Functions of Bioluminscence

Bioluminescence has many functions and it frequently serves multiple roles in the same organism.

(1) Attracting prey: Bioluminescent glow is thought to be an attraction signal. For example, the octopus Stauroteuthis uses its luminous suckers to attract plankton. An anglerfish also attracts prey in a similar manner by using bacteria to produce a kind of glowing lure. A certain type of squid has special light organs which also serve as lures that dangle at the end of long tentacles, like fishing lines.

Some non-luminous predators actively use bioluminescence in their environment to attract or reveal their prey. Elephant seals dive to great depths and feed on fish and squid there.

(2) Escaping from predators: As opposed to glowing, sudden flashes of bioluminescence are thought to act as repellants. Bioluminescence can startle predators, causing them to hesitate in their attack. The bioluminescent display may also serve as a smoke screen—a cloud of sparks or glowing fluid that makes it difficult for the predator to track the location of its escaping prey. Examples of this type of bioluminescent behavior can be found in shrimp and vampire squids. Every species of firefly has larvae that glow to repel predators.

Bioluminescence can also serve as an indication of toxicity or unpalatability. Some plankton in particular have an interesting twist on this mechanism. When a predator of plankton is sensed through motion in the water, the plankton luminesces. This in turn attracts even larger predators which consume the would-be predator of the plankton.

 (3) Inter-species communication: Communication within species is a well-known function of bioluminescence, and is mainly used for reproduction-related activities. A good example is fireflies using their light in courtship. To avoid confusion between members of different types of fireflies, the signals of each species are coded in a unique temporal sequence of flashing. This type of bioluminescent communication is not very common in the sea.

(4) Illumination: Bioluminescence can also be used to illuminate or to induce fluorescence in prey. Some dragonfishes are thought to use bioluminescence to aid in visual searching of prey. For example, 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.

(5) Camouflage or counter-illumination: In the depths of the ocean, it’s much harder to see anything below you than to see the silhouette of what's above. For this reason, some species produce spots of light on their undersides (through ventral photophores), which blur their outlines and allow them to blend in with the light from above. This is known as counter-illumination and is well documented in certain types of crustaceans, cephalopods and fishes. The cookie-cutter shark has one unlit patch on its underside which resembles a smaller fish when viewed from below. When a large predator approaches, the shark can take a large bite and then flee. This allows the cookie-cutter shark to prey on animals that are much larger and more powerful than it is.

Different Kinds of Luminescence

Energy is transferred in many different ways: as heat, as light, or by chemical reactions. When energy is released by matter in the form of light it is referred to as luminescence. An exception is usually made for matter that has such a high temperature that it simply glows; this is called incandescence. Luminescence is far more efficient than incandescence. It neither requires nor generates much heat, so it's sometimes known as “cold light” (from Aristotle’s term).

Chemiluminescence is the emission of light as the result of a chemical reaction. The energy that is released as a result of the chemical reaction excites the product molecules of the reaction. A molecule in this excited state either relaxes back to a lower energy state, with the direct emission of light, or transfers its energy to a second molecule, which becomes the light emitter.

A common example is a glowstick. When the glowstick is bent, chemicals are released and mix together, causing the glowstick to start glowing. Another example of a chemiluminescent reaction is between nitrogen monoxide (NO) and ozone (O₃) which forms NO₂ (nitrogen dioxide) in an excited state. The activated NO₂ emits light when it reverts back to a lower energy state.

Chemiluminescence differs from photoluminescence in that the excited state of the electron is derived from the product of a chemical reaction rather than the more typical way of creating electronic excited states, namely absorption of a quantum or multiple quanta of light. In photoluminescence, light is used to drive an endothermic chemical reaction. In chemiluminescence, light is generated from a chemically exothermic reaction. There are two types of photoluminescence: (i) fluorescence, which involves absorbing and releasing lower energy light almost immediately and (ii) phosphorescence, in which the release of light is delayed, making phosphorescent materials appear to glow in the dark.

Bioluminescence is a naturally occurring form of chemiluminescence, or the emission of visible light by an organism as a result of a natural chemical reaction. Bioluminescence is primarily a marine phenomenon, though bioluminescence can also be found in some land animals (predominantly insects), fungi, bacteria, and protists. It is the predominant source of light in the deep ocean. There are many reasons for this. First, large portions of the ocean either have very dim light or exist in total darkness. Second, the volume of habitat where bioluminescence is effective is vast, allowing natural selection to take place in a huge ecological context. Third, in most of the ocean there is no concealment; the most common functions of bioluminescence in the ocean are for defense against predators or to find or attract prey.

A Brief History of Bioluminscence

Stories about mysterious lights seen over water, mountains, or fields were often attributed to dragons or the power of the gods. Early religious writings of India and China contain the first written reports of bioluminescence in fireflies and glow worms. But it was the Greeks and the Romans who first reported the characteristics of luminescent organisms. Famous Greek philosopher Aristotle (384-322 BCE) described luminescence as “cold light” because it was not associated with an increase in heat. He also made systematic observations of many luminescent marine species. 

The first extensive descriptions of luminous organisms were published by Pliny the Elder (23-79 CE). He discovered luminescence when he ate a clam and ended up with a pair of glowing green lips. Pliny also found that when the luminous material from the clam was mixed with flour, honey, and water, the paste produced light. This light could sometimes last for a whole year, as long as water was being added regularly. In his writings, he described the luminescence of snails, jellyfish, lantern fish, fungi, and glow-worms. Pliny the Elder was also the first person to find practical applications for the light produced by these organisms. He described how a piece of wood rubbed with a fish called Pulmo Marinus could be used as a torch.

Many 15^th and 16^th century voyagers such as Christopher Columbus and Sir Francis Drake referred to mysterious lights in the sea or to a “burning sea” phenomenon. In literature, references to bioluminescence were found in the work of Shakespeare, when Hamlet refers to the fire of the glow worm. Fireflies may even have changed the course of history. In 1634, when a British fleet was trying to land in Cuba, they saw many flashes of light coming from the shore. Attributing the flashes to the gunfire of Spanish forces, the British fleet didn’t disembark, but sailed on. There were, however, no Spanish forces on the island of Cuba at that time. The British simply mistook the flashes of fireflies for a large military force!

The first book devoted to bioluminescence and chemiluminescence was published in 1555 by Swiss naturalist Conrad Gesner. Robert Boyle (1627-1691), famous for Boyle’s law, performed the first chemical studies of firefly luminescence. He hypothesized that air was a requirement for luminescence (this was later modified to oxygen).

Not much advance occurred in the arena of jellyfish luminescence after Pliny the Elder’s descriptions of the same. Many centuries later, German scientist and explorer, Alexander von Humboldt (1769-1859) performed the first recorded jellyfish luminescence experiments. Sicilian Abbe Lazzaro Spallanzani discovered that the material responsible for luminescence in jellyfish was mucus that formed on the edge of the umbrella and on the arms of the jellyfish. During the 16^th and 17^th century, luminescent material was added to medicines solely for the purpose of impressing patients.

In 1885, French pharmacologist Raphael Dubois performed a pivotal experiment in which he extracted the two key components of a bioluminescent reaction from a click beetle. He named these components luciferin and luciferase. They were both named after Lucifer, the fallen angel of light.

E. Newton Harvey (1887-1959), a Princeton University professor, soon became the foremost expert on bioluminescence. He discovered that luciferins (the light-emitting substances occurring in luminescent organisms) and luciferases (enzymes that interact with luciferins) from different animals were specific to a particular species and not interchangeable. He theorized that the inability to interchange luciferins and luciferases across species was evidence of evolution, as each species had adapted to fit its specific needs.

Harvey was soon followed by Osamu Shimomura, who also worked at Princeton University studying the jellyfish. Through his research, he was able to show that a protein, later named GFP (green fluorescent protein), was involved in jellyfish luminescence and that this protein could be isolated from the jellyfish. Shimomura was awarded the Noble Prize in Chemistry in 2008 for his work on GFP.

A journey of a thousand miles begins with a single step

Or a turn of a key, if one decides to take a car. But I digress.

I spent some time searching for and reading reviews of books on bioluminescence on amazon.com. I also did an internet search for articles and websites about bioluminescence. Here is what I have found:

Books: (1) Glowing Genes: A Revolution in Biotechnology by Marc Zimmer, Amherst, New York: Prometheus Books (2005). (2) Aglow in the Dark: The Revolutionary Science of Biofluorescence by Vincent Pieribone and David F. Gruber, Cambridge, MA: The Belknap Press of Harvard University Press (2005). (3) Bioluminiscence: Chemical Principles and Methods by Osamu Shimomura, Hackensack, New Jersey: World Scientific Publication Company Inc. (2006).

I was able to get the first two books from the Austin Public Library and they promise to be interesting and informative reading. I was disappointed that the 3^rd book is not part of the library’s holdings since Professor Shimomura is a giant in the field of bioluminescence, who was awarded the Nobel Prize in Chemistry in 2008 for his discovery of Green Fluorescent Protein (GFP) in jellyfish. I am going to try and get the book via interlibrary loan.

Websites and Articles: There were lots of pages to sift through, but I was able to narrow down the results to the following:

(1) The Bioluminescence Web Page

http://www.lifesci.ucsb.edu/~biolum/

(2) Bioluminescence info and research from the Latz Laboratory of the Scripps Institute of Oceanography

http://siobiolum.ucsd.edu/biolum_intro.html

(3) Bioluminescence in the Sea - Jan 2010 article in the Annual Review of Marine Science

http://www.annualreviews.org/eprint/pbWcm4DyqvQGJ7F2qGkc/full/10.1146/annurev-marine-120308-081028

(4) Bioluminescence article by Professor John Lee, University of Georgia

http://www.photobiology.info/LeeBasicBiolum.html

(5) Bioluminescence article by Steven Haddock, Research Scientist, Monterrey Bay Aquarium Research Institute

http://oceanexplorer.noaa.gov/explorations/09bioluminescence/background/bioluminescence/bioluminescence.html

(6) Detailed scientific article on applications of bioluminescence http://www.promega.com/resources/product-guides-and-selectors/protocols-and-applications-guide/bioluminescent-reporters/

(7) TED talk on Glowing Life in an Underwater World by Edith Widder (CEO and Senior Scientist, Ocean Research and Conservation Association)http://www.ted.com/talks/edith_widder_glowing_life_in_an_underwater_world.html

(8) Scientific American article on 10 shining examples of bioluminescent creatures

http://www.scientificamerican.com/article.cfm?id=bioluminescent-avatar