Bioluminescence flickering in the dark

A survival mechanism adapted to the dark environment

  There are many organisms that emit bioluminescence in the world, and fireflies are one of the more familiar ones.
  If you see fireflies for the first time, you will definitely look at them more. Seeing the flickering yellow-green light in the dark night makes people feel like they are in a wonderful world. This kind of luminous bug does not seem to belong to the earth, but to a magical creature from outside.
  In fact, fireflies are a relatively common creature from Europe to Asia. Fireflies are a type of beetle belonging to the firefly family, some females have no wings and look like larvae. The females hide underground during the day and climb to the roots of the ground plants at night, emitting fluorescent light from their stomachs to attract passing males.
  In an area that includes Australia, New Zealand and neighboring Pacific islands, “glowing bugs” refer to the larvae of gnats, a small fungus that feeds on fungi. Some of these small fungal gnats are carnivores that lure their prey by glowing blue-green through light-emitting organs in their tails. The peculiar landscape of bioluminescence of small fungus gnat larvae attracts tourists from all over the world. For example, the glowworm cave in New Zealand is a famous attraction for viewing this kind of bioluminescence.

Firefly, shimmering yellow-green light in the dark night

  Whether on land at night or in deep sea areas where sunlight is impenetrable, biofluorescence in the dark is a very important means of survival for many species to use to hunt for food or transmit information. Most of the world’s light-emitting creatures live deep in the ocean. It is estimated that 90% of light-emitting organisms live in dimly lit seabeds at depths of 500 to 1,000 meters. Scientists believe that bioluminescence is more common in the ocean than on land because marine species evolved earlier than terrestrial species. Bioluminescence is less common in freshwater environments, possibly because these habitats are later developed and have lower levels of biodiversity.
  Throughout the history of biological evolution, from fireflies to fungi to fish, bioluminescence has evolved many times. Scientists have found that in the deep-sea environment, the vast majority of species are luminescent organisms, and more than 80% of fish species in the deep-sea area emit bioluminescence. Obviously, bioluminescence is an essential survival adaptation mechanism for marine organisms to adapt to the dark seabed environment during the evolutionary process.
How is bioluminescence produced?

  Bioluminescence, the mechanism of light at the molecular level, is one of nature’s most fascinating phenomena.
  Luminescent organisms produce cold light through chemical reactions in their bodies, and the key molecule is a luciferin called lucifer, which means “bringer of light” in Latin.
  The term “fluorescein” was coined by the pharmacologist Rafael Dubois in the 19th century. At the time he was studying clock beetles and bivalve mollusks. Luminescent organisms emit light because luciferin reacts with oxygen under the catalysis of luciferase or photoprotease. In this chemical reaction, electrons are “excited”, transitioning from a lower energy level to a higher energy level, and when the fluorescein relaxes to its normal state, it emits photons that emit light. Different fluorescent organisms contain different types of fluorescein.
  Many light-emitting organisms can synthesize luciferin themselves, such as tiny sea creatures called dinoflagellates. Whenever night falls, large groups of dinoflagellates appear on the sea together, and the sea will light up with a large flickering blue fluorescent light. Some other light-emitting organisms absorb luciferin from food or acquire luciferin through symbiotic relationships with other organisms. These symbiotic organisms are biologically closely related, and through this symbiotic relationship, either both parties can benefit; or only one party can benefit, but the other party is harmless; or the parasitic party can cause harm to the host , but will not put the opponent to death.

Firefly squids emit bioluminescence through many tiny light-emitting organs on their bodies

A bioluminescent bacterium, Vibrio fischeri, resides in the light-emitting organs of the firefly squid

  For example, a bioluminescent bacterium, Vibrio fischeri, resides in the light-emitting organs of the Hawaiian bobtail squid. Vibrio fischeri obtains nutrients from the squid, and in return helps the host hide its figure, so that the squid is integrated with the sea under the moonlight, so that it will not be discovered by predators because of its shadow on the seabed.
  Scientists recently discovered that a small tropical fish known as a “scavenger” has evolved a special ability: by eating, they pick up chemicals from bioluminescent ostracod prey and deliver them to their own glow organ. This special ability, previously found in toadfish, is similar to the ability of poison dart frogs to ingest and store toxins from their prey and the ability of sea slugs to ingest and store chloroplasts.
  Scientists point out that it is difficult to imagine how many intermediate steps the evolution of this trait has gone through, but it is certain that bioluminescence evolution has occurred many times in fish.
How do luminescent organisms use bioluminescence?

  Luminescent organisms can not only emit biofluorescence, but also absorb biofluorescence. Luminescent organisms fluoresce because proteins in their skin or other tissues absorb energy from sunlight and then fluoresce in different colors.
  Some organisms that live in the ocean or on the beach use fluorescence from specific parts of their bodies to prey or communicate. Some bioluminescence deep in the ocean may not have a specific function, but are simply by-products of biochemical reactions taking place in body tissues.

  Green and blue are the most common biofluorescent colors in the ocean because these colors have shorter wavelengths of light and travel the farthest distances in water. Many marine species cannot handle yellow, red or violet because these colors have longer wavelengths. Red biofluorescence is relatively rare in the marine world, but some fish use it to their advantage.
  The deep-sea dragon fish is a marine creature that emits red biofluorescence, which can help the deep-sea dragon fish to illuminate and track its prey without being detected by the other party. The deep-sea dragon fish uses its huge jaws, opens its mouth wide, and kills its prey with its sharp teeth.

Ctenophores fluoresce to ward off predators

  Red fluorescence is also useful for light-emitting creatures that appear on land at night. A beetle called the “apple fruit fly” glows red biofluorescence in the dark. It’s like equipping them with night vision goggles, allowing them to stalk the forest floor at night and ambush unsuspecting prey.
  Many organisms use bioluminescence to ward off predators. Jellyfish often use this strategy, for example: some jellyfish dazzle predators with dazzling bioluminescence; others release flickering glowing particles into the sea as bait; and some jellyfish even sacrifice themselves in times of crisis A part that glows (such as a tentacle that emits bioluminescence) to distract predators and take the opportunity to escape. Some creatures even produce glowing slime that sticks to predators, rendering them incapacitating.
  There are many other marine organisms that use bioluminescence to escape predators. For example, when dinoflagellates glow, they will attract predators’ natural enemies, and the dinoflagellates can take the opportunity to escape; some scale insects, snaketail starfish and sea cucumbers are facing life and death In times of crisis, a body part that emits light is abandoned; some species of shrimp and squid, when escaping quickly, will spray a cloud of black water that emits a faint flash to cover their escape.

Beautiful glowing jellyfish under the sea

Some deep-sea creatures, such as sea gills, scare off predators by emitting biofluorescence

  It’s not just fireflies and marine organisms that emit bioluminescence. Some fungi also use bioluminescence to attract insects, not to hunt but to use insects to spread fungal spores to the ground in more sheltered areas of the forest. Other ways of “spreading seeds” in the animal kingdom include glowing vomit.
  Ostracoids are tiny crustaceans, and there is one species commonly known as “noctilucent shrimp” or “sea fireflies”, and they can be found in marine and freshwater environments around the world. Male ostracods attract mates by spitting out a cloud of glowing mucus. Various ostracods spit out mucus in different shapes, some in a spiral shape, some in a zigzag shape, etc.
  Fireflies are the most famous of the light-emitting creatures. They are not flies, but a beetle of the lamprey family. Many species of fireflies can produce bioluminescence. Biologists believe that they control the intensity of light emitted from the abdomen by regulating the amount of oxygen entering the light-emitting organs. At night, the males send out courtship signals to the females through flashes of fluorescent light, and the females respond with a series of flashes of light at the right time. Each firefly has a different flash pattern, so they usually don’t find the wrong target.
  However, light pollution is disrupting this mating ritual of fireflies. A study published in 2019 found that the bioluminescent courtship behavior of fireflies is severely affected by artificial light. So, please turn off the lights at night so as not to disturb the peace of these little creatures.
  Currently, scientists use bioluminescence as a revolutionary tool in molecular biology. Green fluorescent protein (GFP) occurs naturally in crystal jellyfish. Scientists insert the gene for this bright green green fluorescent protein into cells, which can be used in various biomedical research.
glow-in-the-dark mammal
Which mammals can fluoresce?

  In the 1980s, when specimens of North American possums in museums were irradiated with ultraviolet light, their abdominal fur glowed pink, the first record of biofluorescence in mammals. These species are all nocturnal, so it’s possible that their ability to glow is related to communication or camouflage in low light. In 2019, the phenomenon of pink glow was found in three nocturnal flying squirrels in North America.

Possum’s belly fur glows pink

Platypus glows blue-green under UV light

Wombats also glow under UV light
Will we find more glowing mammals?

  In October 2020, U.S. researchers discovered that platypus emit blue-green light under ultraviolet light. As before, scholars stumbled across this while examining specimens of its skin. Immediately afterwards, researchers at the Western Australian Museum began examining their own collections and found that wombats also glow in ultraviolet light. This not only demonstrates the research value of museum collections, but also makes us look forward to discovering more mammals that emit biofluorescence.