Bioluminescence: lighting up the natural world

The forest floor glows at night

The forest floor is barely visible in the low light conditions when it suddenly bursts into life, becoming a neon green blanket of light.

The source of this eerie light is a bioluminescent fungus, known only by the name given to it by locals: "chimpanzee fire".

Filmmaker Verity White was able to catch this phenomenon on camera for the Congo episode of the BBC/Discovery series Africa using long-exposure time-lapse photography techniques.

This bizarre species was filmed in the Goualougo triangle, near the Dzanga river in Congo Brazzaville.

The existence of the fungus was so little-known that even experienced field scientists had never seen it.

It was only when Ms White asked local guides if they had ever heard of the glowing fungus that its whereabouts came to light.

"On the off-chance of seeing it, I took a time-lapse camera with me," Ms White tells BBC Nature.

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"The scientist I was working with said he'd never seen it, so I thought I'd ask the local Bayaka trackers. The trackers said 'Yes, of course - it's everywhere'."

"It was only ever a long shot - but it worked out."

After the discovery in the Congo the filming continued in laboratory conditions to capture the microscopic details of how the fungus grows.

Shedding some light

Ms White's scenes of the fungus in its forest environment produced a visually compelling piece of footage, but what also emerges from the chance filming is how little is known about such an astonishing natural phenomenon.

Nobody knows what genus the 'chimpanzee fire' fungus belongs to, let alone the species.

Why it grows on the forest floor in the Goualougo triangle is also a mystery, although theories have been put forward, such as attracting invertebrates that in turn spread the fungus' spores.

Bioluminescence is the process in living organisms where the energy from a chemical reaction is released as light. It is the enzyme luciferase that catalyses the reaction of oxygen with the light-emitting chemical luciferin.

Mycena_chlorophanos Just 33 of the 500 Mycena species are light-emitting
Glow-worm hanging on a blade of grass Glow-worms are found in the UK. Females produce greenish-yellow light
Dead moth grub A moth grub glows after death, due to bioluminescent bacteria inside

The reaction is called chemiluminescence: a light-emitting reaction that does not produce heat, rendering it highly energy efficient.

Functions of bioluminescence within natural environments include defence, communication, reproduction and prey attraction.

A wide variety of organisms emit light, including bacteria, fungi, insects, crustaceans, molluscs and fish.

While in marine habitats the use of bioluminescence is widespread, terrestrial bioluminescence is limited to the fungi kingdom and invertebrates such as glow worms, fireflies and click beetles.

Africa - a landmark

Shoebill chick (Balaeniceps rex) on its nest

A study published last year in the journal Naturwissenschaften by a team of scientists from the Slovak Academy of Sciences in Bratislava, Slovakia, suggests that bioluminescent cockroaches demonstrate a further use of defensive luminescence: mimicry of a toxic click beetle species.

The scientists claim that their observations are "evidence for mimicry by light, a new kind of... defensive mimicry".

The research team found that species of cockroach genus Lucihormetica, flashed exactly the same shade of bioluminescence as the highly toxic Pyrophorus genus of click beetles.

The study also proposes that there are greater numbers of bioluminescent species in ocean habitats because environmental changes in marine conditions are not as rapid as those that occur on land.

The use of light displays in firefly mating rituals is well documented, with flash responses of female Photinus species used to successfully attract mates.

However mimicry of female Photinus flash responses by predatory Photuris females not only wins them dinner in the form of the Photinus male, but also his defensive steroids, which provide the Photuris "femme fatales" with immunity to Phidippus jumping spiders.

Bobtail squid, East Timor The bobtail squid exists symbiotically with the bioluminescent bacteria Vibrio fischeri

In late 2012, a Japanese research team studying Asian Luciola parvala fireflies, provided the first report of sexual communication in a female "advertiser" in the Journal of Ethology.

But in understanding this new bioluminescent behaviour, the scientists are presented with a further query. They say: "The current findings... also pose a new important question. What is the role of male flashes in the female advertisement firefly?".

Because in terms of energy-efficiency, if alternative light sources are available, there is no need for an organism to produce its own luminescence.

In a study published last year in the Journal of Insect Conservation, Australian scientists from the Universities of Queensland and Tasmania investigated the impact of cave lighting on bioluminescent glow worm displays in northern Tasmania.

Marakoopa Cave attracts around 30,000 visitors a year to the glow worm [Arachnocampa larvae] displays.

Previous studies showed that artificial lighting can cause Arachnocampa larvae to reduce their light output, but time-lapse photographic techniques were able to show that Marakoopa Cave's glow worm population was undisturbed by the levels of artificial light exposure.

The darkest depths

It makes perfect sense that the ability to produce light is most widespread in the earth's darkest environment: oceans.

Bioluminescence on the tide line, Vaadhoo Island, Raa Atoll, Maldives Bioluminescent plankton lights up a beach at night

For centuries, phosphorescence has amazed and delighted those who witness it. The sea comes alive with glowing waves, washing light along shores and against water-borne objects.

It is in fact blooms of bioluminescent plankton; the effect is startling.

Levels of light are reduced at greater oceanic depths, prompting an estimated 90% of marine animals to display bioluminescence in some form.

Blue and green luminescence is prevalent in marine environments as wavelengths from this part of the light spectrum travel most easily through water.

The array of marine creatures that use bioluminescence to confuse or evade predators, find a mate or attract prey is vast, and the ghostly underwater sights and shapes are distinctly alien.

Big fin reef squid in deep water {Sepioteuthis lessonians} Sulawesi, Indonesia Indo-Pacific Glowing photophores are easily visible around squids' eyes

Dr Jerome Mallefet works at the Laboratory of Marine Biology at the University of Louvain-le-Neuve in Belgium.

His areas of research include luminescence in brittle stars and sharks.

"For many years I have developed a multidisciplinary approach to study luminescence in order to understand the morphology, ecology and physiology around why so many brittle stars glow in the dark.

"More recently we applied the same approach to sharks because little, if not nothing, was known about the luminescence of these cartilaginous fishes while around 50 species out of the 540 shark species are... able to produce light."

Dr Mallefet leads studies on areas such as whether luminescent organisms are able to perceive their own light production and the purposes of luminescence.

Glowing sharks Etmopterus spinax Glowing sharks: Etmopterus spinax

He has worked with Osamu Shimomura, who was awarded the Nobel prize in Chemistry in 2008 for the discovery of green fluorescent protein (GFP) while studying the luminous system of jellyfish.

GFP is widely used in genetic engineering and other bio-medical research, further uses include monitoring environmental pollutants.

Dr Mallefet hopes that his own work will enable us to further understand bioluminescence. "We need to continue fundamental research in bioluminescence in order to discover new applications."

After 30 years studying the science of glowing, he concludes: "It is just magic to see one animal glowing in the dark... after 30 years I am still fascinated by the phenomenon".

The footage of chimpanzee fire can be seen on the BBC One/Discovery Africa series at 21.00 GMT on Wednesday 16 January.

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