The glow of a mushroom field in a dark forest can be beautiful and mysterious. Now, scientists are starting to crack open the mysteries and discover why the gilled fungi illuminate the night.
A new study in Current Biology suggests that glowing mushrooms give off bioluminescent light to attract insects, which then spread the fungal spores far and wide.
The researchers looked at Neonothopanus gardneri, or ‘Flor de Coco,’ a mushroom commonly found in Brazilian coconut forests.
“On a totally dark night, without any moon, if you have your light off, these green mushrooms are basically the only light source you see in the forest besides the fireflies,” researcher Hans Waldenmaier said to NPR.
Mushrooms use up oxygen to create the light, and researchers previously thought that the green glow was continuous and might be a byproduct of the fungi’s metabolism. However, the study reports that the light is actually “controlled by a temperature-compensated circadian clock,” or internal body clock.
The findings indicate that the mushroom only puts out a glow when it would be visible, i.e. at night, and conserves energy during the day.
“Regulation implies an adaptive function for bioluminescence,” said study co-leader Jay Dunlap, PhD, chair of the Department of Genetics at the Geisel School of Medicine, in a press release.
In order to learn more, the scientists designed glowing prosthetic acrylic resin mushrooms and placed them in the woods. The mockups attracted beetles, flies, wasps, ants and other insects, while control prosthetics did not. “It appears that fungi make light so they are noticed by insects who can help the fungus colonize new habitats,” study co-leader Cassius Stevani, PhD, of Brazil’s Instituto de Química-Universidade de São Paulo, said in the press release.
The concept is similar to berry vines producing fruit that is attractive to birds, which then spread the seeds around so the vines can grow in other areas.
“Thus, circadian control may optimize energy use for when bioluminescence is most visible, attracting insects that can in turn help in spore dispersal, thereby benefiting fungi growing under the forest canopy, where wind flow is greatly reduced,” the study concludes.
Bioluminescent mushrooms are relatively rare. Only 71 of the approximately 100,000 fungus species identified by humans are known to glow, according to the study. Among the most famous are the Omphalotus olearius, or jack-o’-lantern mushroom, which grows in Europe and features glowing gills.
Another well-known variety is Armillaria, or honey mushroom, which grows in rotting logs and is thought to be behind alluring foxfire effects that baffled historical wise men like Aristotle and Pliny the Elder.
Other species produce bioluminescent light for a diverse array of purposes. Fireflies are perhaps the most recognizable, flicking their lights on and off on summer evenings to attract mates. Certain fish that live in the depths of the ocean create light to attract prey, while others use it to distract their predators and make a getaway. Glowworms, the name for various types of insect larvae, are believed to illuminate in order to warn would-be attackers that they are toxic.
But we never had a credible explanation for why mushrooms glowed — until now. The next step for scientists is to probe deeper into how the luminescence functions, and take a closer look at insect behavior to verify that they actually disperse the spores.
The results are important for understanding how mushrooms reproduce and continue to fill their crucial role in the planet’s ecosystems. “Without them, cellulose would be stuck in its form, which would impact the whole carbon cycle on Earth,” Stevani said. “I dare to say that life on Earth depends on organisms like these.”