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When the Sun Goes Down, These Mushrooms Glow Bright

Researchers think they know why some bioluminescent fungi only perform at night.
​N. gardneri mushrooms in Gilbués, PI, Brazil. Image: Michele P. Verderane/IP-USP-2008

​Bioluminescence is one of the most beautiful and useful adaptations on the planet. From fireflies to angler fish, an organism's ability to create and emit its own light is a literal beacon of evolutionary sophistication.

It is also a convergent trait that spans many forms of life—including a rare collection of fungi species. Observations of these glowing mushrooms date all the way back to classical Greece, but the evolutionary drivers of fungal bioluminescence have never been understood.

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Now, thanks to new research published today in Current Biology, the motives behind at least one species of glowing mushroom have been explained. A team led by Dartmouth biologist Jay Dunlop discovered that the Brazilian Neonothopanus gardneri fungi glows in sync with its temperature-controlled circadian clock.

"Circadian control may optimize energy use for when bioluminescence is most visible, attracting insects that can in turn help in spore dispersal, thereby benefitting fungi growing under the forest canopy, where wind flow is greatly reduced," the study's authors wrote.​

Panellus stipticus. Image: Ylem/Wikipedia

Dunlop and his colleagues monitored that the amount of energy N. gardneri invested in luminescence. They noted that by day, the mushrooms used less luciferin, reductase, and luciferase—the main compounds behind their trademark glow. But in the evening, the presence of these compounds increased. Dunlop and his team believe that N. gardneri ramps up bioluminescent activity at night to attract a wide variety of insects that, in turn, will carry its spores.

Omphalotus olearius. Image: Noah Siegel/Wikipedia

Dunlap's team tested this hypothesis out further by placing acrylic mushrooms decked out with green LED lights into N. gardneri's habitat. As expected, the faux-shrooms with the LED lights turned on attracted more spore-carrying flies, wasps, ants, beetles and other spore-carrying insects than the control group.

Like so many bioluminescent organisms, these mushrooms aren't putting on enchanting light shows for free. They expect payment from their insect audience, which expand the mushroom's reach across Brazil's lush coconut forests in exchange.

This study represents a big leap forward in understanding the behavior of these little understood light-makers—but there are still other questions that remain unsolved. Whether other species of bioluminescent fungi have different motives and rhythms, for example, remains unclear. Only more research into these living lanterns will help illuminate the underlying mechanisms of their eerie glow.