With the coming of night in Brazil's Coconut Forest, bioluminescent mushrooms dial up their green glow. They attract insects that can carry spores far and wide under the nearly windless canopy. Until recently many scientists thought their dim glow was a random byproduct of mushroom metabolism, related perhaps to the digestion of decaying wood. "Circadian Control Sheds Light on Fungal Bioluminescence" published in Current Biology, however, offers the first solid evidence that mushroom bioluminescence is regulated and purposeful.
Glowing with Purpose
Bioluminescent mushrooms are the only fungi that make their own light, but why they do is an age-old mystery. Aristotle (384–322 BC) and Pliny the Elder (AD 23–79) recognized that the glow they imparted to decaying wood was not fire, and a 17th century Dutch physician reported that Indonesian natives carried bioluminescent mushrooms to light their way through dark forests.1 But how did this serve the mushrooms?
At latest count, only 71 of the 9,000 species of gilled mushrooms glow. In some the glowing parts are mostly hidden underground, but light from "flor de coco" (literally "coconut flowers") — the large Neonothopanus gardneri mushrooms growing beneath Brazilian coconut palms — is easily seen. Locals say it varies, appearing greatest during humid nights following hot days with afternoon showers. Brazilian scientists collaborating with a team from Dartmouth's Geisel School of Medicine have now proven that the luminescent levels of those light-producing molecules follow a nightly cycle that attracts lots of insects.