Why Some Mushrooms Glow In The Dark
A team of scientists recently created some fake, glowing mushrooms and scattered them in a Brazilian forest in hopes of solving an ancient mystery: Why do some fungi emit light?
The question goes back all the way to Aristotle, who is the first person known to have wondered about this, according to Jay Dunlap, a geneticist and molecular biologist at the Geisel School of Medicine at Dartmouth College in Hanover, N.H. He says over the years people have thrown out various explanations for the light — everything from "it's a useless byproduct of metabolism" to "it attracts insects."
This week, in the journal Current Biology, Dunlap and some colleagues report on a series of experiments that suggest at least one kind of mushroom controls when it glows. It lures bugs that then spread the mushroom's spores throughout the dense forest, where there's little wind.
That fungus is Neonothopanus gardneri, a dramatic mushroom that grows at the base of young palm trees in coconut forests in Brazil and emits an eerie green light.
"You just have to turn off your flashlight and the mushrooms stand out if they're there," says Hans Waldenmaier, a researcher in the lab of Cassius Stevani, of Brazil's Instituto de Quimica-Universidade de Sao Paulo.
"On a totally dark night, without any moon, if you have your light off," Waldenmaier says, "these green mushrooms are basically the only light source you see in the forest besides the fireflies."
Work in Dunlap's lab showed that the glow of this particular mushroom was controlled by a biological clock, suggesting that it wasn't just happening accidentally. "We found that light was made mostly at night, and not mostly during the day," says Dunlap.
In hopes of figuring out why, the researchers in Brazil created some fake fungi out of acrylic resin. The impostors "roughly look about the same as the mushrooms we find out in the woods," says Waldenmaier. "We figured that this was a good way of replicating the mushrooms, but without the scent of the mushrooms, which could be attracting the insects."
Inside some of these artificial fungi, they inserted an LED that emitted the right kind of green light. Then they covered the devices — the fake mushrooms that lit up, and the dark ones — with a kind of sticky glue, and put them out in the forest.
"We basically observed to see if there was any difference in the insects that were attracted to the ones that were lit up with the green light and the ones that were dark," says Waldenmaier.
The result? Flies, ants and beetles were found on the lit-up mushrooms in greater numbers, he says. As a follow-up, the team is now aiming infrared cameras at the real glowing mushrooms, to get a better sense of what the insects are actually doing there.
Dunlap remembers seeing his first glowing fungi as a kid, when he was on a camping trip and slept in a rustic shelter. "Looking up at night," he recalls, "there were lines of bioluminescence in the rafters, from where the wood-rotting fungi were bioluminescing."
Making light isn't actually all that common in fungi — scientists have described about 100,000 fungal species, and only 71 glow.
SCOTT SIMON, HOST:
If you're out in a forest at night, you wouldn't be surprised to see the glimmer of fireflies. But you might be startled to look down and see the glow of fungi. Turns out that some mushrooms do gleam in the dark, and not just in Colorado. NPR's Nell Greenfieldboyce reports on one reason why.
NELL GREENFIELDBOYCE, BYLINE: Scientists have discovered about 70 glowing fungi. One of the most dramatic grows in the coconut forests of Brazil. Locals call it the coconut flower. It looks like a plain old mushroom until it gets dark, and then you see its eerie green glow. Hans Waldenmaier is part of a research team at the University of Sao Paulo. I caught up with him when he was doing field work on these mushrooms. He says at night their glow is easy to spot.
HANS WALDENMAIER: You just have to turn off your flashlight and the mushrooms stand out if they're there.
GREENFIELDBOYCE: He says when there's no moon.
WALDENMAIER: If you have your light off, these green mushrooms, you know, they're basically the only light source that you see inside the forest aside from fireflies.
GREENFIELDBOYCE: The question is why would a mushroom glow? Jay Dunlap is a molecular biologist at Dartmouth's Geisel School of Medicine. He says some researchers have argued that the glow was just an accidental byproduct of metabolism.
JAY DUNLAP: In other words, they don't intend to make light, it just sort of happens.
GREENFIELDBOYCE: New work from Dunlap's lab casts doubt on that idea. His group collaborated with those researchers in Brazil to study that green glowing mushroom and found that its light production is controlled by a biological clock.
DUNLAP: We found that the light was made mostly at night and not mostly during the day.
GREENFIELDBOYCE: That suggests it's deliberate. And one possible reason to light up the night is to attract insects. Waldenmaier and his colleagues in Brazil decided to test this possibility by making their own glowing mushrooms. They used an acrylic resin to make mushroom-shaped replicas that were the right size and shape. Inside some of these artificial mushrooms, they put a green LED that made them light up. Dunlap says the researchers coated all of these fake mushrooms with odorless glue.
DUNLAP: So then they just put the mushrooms out in the forest and asked who came and got stuck.
GREENFIELDBOYCE: It turns out that lots more insects got stuck on the fake mushrooms that were making light. The results appear in the journal Current Biology. The researchers say that in a dense forest there's not much winds to carry fungal spores away, so visiting ants, flies and beetles probably do the job instead. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.