Each night, they emit a steady green light in an effort to attract lovesick beetles. Despite the ruse, the fungi and insects have the same motivation: the drive to reproduce.
The mesmerizing glow Agaricales fungi have been observed for hundreds of years. Reports go back as far as the writings of Aristotle in which he describes glowing rotten wood (which we now know was caused by bioluminescent mycelium).
Despite all that time knowing that these fungi exist, the underlying mechanism and evolutionary justification for their appearance weren’t understood until very recently. A study published in Current Biology in 2015 managed to shine some much-needed light on this subject (sorry, I couldn’t resist).
Out of the approximately 100,000 documented fungal species, only 71 are known to exhibit this luminescence. The assumption up to this point was that this small number of fungi were producing their glow around the clock as some obscure byproduct of their metabolism. The authors of this study, however, observed that bioluminescent fungi were generating light in a regular circadian rhythm. They glowed at night and turned the lights off during the day. That finding suggested that the glow wasn’t some energetically expensive metabolic byproduct, but rather a trait with a very deliberate purpose.
The researchers subsequently created a bunch of artificial acrylic mushrooms that they could illuminate with green light (lmax 530 nm) similar to that produced by the fungi.
The researchers wanted to test the hypothesis that the glow of the mushrooms was intended to attract nocturnal insects. These insects would presumably crawl all over the mushrooms and become covered in fungal spores that they would then transport to different parts of the environment. Just as flowering plants have evolved alongside the foraging and/or reproductive behavior of animals to further their reproductive success, so too, perhaps, were the fungi.
They placed illuminated and non-illuminated artificial mushrooms out in their forest test area and coated them in a sticky resin. When they returned over the course of five nights, they discovered that the illuminated decoys not only ensnared some insects as expected, they ensnared more than 3 times the number of insects as their dark counterparts. The insects were mistaking the illuminated fungi for the bioluminescence of potential mates.
With this new evidence in hand, the researchers have since followed up with camera studies to investigate this relationship between the fungi and the arthropods. Their efforts are being supplemented by those of naturalist filmmakers like the team producing Planet Earth II who have made some extraordinary visual records of this behavior.
Researchers have since demonstrated that by glowing at night, the fungi are exploiting the reproductive strategies of insects to advance their own reproductive goals in a marvelous way.
References and Further Reading:
- Anderson G. Oliveira, Cassius V. Stevani, Hans E. Waldenmaier, Vadim Viviani, Jillian M. Emerson, Jennifer J. Loros, Jay C. Dunlap. Circadian Control Sheds Light on Fungal Bioluminescence. Current Biology, 2015
- Cornell Mushroom Blog