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Bioluminescent fungi glow to take advantage of insects looking for love

When it comes to ‘catfishing‘, the bioluminescent fungi of the Agaricales order have the process down to a science.

Each night, they emit a steady green light out into the darkness in an effort to attract beetles and other insects which have love on the brain. Despite the ruse, it turns out that the fungi and insects have the same motivation: the drive to reproduce.

Check out the extraordinary BBC Earth video below or scroll down to read more.

The mesmerizing glow exhibited by bioluminescent fungi has 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 captivating appearance wasn’t understood until very recently.

Mycena chlorophos
Mycena chlorophos (Image: Steve Axford/BBC)

Fortunately for all of us with inquisitive minds, a study published 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 they turned the lights out during the day. This suggested that the glow wasn’t some atypical, energetically expensive metabolic byproduct, but rather a trait with a very deliberate purpose.

The researchers subsequently set about creating a bunch of artificial acrylic mushrooms that they could illuminate with green light (lmax 530 nm) similar to that produced by the fungi.

Mycena chlorophos
Mycena chlorophos (Image: Steve Axford/BBC)

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 different parts of the environment. Just as flowering plants have evolved alongside the foraging behavior of animals to further their reproductive success, so too, perhaps, were the fungi.

They placed their artificial mushrooms, some illuminated and some left dark, out in their forest test area and coated them in a sticky resin in the hopes of ensnaring any insects attracted to the light. 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.

With this new evidence in hand, the researchers have since been following-up with camera studies to further investigate this relationship between the fungi and the arthropods. These 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 like the fantastic one at the start of this post. These investigations have since demonstrated rather conclusively 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 (PDF)
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