Chemical defense explains why so many fungi would develop the ability to synthesize molecules similar to animal neurotransmitters.
The so-called “magic mushrooms” are, technically, fungi that produce psilocybina psychedelic substance with known effects on humans. And they may have evolved for a much less mystical reason than one might think: to function as a chemical defense against insects that feed on mushrooms.
Psilocybin appears in several species around the world, present on all continents except Antarctica. In humans, the compound acts mainly by binding to serotonin receptors in the brain, triggering changes in perception and state of consciousness. But it remained unclear why so many fungi would develop the ability to synthesize molecules similar to animal neurotransmitters.
A team led by Jon Ellisfrom the University of Plymouth, in the United Kingdom, directly tested an old but little-verified hypothesis: that psilocybin has a defensive role against fungivorous invertebrates. To achieve this, the researchers incorporated dried and ground mushrooms (Psilocybe cubensis) into the diet of fruit fly larvae (Drosophila melanogaster) and monitored the entire life cycle of the insects, evaluating survival, development rate and physical changes in adults, according to .
Larvae fed the mushroom mixture had substantially lower survival rates than those in the control group. At lower doses, survival to adulthood was more than halved; at higher doses, only about a quarter of the larvae completed development.
Even among survivors, typical signs of stress during growth were observed: smaller adult flies, shorter bodies and asymmetries between the left and right wings.
The team also evaluated short-term effects on behavior. The larvae were exposed for an hour to liquid extracts of the mushrooms, sweetened with sucrose, and the researchers filmed their movements. The larvae traveled shorter distances, spent less time moving and exhibited more erratic changes in direction, suggesting less motor coordination. According to the authors, this points to interference in the physiology and nervous system of insects with potentially harmful effects, not necessarily “psychedelic” as in humans.
In a second step, the researchers collected seven species of fungi in Dartmoor (United Kingdom) and analyzed invertebrate DNA present in the samples. Psilocybin-producing fungi harbored a distinct set of insects compared to most others, suggesting that these compounds may influence which invertebrates are able to live in or feed on them.
Still, the picture is not linear. An unexpected result was that flies with reduced levels of the serotonin receptor, the typical target of psilocybin, suffered even worse effects.
