If you’ve ever foraged for mushrooms, you might know that varieties containing the psychoactive compound psilocybin differ greatly in size, shape, and color. This can make the task of separating “magic” mushrooms from their mundane (or poisonous) look-alikes quite difficult.
Indeed, there are an estimated 1,147 genera of mushroom-forming fungi, and only 11 distantly related groups are known to produce the serotonin-mimicking hallucinogen. So how did distinct mushrooms evolve to contain the same chemical?
Following a psychedelic (research) journey, scientists from Ohio State University have discovered that the genes for the production of psilocybin were shared between neighboring forest floor mushroom species through an evolution-hacking process called horizontal gene transfer (HGT).
Their study, published in Evolution Letters, compared the entire genome sequences of three distantly related psilocybin species to the genomes of closely related non-hallucinogenic relatives.
The analysis showed that all three species contained a single cluster of five genes that were responsible for psilocybin production, and the sequences for the genes were very similar. Given the complexity of the biochemical process required for fungi to make psilocybin, it is pretty unlikely that these genes just happened to evolve independently multiple times.
Rather, the authors present evidence that after one original species began producing psilocybin, the gene cluster was spread to others through the genetic French kiss that is HGT; wherein chunks of DNA jump from one organism to another during a moment of temporary cell-to-cell contact. Occurring mostly in simple organisms like bacteria and viruses, HGT allows genetic mutations to hop into new species – sometimes to their benefit and sometimes to their detriment.
Because the psilocybin mushroom species have similar lifestyles within the ecosystem – they all grow in damp soil and feed by decomposing either dead wood or dung – an adaptation acquired in one species would be helpful to the rest. And given that the ability to synthesize psilocybin has popped up in hundreds of species and persisted for millennia, it must be a real boon to mushroom survival.
“We speculate that mushrooms evolved to be hallucinogenic because it lowered the chances of the fungi getting eaten by insects,” said lead author Dr Jason Slot in a statement.
Organisms that are at risk of being eaten often adapt chemical defense molecules, called secondary metabolites, that make them poisonous or unpalatable. But instead of killing or repelling their would-be predators as plants do, “these mushrooms are altering the insects’ ‘mind’ – if they have minds – to meet their own needs,” said Dr Slot.
What an insect experiences during a mushroom trip is definitely a subject for another day, but one known side effect is a reduction in appetite. Unfortunately for mushrooms, the same deterrent did not work too well for humans. Despite the risk of extreme nausea, people have been seeking out magic mushrooms for least 3,500 years.