When I tell people I study mushrooms, about 90% of the time I receive a unique look. A kind of perplexing smirk that conveys to me the person in front of me thinks I’m a die heart Grateful Dead fan, and that my favorite holiday is on April 20th(National pot smoking day for all my readers living outside of the States). Mushrooms and hippie culture go hand-in-hand, which is why after two years of writing for this blog, I haven’t really talked about hallucinogenic mushrooms. I wanted to make it clear that the information I communicate here is based on scientific data, you know, empirical evidence. Not feelings or experiences. I simply didn’t want Forest Floor Narrative to be tied to the New Age subculture. But there is no doubt that there are a wide variety of mushrooms that produce psychoactive compounds around the world. These species of fungi along with their hallucinogenic compounds interact with their ecosystems in diverse ways and have been doing so for millions of years. Today, I’d like to describe why these compounds may have evolved.
Psilocybe cyanescens. Photo by Caleb Brown.
Hallucinogenic mushrooms are not confined to just one genus, or family of fungi. Psychoactive compounds have independently evolved several times over. There are at least five families of fungi that produce these mind-altering chemicals. With more and more species being found and categorized each year, this number is more than likely to grow. Brandon Matheny and his team at the University of Tennessee have looked extensively at the genomes of mushrooms within one of these fungal families, the Inocybaceae. Their work reveals that muscarine, another compound hallucinogenic to the mammalian brain, has been produced in the fruiting bodies of fungi for 60 million years. Many species within this family have conserved the alleles required to synthesizing muscarine until the present day, with a smaller subset of living genera within this family to lose this trait. They also found that genera in two separate linages within this this muscarine-producing family transitioned to producing the more commonly known compound psilocybin. In these two genera, the alleles that allow the synthesis of muscarine, have been completely lost, or silenced.
You would think that since hallucinogenic compounds independently evolved several times over, that there would be a clear ecological purpose these substances. However, this is not necessarily true. There are numerous chemical byproducts our own bodies produce that have no function whatsoever. For instance, through our own metabolism, our body produces ammonia. The compound ammonia can be toxic when it reaches high enough concentrations, so the mammalian body transforms ammonia into urea in the liver. Urea is less toxic than ammonia, but still needs to be removed from our bodies eventually. Like ammonia, psilocybin and other psychoactive chemicals may just be an end product of the mushroom’s metabolic activities.
The leading hypothesis right now, is that these fungal compounds evolved to deter mycophagy.Hannah T. Reynolds at Ohio State University and her teamwanted to better understand the evolution and function of these secondary metabolites. Their findings show that horizontal gene transfer of loci that encode for these hallucinogenic compounds have occurred in non-related species. With this, they concluded there must be an important ecological purpose for these horizontally transferred genes. Species they specifically looked into are coprophilic or dung feeding fungi from the genera Psilocybe and Panaeolus. Many species within these genera grow on dung from large herbivores. These habitats are a literal breeding ground for coprophilic insects. These researchers hypothesized that the secondary metabolites deter mycophagy. Psilocybin and other chemicals reduce insects from eating these mushrooms, so these fungi can carry out their ultimate goal; producing and releasing as many spores as possible. With fewer insects feeding on these fungi, the more potential offspring these individuals can produce.
Panaeolus cyanescens. Photo by Andrew Heath.
It really isn’t that simple. Another recent study actually counters this anti-mycophagy hypothesis. Ali R. Awan and his team too wanted a more definitive answer to this ecological question. These researchers reared insects from the Sciaridae, a family of flies known as dark-winged fungus gnats on mushrooms containing psilocybin and non-hallucinogenic species. In both treatments, fly larvae maturation was not deterred. Although only one family of insect was analyzed, the anti-mycophagy hypothesis should be reconsidered. A more compressive study using several orders of invertebrates and mammals should be conducted to see for sure if these metabolites reduce the fitness in the organisms eating these fungi.
There are several competing hypotheses that try explaining the function of hallucinogenic compounds in fungi. We still aren’t exactly sure of its function. These compounds might have evolved to deter mycophagy or they could simply be a byproduct of the mushroom’s metabolism. Although it’s still unclear, one thing is for sure, these compounds didn’t evolve to aid humans in any way. Our species is a mere 200,000 years old and the first hallucinogenic compounds arose at least 60 million years ago. What we experience is a coincidence. Just like in cannabis, the crystalline compound THC interacts with the receptors in human brains and provides many with a favorable high. THC evolved in these plants to deter herbivory. It is by chance some chemicals synthesized in certain plants and fungi have a favorable effect on the human brain.