New research on the evolutionary genetics of fungi reveals that the compound that makes some mushrooms ‘magic’ may have evolved as a defensive mechanism to discourage invertebrates from eating them.
Psilocybin occurs in a diverse group of fungi, with genetic analysis indicating that it may have evolved several times. This led a group of researchers from the Ohio State University in the US to suspect that a mechanism known as horizontal gene transfer may be occurring.
Horizontal gene transfer involves the movement of genetic material between species, carried by mobile cells such as bacteriophages. It is a process associated with stressful environments, and is rare in complex multicellular organisms.
To test their hunch, the team, led by Jason Slot, examined the genomes of three distantly related hallucinogenic mushroom species: Psilocybe cyanescens, known as “wavy cap”; Gymnopilus dilepis, sometimes called “magenta rustgill”, and Panaeolus cyanescens, dubbed “Hawaiian blue meanies”. These were then compared with genomes of three closely related mushrooms that do not have psilocybin.
The researchers found that distantly related fungi in dung and decaying-wood niches showed less variation in their genome content than close relatives in alternative niches. This suggest that the genomes are shaped in part by shared ecological pressures.
The team also examine the evolution of psilocybin cluster genes in the context of evolutionary ecological history. The scientists conclude that the presence of the compound may confer a survival advantage for fungi living in dung and decaying wood – potentially explaining its presence in different species within these environments.
“But our main question is, ‘How did it evolve?,’” Slot says. “What is the role of psilocybin in nature?”
It appears that the biological niche of the psilocybin-containing mushrooms provides a clue. In humans, psilocybin causes profound altered states of consciousness and other symptoms such as increased heart rate and dilated pupils.
In fruit flies, the main effect is suppression of appetite, but there may be other, currently unknown, effects upon the insects that eat mushrooms containing psilocybin.
“We speculate that mushrooms evolved to be hallucinogenic because it lowered the chances of the fungi getting eaten by insects,” says Slot.
The research helps explain a biological mystery and could open scientific doors to studies of novel treatments for neurological disease, he adds.
Tanya Loos is an ecologist and science writer based in regional Victoria, Australia.
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