Scientists have just discovered frightening new facts about the world's most dangerous mushroom. This fungus doesn't reproduce the way it used to, and this ability could help it move to a new area.
Mushrooms are known for their poisonous properties, but in fact, most of these poisons only cause temporary physical discomfort when eaten by humans.
Of all the deaths from mushrooms reported worldwide, 90% are caused by just one extreme species from Europe, namely Amanita phalloides or the so-called death cap mushroom.
Researchers now know how this dangerous species has spread across parts of North America with apparent speed and ease, causing deaths along the way as people mistake the fungus for a delicacy.
In its native Europe, A. phalloides creates new generations by combining genomes with one another. As it turns out, the fungus doesn't need a mating partner to reproduce.
A study led by researchers at the University of Wisconsin-Madison on A. phalloides in the US has found that fungi can produce spores using a single individual's chromosome.
The findings are based on the genomes of 86 fungi collected in California since 1993 and parts of Europe since 1978. Among samples in the US, A. phalloides appears to have been able to reproduce both sexually and asexually for at least 17 years, and possibly as long as 30 years.
Specimens collected in 2014 from two different locations were found to contain the exact same genetic material, effectively making them the same individual fungus. Another individual was collected once in 2004 and again a decade later.
"The diverse reproductive strategies of the invasive A. phalloides likely facilitated its rapid spread, revealing deep similarities between plant, animal and fungal invasions," the researchers wrote in their latest paper.
Asexual spores are formed when a fungus replicates its own set of chromosomes into two identical packages. Whereas sexual spores are formed when two different 'parents' each pass one set of their chromosomes to their offspring.
Many species of mold-forming fungi are known to reproduce by sexual and asexual spores, depending on the circumstances. But until a recent discovery, no one knew that A. phalloides was one of them.
Sexual reproduction allows species to evolve and adapt by introducing more genetic variation into a population. But with an asexual mode, individual fungi can spread quickly and survive for years on their own.
When a mold spore lands on a healthy surface, it will germinate and start fruiting. In this way, asexual spores can spread individual fungi far and wide, without the need for a mating partner or genetically distinct offspring.
The fungus A. phalloides originally came from northern Europe. But over the last few decades, the fungus has been very successful in invading new habitats in other parts of Europe, as well as North America and Australia. Asexual reproduction can be a big reason why this happens.
Interestingly, the researchers found the genes in asexual spores collected in California from 1993 to 2015 were not very different from those in sexual spores produced by the same species in the same region.
According to theoretical models, this suggests that individual A. phalloides can survive for years by replicating themselves until they find another A. phalloides to mate with.
"Some of these fungal offspring interbreed, while others do not, and the cycle repeats," the researchers hypothesized.
Unlike some other poisonous mushrooms which often signify their toxicity with bright colors, the appearance of the death cap is quite simple and can easily fool humans or pets looking for a tasty treat in the woods or parks.
It only takes half a mushroom to kill someone. Without medical intervention, symptoms may appear as soon as six hours after ingestion, and the potential for liver failure soon follows.
Clearly, the spread of death cap is a serious risk to human and animal health. In 2016, during a particularly severe outbreak of local death cap in San Francisco, 14 cases of human poisoning were attributed to the fungus. Usually in the US, cases of this kind exist only a few years.
Now that scientists have a better insight into how death cap spread in North America, perhaps they can start devising strategies to contain the risk.