quality:corruption
Evolution

Many different species of mushrooms are poisonous and contain differing toxins that cause different types of harm. The most common toxin that causes severe poisoning is amatoxin, found in various mushroom species that cause the most fatalities every year. Amanita, or “ the death cap”, is a type of mushroom named for its substantial amount of amatoxin, which has about 10 mg per mushroom, which is the lethal dose. Amatoxin blocks the replication of DNA, which leads to cell death. This can affect cells that replicate frequently, such as kidneys, livers, and eventually, the central nervous system. It can also cause the loss of muscle contraction and liver failure. Despite the severe and dangerous symptoms, amatoxin poisoning is treatable given quick, professional care.

Mushrooms have also been found to have evolved toxicity independently from each other. Researchers have found that different mushroom species share the same type of amatoxin called amanitin. They specifically looked at three of the deadliest species, Amanita, Galerina, and Lepiota. Through genome sequencing, a scientific process that determines the DNA sequence of an organism’s genome, closely related mushrooms obtained genetic information via horizontal gene transfer. Once assimilated, it can then be passed down to an offspring. The researchers also concluded that there is “an unknown ancestral fungal donor,” that allowed for horizontal gene transfer.

Mushroom toxins have appeared and disappeared many times throughout their evolutionary history. Many scientists believe that the toxins evolved in mushrooms are used to deter predation, either from fungivores or mammals. If mushrooms are consumed, it can negatively affect their ability to disperse spores, survive, and reproduce. Snails and insects are fungivores and many have learned or evolved to avoid eating poisonous mushrooms. However, it is believed that mammals pose a higher threat to mushrooms than fungivores, as larger body sizes mean they are more capable of eating an entire fungus in one sitting.

Some phenotypes, or observable characteristics, may co-occur with toxicity, and therefore act as a warning signal. The first potential warning sign is aposematism, which is an adaptation that warns off predators based on a physical trait of an organism. In this case, the researchers were interested in observing whether the color of a mushroom deters predators. This would suggest that toxic mushrooms are of different colors than non-poisonous ones. The visual cue of some colors should be enough for predators to know not to consume the mushroom. The second possible warning sign is olfactory aposematism, a similar concept, but instead of focusing on color, the odor of the mushroom would be what deters predation. This would again indicate that poisonous mushrooms would emit a different odor than non-poisonous ones. Alternatively, is the ability of organisms to learn from other organisms. This would suggest that avoidance of toxic mushrooms is a learned behavior. Organisms may avoid toxic mushrooms if they observed other organisms of the same species consume the fungus. Learned behavior is when an organism learns how to behave based on previous experiences. Some researchers believe that if an organism got sick or observed another organism get sick from consuming a poisonous mushroom, then they would know not to continue consuming it for fear of getting sick again.

An analysis of 245 North American mushroom species and 265 from Europe, revealed 21.2% of the North American species and 12.1% of the European ones as poisonous. After collecting this information, and using a neural network to classify all of the mushrooms based on color and odor, the researchers concluded that there was no correlation between cap color and mushrooms containing toxins. The cap is the top, rounded part of a mushroom and comes in different colors. This proposes that the cap color does not act as a warning sign to deter predators, providing no evidence that poisonous mushrooms may not signal their toxicity through visual or chemical traits. The three deadly mushrooms listed above, Amanita, Galerina, and Lepiota, are all of different colors, consisting of reds, yellows, browns, and whites. A possible theory as to why color is not a factor in determining whether a mushroom is poisonous is the fact that many of its predators are nocturnal and have poor vision. Therefore, viewing the different colors is difficult, and could result in inaccurate consumption. The study, however, did suggest that poisonous mushrooms do emit a smell that is unpleasant and therefore discourages consumption. Despite this result, there is no definitive evidence to suggest if the odor is a result of the production of the toxin or if it is intended as a warning signal. Additionally, many of the odors are not picked up by humans. This could suggest that there is another characteristic difference between poisonous and non-poisonous mushrooms to avoid predation from larger mammals or that there is another purpose for some mushrooms being poisonous that is not dependent on predators.