A zombie mushroom turned out to be much more dangerous than scientists thought: an absolute parasite

In Brazilian carpenter ants, the already difficult life is supplemented by a very strange circumstance - they can turn into real zombies. This is due to infection with a parasitic fungus, whose spores germinate in the body of the insect and affect its sympathetic nervous system. Infected with a parasite, the ant leaves the cosiness of its native nest and goes to wander into the thicket of the forest, the conditions of which are more suitable for the mushroom to fully ripen. Usually the ant clings its paws to the underside of the leaf, after which it freezes, thereby finally sacrificing itself. The fungus continues to develop inside its body until it finally pierces the head section and releases new spores. The whole process takes about 10 painful days, during which most of the time the insect remains alive. Waking nightmare, isn't it?

Zombies in the real world: what the parasite mushroom hides

Science has long known this phenomenon, but until now, scientists have long been unable to understand how exactly the parasitic fungus O. unilateralis plays its role as a puppeteer. It has often been called the “brain parasite, ” but a new study published this week in the Proceedings of the National Academy of Sciences refutes this theory. It turned out that just the brain of the insect remains intact, and the parasite exercises control over its host by introducing into the muscle fibers throughout the body! In fact, an infected ant becomes a kind of “meat armor” and a means of transportation for the fungus, and part of the ant tissue cells in the process are replaced by mushroom ones.

To make this amazing discovery, David Hughes (namely, he first discovered the parasite fungus) began an extensive study in which an international team of entomologists, geneticists, programmers and neuroscientists took part. The aim of the work was to study the cellular interactions between the parasite and its host during the critical stage of the first life cycle - the one during which the ant clings to the leaf with its powerful mandibles.

Stages of infection of an ant with a parasitic fungus

The lead author of the study, Maridel Frederiksen, a doctoral candidate at the University of Basel Zoological Institute, Switzerland, stated that the fungus secretes tissue-specific metabolites into the host, thereby causing changes in gene expression. It also leads to atrophy of the ant's lower jaw muscles, so that the ant will never be able to unclench it and let its body fall to the ground - this would cause the host to die prematurely or put the parasite at extra risk. However, before the start of the work, scientists did not know exactly how the fungus coordinates its actions in order to manipulate the host organism so cleverly.

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Research and discovery

To conduct the study, scientists infected the carpenter ant O. unilateralis. At the same time, some individuals received a dose of a less dangerous, non-zombie fungal pathogen known as Beauveria bassiana - they served as a control group. Comparing the dynamics of the disease caused by these two fungi, the researchers were able to identify specific physiological manifestations of the activity of O. unilateralis in ants.

Using electron microscopes, the group created a three-dimensional model that allows you to determine the location, number and activity of fungal tissues inside the bodies of insects. For this, samples of these tissues were taken with a size of only 50 nm, and the observation was carried out using instruments capable of monitoring and processing the image with a frequency of 2000 times in 24 hours. To analyze the impressive amount of incoming data, scientists turned to artificial intelligence: an algorithm based on deep learning, during the analysis, distinguished differences in the activity of fungal and ant cells. This allowed researchers to clearly see at what stage of the disease the tissues of the body still belonged to the insect, and where they were already transformed into a mushroom.

Computer simulation of how strands of fungal cells grow into host muscle tissue

The results were both extremely interesting and intimidating. O. unilateralis cells spread throughout the ant's body, from the head and thoracic region to the abdomen and legs. Moreover, they were interconnected, creating a kind of collective biological network, which controlled the behavior of ants. Hughes noted that in the end a high percentage of cells in the host's body turned into fungal cells - he literally made the insect a part of himself.

But the most amazing thing was that the brain tissue remained ... intact. “Usually, the behavior of animals is controlled by the brain, transmitting signals to the muscles, but the results of our research show that the parasite controls the behavior of the host through peripheral systems, ” Hughes explains. “Almost like a puppeteer pulling the strings to control the puppet’s movements, the fungus also controls the ant’s muscles by manipulating the owner’s limbs and mandibles.”

Can a parasite affect the brain?

It is still unknown how exactly the fungus causes the ant to move in the direction of a particular leaf. Scientists believe that the fact of the integrity of the brain is actually the key to solving the puzzle: the mushroom uses the potential of the ant brain long enough for it to be alive and able to independently find a suitable "site" for the reproduction of the parasite. Another theory is that the fungus indirectly affects the brain, in particular its sensory functions, in order to “control” the ants and make them leave for the forest.

Gaimodo Charissa de Becker, an entomologist at the University of Central Florida who did not participate in the new study, is convinced that the work done confirms the fact that the fungus can control the host with the help of special secretion compounds that play the role of neurotransmitters. This is indicated primarily by data obtained in the study of the fungal genome.

Why is this so important to us? Understanding the mechanism of zombies opens up a number of perspectives. First of all, it is the synthesis of new biologically active compounds that can be used as powerful drugs. In addition, scientists drew attention to the fact that the fungus Ophiocordyceps kimflemingiae (a related parasite fungus) shows signs of activity within the “biological clock”: some of the fungal genes are active in the daytime, others in the night. Apparently, at night, the fungus activates the secretion of proteins that can interact with the host’s brain, thus ensuring its own dominance over its nervous activity. Who knows, maybe in the future a similar cocktail of implants and neurotransmitters will give us the opportunity to control the human brain and, thus, reveal all its secrets?

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