Parasitic fungi are amazing creations of nature. Unlike their regular relatives, such fungi attack living organisms, penetrate them and feed on them, thereby causing diseases and sometimes death of the host. Most pathogenic (disease-causing) fungi are parasites of plants, but there are also those that parasitize insects and arthropods. One of these is the fungus Cordyceps secunda, a parasite of ants and the inspiration for the creators of the game “The Last of Us”. Recently, however, researchers discovered something truly rare and frightening when they came across a tarantula infected with this “zombie fungus”. In a video posted by field researcher Chris Ketola and his team, you can see the fungus growing out of the spider's body. Lying on the ground next to a yellow-orange tarantula, Ketola explains that a parasitic fungus took over the spider's nervous system and forced it to move to a secluded location. Then, after the spider died, Cordyceps grew through its body, allowing the spores to spread.
This is what a “zombie fungus” Cordyceps looks like when it takes over the body of a tarantula. Image: www.reddit.com
Contents
- 1 Cordyceps – a medicinal parasite
- 2 Life cycle
- 3 Host selection
- 4 Cordyceps and spiders
- 5 New species of Cordyceps
Cordyceps – a medicinal parasite
Cordyceps is a genus of ascomycete fungi, comprising over 400 species, each with unique properties and biological characteristics. However, they all have one thing in common: Cordyceps is an obligate parasite that attacks insects and other arthropods. Among all the representatives of this genus, the most famous are Cordyceps sinensis (otherwise known as Chinese cordyceps or caterpillar fungus), which has medicinal properties, and Cordyceps militaris, used in traditional Chinese medicine.
Surprisingly, the history of cordyceps use goes back to ancient times. In China and Tibet, this mushroom is mentioned in ancient medical treatises that are more than 1,000 years old. Traditionally, cordyceps was used to treat a variety of ailments, including respiratory, kidney, liver, and immune system problems. In ancient China, cordyceps was considered an imperial remedy, available only to members of the upper classes.
Some fungi manipulate the behavior of the hosts they infect to spread their spores. Image: cdn.britannica.com
Cordyceps, however, is more interesting as a rare example of fungal-insect symbiosis. It is often called a “zombie fungus” due to its ability to parasitize its hosts, which are usually ants. The specific metabolic and chemical mechanisms by which these fungi affect the central nervous system of their hosts are still not fully understood and probably vary slightly among the different species of these parasites.
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All of them apparently secrete chemicals that trigger basic motor neuron reactions in their hosts. Thus, ants infected with cordyceps cling to the branch of a tall tree with a death grip, immobilizing their jaws so as not to fall. But first things first.
Life cycle
So, the life cycle of cordyceps begins with the fact that the fungus spores settle on the body of the insect, penetrate its body and begin to grow, absorbing the internal organs. In fact, cordyceps is a complex organism with a well-developed fruiting body. Its main part – the mycelium – grows inside the host's body, eating the internal organs and replacing them with its tissues.
As a result of this process, the insect dies, and from its body the fruiting body of the fungus begins to grow. This process can take anywhere from a few weeks to a few months, depending on environmental conditions and the type of fungus. The fruiting body of Cordyceps is usually elongated and can be several centimeters long. The color varies from bright orange to dark brown, depending on the species. Fungal spores form on the surface of the fruiting body and are then spread into the environment, infecting new hosts.
The parasitic fungus Cordyceps is an amazing creation of nature, representing one of the most striking examples of the interaction between fungi and insects. Image: i.natgeofe.com
- Infection: Cordyceps spores settle on the body of the insect, penetrating its cuticle (outer protective layer) or through the respiratory tract. This is the first and most critical stage in the life of the fungus.
- Growth inside the host: After penetrating the insect's body, the spores begin to develop into mycelium, which takes over the internal organs and tissues. The fungus uses the host's nutrients for its growth and development, gradually killing it.
- Formation of the fruiting body: When the insect's internal organs are completely replaced by mycelium, the fungus forms a fruiting body, which grows out of the body of the dead insect. This fruiting body serves to spread spores and infect new hosts.
- Spread of spores: The fruiting body releases spores into the environment, which can infect other insects, closing the life cycle of the fungus.
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The choice of owners
Each Cordyceps species typically specializes in a specific insect or arthropod species. For example, Cordyceps sinensis infects caterpillars of butterflies of the Hepialidae family, while Cordyceps militaris can infect a wide range of hosts, including butterflies, ants, and other insects. Host selection depends on environmental conditions as well as the biochemical mechanisms that allow the fungus to penetrate and develop inside a particular organism.
Cordyceps is a unique example of parasitism, in which the fungus not only kills its host, but also uses its body as a substrate for its own growth and development. This interaction has a significant impact on insect populations, especially in tropical forests, where Cordyceps plays an important role in regulating insect numbers.
Cordyceps has a complex life cycle that begins with infection of the host and ends with the formation of spores ready to infect new individuals. Image: cdn.mos.cms.futurecdn.net
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Note that the ability to manipulate host behavior is actually very common among numerous parasites and parasitoid groups of organisms, including the very simple single-celled parasite Toxoplasma gondii, which infects rodents and causes them to do very stupid things, in particular, lose all concern for the upper part of your body.
Cordyceps and Spiders
Given the popularity of the HBO series “The Last of Us” based on the game of the same name, only the lazy have not heard of cordyceps. However, in anticipation of the second season, talk of “zombie mushrooms” began to fade away. This would probably have continued if not for a video recently published on Instagram (the social network is banned in the Russian Federation) by a field researcher and his team, who came across a tarantula infected with cordyceps.
The spectacle turned out to be truly frightening – in the video, Chris Ketol is next to a dead spider, strange spikes protruding from its body. Ketola is a field research coordinator for a non-profit organization working in the Peruvian Amazon and Uganda.
“We stumbled upon something truly incredible tonight. The fungus took over the tarantula's nervous system, forced it to move to a secluded area, and then, when the spider died, it grew out of its body, allowing the spores to spread,” Ketola says, lying next to the vibrant yellow-orange tarantula, the parasitic fungus protruding from its dead body.
Chris Ketol shows a Cordyceps-infected tarantula. Image: www.reddit.com
What's most interesting about the whole story is that the species of Cordyceps that infected the tarantula is extremely rare. The researchers note that there are at least two groups of distantly related fungi that infect invertebrates, and biologists are just beginning to understand how exactly the fungi affect their host's behavior.
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New species of Cordyceps
Researchers have previously reported that they have discovered a new parasitic fungus that preys on burrowing spiders in the Atlantic rainforests of Brazil. The rare purple cordyceps also infects invertebrates and hijacks its host, but there is no evidence that it controls the spiders' behavior before killing them. The fungus was discovered in November during an excursion through forests north of Rio de Janeiro to document the region's biodiversity and search for new species.
This is one of the few species of cordyceps that is purple in color. We know about 1% of their diversity, which means we know very little. Fundamental scientific work is needed to study them, write the authors of the discovery.
A purple parasitic fungus found in the Atlantic rainforests of Brazil emerges from the burrow of a trapdoor spider after wrapping itself around an arachnid. Image: i.guim.co.uk
Lead researcher Dr Oscar Alejandro Perez Escobar and Dr Natalia Przelomska, who carried out the sequencing in the field, said their work would confirm the hypothesis of a new species and could be used to speed up the identification of other species in threatened ecosystems.