Climate Change & Fungal Pathogens: Can Cordyceps Fungus Really Start a Zombie Apocalypse?

Hypothesis

         If Cordyceps fungus evolves to adapt to environmental stressors like climate change, then the fungus can evolve to adapt to mammals' high basal temperatures leading to fungal infections.

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Evidence

         To understand whether the cordyceps fungus can evolve through environmental stressors, there need to be past records of fungi capable of doing so in the past. Through studies, individuals can see that fungi do have the ability to evolve due to environmental stressors. Through studies observing global warming on agriculture, the research found that fungi were affected as well.

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What is Cordyceps fungus?

         Cordyceps is a genus of fungi that includes approximately 500 species, some of which include Cordyceps militaris, Cordyceps sinensis, and the most heard of Ophiocordyceps unilateralis. The recent portrayal in pop culture showcases the fungus as being extremely deadly but quite the opposite is true. While Cordyceps does pose deadly to arthropods, the fungus has been used for medicinal uses in traditional Chinese practices for thousands of years (Stone 2023). Cordycepin research has also indicated potential uses in cancer drugs and antiviral medication, even including some forms of Covid-19 treatment. For this reason, there are many efforts made to cultivate Cordyceps in controlled lab environments and on specific insects. By researching what different insects Cordyceps grows best in, the best conditions for the fungus have been investigated. The goal of Dr. Lee’s research was to find what edible insects Cordyceps best produces cordycepin so that these insects can best be used for cultivation. Different insects provided varying nutrients so whilst some insects produced outstanding fruiting bodies of the

fungus, they did not have the highest content of cordycepin. But along with the fungi growing differently on different insects, Cordyceps also has different traits depending on what insect it is attacking. Cordyceps spores affect mostly arthropods, but they have genes specific to affecting that specific insect, according to curator of mycology at the National History Museum of Utah, Bryn Dentinger. These genes make it “not easily transferable to another species” (Heyward 2023) meaning the fungus typically stays within insect families.

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Cordyceps Behavior

          The Cordyceps fungus spreads and grows in what many would describe as a spectacular but terrifying way. The fungus infects an insect, such as an ant, with spores and thus begins the mushroom’s life cycle. It drains nutrients from the ant and then fills the body with mycelia that works its way into the insect’s muscles. The ant is then compelled to climb a high plant stem and the fungus controls all the muscles to contract into a death grip. Finally, the host dies, and the mushroom-fruiting body grows out through the head of the insect, creating a ghoulish but fascinating marvel in nature. The fungus then releases spores from this body which infect nearby insects to start the process over again. Research done by David Hughes at Penn State University has found that during this process, the insect’s brain is still intact and untouched by Cordyceps, but all the networks of nerves and muscles are hijacked so that the host cannot communicate with them. As put by Ed Yong, the ant’s “brain is still in the driver’s seat, but the fungus has the wheel” (2017).

          Whilst Dr. Hughes’ study aimed to understand how the fungus controls an insect’s body, the team discovered another detail of note. The number of spores needed to cause an infection within the host is very specific. In the study conducted with healthy ants, “too few spores [then] the ant can fight off infection” but if there are too many spores, “the ant could die shortly” after from initial dosage and Cordyceps cannot infect the body in the same manner (Ouellette 2019). Such findings show that the fungus has a very specific way of attacking its hosts. On top of that, Hughes stated that “only a few of the spores… will become mature and able to infect healthy ants” which indicates the life cycle of Cordyceps occurs not that frequent. In fact, the danger of the fungus to an ant colony proved to be relatively low in Hughes’ studies.

             Another characteristic of Cordyceps is the fact that it cannot withstand high body temperatures in hosts. This factor is a major contributor to why there are no cases of Cordyceps fungus affecting mammals currently. According to Scott Roberts, MD, assistant professor of medicine (infectious diseases) at Yale School of Medicine, many fungal pathogens like Cordyceps “cannot grow above 98.6 degrees Fahrenheit” (Backman 2023) which is the body temperature of humans and many other mammals. This characteristic makes it more difficult to predict that Cordyceps can possibly spread to mammalian hosts.

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Climate Change & Fungi

            Environmental stressors on a plant or fungi can include many abiotic or biotic factors. Climate change is a prevalent one that was heavily investigated for this research paper. Studies of fungi have found that whilst fungi do withstand stressors and respond, little is still known about what these effects can mean for the fungi. Through studying the lineage of the Cordyceps fungus and the Metarhizium species (a species used mostly for insect biocontrol agents), the genes for behaving as an insect pathogen evolved independently from one another though the two species are related (Zheng 2011).

             Several fungal pathogens evolved new lineages that have new adaptations more capable of withstanding climate change. These mostly include species that infect crops like wheat and grains, but they have been proven to negatively impact human and animal health. Such fungi include Fusarium graminearum (causes Fusarium head blight) and Puccinia striiformis (causes Rust fungus). There is the possibility that if these fungi species evolved to adapt to high temperatures, then Cordyceps can possibly do the same. Atop of that, a new species of fungi emerged with possible connections to climate change and this one has already had outbreaks that have infected people globally. This species is Candida auris (C. auris) and already has impacted human health. Whilst there is no connection to Cordyceps, there is the possibility of this fungal pathogen causing an epidemic with parallels to what pop culture believes to be possible of Cordyceps.

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Agriculture Impacts

             Climate change affects agriculture in a myriad of ways. This paper investigates how climate change affects the fungicides used on crops. Due to rising temperatures in the world, more fungi have affected crops leading farmers to use harsher fungicides on them. These harsher fungicides though lead to resistance being built up in the pathogenic fungi. This means that more mycotoxins can be produced in the infected crops. Mycotoxins (MY) are toxins produced by fungi with “serious health effects related for animal and humans with severe repercussions

(Viergas 2021). Along with the resistance to fungicides being developed, new fungal pathogens can be produced that can also lead to mammal infection which can ultimately be life-threatening.

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Analysis

             As stated in the hypothesis, Cordyceps fungus would need to evolve to withstand higher temperatures to affect mammals. To the evidence found, this fungus is likely not capable of  doing so. Whilst there are lineages of fungi that have adapted in response to climate change such as Rust fungus and FHB, none of these fungi have connections to Cordyceps fungus. Though possible it can evolve adaptations to survive in higher temperatures, there is no evidence in the form of studies to prove this possible, so this portion of the hypothesis is inconclusive. Along with that, as stated earlier, mammals and specifically humans have a high enough body temperature that most fungal pathogens cannot survive in a mammalian host. Insects are cold-blooded meaning that their body temperature varies with that of their environment. This behavior allows fungal pathogens to survive better in insects since the internal temperature of their host matches that of the environment that the fungus is found in (moist, warm climates). Mammals are warm-blooded so there is a constant body temperature maintained and this temperature does not provide the ideal environment for Cordyceps. This high body temperature in mammals is

theorized to have evolved in response to fighting off fungal pathogens which would indicate a form of coevolution. So, if Cordyceps fungus was to evolve to withstand higher basal temperatures then there is a chance that mammals would evolve to have even higher body temperatures but again there is not enough research to support this thinking. Therefore, much of the thinking can be theorized and backed by instances of other fungal pathogens but the conclusion remains inconclusive.

             Another reason that Cordyceps cannot make mammals their next host is because of how many spores it would take to infect a mammalian host. It takes a specific number of spores to inflict a host and cause the behavior seen in arthropods. To make a mammal breathe in enough spores would mean the mammal is within this infected environment for a duration of time considering it takes a considerable number of spores to infect ants which are hosts of a much smaller magnitude according to Hughes’ research mentioned earlier. As stated earlier, if not 

enough spores are present in the host, the host can fight off the infection. On top of that, Hughes’ research indicated that not many spores reach maturity which is needed to infect a host. The likelihood of a mammal encountering enough mature spores to allow the parasitic behaviors of Cordyceps to occur is very unlikely since these are such specific conditions.

  

Synthesis

           Much of the evidence points to the hypothesis being untrue due to inconclusive data. There is simply not enough evidence to truly predict the behavior of Cordyceps fungus in the future. But this research does also provide many reasons as to why the fungus cannot cause infliction on mammals right now such as the fact that it cannot infect mammals due too high basal body temperature and that it is unlikely that a mammal would encounter enough mature spores to get infected.

 

Literature Cited

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