Writer: Ezgi Çakırgöz
In the complex fabric of the natural world, Ophiocordyceps unilateralis stands as an outstanding example of coevolution between fungi and insects. This remarkable parasitic fungus belongs to the genus Ophiocordyceps and exhibits a unique ability to manipulate the behavior of its host, primarily ants.
Ophiocordyceps unilateralis primarily targets ants in tropical rainforests. The life cycle of this fungus begins when its spores attach to and penetrate ant bodies. Once infected, the fungus takes control and causes abnormal behavior in the host. The infected ant is forced to leave its colony and climb to a higher position; Here it secures itself and the fungus consumes the ant's internal tissues, leading to its death. The fungus then releases spores by forming a stalk-like structure from the ant's body, enabling infection of new hosts and continuing its life cycle. This remarkable entomopathogenic fungus offers a fascinating investigation into the evolutionary processes governing unique parasite behaviors. It is famous for its ability to infect ants and manipulate their behavior, and it has an evolutionary process that continues to fascinate the scientific community as we know more about it. (Evans et al., 2011)
It is still unknown exactly how this ophiocordyceps, which sounds quite complex, performs this mind and body control. In BBC's famous Planet Earth documentary, it is claimed that they do this by secreting chemicals that affect the parts of the brain that manage motor functions. However, in an article published in 2017, when experts examined 3D scans of ants infected by the fungus, they discovered that their brains were not touched at all. In other words, the fungus controls the ants by contracting and relaxing their muscles, just like a puppet controlled by a puppet master; It does not touch the signals sent from the brain to the body. (Hess, 2011)
Although it seems impossible for a fungus to control an animal's body, we know that many such parasite-host relationships have emerged in evolutionary history. Let's give an off-topic example. As you know, mice try to stay away from cats under normal circumstances. As soon as a mouse detects a cat's pheromones thanks to its sensitive sense of smell, its brain triggers its fear drive and the mouse moves away. However, if their bodies are infected with Toxoplasma gondii, mice want to become prey for cats. Those who harbor the parasite in their brains do not feel fear due to the decrease in dopamine in the presence of cat smell; On the contrary, dopamine secretions increase and they become curious about the smell. The life cycle of Toxoplasma begins in a rodent such as a mouse and continues with a host such as a cat. Afterwards, the cat spreads these parasites around with its feces. While various other creatures try to eat the nutrients in the feces, they also take Toxoplasma back into their bodies, and the cycle continues. (Flegr, 2017)
There is no consciousness or perception in these manipulation incidents such as the example given, there are endless generations, diversity within these generations, and the survival and further reproduction of the most adaptable ones among this diversity. As a result, more successful manipulators inevitably evolve as generations pass.
The host-pathogen system evolves reciprocally throughout the ecological and evolutionary process. As the parasite secretes a chemical that causes behavioral disorders, hosts change to better detect individuals carrying these chemicals and destroy them early. Because of the diversity among ants, some will be better at detecting Ophiocordyceps infections. Therefore, they will survive easier and longer, and thus these detection mechanisms can evolve. (Evans, 2011)
Ophiocordyceps unilateralis is a testament to nature's astonishing diversity and complexity. The ability to manipulate the behavior of ants for their own reproductive purposes is an intriguing example of the complex interaction between organisms in the natural world. Studying this extraordinary fungus not only reveals the wonders of evolutionary biology, but also offers potential applications that could benefit fields ranging from medicine to agriculture. The complex relationship between Ophiocordyceps unilateralis and ants stands as a fascinating reminder of nature's endless capacity to surprise and inspire.
References
Harry C. Evans, Simon L. Elliot, David P. Hughes, Hidden diversity behind the zombie-ant fungus Ophiocordyceps unilateralis: Four new species described from carpenter ants in Minas Gerais, Brazil. (2011, March 2). PLOS. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0017024
Peter Hess, 'Planet Earth' got zombie Cordyceps fungus wrong, study suggests. (2017, November 9). Inverse. https://www.inverse.com/article/38278-zombie-cordyceps-fungus-ant-brains
H. C. Evans, (2011). Ophiocordyceps Unilateralis: A Keystone Species For Unraveling Ecosystem Functioning And Biodiversity Of Fungi In Tropical Forests?. Communicative & Integrative Biology, p: 598-602. https://www.tandfonline.com/doi/abs/10.4161/cib.16721
J. Flegr. (2017). Effects Of Toxoplasma On Human Behavior. Schizophrenia Bulletin, sf: 757-760. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2526142/