Have you ever wondered whether it was possible for zombies to exist in real life? If so, have you ever wondered about which mode zombies might operate under? In science fiction novels, there are many proposed versions of the undead; some brought about by bacterial infections, others by plant or even alien parasites. It may come as a surprise that the closest zombie condition that we observe in nature is caused by a fungus; Ophiocordyceps Unilateralis.
This tropical fungus, found in both Thailand and Brazil, is a parasite that uses ants as its host. The one deviant behavior it instills in ants is simple yet striking in terms of biological adaptation. This article in The Atlantic, depicts the behavior of an ant shortly after infection. An infected ant will leave its colony behind once there has been enough accumulation of fungal cells in its hemolymph (it is at this point that fungal cells can combine to form a super-organism that takes over the nervous system). This behavior in itself is remarkable in the context that ants are such hive-minded creatures that in general, they would never leave their colony behind. Distanced from the colony, the infected ant will crawl up the stalk of a plant to the underside of a leaf not even a foot off the ground. The parasite finishes off the use of its host when the ant clamps its mandibles on the central vein of the leaf (this is equivalent to you or I biting into something to suspend ourselves before entering rigor mortis). From that point, fungus spores emerge from the ant carcass’ head and rain down on passing ant lines below to restart the parasitic cycle. What makes the deviant behavior of the infected ant so remarkable is that it is essential for the survival of the fungal parasite.
What is also intriguing about Ophiocordyceps Unilateralis is the mechanism in which it takes control over its ant host. One might expect the parasite to completely degrade the host brain, however, it is the opposite that is true. The fungus spreads throughout nearly every part of the Formicidae body except the brain, which is untouched. Current researchers theorize that the fungus has control over the ant’s muscles and body and that if it affects the brain in any way, then it does so chemically from elsewhere in the body. This described mechanism is a very close match to what our culture describes as mind control.
Ophiocordyceps Unilateralis is a fascinating biological specimen and has been more commonly studied over the last few decades. This NCBI article gives a detailed account of why there might be many other fungal species related to Ophiocordyceps Unilateralis that have similar parasitic effects on their hosts. This hypothesis causes one to wonder if there may be some fungal parasite out there that induces a zombie-like state in humans. If this is the case, it may be time to consider mold-free safe zones in your zombie-apocalypse survival plans!
-David Frykenberg (Week 4)
First, I want to say that I really like the topic of your blog. The idea of zombie-existence seems so fascinating and scary at the same time. Second, I have seen many documentaries about this fungus, and I think the process behind it is incredible. The chemicals that are induced by the parasite, completely hijack the ants' CNS and make it do everything against its will and instinct. Crazy! Luckily, the parasite does not affect humans.
ReplyDeleteHowever, there is a parasite that lives in cat feces that is known to influence mice and makes them less afraid of cats. Some scientists suspect that the parasite can jump on to humans, thus lower our awareness of dangerous situations and makes us do stupid live threatening things.
-Gene
Hah! That would explain some observed trends of old cat owners tending to be schizophrenics (thus the iconic cultural image of the crazy old "cat lady"). What you describe is very intriguing; it suggests a mutual relationship between the parasite and the cats. I am very interested to hear more about if this parasite indeed affects humans as it does mice. I don't believe that it couldn't be a possibility.
Delete-David Frykenberg
This post was super interesting to read. I remember watching a video about this in one of my biology classes last year. We never learned about the mechanics of it, though (which I don't understand because that's the best part). From an evolutionary perspective, this seems like such a complex and specific behavior for an organism to exhibit. I'm curious to learn how exactly the fungus knows to occupy every part of the host's body except the brain. And if it affects the brain chemically from somewhere else inside the host, then what does that process look like?
ReplyDeletePosted by Meagan Gustafson
The exact process of how the parasite might affect the ant host brains is still being studied. However, researchers know that the brains of the parasitized ants can't be too damaged because of the intricate behaviors they possess when the fungus is driving its own reproduction. Those who have studied this fungal species say that parts of the ant brain that are most likely destroyed by the parasite are probably the portions having to do with voluntary muscular control (thus giving full muscular control to the parasite).
DeleteAs to your pondering of how such a complex behavior could exist in this fungus evolutionarily, my response is that such a behavior would develop over generations gradually. A good example of a complex biological structure that exists in humans already is the human eye. This biological feature is theorized to have evolved in stages. Such a structure as the eye may have been merely a patch of tissue that was sensitive to light in an ancestor species that developed more over the course of thousands of generations. For the Ophiocordyceps Unilateralis, the behavior it exhibits in ants may have at one time not been so complex and may have even served it a different purpose.
-David Frykenberg