Zombie films are not in short supply. As we enter October, I expect many zombie flicks will be making their rounds on TV. Many are fascinated by the notion of something taking over their bodies and controlling them against their will. This sounds pretty frightening, but could zombies actually exist in nature? While what we see on film is very far-fetched, there is no doubt that zombies are real.
Meet the parasitic fungus with the tongue-twisting scientific name: Ophiocordyceps unilateralis. It has a unique way of reproducing. The fungus infects carpenter ants in the rainforests of Thailand and turns them into zombies. An ant infected with this fungus leaves its nest around noon, a peculiar time for this ant to take a stroll. It will then move about randomly. This is also bizarre behavior for this ant as they usually follow well-defined chemical trails. The ant then locates a plant not far from the nest and climbs to a height of around 25 centimeters, where it will bite into a central vein on the plant’s leaf and hang there.
A few days later, a fungus bursts out from the back of the ant’s head, like something from an “Alien” film. The fungus grows a fruiting body and spreads fungal spores, passing on the fungal DNA to a new generation. The spores will infect future carpenter ants as they forage, and the cycle will repeat.
A quick scan of the plants near the ant nest reveals a graveyard of tiny ant bodies still clinging to their leaves, with fungal parasites sprouting from their heads. A frightening sight if one takes the time to contemplate what has occurred. A view like this would almost certainly make the first to observe it pause and ponder what on Earth had caused such an event to occur?
The answer lies with DNA. The ant was not walking from the nest at noon or climbing plants to bite leaf veins; it was the fungus in an ant costume. This is termed the extended phenotype.
The ant is actually the fungus, by extension. When the ant bites the leaf vein, about half of its brain cells are not its own, and fungal cells extend into the ant’s muscle tissue. When analyzing the DNA of the fungus, scientists found many genes that produce enterotoxins, known to impact chemical communication.
Behavior in biology often boils down to neurochemistry. Once the ant is dead, the fungus switches off the zombie control genes and activates the genes that will digest the ant, make the fungus grow and produce the fungal spores. The fungus, directed by its own DNA code, has zombified the ant so that it can walk to the perfect location to release its spores. Inside that tiny spore that will infect another ant is the DNA code of the fungus. The code carries all the directions needed to repeat this story.
A better question might be, is the fungus just the zombie of its own DNA code?