A fungus that forces carpenter ants to do its bidding.
By Veena Ramachandran:
Zombies–-creatures you thought only existed in movies, well in some tropical rainforests, this figment of imagination becomes a reality. Ophiocordyceps unilateralis is a fungus that infects unsuspecting ants. The fungus controls and makes ants clamp onto stems of leaves, and then leaves the ants to die. Using the ant’s remains as a food source, it grows, finally ending with its toxic spores blooming out of the ant’s head, and then continues the cycle on yet another unsuspecting ant. However, one thing remains unclear, how does the fungus control these ants?
David P Hughes of Harvard University and his team conducted a study that shows the precision with which the fungus controls its hosts, leading them to a suitable environment for its growth. Hughes’ study led him to a forest in Thailand, where his team found that the infected carpenter ants are almost always found clamped onto the undersides of leaves that are 10 inches from the ground below. Additionally, most ant carcasses were found on leaves sprouting from the northwest side of the plant. Here, researchers found that these specific locations allowed for the temperature, humidity, and sunlight to be at an optimal level for the fungus to grow and reproduce. To manipulate these variables, researchers placed leaves with infected ants at higher locations, or on the forest floor, and recorded failed development and stunted growth of the fungus.
"The fungus accurately manipulates the infected ants into dying where the parasite prefers to be, by making the ants travel a long way during the last hours of their lives," Hughes said.
However, this journey to a specific breeding site is only part of the process.
Once the host is safely clamped onto an ideal site, the fungus has to use the carcass for food. As the fungus spreads within the body, it converts the ant’s innards into edible sugars to help the fungus grow. However, it conveniently leaves the muscles controlling the mandibles intact, in order for the body to keep gripping the leaf. The fungus doesn’t consume the ant’s outer shell so that it has its own armor-like contraption to prevent other microbes and fungi from interfering.
Due to the many deaths of ants over hundreds of years, carpenter ants are aware of this fungus but still lack the evolutionary capabilities to fight against it. Instead, they try to stray far away from infected carcasses so that they won't unknowingly contract this parasite. Ants also may have developed the innate ability to try and keep their foraging trails away from infected areas, but more research is needed to confirm this claim.
The mechanisms O. unilateralis uses to control carpenter ants remain unknown, “That is another research area we are actively pursuing right now,” Hughes states. However little we know right now, this much is crystal clear: O. unilateralis has evolved highly specialized abilities to target carpenter ants as its host.
Image Credit: The bullet ant | © Christian Vinces/Shutterstock
Bibliography: https://www.sciencedaily.com/releases/2009/08/090811161345.htm
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