An early episode of the beloved BBC show Planet Earth made it clear that Cordyceps fungus is one of the most gruesome killers in the world. Forget sharks, bears, lions, or whatever that gleaming pair of eyes hiding in the bushes might be. Targeting insects, the terrifying parasitic fungus infects their bodies and controls their movements, eventually killing them and using their discarded corpses to breed its spawn.
In the case of ants, for instance, Cordyceps seems to cause the poor insects to clamp their jaws onto a branch and wait for death. While scientists have long suspected that, on a mechanistic level, the fungus infects its hosts’ brains to control behavior, new research in the Proceedings of the National Academies of Science suggests they were wrong all along.
In the paper, published Tuesday, a team of researchers at Penn State University and the University of Notre Dame reveal that Ophiocordyceps unilateralis sensu lato, the specific type of Cordyceps fungus that infects carpenter ants (Camponotus castaneus), controls the behavior of its victims by only controlling their muscles. It turns out the “zombie” Cordyceps fungus leaves ant brains intact!
Using electron microscopy and 3D imaging, researchers scanned carpenter ants affected with their specific type of Cordyceps fungus and found that, while the fungus permeated the ant’s muscles, it had not penetrated into the brain. The fungus seems to take control the muscles of the host ant, causing it to climb to a high place and clamp its mandibles onto a branch. This way, when the fruiting bodies of the fungus burst from the dead host ant’s exoskeleton, the spores fall on as large of an area as possible.
“Normally in animals, behavior is controlled by the brain sending signals to the muscles, but our results suggest that the parasite is controlling host behavior peripherally,” senior author David Hughes, Ph.D., associate professor of entomology and biology at Penn State, said in a statement. “Almost like a puppeteer pulls the strings to make a marionette move, the fungus controls the ant’s muscles to manipulate the host’s legs and mandibles.”
They figured out this strange mechanism of action by training a computer in deep learning algorithms to differentiate between ants’ body cells and the fungus cells. This yielded brilliant 3D scans of ants’ bodies, which you can see below. The fungus (yellow) is shown infecting ants’ muscles (red):
This construction was made from 2,000 slices, 50 nanometers thick, of infected ant tissue, viewed through an electron microscope.
“By stacking these slices, we could reconstruct them in 3D, giving us a micron-level view of the interaction between the fungus and host, with incredibly high resolution,” Hughes said.
“This is an unprecedented view of how a manipulator controls its host.”
If you liked this article, check out this video about the liquid-like properties of ants.