Zombie Fungi Control and Then Kill Ant Hosts
The zombie apocalypse is already underway, if you're an ant. A certain type of fungus, nicknamed "zombie ant fungi," attaches itself to the host's head and secretes chemicals into its brain in order to control its behavior. It forces the ant to latch onto plant material with its jaw, and then kills it, allowing the fungi to release spores, proliferate, and infect other hapless hosts.
Now, even more disturbingly, a new study shows that these spores actually know the difference between their host species and other species of ants. Researchers from Penn State and the University of Munich injected the spores into both the host species that is infected in nature and other species of ants. They found that the fungi infected and killed all ant species, but could only control the behavior of its natural host. The authors state in the research paper, "We show that the fungus can kill all ant species tested, but only manipulates the behavior of those it infects in nature."
The specificity of the fungus's behavior led the researchers to study the chemicals secreted during the behavior manipulation. "Fungi are well known for their ability to secrete chemicals that affect their environment," noted lead author Charissa de Bekker, a Marie Curie Fellow at Penn State, and Ludwig Maximilian of the University of Munich. "So we wanted to know what chemicals are employed to control so precisely the behavior of ants."
In order to study the chemicals, the researchers removed the brains from the ants, grew cultures of the fungus alongside them, and observed the chemicals secreted in response to the target hosts' brains as opposed to other species' brains. "This was 'brain-in-a-jar' science at its best," said co-author David Hughes, assistant professor of entomology and biology at Penn State. "You don't get to see a lot of behavior with fungi. You have to infer what they are doing by examining how they grow, where they grow and most important, what chemicals they secrete... It was necessary to reduce the complexity associated with the whole, living ant, and just ask what chemicals the fungus produces when it encounters the ant brain."
They found that the fungi did, in fact, behave differently in response to the target brains, and two chemicals in particular, guanobutyric acid (GBA) and sphingosine, were found in greater concentrations when the fungi were exposed to their natural host. But according to de Bekker, these chemicals do not represent a simple answer to these fungi's abilities: "There is no single compound that is produced that results in the exquisite control of ant behavior we observe. Rather, it is a mixture of different chemicals that we assume act in synergy. But whatever the precise blend and tempo of chemical secretion, it is impressive that these fungi seem to 'know' when they are beside the brain of their regular host and behave accordingly."
According to Hughes, "This is one of the most complex examples of parasites controlling animal behavior because it is a microbe controlling an animal-the one without the brain controls the one with the brain.. We can now begin to understand how the fungi pull off this impressive trick."