Researchers wanted to see how Ophiocordyceps infects ants, causing them to turn into “zombies”, through the release of chemicals like aflatrem, which impacts their movement and alters their genes.
If you’ve ever seen the HBO show The Last of Us, you might be familiar with the idea of a fungus controlling the behaviour of its host. Read of for a real-world example of this phenomenon.
Introduction
Imagine an ant suddenly starts acting weird. It leaves its job and relatives in the nest, climbs up a nearby plant, walks like it’s dizzy, clamps its jaws onto a leaf or twig, and stays there until it dies. It sounds like something out of a creepy movie, right? But this happens in real life. It is caused by a strange fungus that turns ants into “zombies”!
This fungus is called Ophiocordyceps. When it infects an ant, it releases biomolecules to slowly take over the ant’s body and brain. It makes the ant leave its colony to find a high place to firmly attach itself. Then the fungus eats the ant from the inside, grows out of the ant’s body, and spreads its spores. From high above the ground, these spores float down on the wind, ready to infect the next ant.
One typical behavior we see in zombie ants is the “zombie walk”. The ants start to walk clumsily, like the zombies we see in movies. One possible reason is that the fungus releases a chemical similar to aflatrem. Aflatrem is a toxin that can cause shaking and poor coordination in animals like cows. This made us wonder: do these chemicals have anything to do with zombie ants’ strange behavior? And if so, how do they affect the ants’ genes? These are the questions we wanted to answer.
Methods
We collected three Camponotus floridanus ant colonies from the arboretum at the University of Central Florida. Each colony had 100–200 ants.
To test the effects of aflatrem, we injected ants with different doses of the chemical. Because aflatrem is not soluble in water, we dissolved it in 10% acetone. To make sure acetone is safe for ants, we tested it using the following two control groups:
7 ants from each colony injected with a salt solution called Phosphate Buffered Saline (PBS) and
7 ants from each colony injected with 10% acetone suspended in PBS.
PBS has the same osmolarity as insect blood. This means it has the same number of solute particles per unit of liquid. This is important because water likes to flow to areas containing more solutes to balance the osmolarity. If the buffer we add has too many or too few solutes, the water inside the insect’s blood cells will move out or in. This causes the cells to either shrivel up or burst. This is exactly why hospitals use saline for patients.
Once we determined that a 10% acetone/PBS solution was safe to use, we added increasing amounts of aflatrem to make our test groups for our study:
7 ants from each colony injected with 10 ng aflatrem,
7 ants from each colony injected with 50 ng aflatrem,
7 ants from each colony injected with 100 ng aflatrem, and
7 ants from each colony injected with 500 ng aflatrem.
We recorded the ants’ behavior for 30 minutes. We tracked their resting, grooming, walking, climbing, biting, and staggering behavior. A computer program also helped us measure the ants’ speed and movement.
Once we had our results for the behavior, we extracted RNA from the heads of ants in both our PBS group and our 500 ng aflatrem group. This was to check if aflatrem changes how much genes are turned up or down in the brain as well. We looked at the RNA by sequencing which genes were being used and how much. We then compared the results from each group to see which genes were affected by the aflatrem. We also compared them to previous data for ants infected by the fungus.
Results
So, how did different doses of aflatrem affect the ants’ behavior?
The more aflatrem the ants got, the more time they spent resting.
As the amount of aflatrem increased, the ants moved more slowly.
More aflatrem did not affect the distance the ants traveled.
Ants that received higher doses of aflatrem staggered more as they walked.
Plus, we found that 261 genes were turned up or down in the ants that got aflatrem! Some of these genes control muscle contractions and how signals travel between muscles and the brain. Others are responsible for the ants’ sense of smell and communication.
We found that 113 of the genes affected by aflatrem were also affected by the fungus during infection. Some genes, like those for smell and muscle function, were affected in similar ways. Others were affected in different ways.
Discussion
Parasites, like Ophiocordyceps, have some strange ways of controlling their hosts. This fungus turns ants into “zombies,” making them act in ways that help the fungus grow and spread. It’s fascinating how some parasites are able to manipulate behavior.
The more aflatrem that ants received, the more they staggered and had trouble moving. This “zombie walk” behavior suggests that aflatrem-like chemicals are playing a role in how the fungus controls the ants. The fungus likely uses these chemicals to slow the ants down and keep them at a high location. This way, the ants are in the right spot for the fungus to grow and spread its spores with the wind more effectively than it can on the forest floor.
We also discovered that aflatrem affects genes responsible for muscle control. Some genes that help the ants move were less active. This change may explain why the ants staggered and had difficulty walking. This means the fungus and aflatrem both target similar pathways in the ants, leading to the same behaviors.
Conclusion
So, the next time you see an ant, remember there’s more going on than you might think! Tiny creatures like ants have fascinating stories to tell. Whether you’re watching ants in your backyard or working on a science project, every little detail matters. Keep questioning and keep learning. You might discover amazing stories hidden all around you!
