Project Results

A huge number of parasites can change the behavior of the organisms they infect. In some cases, parasites can even make their hosts display completely new behaviors. We understand very little about the mechanisms and pathways behind this interaction. To learn more, we investigated how a specific fungus changes the behavior of ants, by turning them into “zombie ants”. The infected zombies climb high and latch onto twigs just before they die, which helps the fungus to spread its spores a further distance.

Our results suggest that the fungus takes over the brain, secreting LSD-like compounds, expressing proteins that change serotonin and dopamine levels in the brain, and altering the ability to communicate with nearby ants. Our genome and transcriptome dataset, obtained using both field and lab techniques, allowed us for the first time to dive a bit deeper into the mechanisms used to regulate behavior. In the long run this work might even lead to discoveries related to human brain health.

About This Project

Ask the Scientists

What is the context of this research?

Parasites exist in all shapes and sizes, across all phylogenetic kingdoms and in all ecosystems. Some of these parasites can attack a broad host range while others have specialized towards a certain host. Many of these specialists developed a nifty toolbox to parasitize their hosts and transmit to the next.

One of the most intriguing tools to promote disease transmission is the manipulation of host behavior. The protozoan Toxoplasma gondii for instance makes mice attracted to cats so it is more likely they will get eaten and the parasite gets transmitted to its final host. Another great example is the gordian worm that makes its cricket host jump into water so the worm can come out and mate.

A third example is the system I work on in which the fungus Ophiocordyceps unilateralis controls the brain of Carpenter ants. The fungus makes the infected ant climb up the vegetation and bite onto a leaf or a twig. There the ant dies after which the fungus starts forming a spore carrying structure from the neck to spread the disease to other ants. We know the stereotypical biting behavior must be caused by the parasite because this is something the ant otherwise would not do. Measuring behavior in general is a difficult task so this obvious influence caused by the parasite makes the Ophiocordyceps-ant host interaction a perfect system for anyone interested in studying the mechanisms underlying parasitic brain control leading to manipulation of host behavior.

What is the significance of this project?

Researchers become more and more aware of the fact that some parasites manipulate host behavior for their own benefits. Though the general interest in host brain manipulation grows, not much is known about the mechanisms underlying this phenomenon. We don't exactly know what genes and compounds are involved both from the parasite and the host point of view. The reason for this is that the complex parasite-host interactions that are at play here are very difficult to tease apart.

However, with the recent advancements we have made in the lab and the newest state-of-the-art techniques, this should be possible. In this research project I therefore want to take the first steps towards unraveling the fungal parasite genes that are of importance during ant host manipulation by making use of those novel techniques. By comparing the fungal genes that are expressed during the event of ant host manipulation with the genes that are expressed after the host died and during fungal growth in artificial medium, I will discover how this parasite is able to create zombie-like host behavior.

One of the reasons for studying this interesting parasite-host interaction are the useful applications it harbors. Next to this research just being fascinating we expect to find compounds that are interesting for medicine. In fact, the (Ophio)cordyceps fungi are famous for the medicinally interesting compounds they secrete. Also, if we learn more about how parasites change behavior we could apply this in neuromedicine approaches. In fact, when we would know how these parasites co-opt behavioral plasticity of their host, we could learn more about how behavior is regulated chemically in general. The first data (which is the data generated in this project) will push us in the right direction with this.

Last but not least, the insect infecting fungi are widely used in natural pest control applications. By learning more about the brain manipulating species, we will thus learn if these fungi might be good candidates for those type of applications as well.

What are the goals of the project?

The goal of this project is to discover how a fungal parasite can manipulate ant host behavior. I have already performed the experiments in the lab in which Ophiocordyceps infected ants were sampled at the moment of manipulated biting behavior and after death. To be able to discover which fungal genes are establishing this I will make frozen sections of infected ant heads. From these sections I will collect the fungal cells that have been manipulating the brain using a laser capture microscope. I already have extensive experience using this equipment (you can find my PhD thesis here), which guarantees my capability to carry out these experiments.

From these cells RNA will be extracted and amplified to be able to look at the expression of genes that are in play. Subsequently, these samples will be used for RNA sequencing. This part will be done by experts of the sequencing facility at Penn State. This will result in a wealth of data which will not only help me answer the main research question for this project, but will also provide me with extensive information that will become helpful in and could form the basis for future projects.

Finally, I will analyze the datasets and will seek advice on a regular basis from experts within the bioinformatics center at Penn State for this. In preparation, I am already taking an Applied Bioinformatics course taught by the director of this center.