How does a parasite create zombie-like behavior?

BiologyEcology
Open Access
$4,507
Raised
104%
Funded on 12/31/13
Successfully Funded
  • $4,507
    pledged
  • 104%
    funded
  • Funded
    on 12/31/13

About This Project

Some parasites are able to manipulate the behavior of their hosts. One striking example is the "zombie ant" phenomenon, where ants infected by a parasitic fungus are manipulated to bite into vegetation followed by death and fungal growth out of the ant's neck. This research project aims to unravel how this parasite establishes zombie-like host behavior by discovering the genes that are important.

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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.

Budget

  • $72cryosectioning ($12/hour * 6 hours)
  • $540laser capture microscopy ($45/hour * 12 hours)
  • $330RNA extraction kit
  • $1,400RNA amplification and library prep kit
  • $1,964RNA seq (2 lanes which will fit all the samples)

Your funding will help me pay the hourly fee for the time needed on state-of-the-art equipment to collect the fungal cells out of frozen infected ant heads that have been manipulating the brain (cryosectioning and laser capture microscopy).
From these cells RNA will be extracted and amplified towards DNA libraries to be able to look at the expression of genes that are in play. Part of the funding will therefore be used to buy kits for this.
Subsequently, these libraries will be used for RNA sequencing. Two lanes of the sequencer will be used which will be sufficient to run all 5 biological replicates of each of the 3 sample types. A big part of the funding will thus go towards this.
Finally, I will analyze the data. My time is paid for by my Marie Curie Fellowship so your funding will solely be used to pay for equipment time, sample preparation and sequencing.
This will result in an immense amount of data that will answer the research question proposed here, but will also be greatly informative for future projects.

Meet the Team

Charissa de Bekker
Charissa de Bekker

Background

During my Master's and PhD (both at Utrecht University in The Netherlands), I specialized in biomolecular sciences and more specifically fungal genetics. Being extremely interested in fungal complexity, for my postdoc I moved to State College, Pennsylvania to study the "zombie ant fungus" Ophiocordyceps. Here I work within a multidisciplinary team which studies all aspects of parasitic behavioral manipulation such as host behavior, disease dynamics and ecology, but also parasite taxonomy and the molecular mechanisms underlying this phenomenon. I am the driving force behind the molecular work using the knowledge I gained and the techniques I developed during my PhD. Together, we are paving the way to establish the zombie ant system as a model to study parasitic behavioral manipulation.

Additional Information

In short, this project aims to learn more about how a relatively "simple" organism such as a fungus can establish mind-control in a relatively much more "complex" organism such as an ant. The parasitic mind-control in this case results in stunning still lives of ant cadavers with beautiful fungal structures emerging from them:



A lot of these so called "zombie ants" are found biting in to leaves in different parts of the world. That they are firmly clamped on by their jaws becomes clear when the cadaver is carefully removed. Major scars can be seen on these leaves:



In fact, due to these scars, that were also found in a 48-million year old fossil, researchers were able to determine that this parasitic mind control in ants is not something that has recently developed:



Fairly recent studies have shown how it is possible that we find zombie ants biting these leaves, even after death. The fungus causes atrophy in the muscles making it impossible for the jaws to release so they are stuck in the biting position:


Also, have a look at this video in which Joao Araujo and Dr David Hughes from the Hughes Lab explain the Zombie ant lifecycle:



So, at this point in time we already have quite some information on these Zombie ants, however we don't know a whole lot about the genes and compounds involved. Well, that is exactly where this project comes in: trying to unravel the mechanisms that underly parasitic brain manipulation. This will not only provide us with more information from a biological perspective since the findings of this project are also expected to be of interest to the medical sciences.

If you still have some unanswered questions, have a look at the iAMA I did on Reddit. Many people got involved and asked me all kinds of things related to this subject, and I tried my best to answer as many as possible. Maybe your question was asked there as well!