Field note by Chenhua Li, PhD candidate
Co-advised by Dr. James Wasmuth (University of Calgary, Calgary, Alberta, Canada) and by Dr. Cameron Goater (University of Lethbridge, Lethbridge, Alberta, Canada)
I work on the zombie ants system. These ants are ‘zombified’ by the lancet liver fluke Dicrocoelium dendriticum on a daily basis. From late evening to early morning, when the temperature is low, the infected ants climb and cling to the top of vegetation. This corresponds to the time when ruminants feed, and thus likely facilitates the transmission of the larval flukes inside the ants into their definitive ruminant hosts. When the sun rises and the temperature increases, the infected ants detach from the vegetation and return back to their normal behavior. For my PhD I’m using an -omics approach to figure out how the parasites achieve this temperature-dependent zombification.
After the early morning you can’t easily tell the zombified from the non-zombified ants. In order for this early bird to catch the worm(s), I had to spend the night at the Cypress Hills Interprovincial Park in southeast Alberta, get up before sunrise, and crawl through the fields on my hands and knees looking for zombie ants. I trained my eyes to observe the details on top of the grass and flowers, in order to pick up those with ants attached on top.
Images. Left: View of the Cypress Hills Interprovincial Park in Alberta, Canada. Center: Me holding one flower with many attached ants in the field. Right: Attached ants in the lab.
I then needed to isolate the brains from my field-collected ants. And, yes! They do have brains, and they are tiny!
I often get the question: “What machine are you using for ant brain dissection?”
The challenge of using myself as the ‘machine’ is that I need to keep my hands perfectly steady, which means feeding myself constantly to avoid shakes caused by low blood sugar. When dissecting with a pair of super fine tweezers, any level of shaking would be highly exaggerated under the scope.
When I first started, it took me more than 15 minutes to dissect a single brain, but ‘practice makes perfect’. After hundreds of dissections during my first field season, I can now dissect out an ant’s brain in 2-10 seconds!
We used walk-in plant growth chambers set at different temperatures to recreate the temperature-dependent zombie behaviors in the lab. Because I wanted brains from ants that were attached to vegetation and those that were not, and because these behaviors are temperature dependent, I needed to collect my ants and dissect them at certain temperatures. One of those temperatures was 10C (50F).
So how does one maintain and dissect ants at such a low temperature?
Here, creativity comes into play. Ideally, I wanted to have a customized small glass cube, with the inside of the cube held at 10C, and two holes on the sides with sleeves so my hands could access the ants. The glass cube also needed to be small enough to fit under a dissection scope. We just couldn’t make this work in the end.
Then, two of my labmates in Dr. Cameron Goater’s lab had a great idea. What if we could build an insulated addition to a growth chamber held at 10C, so I could stand outside of the chamber and reach inside to do the dissections? We were trying to figure out what equipment we could use to build this set-up, and we settled on the equipment we had at hand, which in this case was kid toys. We then put a tarp over this setup to hold the required temperature. With this setup I needed to lean forward into the growth chamber for the entire dissection period. Unfortunately, this was not a comfortable position to hold for a long time. Cam and I came to the conclusion that I should walk in the walk-in growth chamber (just as the name indicates), and do my dissections inside of it.
Once inside the growth chamber, there was cold air constantly blowing toward my face. Not surprisingly, it literally felt like being inside a fridge. I had to go outside of the growth chamber and jump around every hour to warm myself up, and then go back to my dissections.
Another problem was that the chamber door only opens from the outside! To avoid spending a night alone in a freezer in the basement, I needed someone to accompany me from outside of the chamber.
Images: Ant brain dissection of me in the ‘green fridge’ (walk-in plant growth chamber). Photo by Xiaoli Wang.
Here, I need to introduce my heroic secret personal research assistant – my mom, Xiaoli Wang. She came to visit me from China, and she was involved in so many ways. For many hours and days of dissections, my mom sat outside the growth chamber. Because the dissecting area inside the growth chamber was too small for me to keep a pen and paper, my mom kept her ears close to the ajar chamber door to record the information as I shouted it out to her.
Besides the note taking and making sure I wasn’t locked inside the chamber, my mom also helped collect ants in the field, and fed me from time to time. When I had to work late nights and weekends, my mom cooked a meal and brought it to me in a pot right to the school, along with a bottle of coke! We ate in a corner of the floor together. Then, she joined me for dissections and took notes until 2 A.M. several times!
Images: My mom brought me home-cooked food while I was working after hours and we had dinner together in a corner of that floor before she joined me for research.
I had to employ a lot of unscientific methods, and recruit willing volunteers to help me with my field and lab work (even providing me with meals). I anticipate these unexpected experiences as a PhD student will all be worthwhile when we understand how the parasite zombifies ants in the end!
Edited by Kelly Weinersmith