Hendricks, Katelyn
Do Antarctic Tardigrades Survive Better When They Are Wet or Dry When Exposed to Freeze/Thaw Cycling?
Faculty Mentor: Byron Adams, Biology Department
Introduction
:
Substantial amounts of evidence prove that there are drastic climate changes taking
place everywhere on Earth. Antarctica, the home to microscopic tardigrades, or water
bears, is no exception. Tardigrades have distinct roles and adaptations that allow them
to survive the harsh climates of their environment. Because of climate change in
Antarctica, there is a clear increase in the presence of liquid water and freeze/thaw
cycles. This correlation raises the question of whether or not the increase of freeze/thaw
cycles in Antarctica could result in increased tardigrade mortality. Normally, tardigrades
experience the majority of their freeze-thaw cycles in a desiccated state, and don’t have
to survive the additional challenges that come with freezing water molecules in their
cells and tissues. But with climate change, these freeze/thaw cycles not only occur
more frequently, but also when the animals are wet, as opposed to freeze-dried. My
project tested this correlation between increased Antarctic freeze/thaw cycles and the
increased mortality rate of tardigrades. From my research thus far, I plan to see the
correlation that increases in mortality are the result of exposure to various numbers of
freeze/thaw cycles. These results can possibly show how Antarctic soil ecosystem
functioning might eventually change because of the tardigrades importance in the
nutrient cycle of the soil.
Methodology
:
My mentor, Dr. Adams, travels to Antarctica annually to collect soil samples that contain
a variety of microscopic organisms. He shipped these soil samples to our lab where I
examined them and picked out the individual alive tardigrades needed to carry about my
experiment. Originally, I had planned on collecting 300 tardigrades to create a large
enough sample size, but I soon realized that this was highly unrealistic. I “picked” out a
total of 60 alive tardigrades out of the Antarctic soil underneath a microscope. Before I
began my series of freeze/thaw cycles, I did my best to mimic the natural conditions of
Antarctica as closely as possible. This was much harder than I expected it to be, and I
spent a lot of my time growing food sources to create “happy” conditions for my
tardigrades. I also had to research Antarctic conditions, specifically environmental
conditions of the Dry Valley in Antarctica, were these microscopic organisms came
from. I spent much of my time playing with temperatures, lighting, making plates for
them to live on, and creating food sources of moss and algae and growing these under
special lighting. I then examined how tardigrades survived under different soil conditions
to keep them alive to then preform freeze/thaw cycles. I then separated the tardigrades
into three seperate treatments. The first treatment contains 20 individuals (tardigrades)
which will live under wet conditions as they are exposed to through freeze/thaw cycles.
The second treatment also 20 individuals that will live under dry conditions when they
go through freeze/thaw cycles. My third treatment (my control) also contains 20 individuals,
which will go through identical processing with the exception of the
freeze/thaw cycles. Since I spent so much time researching ideal conditions for
tardigrades, and because my project is ongoing, I have yet to preform the actual
freeze/thaw cycles. I have placed each replicate on lipid agar plates supplemented with
algae, cyanobacteria, and light to promote ideal conditions for culturing. I will begin
performing freeze/thaw cycles on treatments 1 and 2 by keeping all of the replicates on
an ice block at all times to keep the conditions as closely related to Antarctica and to
buffer the temperature. For the first freeze cycle, I will bring my treatments to room
temperature (15 degrees C) using an incubator. I will then place these treatments back
onto an ice block and allow their temperatures to reach -10 degrees C. This will take 1
to 2 days as this is how long Antarctic cycles usually persist. After the first freeze cycle,
I will conduct the first thaw cycle by reversing the order, going from -10 degrees C to 15
degrees C. After the first freeze/thaw cycle is conducted of Treatment 1 A and
Treatment 2 A, I will open the tubes of treatment 2 (the dry) and add water to see how
many survived. I will also look at the results of treatment 1 (wet) to see how they
survived. I complete this process 10 times in total running a freeze/thaw cycle on every
replicate per treatment (A-J). During each cycle, I will record how many tardigrades
survived on an excel spreadsheet. When finished, I will analyze my data using an
analysis of variance. As I considered other options of analyses, I decided ANOVA is analysis of variance. As I considered other options of analyses, I decided ANOVA is the
best approach because of the multiple means from multiple treatments in my data. I will
compare the 10 replicates in each treatment to my control (treatment 3) and if there is a
significant difference in means between the two, I will be able to reject my null
hypothesis.
Results
:
With the research I have done thus far, I plan to see that going through these
freeze/thaw cycles while containing moisture instead of being dried out increases the
mortality of tardigrades, but I need further data and an analysis to prove that this is the
case. I will complete my project within the next coming months as I plan to present my
research and data that the annual Scientific Committee on Antarctic Research meetings
in Belgium this summer.
Discussion
:
If there is evidence to conclude a direct correlation between climate change, moisture
levels in tardigrades, and their mortality rates, I plan to go ahead and set up my next
project. This project would consist of transcriptome sequencing to see how tardigrades
are responding to the effects of climate change, and their capacity to adapt to these
conditions. Eventually, I aspire my research to serve as a foundation for a scientific
article I will write and submit to the scientific journal Polar Biology.
Conclusion
:
I am looking to extend the results of my experiment back to a larger body of science. I
expect that my data will support predictive models showing climate change’s relation to
Antarctic species diversity. Ultimately, with these results, I can become closer to
understanding how Antarctic ecosystems will respond to climate change.