Hannah Meier: Transgenerational behavioral plasticity in Chlamydomonas reinhardtii

In this new post, Hannah Meier from Reed College (USA), presents her work ‘Temperature mediated transgenerational plasticity influences movement behavior in the green algae Chlamydomonas reinhardtii’. She highlights the importance of historical effects on organisms, discusses the implications of climate change, and emphasizes the importance of good mentorship in STEM.

Eine Deutsche übersetzung dieses artikels ist hier verfügbar!

About the Paper

In this paper we explored whether past environments experienced by an individual or population can affect the current behavior of individuals and populations across generations, focusing on the motile green algae, Chlamydomonas reinhardtii. The inspiration for this project came from our previous research—undertaken by the Fey lab team—that looked at behavioral thermoregulation as a way for populations to buffer the effects of anthropogenic climate change. We wanted to know whether behavior could be affected by both the environment the present individual itself was experiencing in addition to those experienced by previous generations. We hypothesized that this would contribute to our understanding of what factors can modify or constrain behavioral thermoregulation.

Chlamydomonas reinhardtii particles (Credit: Greta Glover, 2018)

Freshwater ecosystems are significantly affected by climate change due to surface temperatures increasing, increased evaporation rates, and decreased mixing between water column layers which may increase the risk of local extinction in these ecosystems. Research has shown that some organisms can use their behavior to minimize the impacts of climate warming or allow population persistence in changing environments. Yet, comparatively little work has focused on the role of transgenerational plasticity in mediating an organism’s ability to effectively navigate novel thermal conditions.

We decided to explore this in a motile green algae species because of the genetic similarity between individuals and the relatively short acclimation period. This species (C. reinhardtii) has been shown to acclimate to its thermal environment within two weeks which represents around 20 generations in ideal conditions. This project allowed us to look at snapshots of the process of acclimation in real time.

When we began looking into research on the topic of transgenerational behavioral plasticity, we noticed that much work was done looking at the connection between parent and offspring environmental conditions, but little work had been done across multiple generations. This system allowed us to investigate this question across many (~20) generations which puts our paper among only a few others that have looked for transgenerational behavioral plasticity across this multitude of generations. We found that the historic acclimation environment can affect the movement behavior of C. reinhardtii in novel environmental conditions for up to 10 generations.

Hannah Meier and Dr. Samuel Fey collecting phytoplankton samples (Credit: Alisha Jucevic, 2021)

About the Research

This paper is relevant outside the scope of phytoplankton ecology because it suggests that in order to predict how populations will respond to climate change, we must consider their historical environmental conditions. Our work helps to improve predictions on how effectively populations can navigate novel thermal environments and suggests that their previous thermal exposers can constrain their movement patterns in the present. For example, even if populations become acclimated to thermally stressful environments their ability to navigate away from these environments may decrease over time.

Throughout the data analysis, one of the things that challenged us was how to separate out movement by individual particles from drift due to fluid dynamics versus active movement. We did a lot of work to troubleshoot this problem via our statistical analyses. Initially, we used Hidden Markov Models to categorize moving vs. non-moving particles but decided that this would not differentiate between movement and drift. We finally decided that we would set a velocity threshold based on observations made while testing our null hypothesis to differentiate between drift and movement by referencing the median velocity over time. To determine this, we collected additional data where particles were placed into a 60 OC water bath for 20 minutes to monitor heat-inactivated particles. This troubleshooting took several months, but ultimately this seemed to be the most sound approach for categorizing movement.

Left: A 100-mL beaker filled with six test tubes filled with phytoplankton samples Right: phytoplankton stock solutions (Credit: Alisha Jucevic, 2021)

We were surprised by the number of generations affected by the original environment. When we began the experiment, we did expect acclimation temperature to significantly affect movement behavior for more than a single generation due to what we knew about the effects of gradual plasticity on demographic processes, but we did not expect these effects to persist for 10 generations. One of the major questions that came out of this work is what mechanisms cause this to be the case? We have yet to find an answer to this question, but it will be important for investigating how transgenerational plasticity will affect behavior in other species and systems.

Our hope is to continue to improve predictions on how anthropogenic climate change will alter population persistence and community composition in freshwater ecosystems. Phytoplankton are a critical player in the worlds primary production and understanding specifically how climate change will affect this group of organisms is vital. These two things motivate all of the research I have done in the Fey Lab at Reed College, and this paper came out of our desire to address both simultaneously. Looking forward, we hope to understand why the effects of temperature persist for as long as they do, and what factors give species the ability to (or prevent them from) using behavioral thermoregulation to navigate thermally stressful environments. 

About the Author

The author Hannah Meier, 2022

I am currently a research assistant in Dr. Samuel Fey’s lab at Reed College, USA, where I received my B.A. in biology in 2021. During my sophomore year at Reed, I took an introductory biology course taught in part by Dr. Fey and it quickly became my favorite class. I received research grants from the biology department from my sophomore year onwards to do research in the Fey lab during my summers and quickly became interested in questions surrounding thermal acclimation and phenotypic plasticity. During my final year at Reed, I worked on my senior thesis remotely due to the COVID-19 pandemic so I had to design a research project that I would be able to complete without lab access. Dr. Fey, alongside his lab manager Tamara Layden, helped me design the experiment that turned into this manuscript. My work was focused on the data analysis, and I was ultimately able to work alongside Dr. Colin Kremer, Dr. Anna Ritz and Dr. Fey to figure out the statistical analysis. In particular, Colin Kremer (currently faculty at University of California, Los Angeles) and I spent a lot of time working together on the final aspects of data analysis on the challenges related to drift versus movement.

When I think about the person who has inspired me most to pursue ecology, I have to think about Dr. Fey. His genuine excitement and passion for this field is infectious, and beyond that, he has always been an understanding and supportive mentor. To me the mark of a great scientist and educator is someone who gives their students guidance to come up with their own questions, critically analyze how best to tackle these questions, and push themselves to go out of their comfort zone to do so, all of which Dr. Fey has done for me.

One of the most defining moments in my early education was being humiliated in front of my class for failing a test in a high school math class. I was absolutely crushed by this experience, and it took a long time for me to build the confidence to pursue a career in a math-heavy field. To me, it is important to share this story to illustrate how important good mentorship is, and how detrimental the opposite can be. My career trajectory would have been drastically different if I had not had the supportive mentorship I received from my professors at Reed.

Ecology has given me the opportunity to investigate questions about population persistence in the face of climate change, a topic that has interested me since I was a child. I have appreciated the opportunity to design my research project and see it through to publication. Having to revisit the same data for over 2 years was frustrating at times, yet the process of revising my workflow helped to deepen my understanding of the subject matter.

Enjoyed the blogpost? Read the research here!

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