Kimberley Lemmen: Surprise! Rapid heritable adaptation can occur without initial standing genetic variation

In this new post, Kimberley Lemmen—a post-doc working at the University of Zurich, Zurich, Switzerland—discusses her paper: Experimental evidence of rapid heritable adaptation in the absence of initial standing genetic variation—recently shortlisted for the 2022 Haldane Prize for Early Career Researchers.

About the paper

The microzooplankton Brachionus calyciflorus was used in this study to investigate if heritable adaptation can occur in the absence of standing genetic variation (credit: Steven Declerck & Suzanne Wiezer)

Environmental change presents a fundamental challenge to populations because the traits that previously allowed individuals to grow, survive, and reproduce may not be suitable in new conditions. One way that organisms can persist in the face of changing environments is through heritable adaptation—a change in traits that is passed down between generations. Selection on standing genetic variation is widely regarded as the primary process by which rapid heritable adaptation occurs. However, some populations with little or no genetic variation are nevertheless successful in the face of changing environments. Recent studies have suggested alternative pathways by which heritable adaptation can occur, including environmentally induced genetic modifications (e.g., point mutations, transposable elements) and non-genetic heritable phenotypes (e.g., methylation patterns, small RNAs). However, experimental evidence supporting if, and to what extent, these sources of phenotypic variation can produce a rapid adaptive response is currently sparse.

Kimberley working with her experimental populations (credit: Kimberley Lemmen & Romana Limberger)

In this study, we investigated whether rapid heritable adaptation could occur in the absence of standing genetic diversity. To do so we exposed replicate populations of the asexually reproducing monoclonal microzooplankton—Brachionus calyciflorus—(i.e., no initial genetic diversity and no recombination) to culturing conditions that selected for phenotypic variants with elevated population growth and provided them with either high- or low-phosphorus food. We found that populations with a history of exposure to low-phosphorus food exhibited higher population growth rates under low-phosphorus food conditions than populations with a high-phosphorus exposure history. Our study thus provides a clear example of rapid (six generations) heritable local adaptation in response to exposure to a stressful environment based on de novo heritable variation in an animal population.

Although standing genetic variation is considered essential for rapid heritable adaptation, we find that alternative sources of phenotypic variation may also play a role and could aid in the establishment and persistence of low-diversity populations. Given the unprecedented rate and magnitude of current environmental change, it is important to understand all possible mechanisms that organisms may use to persist and adapt. This study suggests that the production of heritable phenotypes in response to environmental conditions may play an underappreciated adaptive role.

About the research

Common Garden Cultures (credit: Kimberley Lemmen)

The thing I enjoyed most about this project was having the opportunity to do a deep dive into a field of research in which I had limited experience. My primary field of study is eco-evolutionary dynamics, where it is assumed that populations must have substantial genetic variation for rapid heritable adaptation to occur. Before working with my co-author, Koen Verhoeven, I didn’t fully realize that heritable change could occur on ecologically relevant timescales in populations without genetic diversity. This project provided me with the opportunity to learn about non-genetic inheritance and the production of environmentally induced genetic variation—two processes which I hadn’t previously considered as being important to heritable adaptation to environmental change. One of my goals with this paper was to introduce readers to the importance of de novo heritable variation in an understandable but also nuanced manner, and get them as excited about these processes as I became.

Unfortunately, I have not had a chance to continue this research. When we first conceived of this experiment, we had no idea if we would see any heritable response to the exposure treatment. Such responses had been documented in plant populations, but little was known about the potential in animal populations. As such, we knew the project was “risky” and thought it was best to leave it as a stand-alone experiment until we had an idea of the results. I have now left the Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands, and am working in a different field of study. It would be great if someone in the future followed up on this work by investigating the mechanisms that generated the response we observed.

About the author

Kimberley hiking in the Switzerland where she is now a post-doc at the University of Zurich (credit: Cam Hudson)

I am an evolutionary ecologist who focuses on understanding how adaptation to environmental change impacts species interactions and ecosystem processes. I began my research career at Queen’s University in Kingston ON, Canada, where I did both my BSc and MSc. For my PhD, I moved to Wageningen in the Netherlands to study how primary consumers mitigate the negative impacts of stoichiometric mismatch with their food resources, using both heritable and non-heritable adaptation. This work was conducted at the Netherlands Institute of Ecology with Steven Declerck. As my research thus far had been focused on population-level responses to environmental change, for my next step I wanted to work with a group that studied community-level processes. I am now a post-doc at the University of Zurich with Frank Pennekamp exploring the importance of higher-order interactions on community dynamics.

As a child, I had a lot of exposure to the outdoors and STEM (I think my dual-working parents enrolled me in every science-themed summer day camp program that was offered in my city), but, unlike many of my peers, I didn’t have a passion for ecology/natural history at an early age. For my undergraduate studies, I enrolled in the general science program, but I kept my studies quite broad and took many social science courses. The moment I truly got hooked on ecological research was during a field course in the summer between my second and third year. In that course, I learned how to design and conduct field-based experiments, and to my surprise, I really enjoyed the process of discovering these answers. From that moment on I started to gravitate towards ecology and evolution courses, eventually participating in a research-based fourth-year honours thesis course that my department offered, and the summer research program that led me to my master’s research.  

Now that I am a lab-based ecologist, my favourite thing to do in my spare time is to get outdoors. Living in Switzerland I’m super lucky to have the opportunity to go up into the mountains regularly—I love hiking in summer and snowshoeing in winter. When I’m back in Canada, my outdoor activity of choice is backcountry canoeing (one of my prized possessions is a hand-carved paddle that I received as a graduation gift when I defended my master’s thesis).

Kimberley canoeing on Big Rideau Lake in Ontario, Canada (credit: Cam Hudson)

The thing I enjoy most about being an ecologist is breaking down complex systems into their different parts to try and understand how everything fits together. This sometimes leads to me taking my vacuum apart and not being able to build it back together again. Luckily being an ecologist, I can focus this curiosity on my research studying how organisms respond to environmental change and the potential for that change to modify the environment.Conversely,the worst thing about being an ecologist, for me, is regularly having to confront the devastating impact that anthropogenic environmental change is having on the planet.

If I had to provide one piece of advice to other ECRs, it would be to build a supportive and sharing peer community for yourself. This is important because doing a PhD and being an academic is hard. For me, it was very important to have a network of people that understood what I was going through during both the happy and tough phases of my scientific journey. I also think that sharing resources is a key tool in supporting your peers. In fact, many of my achievements have come from information that was shared with me by my friends and colleagues. Never be afraid to ask for examples of applications (grants, jobs, awards) or assume that because someone isn’t asking for something they wouldn’t benefit from the information being shared.

I would also encourage early career researchers to prioritize the needs of their personal life such as being close to a partner/family or living in a community where they feel safe and accepted. This can often be difficult, as young academics we are expected to sacrifice our personal lives and give so much of our time to be competitive in a tough job market. I struggle with doing this but luckily have had positive outcomes when I managed to do so.

Enjoyed the blogpost? Read the research here!

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