Experimental Life

A drama in many acts
Published in Ecology & Evolution
Experimental Life

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Microscopic life

adapts to heaven and hell.

Exchanging angels. 

Student: Since very early in my bachelor’s back in Colombia, I remember reading papers in scientific journals and being dazzled by how clear scientific questions aligned with succinct structure and elegant experimental design. Back then I could only imagine that there was a scientific brain out there who out of nowhere had this brilliant idea, went on testing it and then wrote it down in a manuscript. This is what teachers told us at school, or what we could read in the biography of admirable scientists. The over 6 years of work that resulted in the manuscript by Tusso et al. 2021 showed me how far from reality I was back then.

Professor: I had just received an ERC Starting grant to work on the genetics of speciation in an avian hybrid zone. Despite all the opportunities offered by the latest technology to address this question in this system, I have always envied experimental evolutionists in their ability to trace the evolutionary process in real time. I was aware of a young master student in the neighbouring lab of Simone Immler who simulated the evolution of anisogamy with yeast. Yet, this seemed far detached from our own work in speciation. 

Student: Apparently, a professor in the department of Ecology & Genetics, Uppsala, just received a grant and there was free food and drinks, including fancy champagne. So I was like, “yeah! Sure, let’s go!”. During the event, the tall professor, who I had previously only seen walking fast in the corridors of the department, gave some words about the grant. It apparently dealt with the process of divergence from one population into two species in natural populations. I was thrilled, since at that time, my master thesis project on the evolution of anisogamy using fission yeast had just failed. A couple of weeks of intense reading, several discussions with colleagues and tons of sketches in my notebook had materialized in an alternative idea for my thesis: an experiment testing the effect of gene flow on speciation using the yeast system. I was determined to continue this project.  So I contacted Prof. Wolf by email. Although my intention was to start a PhD, in the email I just wrote “During the last semester I've been working in an evolutionary experiment in sympatric speciation…” “We have gotten very promising results which I would like to share with you…” I mean, who would have said no to that email. Right?

Professor: I am happy to discuss your ideas. This week is terribly busy though. Can we take it next week Monday? /Jo

Student: Wow, short reply.

Monday, November 13, 2014, Uppsala, Sweden. 1 o’clock in the afternoon - snowflakes slowly settling on the roof. (Picture a dark Swedish winter day).

Student: During the previous week I have been preparing for this meeting. This is when I actually got to read about Jochen’s work and fully realized its relevance to the experiment. I even prepared some slides to show the results we had got so far. So, I approached the door (unusually closed; what does that mean?) and ... Knock, knock. 

Professor: I was in the middle of writing a manuscript, when somebody knocked on my door. Aaarg, sure it is Monday, it must be that student wanting to discuss the evolutionary experiment. Ah well, let’s see. – “Please come in!”

Student: It soon turned out that all my preparation was an overkill. I did not have to do much in the meeting. I started presenting the project, and very quickly I could see the excitement on the professor’s face. Very soon he was the one talking and commenting on the potential of the project. At some point, he even got up from his desk and started drawing sketches and matrices, and making suggestions on how to improve the project. Just as those film scenes … The meeting lasted for over three hours!

Professor: It took a while before I could cut my way through the student’s Spanish accent. But this didn’t disguise that there was a young man who had a thorough understanding about evolution and had thought about a promising experiment with yeast. It took me another while to get to grips with the yeast biology, but soon saw millions of opportunities (had I only known ‘millions’ was an underestimate…). 

Student: In the middle of the excitement he then said – “so, Simone told me you would like to continue the project as a research assistant for a few months” – “No, no, what I want is to start a PhD project!” I replied. His face suddenly changed. Now his excitement was not equally clear. – “well… I was not planning to have a new PhD student… I need to check my budget… let’s talk in a couple of weeks”.

Professor: Exhausted after three hours of playing cerebral squash I felt we absolutely needed to do this experiment. This was simply a great opportunity to explore the options of experimental evolution for speciation research. And Sergio clearly was the right person to explore that with. He had opened a door to the future I just needed to walk through. If it wasn’t for the funding… Lucky enough this was good timing and I eventually could make it work. So Sergio joined our team as a PhD student. 

Student: Jochen’s excitement soon turned into action. The experiment exploded from an initially modest 20 populations to 136, from two to four treatments, and in general the scale of the whole project greatly expanded. All these changes forced us to introduce a new Phase III in the experiment, and to get more people involved in the project. Among them, Bart Nieuwenhuis, an evolutionary microbiologist whose experience and theoretical background has been of invaluable help. What remained constant all this time was the enthusiasm, regularly filling three to four hours of discussion. Maybe we should have kept a record of the number of hours invested in discussing the big picture, and the many little but crucial details. At some point we started bringing cookies to supply brains with sugar.

Professor: After we had eventually figured out all the conceptual and technical details and Phase III was running smoothly I moved to LMU Munich, and with it the entire experiment. This could have meant havoc or serious damage to the project. But I managed to convince Sergio and Bart to move along; and while I was struggling with setting up new courses and lectures, within a matter of weeks, Phase III was up and running again.

Student: Running the experiment was not the end. After years of data and sample collection, we were immersed in literally hundreds of tables and figures. The project that started under the assumption that conditions in experimental evolution were highly controlled, rapidly showed to be highly complex and dynamic. We had populations for which we knew their evolutionary history, and even then, explaining the emergence of multiple interacting phenotypes and their genetic basis turned out to be nothing close to trivial. We spent over a year just digesting the outcome of the experiment, trying to write a first draft of manuscript, and after that, several months rewriting the manuscript and making it readable. The final submitted manuscript was the version 9.2. 


On a dark yet fateful Swedish winter day, a student approached a professor. In his bag he carried the plan for an experiment that started off to understand the primeval evolution of separate sexes. Guided by the wise words of their companions, the two protagonists of our drama set out on a journey that lasted over six years. After many experimental rearrangements, after several grant applications, after writing who knows how many pages of code, after a move across countries they managed to extract some insight into the dynamics of adaptive divergence.  Read for yourself.

 Sergio Tusso & Jochen Wolf


Tusso, S., Nieuwenhuis, B. P. S., Weissensteiner, B., Immler, S. & Wolf, J. B. W. Experimental evolution of adaptive divergence under varying degrees of gene flow. Nature Ecology & Evolution 1–12 (2021) doi:10.1038/s41559-020-01363-2.


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