The search for rotifers continues

“Thank you”, I whispered in a soft voice while driving by the rayon and plating factories surrounding Lake Orta. “Thank you for giving me a PhD”.

Brachionus calyciflorus

The wastewater of those factories polluted the lake with copper and ammonium sulphate from approaching the mid-nineteen hundreds until the end of the last century. This history of pollution makes Lake Orta an interesting ecosystem to study, and sets the perfect stage for my PhD: the life-history responses of the rotifer Brachionus calyciflorus to past environmental changes (i.e. industrial pollution) and the underlying eco-evolutionary processes.

To study this, I (try to) resurrect rotifers from up to 80 year old lake sediments that contain their resting eggs, and compare the performance of these rotifers under different experimental treatments. As I have had some difficulties getting resting eggs from the post-pollution conditions, I decided to go to Lake Orta to get the most recent Brachionus calyciflorus: the ones that are currently swimming around.

Sampling Lake Orta with a plankton net.

Together with Diego Fontaneto of the ‘Istituto per lo Studio degli Ecosistemi’, I drove around the lake, and found five spots to easily enter the lake to collect zooplankton with a plankton net. This net made of fine nylon mesh is pulled through the water horizontally and the animals are captured in a vial at the bottom of the net.

A quick look together with Diego revealed that we captured tons of animals, but probably no Brachionus. A more thorough look together with our summer research assistant Conor Waldock confirmed this suspicion, but we have still some bottles of water to go through, so we keep on hoping. And otherwise, our hope lies in the sediment samples of Lake Orta that I also brought back from the trip.

The reason why we didn’t find any Brachionus in our water samples? Probably because the water was still too cold due to the relatively bad summer, and there have been no big algae blooms yet of which Brachionus could profit. I guess this means I have to go back next month to again sample Italian ice cream… Ehm, Lake Orta I mean.

Diego Fontaneto (left) and Conor Waldock looking at the harvest of the sampling day: water and mud.

Thinking hard and digging deep is facilitated by isolation

‘Think hard and dig deep, without being canalized by the ideas of others published in literature. Not very often do you get a chance like this offered to you. Take the challenge.’ And all the students participating in the Guarda Evolutionary Biology course took the dare set by Dieter Ebert, Sebastian Bonhoeffer, David Queller, and Joan Strassmann.

DSC04117In the idyllic Swiss village of Guarda, twenty-eight MSc/PhD-students interested in evolutionary biology were selected for a week of isolation, and given time to devote themselves to writing a grant proposal on any question they thought was worthwhile pursuing. The only requirements were that you had to collaborate in a group of 4-5 students, and choose a topic that was not related to your field of research at all. Oh, and you were not allowed to look for information in books or on the Internet: it was only tolerated to use the creativity of your own mind, the mind of your fellow students, and of the faculty members.

In just 15 working hours, the first draft of the grant proposal (including idea, hypotheses, and well-thought out experiment) had to be handed in. The faculty members granted every group 20 minutes to undergo their severe but justified feedback on the proposal. Six working hours after this feedback, the revised version had to be handed in, which got another feedback round. Five hours after this round, the final version and a presentation had to be ready. On top of that, there was an armchair lecture by one of the faculty members every evening, and you were (happily) obliged to offer all of them a hand cooked dinner during one of the days in the week.

DSC04061This has been one of the most inspiring courses I ever took that has brought me back to basic scientific thinking: What is an interesting and important question in (evolutionary) biology? How would you solve that question? Is your hypothetical experiment really answering that question? Does working within a group of complete strangers full of enthusiasm facilitates the brainstorming, discussing and writing-up process, or do you might have to learn a lot in how to successfully listen, be open-minded, and collaborate?

After this highly motivating and encouraging course (e.g. why not embrace serendipity in your scientific work?), we got home extremely exhausted, to find out that the project we proposed was at the moment being presented at the big Evolution meeting in North Carolina: how mutualistic interactions could alter the dynamics of natural selection.  I think that’s what you call Zeitgeist.

Photo by Joan Strassmann

Attendance ‘Bayesian population analyis using WinBUGS’-course

‘Don’t feign to be stupid.’ This well-chosen phrase of Marc Kéry introduced some of our group members to the world of Bayesian Statistics (where the use of your previous knowledge on the parameter you’re interested in, the prior distribution, plays a role). Together with Michael Schaub, Marc taught the inspiring course entitled ‘Bayesian population analysis using WinBUGS’ based on the book of the same name.

I was impressed by how they managed to cover almost the whole book within 5 days: starting with a gentle introduction to the analysis of distribution, abundance and population dynamics using a Bayesian framework, followed by an introduction to the software WinBUGS and implementation of mixed models in it, and finishing with some examples of the implementation of Integrated Population Models in WinBUGS. Lectures were alternated with useful exercises.

I think all the participants are after this course better trained in making a balanced decision whether they want to make use of the full knowledge they have, or use the veil of stupidity to make big discoveries (Schwartz, 2008).


If everything else fails, try Triops

Sometimes Science is nothing more than checking assumptions. This holds true whether you are a theoretical biologist (e.g. checking model assumptions), experimental biologist (e.g. checking assumptions of experimental design), or just love doing statistics (as we all do). During the first weeks of my PhD, I found out that I perhaps needed to check the basic assumption my supervisor has about me: that I would be able to let eggs hatch in the lab. Until now, I have been unable to let the desired rotifer eggs hatch, but I can proudly announce that since five days we have some pets in our office: Triops! These crustaceans are considered ‘living fossils’, and just as the rotifers I’m investigating, their eggs can remain in a state of diapause for a prolonged period of time.

Assumption “I have the capacity to let resting eggs hatch under laboratory conditions”: Check!


Triops X, one of our new office pets
Triops X, one of our new office pets

Tied to two females and more will follow… – Preparations for rotifer resurrection ecology

My science: all about bags of mud

Today I felt like going on a first (blind) date: being nervous and excited at the same time. Or perhaps this is more what marriage feels like: eager to be tied to your partner(s) for the coming years while knowing it has a high change of being a love-hate relationship. Today, my diapausing females arrived.

They were brought to our lab by Diego Fontaneto and Stefano Gerli of the Istituto per lo Studio degli Ecosistemi. Just like a first date I didn’t know what to expect, and I couldn’t trust that the outside would be a representation of the inside (which of course is the most important part): I was given bags of mud.

The mud comes from different layers of the sediment cores obtained from Lake Orta in Italy. This mud harbours the resting eggs (diapausing females) of the rotifers I will be using to investigate the relative contribution of ecological and evolutionary processes involved in the populations’ responses to changing environments. More information on how I will use resurrection ecology to address this topic will follow hopefully relatively soon.

Resting egg of Brachionus calyciflorus
Resting egg of Brachionus calyciflorus

Diego and Stefano taught us the necessary knowledge and skills on how to extract the eggs from the sediment. As I expected to find a lot of eggs in the mud, I had already designed a small experiment to be able to put the females directly to scientific use. However, in the small sample we investigated, we could only find 2 resting eggs of the rotifer species I will be using (Brachionus calyciflorus). As this is by far not enough for a proper experiment, we decided to put the females on hold: we stored them in the fridge.

To make up for the non-exciting mud picture, hereby a picture of what everyone thinks Science is about: green bubbly liquid. This is how we culture our algae, which we use as a food source for the rotifers.

What Science is presumed to be all about: green bubbly liquid

Meet the Rotifer Family

IMG_1387As from Thursday onwards, we are now part of the Family of Rotiferologists. This will be the most important family to deal with in my coming PhD years. Arpat, Stefan and I were welcomed by Diego Fontaneto (Uncle Rotifer) at the ‘Istituto per lo Studio degli Ecosistemi’ in Verbania (Italy). This Institute resides in a big manor house near an idyllic lake: the perfect place to retreat to when one has to write up an article as there is no distraction besides some thorough scientific discussion (which is always welcome) and the sound of calling gulls.

The scientists at this Institute have great knowledge on aquatic ecosystems and the invertebrates that are part of such an ecosystem (for example rotifers). During the two days we visited them, they have shared their knowledge on how to resurrect resting eggs from sediment cores obtained from Lake Orta (a great place to eat an ice cream). So now we are able to bring the past back to life in our lab in Zürich.

More information on the details of my PhD project and the bizarre world of rotifers will follow relatively soon. So keep an eye on this blog if you want to know why even the NASA thinks that rotifers are rather exciting animals…


Hedwig Ens | PhD Student

I found the joys of scholarly publishing and science communication: I work at Frontiers’ Editorial Office (scientific open-access publisher) in Lausanne looking after three Field Journals (Frontiers in Microbiology, Frontiers in Ecology and Evolution, and Frontiers in Nutrition), and I am a freelance science writer writing about everything in the realm of Science.

My CV tells me I qualify myself as an evolutionary ecologist. This means I thoroughly enjoy working in the invigorating field of research that integrates the fields of population ecology, life history and trait evolution, thereby recognizing that the critical element of understanding dynamically evolving populations can only be captured by using knowledge on the eco-evolutionary feedback loop. So recognizing that evolution is shaped by ecology, and ecology in its turn is affected by evolutionary dynamics. I am an enthusiastic empirical experimental biologist with a broad range of interests, all within the general theme of the interactions between organisms (ranging from individual to species level) and their environment (biotic and abiotic) and the effect it has on both ecology and evolution.

An aim of my PhD is expanding the knowledge on the usability of resurrection ecology for decomposing a population’s demographic and phenotypic dynamics into its major contributors (ecological and evolutionary processes) and their relative contributions. Having worked on different systems in both ecology and evolution, I am now for the first time in my life using an aquatic model organism: the rotifer Brachionus calyciflorus. I will design experiments making use of its fascinating lifecycle and life history to both test and contribute to the formulation of new theory on the feedback loop of evolutionary and ecological dynamics using a trait based demographic approach. This PhD will therefore hopefully shed light on the relative importance of the evolution-to-ecology and ecology-to-evolution pathways, and aid in understanding the role of environmental change in determining population fluctuations.

By literally bringing the past back to life, the tool of resurrection ecology can be used in a wide variety of research topics. It is for example possible to study the implications of microevolutionary change in the recent past, the evolution of phenotypic plasticity, the evolutionary response to climate change, etc.

2013-2014 PhD student, Institute of Evolutionary Biology and Environmental Studies,
University of Zurich, Switzerland
2012-2013 Teaching Assistant, University of Amsterdam, The Netherlands
2009-2012 MSc in Biological Sciences, track Ecology & Evolution, University of Amsterdam, The Netherlands. Projects at the Netherlands Institute of Ecology, Imperial College London, and the University of Oxford
2006-2009 BSc in Biology (Ecology & Biodiversity), University of Amsterdam, The Netherlands

Resurrecting population responses to past environmental changes from lake sediments

Piero Guilizzoni from the Institute of Ecosystem Study during sediment sampling in 2012.

In this project, we investigate life-history responses of a freshwater rotifer, Brachionus calyciflorus, in retrospect. This is possible because brachionid rotifers produce dormant stages, so-called resting eggs, some of which remain viable in lake sediments for decades.

During the last century, Lake Orta – a deep, subalpine lake in northern Italy – was severely affected by industrial pollution. In 1926, a newly established textile factory began to discharge copper- and ammonium-sulphate contaminated sewage into the lake. The following acidification of the lake resulted in a dramatic decrease in rotifer diversity and an accumulation of resting eggs in the sediments. From the late 1950s onward, pre-treatment of the sewage prior to discharge gradually improved the quality of the lake water, and recovery was further accelerated by whole-lake liming in 1989 and 1990. Ten years after these liming efforts, the pH of Lake Orta had returned to pre-pollution levels, and copper was virtually absent from the water column.

In collaboration with the Institute of Ecosystem Study in Verbania, Italy, we collected sediment cores from different basins of Lake Orta. Back in the laboratory in Zürich, we screen these cores for brachionid resting eggs, which we try to hatch. Subsamples of rotifer lineages established from successfully hatched resting eggs are then subjected to a variety of treatments mimicking selected water parameters of historic lake conditions. Using such a ‘resurrection ecology’ approach allows us to investigate the adaptive value of life-history differences among rotifer lineages from different sediment layers, with each layer representing a distinct period in the well-documented pollution history of Lake Orta.


The video shows a B. calyciflorus female carrying five male eggs.


In collaboration with: