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.

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…


Mollie Brooks, our new quantitative ecologist

We have a new quantitative ecologist joining our ranks, Mollie Brooks, who is a recent PhD graduate from University of Florida, Gainesville. Fresh out of Ben Bolker’s group, Mollie is bringing with her much needed skills in statistical and demographic analysis, and to our pleasant surprise, in baking!

During her postdoc, Mollie will contribute to our research projects on early warning signals and resurrecting past eco-evolutionary responses.


Stefan Sommer | Research Assistant

I am an experimental biologist contributing to projects that aim at prediciting and resurrecting population responses to environmental change. I conduct laboratory experiments, supervise students, and assist in teaching.


ResearchGate | ORCiD



  • Since 2012, Research Assistant, Department of Evolutionary Biology and Environmental Studies – Population Ecology, University of Zürich, CH
  • 2010–2012, Research Assistant, Department of Evolutionary Biology and Environmental Studies – Sexual Selection and Speciation, University of Zürich, CH
  • 2008–2009, MQRES Fellow, Centre for the Integrative Study of Animal Behaviour, Macquarie University, Sydney, AUS
  • 2002–2008, Research Assistant, Institute of Zoology, University of Zürich, CH
  • 2000–2002, Temporary Employee, Koller Auctions Zürich, CH
  • 1994–2000, Studies in Biology, Diploma in Zoology, University of Zürich, CH
  • 1989–1994, Studies in Architecture, Swiss Federal Institute of Technology Zürich, CH

Stefan Sommer, our new rotifer meister

Many long-term studies on larger vertebrates provide us with only a single time series to study population dynamics. To test all the interesting hypotheses arising from these studies, we have to shrink those systems into tubes and replicate under different treatments. For this, with the invaluable help of Dr. Diego Fontaneto (Institute of Ecosystem Studies, Italy), we chose the rotifers as our experimental system. It didn’t take too long for us to realize that we needed expert help. And that help arrived as a swiss-army-knife of a guy: Stefan Sommers, our research associate, rotifer-meister, orchestrator of our microcosm lab!

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.


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