In Focus: Carolin Sommer-Trembo delves into the reasons behind biodiversity

“Where’s the big guy gone?” Carolin Sommer-Trembo is scouring the two-meter long aquarium. The big guy is a cichlid – more precisely a cyphotilapia frontosa. “He died,” the lab assistant replies. Sommer-Trembo peers sadly into the aquarium: “Old age, unfortunately,” she explains. The fish with the black dorsal fin and bulging forehead had become something of a favorite over the past three years.

Sommer-Trembo arrived at fish somewhat by chance when she joined a research group for her doctoral dissertation. She stuck with the creatures and the researcher from Freiburg has now been studying cichlids as a postdoc for four years. She wants to know how curious the creatures are and what effect this curiosity has on the emergence of new species. “Cichlids are masters of forming new species,” she explains. In Lake Tanganyika, which extends from Zambia along the border of Tanzania all the way to Burundi, there are 240 different species of cichlid.

Fascinating creatures, frustrating technology

Sommer-Trembo keeps heading back to Lake Tanganyika for her research, last time in 2020 during the pandemic. She spends several weeks diving and searching for new specimens, running behavioral tests and taking DNA samples. She captures the behavioral tests on camera and evaluates the data in Switzerland.

Over the course of her visits she has analyzed over 800 individual fish. It has not been without its frustrating moments. But the fish were never to blame. “Any stress is always to do with the technology. When we find a specific fish in the depths of the lake and bring it slowly to the surface – and then the camera packs up during the experiment because of the heat, that’s extremely frustrating,” comments Sommer-Trembo.

Malaria infection

She is passionate about her work, waxes lyrical about the trips to Africa and excitedly points out the evaluated data she is using to write her paper. Although she spends most of her time in front of a computer screen at the moment, the avid researcher remains highly motivated: “The best thing about science is the freedom of thought.”

But the research has had the occasional downside too: on one of her field trips, she contracted malaria – at the same time as her field assistant. She struggled with extreme nausea and had difficulty swallowing the essential medicines. Looking back, she sees her illness more as an anecdote than a pivotal experience. “Four days later we were back at work. After all, we had a tight schedule,” she shrugs.

Collaboration with Cambridge

In Basel too a large part of her work consists of behavioral tests. While Sommer-Trembo and her research group brought some fish specimens back from Zambia, many were bred here. Her laboratory in the Department of Environmental Sciences features stacked rows of aquariums containing cichlids. Sometimes the creatures swim in pairs, sometimes in groups of 20, some are just a few centimeters long and fairly dull, others are palm-sized with flamboyant patterns.

The biologist studies the fish for two years from the time they hatch and regularly tests their behavior. She even continues to study some of them beyond their lifespan: “In the past six months I’ve been busy dissecting fish brains.” An exciting collaboration is currently taking place: Sommer-Trembo’s research group is working with researchers in Cambridge to modify the DNA regions responsible for curiosity using CRISPR/Cas gene editing. They may soon be able to make a curious fish more timid. And they are looking into the question of whether the same genes also control curiosity in other groups of animals.

Either dance or science – not both

The evolutionary biologist moved to the University of Basel after completing her doctorate. She had met Professor Walter Salzburger at a conference and was intrigued by his research project. Her doctorate, which she completed in Frankfurt, involved research into personality traits in fish. Prior to that she was based in Hohenheim and Tübingen. She points out that the fact she has focused so intensively on fish is more by accident than design: “I’m not a typical fish freak – I can’t recognize every species just by looking at it. I could just as easily have ended up researching the speciation of wasps,” says the 33-year-old.

But she ended up in Basel with the curious fish. On the curiosity scale she uses to rate her fish she would score full marks. She says she’s not afraid to try anything – even bungee jumping.

Sport is one of her passions. She took up dancing as a child and even made it to the world championships in Ballroom and Latin. “Then I had to decide: science or sport. I wasn’t getting enough sleep trying to do both,” she recalls. She chose science. And she has no regrets.

The future is not yet clear. Technically, her contract ran out two years ago but was extended due to the pandemic, allowing her to obtain funding again. She is not sure how things will pan out in 2023. But she is not worrying about that just yet. “I can’t focus too much on that at the moment. Otherwise I won’t be able to concentrate on my current work, particularly publishing.”

Sommer-Trembo’s father is a physics professor, so she is familiar with the career path to professorship. And is aware that a lot of academics do not get that far. “Of course I studied with the goal of being awarded a professorship – that’s something we all share in the research group.” However, she recognizes that there are not enough posts to go round. “In a pinch I’ll take my doctorate with me and go and work at McDonald’s for six months. And maybe a new door will suddenly open.”

Popularizing science

In the meantime, the biologist has a second string to her bow. She blogs about her work, attempting to make science accessible to a broader audience. She not only enjoys the project but feels it is important too. “The pandemic has shown how important scientific communication is,” she emphasizes.

In her blog she calls herself the “dirty-field-biologist”. The name is no accident: “During the field research for my doctoral dissertation in Mexico there was one point when we were standing chest-deep in a river, fully dressed, looking for these specific fish. And every possible kind of filth came floating downstream towards us – including feces. Hence the name.” She is not one to let “little things like that” get in the way of her research.