The mathematician with biological ambitions

Tanja Stadler is one of those mathematicians who applies her knowledge to problems that exist in the real world – in her case, questions relating to biology. However, she is barely able to directly observe the processes that she investigates. Stadler is interested in macro-evolution, phylogenetics and epidemiology: she uncovers how species evolve or decay and how infectious diseases spread.

“I try to understand what has happened in the past in order to make predictions about the future,” says Stadler. Unlike classic palaeontology, she does not go digging for fossils but instead relies on genetic information, mathematical paradigms and statistical flair. And she is very successful: Stadler received one of the coveted ERC starting grants in the summer and now she has been awarded the Latsis prize – the most important distinction for emerging ETH researchers – for her contribution to phylogenetic reconstruction.

Fascinated by phylogeny

“The recognition of my work by an independent commission of experts is the thing that pleases me the most,” says the 32-year-old German, who came to ETH Zurich as a post-doctorate student in 2008. She had, however, discovered her research specialism earlier on. In 2005, as she was nearing the end of her studies of applied mathematics at the Technische Universität München, she read a book on phylogenetics by Mike Steel, a mathematician from New Zealand. She was so fascinated by the subject that she contacted him and shortly afterwards travelled to New Zealand to do research at the University of Canterbury for three months. Stadler extended her stay and wrote her thesis under Steel’s supervision – on statistical modelling of speciation and extinction. Not only did she return home with a wealth of experience, she also gained a research specialism in which she subsequently completed her doctoral studies at the Technische Universität München.

Following her dissertation, Stadler wanted to specialise in biology and found the Institute of Integrative Biology (IBZ) at ETH Zurich, with the key areas of evolution and ecology. “The perfect environment for post-doctorate research,” she recalls. Stadler has been junior group leader at the IBZ since 2011, working with Sebastian Bonhoeffer, professor for theoretical biology.

A glimpse into evolution

The conceptual basis for Stadler’s research is the phylogenetic tree – a diagram that shows evolutionary relationships, similar to a family tree. Stadler derives these trees from sequenced genetic information and in this way has examined, for instance, the phylogeny of mammals living today. Her analysis indicates that the evolution of the mammal must have started long before the extinction of the dinosaur, thus countering the prevalent doctrine of palaeontology, which – based on fossil data – implies the opposite. “It is unclear which source tells the true story – the fossils or the genes,” says Stadler. Her approach consists of combining both sources: she is working on pooling genetic information with paleontological data, such as fossils, to identify the key factors in evolutionary processes.

Epidemics on the trail

Similarly, Stadler is also defining the driving forces in epidemics. Through the IBZ, Stadler has access to HIV gene databases that she uses to test her paradigms. “The HIV virus mutates so quickly that every patient basically carries their own viral population,” she explains. The phylogenetic trees derived from the viral genes reflect the history of transmission and enable conclusions to be reached on whether the epidemic is spreading or is in decline, the speed at which this occurs and the infection rate. These parameters enable epidemiological paradigms to be improved: together with Gabriel Leventhal, a doctoral student in Bonhoeffer’s group, Stadler has succeeded in developing a new, realistic paradigm for the spread of HIV.

Such findings are also of interest to the public health authorities, as they can help in the formulation of measures to deal with infectious diseases, such as resistant pathogens. Stadler would like to be able to reach the stage in her research where, for future infectious diseases, she is able to quickly assess whether and how dangerous a pathogen is and how it spreads.

Her chances of success look good: ETH has just offered the ambitious young researcher a position as an assistant professor in the Department of Biosystems Science and Engineering (D-BSSE) in Basel. This means that Stadler can continue with her research. “I am on cloud nine,” she says happily.