Currently, these questions are typically addressed from opposing angles and backgrounds: while studies on populations of individually marked wild birds and mammals provide ecologically meaningful, but often rudimentary estimates of genetic variation, controlled breeding experiments with genetic model organisms like Drosophila can provide a far more detailed description of the genetic architecture underlying phenotypic variation. In such systems, however, the fitness consequences of this variation are incredibly difficult to study on an individual level and in an ecologically meaningful way. Extrapolating findings from genetic model organisms to their wild relatives, and natural populations in general, is thus fraught with problems. Hence, although both approaches each have their own unique strengths and weaknesses, and should be considered as complementary rather than opposing, the two are remarkably rarely combined.

However, slowly but surely, the gap between genetic model and non-model species is closing. In fact, these are particularly exciting times for the study of the evolutionary genetics of natural populations, as recent developments in molecular genetics have opened up a range of possibilities that long have been unattainable, bringing us closer to a truly mechanistic understanding of the evolutionary process in the wild. I believe that it is this continued integration of laboratory and field studies, and of ecological, molecular, and quantitative genetic approaches, will provide us with unique new insights into the evolutionary dynamics of natural populations. As a matter of fact, I believe that it is only such a pragmatic and multi-disciplinary approach that can get us anywhere near a truly mechanistic understanding of the evolutionary processes responsible for the generation and maintenance of the ubiquitous levels of morphological and behavioural diversity we see in the world around us. This will bring us closer to answering a number of fundamental outstanding biological questions, but it will also give us a much needed deeper understanding of the impact of the unprecedented rates of environmental change currently experienced by organisms around the globe.

current projects

The genetic basis of inbreeding depression in a natural bird population

Inbreeding depression, the reduced survival and performance of individuals with related parents, is one of the oldest and longest standing topics in evolutionary genetics. The continued interest in inbreeding depression stems from the fact that it affects a large number of phenomena in biology, ranging from fundamental biological processes such as the choice of mating partner and the decision to leave one's birth place to conservation of endangered species, as well as human and animal health and productivity. Studies on inbreeding depression therefore contribute to both basic and applied research. However, despite a century of research on the genetic basis of inbreeding depression, the relative importance of various genetic causes is still debated. In this study, Lukas Keller and I aim to elucidate the genetic basis of inbreeding depression in a natural bird population. Our study combines extensive field data on survival and reproduction of song sparrows (Melospiza melodia) on Mandarte Island, Canada, with modern molecular genetic approaches and recently developed statistical tools. The population of song sparrows on Mandarte Island has some of the most complete and extensive pedigrees of any natural population. Analyses of inbreeding and its consequences in this population have revealed significant inbreeding depression in several fitness components, making this population an excellent system to quantify the genetic basis of inbreeding depression.

Individual-level causes and population-level consequences of variation in fitness

Switzerland has only a very small number of wild and unmanipulated bird and mammal populations where individuals are marked individually and individual life-histories are being recorded. One of the few of such studies is that of a wild snow vole population (Chionomys nivalis), located in the Swiss Alps. This study population was established in 2006 by Dr. Peter Wandeler.
Given its in many ways extreme environment, this population provides an excellent system to link life-history theory, quantitative genetics and population ecology to study the effects of environmental variation and climate change on the evolutionary dynamics of isolated populations. Furthermore, their relatively close relatedness to house mouse and rat ensures the availability of a range of genetic and genomic tools.

The evolutionary genetics of life and death in humans

In this project, we take an evolutionary approach to variation in human reproductive success and lifespan, and try to understand how these are being shaped by genes and the environment. we do this by combining genealogical data with a range of other types of datasets. This can provide us with insights into how important life-history traits, like age at first reproduction, family size and lifespan, as well as a range of socio-economic variables, (co)vary among individuals, villages and regions, and how they have changed over time. By subsequently combining these data with ideas from population and quantitative genetics and life-history theory, we can make a first step towards elucidating the role of genes in shaping life and death, in the past and in the present.
In an attempt to obtain a better understanding of the effects of inbreeding in humans, I am working together with Pietro Martini, also a student at the University of Zürich, and his uncle Luigi. Together they reconstructed the genealogies of the inhabitants of their hometown, a small and isolated Swiss village. This has resulted in a unique data set consisting of over a thousand individuals, with records going back as far as the 17th century. From this we are able to estimate the relatedness of all married couples, as well as the level of inbreeding for each individual, and relate that to reproductive success (Postma et al. 2010). In 2011, Anja Bürkli used another genealogical dataset to estimate the strength of selection on age at first and last reproduction, as well as on lifespan, and combined this with estimates of genetic variation to predict the rate and direction of evolutionary change.

The giants of Aldabra

Aldabra tortoise In 2011, Dennis Hansen, Lindsay Turnbull, Gabriela Schaepman-Strub and myself initiated the Zurich-Aldabra Research Platform (ZARP) with money from the Forschungskredit of the University of Zurich. ZARP is a multi-disciplinary collaboration between scientists based mainly at the University of Zurich and the Seychelles Islands Foundation (SIF) that aims at supporting local SIF staff based on Aldabra Atoll in their research on the Aldabra giant tortoise.
Our goal is to establishing a detailed study of the Aldabra giant tortoise, the last remaining native population of giant tortoises in the Indian Ocean. Our main focus is a sub-population on the third largest island, Picard. Here we hope to sample as many individuals as possible and to reconstruct family relationships, together with information on pathogen loads and nutritional status. This will be complemented by an island-wide survey of other animals.
Furthermore, tortoise densities on Aldabra are extremely high and herbivore biomass per unit area generally exceeds that typically found in ecosystems dominated by large mammalian herbivores. The vegetation on Aldabra is highly seasonal, and we plan to uncover the links between climate, vegetation and tortoises using satellite images, LIDAR, long-term tortoise counts and vegetation exclusion plots. This will provide vital information on the possible impacts of climate change on the atoll.

Y linkage of male ornamentation in guppies

Male guppies are remarkable for their highly polymorphic colour patterns. Interestingly, there are several lines of evidence suggesting that at least part of the genetic variation underlying male coloration is linked to the Y chromosome. As a consequence, guppies provide a fascinating case study into the causes and consequences of sex-linked genetic variation. In this project, Rob Brooks and I are using data from a multi-generation breeding experiment to estimate the amount of quantitative genetic variation underlying male ornamentation, both on and off the Y chromosome.
Despite a growing awareness that organisms are not one-dimensional, the great majority of studies on the evolution of colour traits continues to reduce an animal's phenotype to a single measurement of one single trait. Evidence is however rapidly accumulating that this univariate approach provides us with an overly simplistic description of an individual's phenotype, and thereby it is unable to advance our understanding of the evolution of complex phenotypes like male ornamentation in guppies. For example, different traits, but also different aspects of the same trait, may provide different types of information, and correlations among them may severely limit there evolutionary trajectory.
A number of recent developments in multivariate quantitative genetics have provided us with a powerful set of tools to analyse the genetics underlying multivariate colour signals, and to describe the correlations among them. This can provide us with the relative roles of genes and environment in shaping variation in male colouration, and it allows for the identification of the major axes along which selection can operate. Finally, it allows us to directly test for associations between the major axes of both autosomal and Y-linked genetic variation on the one hand, and independent measures of quality and attractiveness on the other.

phd research

In 2001 I started my PhD at the Department of Animal Population Biology at the Netherlands Institute of Ecology, to work on the evolutionary genetics of life-history traits in great tits (Parus major). During these four and a half years I gained ample experience with the estimation of quantitative genetic parameters and selection pressures from long-term data sets. I focussed on the population on the island of Vlieland in particular, where I also spent four field seasons.
Vlieland is one of the smaller islands in the Dutch part of the Wadden Sea (53.17°N, 5.03°E, 3258 ha). The population consists of five more or less spatially separated woodlands (total surface ca 300 ha) and a small village. The landscape between the woodlands consists mainly of dunes and is unsuitable habitat for great tits.
Since nest boxes are available in excess in all suitable nesting habitat, it is possible to monitor the complete population and to ring all chicks that are born on the island each year. As a result of the isolated nature of the population, immigration rates are relatively low, whereas local recruitment rates are high. This makes it possible to reconstruct individual pedigrees in great detail, and to obtain relatively accurate fitness measures for all individuals. These characteristics make Vlieland exceptionally suitable for a study into the evolutionary genetic of wild populations.

An electronic version my thesis can be found here

prospective students

Any specific projects that are available will be advertised here. However, I am always looking for motivated students. So if you have an interest in evolutionary biology, behavioural ecology and (population or quantitative) genetics, and in particular in the interface between them, then don't hesitate to contact me to discuss the possibilities.