Currently, the above 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. However, in such systems 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, there is currently remarkably little interaction between them.

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 this continued integration of laboratory and field studies, and of ecological, molecular, and quantitative genetic approaches, will not only provide us with unique new insights into the evolutionary dynamics of populations, but 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.

Inbreeding in a small and isolated Swiss village

Despite overwhelming evidence for a negative effect of inbreeding in plants and non-human animals, its effect on fitness in humans remains subject to debate. In fact it was Darwin (who married his cousin and feared that the poor health and early death of several of his ten children was the result of "a serious form of inheritance from my poor constitution") who "wished that the truth of the often repeated assertion that consanguineous marriages lead to deafness and dumbness, blindness, etc., should be ascertained". His request for a large-scale investigation was turned down, and even today good evidence for negative fitness effects of inbreeding in humans remains remarkably scarce.
In this project we attempt to obtain a better understanding of the effects of inbreeding in humans. For this I am working together with Pietro Martini, a student at the University of Zürich, whose uncle has 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 both reproductive success and lifespan.

Scent of a vole

In collaboration with Peter Wandeler and Florian Schiestl, we are using gas chromatography to characterise pheromones in a wild snow vole (Chionomys nivalis) population. Whereas humans invest considerable time and money to mask their bodily odours, most other animals go through great lengths to make their smell stand out from the crowds. Indeed, they often produce volatile compounds, or pheromones, which may signal not only their presence, but also their quality, to either competitors or potential mates. However, despite its pivotal role, when describing an animal's phenotype, its scent is usually neglected. The one exception to this rule is the house mouse (Mus musculus), for which we now have a relative detailed knowledge of the complex set of pheromones present in their urine, as well as their functional significance. However, as the great majority of this work has focused on inbred lines, kept under highly artificial laboratory conditions, the fitness consequences of variation in scent are incredibly difficult to study on an individual level and in an ecologically meaningful way. In this project we are taking our knowledge on the mechanisms underlying olfactory communication in the house mouse to the wild.
As part of an ongoing long-term study on a wild population of snow voles, we are collecting urine samples throughout the breeding season for most individuals. These samples are subsequently analysed using gas chromatography and mass spectrometry. When combined with the genetic and ecological data available for this population, this will hopefully provide us with unique insights into the genetic and environmental sources of individual variation in scent, and how this variation is being shaped by both natural and sexual selection.

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 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.