Kees van Oers

• Prof. Dr.
• Special Professor at Wageningen University & Research

Anthropomorphic activities have a large impact on ecosystems in many ways, one of which is how animals behave. Non‐motorised nature recreation is a popular human activity of which the impacts on nature are largely unknown. These activities, which include hiking, biking, pet walking and horseback riding, tend to increase during the commencement of t...

Variation in age structure influences population dynamics, yet we have limited understanding of the spatial scale at which its fluctuations are synchronised between populations. Using 32 great tit populations, spanning 4° W–33° E and 35°–65° N involving > 130,000 birds across 67 years, we quantify spatial synchrony in breeding demographic structure...

Animals living in cities are smaller than their conspecifics from rural areas but whether such differences are caused by genetic differences or food constraints remains untested. We performed a multi-generation common garden study where we raised great tits (Parus major), originating from eggs collected from multiple Dutch cities and forests under...

To forecast how fast populations can adapt to climate change, it is essential to determine the evolutionary potential of different life-cycle stages under selection. In birds, timing of gonadal development and moult are primarily regulated by photoperiod, while laying date is highly phenotypically plastic to temperature. We tested whether geographi...

Maternal hormones can profoundly impact offspring physiology and behaviour in sex‐dependent ways. Yet little is known about the molecular mechanisms linking these maternal effects to offspring phenotypes. DNA methylation, an epigenetic mechanism, is suggested to facilitate maternal androgens' effects. To assess whether phenotypic changes induced by...

Information on individual age is a fundamental aspect in many ecological and evolutionary studies. However, accurate and non-lethal methods that can be applied to estimate the age of wild animals are often absent. Furthermore, since the process of ageing is accompanied by a physical decline and the deterioration of biological functions, the biologi...

Behavioural traits are under both genetic and environmental influence during early life stages. Early environmental conditions related to the amount and type of food have been found to alter behaviour in many organisms. However, how early life diet affects the variation in and the correlation between behavioural traits is largely unknown. Using a m...

Maternal hormones can profoundly impact offspring physiology and behaviour in sex-dependent ways. Yet little is known on the molecular mechanisms linking these maternal effects to offspring phenotypes. DNA methylation, an epigenetic mechanism, is suggested to facilitate maternal androgens’ effects. To assess whether phenotypic changes induced by ma...

Environmental variation can shape the gut microbiome, but broad/large‐scale data on among and within‐population heterogeneity in the gut microbiome and the associated environmental factors of wild populations is lacking. Furthermore, previous studies have limited taxonomical coverage, and knowledge about wild avian gut microbiomes is still scarce....

Anthropogenic climate change has led to globally increasing temperatures at an unprecedented pace and, to persist, wild species have to adapt to their changing world. We, however, often fail to derive reliable predictions of species' adaptive potential. Genomic selection represents a powerful tool to investigate the adaptive potential of a species,...

Spatio-temporal variation in age structure influences social and demographic functioning, yet we have limited understanding of the spatial scale at which its fluctuations are synchronised between wild populations. Using 32 great tit populations, spanning 3200km and >130,000 birds across 67 years, we quantify spatial synchrony in breeding age struct...

A major aim of evolutionary biology is to understand why patterns of genomic diversity vary within taxa and space. Large‐scale genomic studies of widespread species are useful for studying how environment and demography shape patterns of genomic divergence. Here, we describe one of the most geographically comprehensive surveys of genomic variation...

Adverse, postnatal conditions experienced during development are known to induce lingering effects on morphology, behaviour, reproduction and survival. Despite the importance of early developmental stress for shaping the adult phenotype, it is largely unknown which molecular mechanisms allow for the induction and maintenance of such phenotypic effe...

Environmental variation can shape the gut microbiome, but majority of studies use captive-bred species, while data on large-scale variation in the gut microbiome and the associated environmental factors is lacking. Furthermore, previous studies have limited taxonomical coverage, and for example knowledge about avian gut microbiomes is still scarce....

The recognition that climate change is occurring at an unprecedented rate means that there is increased urgency in understanding how organisms can adapt to a changing environment. Wild great tit (Parus major) populations represent an attractive ecological model system to understand the genomics of climate adaptation. They are widely distributed acr...

Cognitive flexibility controls how animals respond to changing environmental conditions. Individuals within species vary considerably in cognitive flexibility but the micro-evolutionary potential in animal populations remains enigmatic. One prerequisite for cognitive flexibility to be able to evolve is consistent and heritable among-individual vari...

Mate choice is a key component of reproductive biology. Females often prefer certain males but do females modulate their reproductive investment depending on whether they are mated with their preferred partner? We investigated this question in great tits ( Parus major ) where we subjected 36 females to a six‐choice mate preference test. Male morpho...

The environment experienced during early life is a crucial factor in the life of many organisms. This early life environment has been shown to have profound effects on morphology, physiology and fitness. However, the molecular mechanisms that mediate these effects are largely unknown, even though they are essential for our understanding of the proc...

As environmental fluctuations are becoming more common, organisms need to rapidly adapt to anthropogenic, climatic, and ecological changes. Epigenetic modifications and DNA methylation in particular, provide organisms with a mechanism to shape their phenotypic responses during development. Studies suggest that environmentally induced DNA methylatio...

Animal personality, consistent individual differences in behaviour, is an important concept for understanding how individuals vary in how they cope with environmental challenges. In order to understand the evolutionary significance of animal personality, it is crucial to understand the underlying regulatory mechanisms. Epigenetic marks such as DNA...

Eavesdropping on interactions between conspecific animals provides a low‐cost method for assessing other individuals. Asymmetries in territorial counter‐singing interactions in songbirds provide a rich source of information for eavesdroppers about differences between the singers. Yet, little is known about the relationship between interactive singi...

Motor inhibition refers to the ability to inhibit immediate responses in favour of adaptive actions that are mediated by executive functions. This ability may be an indication of general cognitive ability in animals and is important for advanced cognitive functions. In this study, our aim was to compare motor inhibition ability of two closely relat...

Disentangling the interaction between the genetic basis and environmental context underlying phenotypic variation is critical for understanding organismal evolution. Environmental change, such as increased rates of urbanization, can induce shifts in phenotypic plasticity with some individuals adapting to city life while others are displaced. A key...

Intensive hunting activities such as commercial fishing and trophy hunting can have profound influences on natural populations. However, less intensive recreational hunting can also have subtle effects on animal behaviour, habitat use and movement, with implications for population persistence. Lekking species such as the black grouse (Lyrurus tetri...

Identifying the environmental drivers of variation in fitness‐related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness‐related trait values...

Territorial animals often respond less aggressively to neighbours than strangers. This ‘dear enemy’ effect is hypothesized to be adaptive by reducing unnecessary aggressive interactions with non-threatening individuals. A key prediction of this hypothesis, that individual fitness will be affected by variation in the speed and the extent to which in...

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species’ range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two co-familial Eur...

The field of molecular biology is advancing fast with new powerful technologies, sequencing methods and analysis software being developed constantly. Commonly used tools originally developed for research on humans and model species are now regularly used in ecological and evolutionary research. There is also a growing interest in the causes and con...

Territorial animals often use signals to advertise territorial occupancy within their larger home ranges. Songbirds are among the best-studied territorial signaling taxa, and when competitors start singing during a territorial intrusion, residents usually show elevated spatial and vocal responses. These responses could be used by intruders and dist...

Several reduced representation bisulfite sequencing methods have been developed in recent years to determine cytosine methylation de novo in non‐model species. Here, we present epiGBS2, a laboratory protocol based on epiGBS (Gurp et al., 2016) with a revised and user‐friendly bioinformatics pipeline for a wide range of species with or without a ref...

Globally increasing levels of artificial light at night (ALAN) are associated with shifting rhythms of behaviour in many wild species. However, it is unclear whether changes in behavioural timing are paralleled by consistent shifts in the molecular clock and its associated physiological pathways. Inconsistent shifts between behavioural and molecula...

Different bird species have completely different parent-offspring interactions. When food is plentiful, the chicks that are begging the loudest are fed the most. When food is scarce, bird species instead feed the largest offspring. While this variation could be due to parents responding to signalling differently based on food availability, it could...

The profiling of epigenetic marks like DNA methylation has become a central aspect of studies in evolution and ecology. Bisulfite sequencing is commonly used for assessing genome‐wide DNA methylation at single nucleotide resolution but these data can also provide information on genetic variants like single nucleotide polymorphisms (SNPs). However,...

Anthropogenic pollution is known to negatively influence an organism’s physiology, behaviour, and fitness. Epigenetic regulation, such as DNA methylation, has been hypothesized as a potential mechanism to mediate such effects, yet studies in wild species are lacking. We first investigated the effects of early-life exposure to the heavy metal lead (...

Significance A key question in behavioral ecology is whether individual differences in behavior are adaptive rather than merely representing “noise around an adaptive mean.” We show strong evidence for spatial and temporal variation in survival and recruitment selection both within and among West European great tit ( Parus major ) populations, impl...

Pollutants, such as toxic metals, negatively influence organismal health and performance, even leading to population collapses. Studies in model organisms have shown that epigenetic marks, such as DNA methylation, can be modulated by various environmental factors, including pollutants, influencing gene expression, and various organismal traits. Yet...

p>Observing interactions between others can provide important information to individuals. Male songbirds often engage in singing contests where they vary the type and timing of signals and provide eavesdropping individuals with information about their competitiveness. How this information is used and its effect on subsequent spatial behaviour and r...

Environmental change, such as increased rates of urbanization, can induce shifts in phenotypic plasticity with some individuals adapting to city life while others are displaced. A key trait that can facilitate adaptation is the degree at which animals respond to stress. This stress response has a heritable component and exhibits intra- and inter-in...

Territorial animals often exhibit the dear enemy effect, in which individuals respond less aggressively to neighbours than to other individuals. The dear enemy effect is hypothesized to be adaptive by reducing unnecessary aggressive interactions with individuals that are not a threat to territory ownership. A key prediction of this hypothesis, that...

Adapting to environmental change is a major challenge faced by animals and the role of individual behavioural differences in facilitating this process is currently the focus of much research. Innovation, the generation of a novel behaviour or use of a known behaviour in a novel context, is one form of behaviour that enables animals to respond to ch...

Early developmental conditions are known to have life-long effects on an individual’s behavior, physiology and fitness. In altricial birds, a majority of these conditions, such as the number of siblings and the amount of food provisioned, are controlled by the parents. This opens up the potential for parents to adjust the behavior and physiology of...

Species with a circannual life cycle need to match the timing of their life history events to the environment to maximize fitness. But our understanding of how circannual traits such as timing of reproduction are regulated on a molecular level remains limited. Recent studies have implicated that epigenetic mechanisms can be an important part in the...

Background DNA methylation is likely a key mechanism regulating changes in gene transcription in traits that show temporal fluctuations in response to environmental conditions. To understand the transcriptional role of DNA methylation we need simultaneous within-individual assessment of methylation changes and gene expression changes over time. Wit...

Globally increasing levels of artificial light at night (ALAN) are associated with shifts in circadian rhythms of behaviour in many wild species. However, it is still unclear whether changes in behavioural timing are underlined by parallel shifts in the molecular clock, and whether such internal shifts may differ between different tissues and physi...

Pollutants, like toxic metals, negatively influence organismal health and performance, even leading to population collapses. Studies in model organisms have shown that epigenetic marks, such as DNA methylation, can be modulated by various environmental factors, including pollutants, influencing gene expression and various organismal traits. Yet exp...

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long‐term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild...

Recently, a petition was offered to the European Commission calling for an immediate ban on animal testing. Although a Europe-wide moratorium on the use of animals in science is not yet possible, there has been a push by the non-scientific community and politicians for a rapid transition to animal-free innovations. Although there are benefits for b...

Synopsis The search for the hereditary mechanisms underlying quantitative traits traditionally focused on the identification of underlying genomic polymorphisms such as single-nucleotide polymorphisms. It has now become clear that epigenetic mechanisms, such as DNA methylation, can consistently alter gene expression over multiple generations. It is...

Quantifying the direction and strength of mate preference is essential to improve our understanding of sexual selection. Experimental designs, however, often do not consider how individuals evaluate and compare the available options, which may affect the results significantly. Preferences are often assumed to be absolute, with individuals assigning...

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild...

Recently, a petition was offered to the European Commission calling for an immediate ban on animal testing. Although a Europe-wide moratorium on the use of animals in science is not yet possible, there has been a push by the non-scientific community and politicians for a rapid transition to animal-free innovations. Although there are benefits for b...

epiGBS is an existing reduced representation bisulfite sequencing method to determine cytosine methylation and genetic polymorphisms de novo. Here, we present epiGBS2, an improved epiGBS laboratory protocol and user-friendly bioinformatics pipeline for a wide range of species with or without reference genome. epiGBS2 decreases costs and time invest...

Conspicuous male signals often play an important role in both attracting mates and deterring rivals. In territorial species with extrapair mating, female and male forays to other territories may be an important component underlying female choice and male mating success and might be influenced by male advertisement signals. Yet, whether off-territor...

Anthropogenic noise levels are globally rising with profound impacts on ecosystems and the species that live in them. Masking or distraction by noise can interfere with relevant sounds and thereby impact ecological interactions between individuals of the same or different species. Predator-prey dynamics are particularly likely to be influenced by r...

Climate change significantly impacts natural populations, particularly phenology traits, like the seasonal onset of reproduction in birds. This impact is mainly via plastic responses in phenology traits to changes in the environment, but the molecular mechanism mediating this plasticity remains elusive. Epigenetic modifications can mediate plastici...

Anthropogenic pollution is known to negatively influence an organism's physiology, behavior and fitness. Epigenetic regulation, such as DNA methylation, has been hypothesized as one mechanism to mediate such effects, yet studies in wild species are lacking. We first investigated the effects of early-life exposure to the heavy metal lead (Pb) on DNA...

Background: Seasonal timing of breeding is a life history trait with major fitness consequences but the genetic basis of the physiological mechanism underlying it, and how gene expression is affected by date and temperature, is not well known. In order to study this, we measured patterns of gene expression over different time points in three diffe...

The timing of breeding is under selection in wild populations as a result of climate change, and understanding the underlying physiological processes mediating this timing provides insight into the potential rate of adaptation. Current knowledge on this variation in physiology is, however, mostly limited to males. We assessed whether individual dif...

Animal personality traits are often heritable and plastic at the same time. Indeed, behaviors that reflect an individual's personality can respond to environmental factors or change with age. To date, little is known regarding personality changes during a wild animals' lifetime and even less about stability in heritability of behavior across ages....

Seasonal timing of reproduction is an important fitness trait in many plants and animals but the underlying molecular mechanism for this trait is poorly known. DNA methylation is known to affect timing of reproduction in various organisms and is therefore a potential mechanism also in birds. Here we describe genome wide data aiming to detect tempor...

Epigenetic mechanisms can alter gene expression without a change in the nucleotide sequence and are increasingly recognized as important mechanisms that can generate phenotypic diversity. Most of our current knowledge regarding the origin and role of epigenetic variation comes from research on plants or mammals, often in controlled rearing conditio...

Background: Birdsong, a key model in animal communication studies, has been the focus of intensive research. Song traits are commonly considered to reflect differences in individual or territory quality. Yet, few studies have quantified the variability of song traits between versus within individuals (i.e. repeatability), and thus whether certain...

The physiological mechanisms underlying avian seasonal timing of reproduction, a life‐history trait with major fitness consequences, are not well understood. Comparing individuals that have been selected to differ in their timing of breeding may prove to be a promising in studying these mechanisms, making selection lines a valuable tool. We created...

Chromosome inversions have clear effects on genome evolution and have been associated with speciation, adaptation and the evolution of the sex chromosomes. In birds, these inversions may play an important role in hybridization of species and disassortative mating. We identified a large (≈64 Mb) inversion polymorphism in the great tit (Parus major)...

Circadian rhythms are ubiquitous among taxa and are essential for coping with recurrent daily events, leading to selection on the properties of the clock underlying these rhythms. To quantify this selection in the wild, we need, however, to phenotype wild individuals, which is difficult using the standard laboratory approach for which individuals n...

Seasonal timing of reproduction is a key life-history trait, but we know little about the mechanisms underlying individual variation in female endocrine profiles associated with reproduction. In birds, 17β-oestradiol is a key reproductive hormone that links brain neuroendocrine mechanisms, involved in information processing and decision-making, to...

Inferring adaptation and evolutionary change by combining data from field studies and genomics is an exciting new area in evolutionary biology but also presents challenges. These challenges are particularly acute when the focal trait has a polygenic architecture, because many long‐term field studies are sample‐size‐limited compared to studies of hu...

Gathering information about the environment, such as the location and quality of food, is crucial for an animal's survival, particularly in a changing environment. An animal can collect 'personal information' by interacting with the environment itself, or it can collect 'social information' by observing the behaviour of others. The use of these two...

In seasonal environments, timing of reproduction is a trait with important fitness consequences, but we know little about the molecular mechanisms that underlie the variation in this trait. Recently, several studies put forward DNA methylation as a mechanism regulating seasonal timing of reproduction in both plants and animals. To understand the in...

A major aim of evolutionary biology is to understand why patterns of genomic variation vary among populations and species. Large-scale genomic studies of widespread species are useful for studying how the environment and demographic history shape patterns of genomic divergence, and with the continually decreasing cost of sequencing, such studies ar...

Background A widely used approach in next-generation sequencing projects is the alignment of reads to a reference genome. Despite methodological and hardware improvements which have enhanced the efficiency and accuracy of alignments, a significant percentage of reads frequently remain unmapped. Usually, unmapped reads are discarded from the analysi...

Background: A widely used approach in next-generation sequencing projects is the alignment of reads to a reference genome. A significant percentage of reads, however, frequently remain unmapped despite improvements in the methods and hardware, which have enhanced the efficiency and accuracy of alignments. Usually unmapped reads are discarded from t...

Artificial light at night (ALAN) is increasingly recognized as a potential threat to wildlife and ecosystem health. Among the ecological effects of ALAN, changes in reproductive timing are frequently reported, but the mechanisms underlying this relationship are still poorly understood. Here, we experimentally investigated these mechanisms by assess...

Understanding the causes and consequences of population phenotypic divergence is a central goal in ecology and evolution. Phenotypic divergence among populations can result from genetic divergence, phenotypic plasticity or a combination of the two. However, few studies have deciphered these mechanisms for populations geographically close and connec...

Wind is an important abiotic factor that influences an array of biological processes, but it is rarely considered in studies on plant–herbivore interactions. Here, we tested whether wind exposure could directly or indirectly affect the performance of two insect herbivores, Plutella xylostella and Pieris brassicae , feeding on Brassica nigra plants....

High density SNP microarrays (‘SNP chips’) are a rapid, accurate and efficient method for genotyping several hundred thousand polymorphisms in large numbers of individuals. While SNP chips are routinely used in human genetics and in animal and plant breeding, they are less widely used in evolutionary and ecological research. In this paper we descri...

Background: Understanding variation in genome structure is essential to understand phenotypic differences within populations and the evolutionary history of species. A promising form of this structural variation is copy number variation (CNV). CNVs can be generated by different recombination mechanisms, such as non-allelic homologous recombination...