Title Promoter Affiliations Abstract "Testing big evolutionary hypotheses with small organisms" "Yves Van de Peer" "Department of Plant Biotechnology and Bioinformatics" "Polyploids, organisms that underwent a whole genome duplication (WGD), possess one extra copy of their genome, which is free to evolve new functionality. Many WGDs are accordingly found in very successful eukaryotic lineages characterized by particular biological innovations and/or diversifications. However, the possession of two complete genomes is generally not well tolerated by cells leading to harmful effects on the overall fitness and fertility of the organism. This results in a paradox between the observed immediate negative effects of WGD, and their attributed longterm positive effects. In previous work, we found that many plant polyploids became established during the last mass extinction event. Present-day polyploids are also more abundant in stressful environments such as the Arctic. We therefore hypothesize that stress can enhance polyploid establishment, because their plastic phenotypes and genotypes can enable rapid adaptive changes that allow survival. To test this hypothesis, we propose an evolutionary experiment based on a unicellular green algal model system. First, we will artificially create polyploid strains and subject them to a wide variety of stressors to quantify their survival. Second, we will select the most successful polyploid populations and sequence their complete genomes every few generations to identify the genomic features that allow their success. Such an experiment will significantly contribute to our understanding of polyploid organisms." "Testing viral evolutionary hypotheses using Bayesian phylogenetic inference and visualization." "Philippe Lemey" "Laboratory of Clinical and Epidemiological Virology (Rega Institute)" "In this project, I propose to work on state-of-the-art Bayesian phylogenetic inference and visualisation techniques to investigate the phylodynamics of pathogens.Specifically, I will advance a model to capture how evolutionary processes change through time by implementing the capability to incorporate and test covariates. I will design a stochastic modeling approach with associated inference machinery to detect variation in natural selection dynamics throughout evolutionary history. Both approaches will be implemented in a dedicated software package and will be supported by massively parallel computations on specialized devices. Finally, I will generalize the visualization of spatiotemporal history to any trait of interest resulting from such analyses and support flexible, interactive visualizations." "Separation, identity and intimacy during adolescence and emerging adulthood: Prospective testing of epigenetic hypotheses" "Department of Developmental, Personality and Social Psychology" "Separation-individuation theory (Blos, 1967) and EriksonU+2019s (1968) lifespan developmental theory claim that the developmental tasks of separation, identity and intimacy follow each other in a sequential order during adolescence and emerging adulthood. Using new conceptualizations and longitudinal research with adolescents aged 15 to 22 years, this research project prospectively tests the central hypotheses (phasing and conditionality) of this epigenetic principle." "Separation, identity and intimacy during adolescence and emerging adulthood: Prospective testing of epigenetic hyptheses" "Separation-individuation theory (Blos, 1967) and Erikson's (1968) lifespan developmental theory claim that the developmental taks of separation, identity and intimacy follow each other in a sequential order during adolescence and emerging adulthood. Using new conceptualizations and longitudinal resesarch with adolescents aged 15 to 22 years, this research project prospectively tests the central hypotheses (phasing and conditionality) of this epigentic principle." "Orchids and dandelions: Meta-analytic and empirical tests of the differential susceptibility hypothesis" "Ivan Mervielde" "Department of Developmental, Personality and Social Psychology" "This project combines meta-analytical and empirical research to purport a more comprehensive test of the differential susceptibility hypothesis, postulating that children vary in their temperamental sensitivity to environmental influences, such as parenting." "Reproducibility, robustness, and test severity: New insights for research workers in psychology" "Wolf Vanpaemel" "Quantitative Psychology and Individual Differences" "This dissertation provides new insights into three paramount topics of psychological research: reproducibility, robustness, and severity.A statistical result is reproducible if independent researchers with adequate skills can verify its correctness through the identification and execution of the underlying calculations on the same dataset. Lacking a culture of data sharing and re-analysis very little is known in the field of psychology about the amount of reporting errors in scientific publications nor the amount of effort it takes to verify other researchers' empirical work. To shed light on this topic, Chapter 1 reports on the results of a comprehensive study that investigated the reproducibility of the major statistical conclusions drawn in 46 papers published in 2012 in three APA journals. Through an in-depth analysis of our reproduction efforts and the types of mistakes found, we develop a new taxonomy for reproducibility, give practical recommendations on how to achieve reproducibility, and discuss the challenges of large-scale reproducibility checks as well as promising ideas that could considerably increase the reproducibility of psychological research.Preferably, statistical findings are not just reproducible but also robust with respect to reasonable alternative data analyses. To assess the robustness of an empirical finding, Simonsohn et al. (2020) proposed specification curve analysis (SCA), a creative statistical method that combines the inferences of all reasonable and feasible ways to analyze a set of raw data with respect to some scientific hypothesis. In Chapter 2, we first reiterate the essentials of this method and discuss theoretical issues. Afterwards, we show through extensive simulations that the SCA procedure often produces invalid p-values. Furthermore, we find that simpler alternatives outperform the SCA procedure in all studied scenarios.Chapter 3 is the serendipitous result of a research project that required to simulate data from models that are specified via partial correlation structures. In this chapter, we derive necessary and sufficient conditions for the eigenvalues of differently defined partial correlation matrices so that the correlation structure is a valid one. Equipped with these conditions, we derive simple conditions on the partial correlations for frequently assumed sparse structures. Further, we show that valid partial correlation matrices can be created via a simple formula that can be used in conjunction with existing algorithms for the generation and approximation of correlation matrices.Having found reproducible and robust empirical patterns, psychological researchers often want to know what this implies for the scientific hypothesis of interest. From a Popperian perspective, the corroboration status of a scientific hypothesis should be changed to the extent that it was able to pass a severe test, that is, to the extent that it was used to correctly predict something risky. In Chapter 4, we propose a data-driven method that allows the quantification of the riskiness of an empirical prediction that was derived from a substantive hypothesis of interest. We demonstrate this approach with an empirical investigation on the relation between watching TV in early childhood and later inability to concentrate well." "The use of river valleys by prehistoric hunter-gatherers: a study in the eastern Flemish Valley." "Philip Van Peer" "Archaeology, Leuven" "River valleys and basins have played a primordial role in the ecology of prehistoric huntergatherers, from their earliest Palaeolithic appearance to the last nomadic groups of the Holocene. Regional distribution maps unvariably show the close association of human occupations and hydrographic features. Obviously, the latter were important in huntergatherer subsistence but they may also have functioned as demographic corridors or sink/source refuges (Finlayson 2013). The aim of the project, essentially designed as a fieldwork project in the Flemish Valley, is twofold. First, and most of all, it intends to contribute to a better general understanding of the role of wetlands in the settlement systems of hunter-gatherers in northwestern Europe. Second, it wants to start building the empirical base to eventually test the far reaching hypothesis that the Flemish Valley of coastal Belgium was a demographic refuge for Neanderthal groups during the contact period with modern humans. While the present evidence to even remotely support this idea is extremely thin indeed, there are some observations to suggest that as a research hypothesis, it is not premature. Given the completely random character of archaeological surveys for Pleistocene sites so far, the number of Middle Palaeolithic findspots here is surprisingly high. Most of these locations are situated along the southern fringe of the Valley, adjacent to the limestone regions of the Meuse basin and northern France (Locht and Depaepe 2011) with their wellestablished Middle Palaeolithic occupations. Stratigraphic observations are almost nonexistent but, very prudently, it would seem that they mostly belong to the Hengelo interstadial. Thinking further in terms of demographic corridors on a latitudinal gradient, according to the rhythm of Pleistocene climatic variation, the Flemish Valley with its very distinct morphology may have been an attractive area for settlement. The Flemish Valley (Tavernier and De Moor 1974) is a ~2000 km² depression in northern Belgium that was eroded during the Saale glaciation. It has a large eastern tributary valley (the Eastern Branch) in which the present rivers Zenne and Demer flow. The Valley contains a deep sequence of Upper Pleistocene sediments, with basal peats of Eemian age around its fringes. The few recorded sections that exist indicate that this is a high resolution geo-archive at least for certain episodes during the Upper Pleistocene. Yet, there has never been an attempt at systematic survey for sites in stratigraphic context even if stone tools and probably associated faunal remains have shown up whenever quarry activities were carried out. Only in very recent times, on the occasion of the extension of the Antwerp port, primary context Mesolithic site clusters in the central part of the Valley have begun to be investigated (Crombé 2005). As far as knowledge of the Valley’s Pleistocene occupation history is concerned, the only evidence so far available are small out-of-context lithic assemblages randomly collected by amateur archaeologists. The project proposes to set up a program of systematic field research in the Eastern Branch. Two portions of the present Demer basin are selected, in function of the two research questions mentioned above. The first is located upstream in the large plain of Halen-Schulen, the southeastern entrance to the Valley. At the site of Stevoort-Kanenveld, my research group has carried out a preliminary heritage project. It appears that this is a stratified Holocene site with several occupation levels ranging from Mesolithic into the Bronze Age, the first of its kind in the Eastern Branch. Pollen records from deep peat deposits that can be tied into the site stratigraphy show the effects of the 9,3 and 8,2 ka climatic downturns. Large scale excavations are imperative. The high resolution record preserved here will inform us on the function of alluvial plains in the settlement system of postglacial hunter-gatherers and their possible responses to such climatic events. The second research area, the Lower Demer valley between the city of Aarschot and the confluence with the river Dyle, is chosen in function of the Flemish Valley refuge hypothesis. In its present lower course the Demer is an incising meandering river due to the upstream existence of the Halen-Schulen plain mentioned above (De Smedt 1973). In that large floodplain the Demer deposits most of its sediment load allowing it to incise downstream. Whether there is a causal relationship to this specific geomorphology is at present unclear, but the Lower Demer valley is especially rich in prehistoric sites, including a number of Middle Palaeolithic findspots. Therefore, it is ideally suited to start a systematic survey of Middle Palaeolithic regional site distributions. Our aim is to locate primary context locales by means of an extensive and systematic deep sounding survey with a mechanical auger. Making use of the detailed geomorphological mapping of the Lower Demer Valley (De Smedt 1973) we shall single out zones where older Pleistocene terraces are preserved. There are indications that sites are associated with these terraces while Upper Pleistocene sediment covers are comparatively thin here. Thus, they should be within survey reach. Obviously, a full test of the refuge hypothesis would require an effort at a scale that largely transgresses the capacity of a 4yr project. Within the latter, our aim is to provide the first elements of solid empirical evidence, both in terms of data density and chronological resolution, that will ultimately allow to resolve a historic question of large importance for our understanding of recent human evolution." "Delay Aversion in Adolescent Attention Deficit/Hyperactivity Disorder: Refining the Brain Endophenotype." "Marina Danckaerts" "Developmental Psychiatry, Orthodontics, Clinical Psychology" "Attention Deficit/Hyperactivity Disorder is a common mental disorder of childhood with a poor prognosis, if not treated effectively. The current application focuses on delay aversion (DAv), an important altered motivational process in individuals with ADHD. Extensive behavioural evidence exists, supporting the DAv hypothesis as one important marker explaining ADHD individuals preference for small immediate rewards over larger delayed rewards. Within contemporary heterogeneic neuropsychological models of ADHD, DAv may represent one neurodevelopmental pathway explaining a substantial proportion of symptom variation. The neurobiological studies of this pathway in ADHD, so far, have mainly focused on altered brain responses to rewards, rather than to the anticipation or experience of delay as such. We recently published compelling results of a pilot study, applying functional neuro-imaging during an experimental task, developed in collaboration with Sonuga-Barke (who first formulated the DAv hypothesis) to index the motivational significance of DAv (i.e. the motivation to escape delay as a driver of an impulsive choice): the Escape Delay Incentive (EDI) task. In a small sample, we visualized brain activation effects for the impact of cues signaling inescapable delay and the opportunity to escape delay, independent from (monetary) reward cues, producing hyperactivation in brain regions sensitive to negative motivational affect (amygdala and insula) on trials with inescapable delay as opposed to escapable delay in the ADHD subjects compared to controls. The proposed three studies of the current project envisage to study the brain signature of DAv extensively. In study 1, we will add a control condition to the EDI and impose different levels of delay within the task. This will allow to dissociate the neural signature of reinforcing effects of delay escape and the punishing effects of delay imposition from each other and to establish a delay dose response curve. In study 2 we will contrast cues predicting various modes of delay to cues predicting modes of monetary rewards, in order to test the specificity of the neural delay activation pattern. Study 3 will investigate the neural processing of delay aversion and executive functioning in ADHD subjects by contrasting the EDI with a commonly used task shown to activate more dorsal executive networks (the Stop Signal Task of inhibitory control), thereby testing the dual pathway hypothesis. We hypothesize that these neural activation pathways will be dissociable from one another and that the separate neural activations will be correlated with performance on delay and executive function-related behavioural paradigms outside the scanner. Through these experiments we expect to provide a fundamental basis to the DAv dysfunction and to the dual pathway model in ADHD. Such fundamental understanding of the pathogenesis of ADHD will stimulate the development of targeted innovative treatments for this challenging disorder." "Measuring and Modelling Hydrological Surface Connectivity" "Guido Wyseure" "Division of Soil and Water Management, Division of Geography and Tourism" "Hydrological connectivity describes the internal linkages between runoff generation in upper parts of the catchment and the receiving water. It is quantified as the ratio of the runoff reaching the catchments outlet and the total internal runoff generation. It thus effectively bridges the gap between the point-scale separation of rainfall into soil water storage and (sub-)surface runoff as opposed to what we see as response at the hillslope or catchment scale. In between both, significant water redistribution from runoff source areas into sinks may occur such that isolated active areas in upslope regions may become disconnected and may not contribute to the actual outflow. This pattern-process interaction is one of the main reasons why hydrological observations at laboratory or plot scale are inadequate to explain the phenomena witnessed on hillslopes and in catchments and is why hydrological connectivity has become, in the last decade, a central concept in hydrology, particularly in semi-arid environments. The overall purpose of this dissertation is to identify which factors control the connectivity of a hillslope and to discuss how this reflects on data collection and modelling.While traditionally hydrological variables are estimated through point observations dynamically varying in time, connectivity stresses the need to also account for space. It is the spatiotemporal heterogeneity in infiltration capacity and rainfall intensity that determines connectivity or disconnectivity with complex and spatially varying thresholds governing which parts of the domain are active and which contributing and which dominant processes affect storage, redistribution and connectivity. Once established that it is the spatial pattern of heterogeneous runoff generation and abstraction and not merely the statistical distribution of this heterogeneity, we ask ourselves which aspects of pattern determine the connectivity and which are negligible. We test a number of hypotheses by opposing landscape metrics with the modelled hydrograph of a virtual hillslope. Each metric describes a different characteristic of the pattern and their variable correlation with connectivity can thus supply an objective criterion to ascertain what controls connectivity. The aggregation of runoff source areas in interaction with the flow distance to the outlet dominate in the presence of a mosaic of runoff sinks and sources. When the area reacts more homogeneous, e.g. due to high rainfall intensity, the pattern disappears and it becomes mainly the travel time distribution that governs connectivity. While the used landscape metrics could only partially predict the connectivity, they are insightful tools for hypothesis testing and, we believe, can reversely be used in basin classification and the identification of dominant processes. If we establish a link between a certain metric and a particular basin functioning, we may also decide upon a range of values of that metric that a basin should fulfil in order to be classified in a particular class.We propose randomness of pattern as an important characteristic of heterogeneity to distinguish two classes: when the heterogeneity is random, its particular configuration becomes superfluous and only the statistical distribution of its properties remains of interest. If, on the other hand, the heterogeneity expresses clear spatial configuration or gradients, accounting for this configuration is indispensible. This has important implications for modelling as well as for data collection. If the particular spatial configuration has no influence on the outcome, it also does not need to be explicitly modelled. The degrees of freedom of the model can therefore be reduced to a smaller number of parameters that set the statistical distribution rather than having one uncorrelated parameter for each spatial element in the modelling space which would clearly lead to the problem of equifinality. If we can only parameterise those spatial aspects that matter, we effectively reduce the overparamaterisation that plagues modern distributed modelling. As for data collection: since the exact spatial configuration of random patterns is redundant knowledge, a sparse data collection that settles the statistical distribution of heterogeneity suffices in that case; while in the presence of significant configuration, data sampling strategies should be tailored to capture the spatial patterns.If we want to gain a better understanding of processes, we need to build models that can test hypotheses and collect data that allows to falsify the hypotheses. Both the reconfirmation of space as a crucial dimension beside time and the observation that non-random pattern matters, emphasises the need in connectivity related problems for data that can sample dense spatial variations in hydrological state variables and processes. We explore a combination of Electrical Resistivity Tomography (ERT) and Time Domain Reflectometry (TDR): ERT samples spatial averages and can be translated to a dense 3D resistivity distribution. TDR, on the other hand, is a point-scale measurement and is used to supply a transformation between resistivity and water content, the so-called pedophysical relation. By collecting data both before and after a concentrated flow experiment in a semi-arid gully, we map the total infiltration that occurred by taking the difference between the estimated water distributions before and after. The straightforward three-step scheme (ERT inversion, transformation to water content, subtraction) returns, however, an invalid solution. To improve the outcome, we developed an alternative inversion that constrains the outcome to comply to our knowledge of the experiment and that jointly inverses ERT and TDR while optimising the pedophysical parameters. Although these alterations effect significant improvements, the signal-to-noise ration in the data and the poor resolution of the outcome undermine the reliability of the obtained infiltration map. We were therefore unable to utilise it in further hypothesis testing or modelling. Nonetheless, we believe that ERT and TDR sampling in combination with our proposed inversion scheme can potentially give insightful results." "Essays on household behavior in the mortgage market and house price dynamics." "Erik Buyst" "Research Centre of Economic History, Leuven, Department of Economics, Leuven" "The housing market depends critically on credit market conditions and the link between housing and credit has recently attracted considerable interest in empirical papers. The strong interlinkage between both markets raises numerous question: How do borrowers choose between different mortgage products?  How do households make reinvestment decision for their largest single component of household wealth? How are housing and mortgage markets interlinked? What are long-run fundamentals in house prices? In this dissertation we study these household choices on the housing and mortgage market and the resulting market outcomes. We now briefly summarize the research in the different chapters.Even after the crisis, house prices are overvalued according to price-to-income ratios in many countries. As unsustainable house prices may raise concerns about financial stability, it is important to understand the factors behind the evolution of house prices. In the first chapter, we introduce the borrower’s ability to pay (ATP) as a new long-run house price fundamental. ATP represents the borrowing capacity of a household, given a fixed fraction of income that goes to mortgage payments. An important contribution is that ATP also incorporates specific mortgage characteristics and the mortgage interest deduction (MID). Therefore, ATP takes into account the effect of changes in interest rates, fiscal rules and mortgage product innovation.We apply the model to the United States of America, United Kingdom, Belgium, the Netherlands, Sweden, Norway, Finland and Denmark. Conventional and panel cointegration tests indicate that house prices and our measure of ATP adjusted for the MID and mortgage characteristics are cointegrated in a statistically significant fraction of the countries. When the mortgage product innovations and the MID are excluded from the measure of ATP, the null hypothesis of no cointegration in all countries is not rejected. This confirms our hypothesis that it is necessary to model the changes in mortgage characteristics and tax rules.  Other evidence indicates that the elasticity of house prices with respect to changes in ATP is close to one and Granger-causality tests indicate that the measure of ATP Granger causes house prices. Evidence in the other direction is much weaker. Finally, we test the ATP model against more conventional user cost models and find evidence that the speed-of-adjustment from disequilibrium is faster in the ATP model. Therefore, the ATP framework provides an intuitive alternative to standard house price models. As the first chapter indicates that mortgage characteristics have important implications for house price evolutions, we study the mortgage choices that individuals make in the subsequent chapters. In the second chapter, we study the choice between fixed rate mortgages (FRM) and adjustable rate mortgages (ARM) using data from Belgium and its Flemish region. For many households, the choice between fixed and adjustable rate mortgages is probably the most important choice with respect to the mortgage contract. In the aggregate, the individual mortgage choices have important policy implications for the transmission mechanism of monetary policy through the effect of mortgage payments on household budgets. The dominant share of adjustable rate mortgages in the UK was mentioned as an important reason by the United Kingdom’s economics and finance ministry (HM Treasury 2003a, 2003b) for opting out in the third stage of the Economic Monetary Union to introduce the euro.Notwithstanding the different ways monetary policy shocks are propagated, there still remains large cross-country variation in mortgage shares within the Eurozone. Whereas the variation in market share over time is small in most countries, the structure of the Belgian mortgage market varied significantly during the last decade. In this paper we seek to understand this variation in the mortgage structure over time. The results indicate that households base their decision on initial mortgage payments and do not consider expected changes in ARM rates. This results in a remarkable large variation in mortgage structure over time in comparison to other countries. Borrowers who expect to move in the near future are more likely to choose the FRM. As all mortgages are portable by law, mobile borrowers prefer to reduce variability in mortgage payments, which was not observed in previous empirical studies. Survey evidence suggests that many American and European consumers do not spend a lot of time comparing mortgage products. Indeed, many American consumers spend the same amount of time choosing where they want to go on vacation and more time researching the next car they want to buy (Finkelstein, 2010). In Europe, mortgage shopping does not appear to be fun either. Survey evidence from the Eurobarometer suggests that 21 percent of respondents in the 27 member states of the European Union did not compare mortgage products and took the first mortgage that they looked at.In the third chapter we show, however, that mortgage shopping is associated with a substantial monetary payoff. Therefore, we bring a unique dataset in the discussion from a website where borrowers (not the lenders) can post their complete set of received mortgage rate offers. A borrower who shops for 5 mortgage offers, is able to save 7000 euro in net present value on average. The results indicate that the decision to continue shopping is not much affected by the savings from mortgage shopping, but rather by the time spent comparing prices. Indeed, the time spent between the first and fifth offer is only 13 days for the median borrower. The potential savings suggest sub-optimal mortgage shopping as the opportunity cost of time to renegotiate additional quotes is unlikely to be that high.In the fourth chapter we study how the interaction between house prices and mortgage debt may influence reinvestment and mobility decisions. The severe drop in US house prices in 2006-2007, led to a large increase in the number of households facing an outstanding mortgage debt that exceeded the value of their house. The increase in negative equity has increased concern that underwater households are less mobile and decrease housing reinvestment. The large costs associated with the reinvestment and move decisions urge households to consider future expectations. Although this forward-looking behavior may affect reinvestment and mobility decisions, previous studies have often ignored to take them into account. Therefore, we bridge the gap between the reinvestment, mobility and dynamic literature and estimate a dynamic discrete choice model in which an owner-occupier can either reinvest, move or do nothing. Our findings indicate that negative equity reduces reinvestment and mobility among young households, but not among senior citizens. Furthermore, negative equity decreases reinvestment in non-recourse states, but not in recourse states. "