Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The gender wage gap among China’s rural–urban migrants
    Wu, Yan ; Pieters, Janneke ; Heerink, Nico - \ 2020
    Review of Development Economics (2020). - ISSN 1363-6669
    China - gender wage gap - migration

    In this study, we present new empirical evidence on gender wage differences among rural–urban migrants in China. We use a data set that includes migrants residing in urban communities and those living at their workplaces—the latter were not included in the previous studies. We find that the gender wage gap among migrants is 16%–18% and does not differ between migrants living at workplaces and those living in urban communities. However, gender differences in industry sorting play a more important role for migrants living at their workplaces, whereas differences in education and experience are of importance for those living in urban communities. Overall, differences in the returns to characteristics are the main driver of the gender wage gap, especially for migrants living in urban communities.

    Randomization for women's economic empowerment? Lessons and limitations of randomized experiments
    Pieters, Janneke ; Klasen, Stephan - \ 2020
    World Development 127 (2020). - ISSN 0305-750X

    Worldwide, policy-makers and academics alike are searching for ways to enhance women's economic empowerment. One important route to economic empowerment – paid employment – still shows wide gender disparities. We discuss some lessons from randomized evaluations of microfinance, business training, and other interventions aimed at increasing women's employment and earnings. We then point at important barriers related to women's responsibility for childcare and domestic duties as well as other social norms. To improve policies for gender equality, we need to understand how norms affect women's labor market entry and trajectories, what works to mitigate their impact, and how they can change. We argue that RCTs can help us find answers, but that we also need to keep studying macroeconomic changes, non-randomized development and gender policy interventions, and large-scale micro-level panel data capturing employment dynamics.

    Parental unemployment and child health in China
    Pieters, Janneke ; Rawlings, Samantha - \ 2020
    Review of Economics of the Household 18 (2020)1. - ISSN 1569-5239 - p. 207 - 237.
    Child Health - China - Nutrition - Unemployment

    This paper studies the causal effect of maternal and paternal unemployment on child health in China, analyzing panel data for the period 1997–2004, when the country underwent economic reforms leading to massive layoffs. Using a FE-IV strategy, we find that paternal unemployment reduces child health, while maternal unemployment has beneficial child health impacts. Analysis of channels shows that paternal and maternal unemployment have different effects on income, time use, and children’s diets. Though many estimates are imprecise, a key finding is that paternal unemployment significantly reduces children’s fat intake and dietary diversity. To the best of our knowledge, this is the first evidence on the causal effect of parental unemployment on the nutrient intake of children aged 0–17. In all, our estimates are consistent with the notion that traditional gender roles can explain why mothers’ and fathers’ unemployment affect child health differently.

    Incentives and the Diffusion of Agricultural Knowledge: Experimental Evidence from Northern Uganda
    Shikuku, Kelvin Mashisia ; Pieters, Janneke ; Bulte, Erwin ; Läderach, Peter - \ 2019
    American Journal of Agricultural Economics 101 (2019)4. - ISSN 0002-9092 - p. 1164 - 1180.
    We present results of a randomized evaluation that assesses the effects of different incentives for diffusion of agricultural knowledge by smallholders in northern Uganda. Randomly‐selected disseminating farmers (DFs) from a large sample of villages are assigned to one of three experimental arms: (a) training about climate smart agriculture, (b) training plus a material reward for knowledge diffusion, and (c) training plus a reputational gain for knowledge diffusion. We find that leveraging somebody's reputation (or social recognition) has a positive impact on DFs' experimentation and diffusion effort. This impact is stronger than that measured in the private material rewards treatment.
    WUR: Too Good To Go is effectief instrument tegen voedselverspilling
    Stroosnijder, Sanne ; Haar, Sandra van der; Zeinstra, Gertrude ; Timmermans, Toine - \ 2019
    Visualizing trypanosomes in a vertebrate host reveals novel swimming behaviours, adaptations and attachment mechanisms
    Dóró, Éva ; Jacobs, Sem H. ; Hammond, Ffion R. ; Schipper, Henk ; Pieters, Remco P.M. ; Carrington, Mark ; Wiegertjes, Geert F. ; Forlenza, Maria - \ 2019
    eLife 8 (2019). - ISSN 2050-084X
    host-pathogen interaction - infectious disease - microbiology - swimming behavior - Trypanosoma carassii - zebrafish

    Trypanosomes are important disease agents of humans, livestock and cold-blooded species, including fish. The cellular morphology of trypanosomes is central to their motility, adaptation to the host's environments and pathogenesis. However, visualizing the behaviour of trypanosomes resident in a live vertebrate host has remained unexplored. In this study, we describe an infection model of zebrafish (Danio rerio) with Trypanosoma carassii. By combining high spatio-temporal resolution microscopy with the transparency of live zebrafish, we describe in detail the swimming behaviour of trypanosomes in blood and tissues of a vertebrate host. Besides the conventional tumbling and directional swimming, T. carassii can change direction through a 'whip-like' motion or by swimming backward. Further, the posterior end can act as an anchoring site in vivo. To our knowledge, this is the first report of a vertebrate infection model that allows detailed imaging of trypanosome swimming behaviour in vivo in a natural host environment.

    Credit, insurance and farmers’ liability: Evidence from a lab in the field experiment with coffee farmers in Costa Rica
    Naranjo, María A. ; Pieters, Janneke ; Alpízar, Francisco - \ 2019
    Journal of Economic Behavior and Organization 166 (2019). - ISSN 0167-2681 - p. 12 - 27.
    Agriculture - Credit - Insurance - Liability

    This paper examines the effect of farmers’ liability on demand for credit with and without insurance. We test predictions of a theoretical model in a lab in the field experiment with coffee farmers in Costa Rica. Farmers choose how much to invest in six different settings, described on the one hand by whether the loan is insured or not, and on the other by their liability. Our results show that the uptake of loans bundled with insurance is significantly higher than the uptake of loans without insurance, when farmers are liable for sure, and when there is uncertainty about their liability. In the case of limited liability, the uptake of credit is high irrespective of whether the loans are insured or not. Our results suggest that in order to increase the uptake of insurance as a strategy to increase private investment and reduce the vulnerability of farmers to shocks, it is important that farmers are liable with at least some probability.

    Data from: Reorientation and propulsion in fast-starting zebrafish larvae: an inverse dynamics analysis
    Voesenek, C.J. ; Pieters, R.P.M. ; Muijres, F.T. ; Leeuwen, J.L. van - \ 2019
    3D motion tracking - C-start - escape response - kinematics - larval fish - swimming performance - Danio rerio
    Most fish species use fast starts to escape from predators. Zebrafish larvae perform effective fast starts immediately after hatching. They use a C-start, where the body curls into a C-shape, and then unfolds to accelerate. These escape responses need to fulfil a number of functional demands, under the constraints of the fluid environment and the larva's body shape. Primarily, the larvae need to generate sufficient escape speed in a wide range of possible directions, in a short-enough time. In this study, we examined how the larvae meet these demands. We filmed fast starts of zebrafish larvae with a unique five-camera setup with high spatiotemporal resolution. From these videos, we reconstructed the three-dimensional swimming motion with an automated method and from these data calculated resultant hydrodynamic forces and, for the first time, 3D torques. We show that zebrafish larvae reorient mostly in the first stage of the start by producing a strong yaw torque, often without using the pectoral fins. This reorientation is expressed as the body angle, a measure that represents the rotation of the complete body, rather than the commonly used head angle. The fish accelerates its centre of mass mostly in stage 2 by generating a considerable force peak while the fish "unfolds". The escape direction of the fish correlates strongly with the amount of body curvature in stage 1, while the escape speed correlates strongly with the duration of the start. This may allow the fish to independently control the direction and speed of the escape.
    Reorientation and propulsion in fast-starting zebrafish larvae: an inverse dynamics analysis
    Voesenek, Cees J. ; Pieters, Remco P.M. ; Muijres, Florian T. ; Leeuwen, Johan L. van - \ 2019
    Journal of Experimental Biology 222 (2019)14. - ISSN 0022-0949
    Most fish species use fast starts to escape from predators. Zebrafish larvae perform effective fast starts immediately after hatching. They use a C-start, where the body curls into a C-shape, and then unfolds to accelerate. These escape responses need to fulfil a number of functional demands, under the constraints of the fluid environment and the larva's body shape. Primarily, the larvae need to generate sufficient escape speed in a wide range of possible directions, in a short-enough time. In this study, we examined how the larvae meet these demands. We filmed fast starts of zebrafish larvae with a unique five-camera setup with high spatiotemporal resolution. From these videos, we reconstructed the 3D swimming motion with an automated method and from these data calculated resultant hydrodynamic forces and, for the first time, 3D torques. We show that zebrafish larvae reorient mostly in the first stage of the start by producing a strong yaw torque, often without using the pectoral fins. This reorientation is expressed as the body angle, a measure that represents the rotation of the complete body, rather than the commonly used head angle. The fish accelerates its centre of mass mostly in stage 2 by generating a considerable force peak while the fish ‘unfolds’. The escape direction of the fish correlates strongly with the amount of body curvature in stage 1, while the escape speed correlates strongly with the duration of the start. This may allow the fish to independently control the direction and speed of the escape.
    Individual preferences and farm-level decisions : experimental evidence from Costa Rica
    Naranjo Barrantes, María Angélica - \ 2019
    Wageningen University. Promotor(en): E.H. Bulte, co-promotor(en): J. Pieters. - Wageningen : Wageningen University - ISBN 9789463439367 - 147

    This thesis contributes to the understanding of individual preferences and farm-level decision making, in interaction with the institutions and government policies that can influence these decisions. Decisions on investments and input used, decisions on whether or not to support local agricultural cooperatives, decisions the demand of credit with or without insurance, and decisions of voluntary certification schemes that have an impact on the livelihood of small farmers in developing countries. I used standard econometric methods to analyze the survey and data collected from three lab-in-the-field experiments, and a one quasi-experiment all implemented with real subjects: coffee farmers in rural Costa Rica.

    Chapter 1 starts with an overview of the main topics: individual preferences and farm-level decisions. It introduces the concept of risk preferences, social preferences, formal market-based strategies and certification schemes, that can be adopted by farmers to manage risks. More specifically, it presents the research questions, methodology, empirical strategy the study area and explains how the data was collected for the subsequent main chapters of the thesis.

    In Chapter 2, we evaluate a survey-based method to other methods that elicit farmers’ risk attitudes. For both researchers and practitioners, surveys can be easier to implement than field experiments in developing countries. We first assess correlations between a context-free survey estimate of risk-taking and context-specific risk preferences. Then, we test whether survey data predicts risk-taking behavior in an incentivized experiment. Finally, we show how the different estimates of survey risk preferences relate to real-life farming choices in a population of coffee farmers in Costa Rica. Our results indicate that one should be careful when extrapolating risk attitudes across contexts. Context-neutral and context-specific survey questions elicit different risk preferences. While the context-free survey estimate of risk preferences predicts risk-taking behavior in a context-free risk experiment, and context-specific estimates are associated with risk-taking in the same agricultural real-life context , the context-free survey estimate of risk-taking is not associated with actual risk-taking behavior in the agricultural setting. Connecting these methods to farm practices, we find that higher willingness to take risk is associated with the implementation of agricultural practices that require more farm investment. In contrast, farmers who report less willingness to take risks are more likely to have higher expenditures on fertilizer use. Researchers interested in using risk preferences as inputs into the design of policy instruments should make sure that preferences are elicited in the specific context targeted by the potential policy instrument.

    Chapter 3 tests the internal and external validity of the typology of a conditional cooperator classified by using a public goods game together with the strategy method. Individuals categorized as conditional cooperators adapt their behavior to the group to which they belong. In Costa Rica, coffee farmers are traditionally organized in agricultural cooperatives, a setting very similar to the scenario presented to an individual facing the strategy method in a public goods game: how much to cooperate, given what others do. Our results show that conditional cooperators believe they contribute to the public good by matching the contribution of others in the experiment. However, we find no evidence that those classified as conditional cooperators in the experiment also behave this way when it comes to bringing coffee to the local cooperative in real life. We show supporting evidence to conclude that the typology of a conditional cooperator is internally consistent, but do not find evidence that the typology of conditional cooperators is externally valid. Our paper is a contribution to the external validity of context-free experiments and helps in understanding cooperative behavior relevant to the sustainability of agricultural cooperatives in the developing world.

    In Chapter 4, we examine the effect of farmers’ liability on demand for credit with and without insurance. We test predictions of a theoretical model in a lab in the field experiment with coffee farmers in Costa Rica. Farmers choose how much to invest in six different settings, described on the one hand by whether the loan is insured or not, and on the other by their liability. Our results show that the uptake of loans bundled with insurance is significantly higher than uptake of loans without insurance, both when farmers are liable for sure for their debt, and interestingly when there is uncertainty about their liability. When farmers are not liable for their debt, i.e. under limited liability, the uptake of credit is high irrespective of whether the loans are insured or not. Our results suggest that in order to increase the uptake of insurance as a strategy to increase private investment and reduce the vulnerability of farmers to weather events which may lead to serious crop failure, it is important that farmers are liable with at least some probability. In terms of policy design, our results show that the “principle” of limited liability does not have be abandoned altogether in order to generate an increase in the uptake of insured credit.

    Chapter 5 evaluates the environmental impacts of organic coffee certification. Eco-certification of coffee, timber and other high-value agricultural commodities is increasingly widespread. In principle, it can improve commodity producers' environmental performance, even in countries where state regulation is weak. But eco-certification will have limited environmental benefits if, as one would expect, it disproportionately selects for producers already meeting certification standards. Rigorous evaluations of the environmental effects of eco-certification in developing countries that control for selection bias are virtually nonexistent. To help fill this gap, we use detailed farm-level data to analyze the environmental impacts of organic coffee certification in central Costa Rica. We use propensity score matching to control for selection bias. We find that organic certification improves coffee growers' environmental performance. It significantly reduces chemical input use and increases adoption of some environmentally friendly management practices.

    To conclude, Chapter 6 presents a synthesis and the previous core chapters. Conclusions, lessons learned and policy recommendations of individual chapters are reconsidered. Subsequently, results are placed in a thesis-wide perspective and finally, general conclusions made.

    Oxidative stress and immune aberrancies in attention-deficit/hyperactivity disorder (ADHD): a case–control comparison
    Verlaet, Annelies A.J. ; Breynaert, Annelies ; Ceulemans, Berten ; Bruyne, Tess De; Fransen, Erik ; Pieters, Luc ; Savelkoul, Huub F.J. ; Hermans, Nina - \ 2019
    European Child & Adolescent Psychiatry 28 (2019)5. - ISSN 1018-8827 - p. 719 - 729.
    ADHD - Antioxidants - Diet - Immunity - Oxidative stress

    The objective of this study is to compare oxidative stress and immune biomarkers between attention-deficit/hyperactivity disorder (ADHD) patients and controls without ADHD. A case–control comparison between 57 paediatric (6–12 years) untreated ADHD patients from the Antwerp University Hospital and 69 controls without ADHD from random schools in Flanders, Belgium, was conducted. Erythrocyte glutathione (GSH) and plasma lipid-soluble antioxidants (retinol, α-tocopherol, γ-tocopherol, retinyl palmitate, β-carotene, and co-enzyme Q10) were determined by HPLC with electrochemical detection, plasma malondialdehyde (MDA) by HPLC with fluorescence detection, plasma cytokines (interleukin (IL)-1β, IL-5, IL-6, IL-8, IL-10, tumour necrosis factor (TNF) and interferon (INF)-γ) and immunoglobulins (IgE, IgG and IgM) by flow cytometry and urinary 8-hydroxy-2′deoxyguanosine (8-OHdG) levels by ELISA assay. Dietary habits were determined by a food frequency questionnaire. Plasma MDA levels were on average 0.031 µM higher in patients than in controls (p < 0.05), and a trend for higher urinary 8-OHdG was observed. Erythrocyte GSH and plasma retinyl palmitate levels, as well as IgG and IgE levels, were higher in patients than in controls as well (on average 93.707 µg/ml, 0.006 µg/ml, 301.555 µg/ml and 125.004 µg/ml, resp., p < 0.05). Finally, a trend for lower plasma IL-5 levels was observed. After Bonferroni correction for multiple testing, the difference in GSH levels remained statistically significant (nominally significant for retinyl palmitate), while significance was lost for MDA, IgG and IgE levels. Dietary habits do not appear to cause the observed differences. These results point at the potential involvement of slight oxidative stress and immune disturbances in ADHD.

    Applying the adverse outcome pathway (AOP) for food sensitization to support in vitro testing strategies
    Lozano-Ojalvo, Daniel ; Benedé, Sara ; Antunes, Celia M. ; Bavaro, Simona L. ; Bouchaud, Grégory ; Costa, Ana ; Denery-Papini, Sandra ; Díaz-Perales, Araceli ; Garrido-Arandia, María ; Gavrovic-Jankulovic, Marija ; Hayen, Simone ; Martínez-Blanco, Mónica ; Molina, Elena ; Monaci, Linda ; Pieters, Raymond H.H. ; Villemin, Clelia ; Wichers, Harry J. ; Wróblewska, Barbara ; Willemsen, Linette E.M. ; Roggen, Erwin L. ; Bilsen, Jolanda H.M. van - \ 2019
    Trends in Food Science and Technology 85 (2019). - ISSN 0924-2244 - p. 307 - 319.
    Adverse outcome pathway - Dendritic cells - Epithelial cells - IgE-mediated food allergy - In vitro models - T and B cells

    Background: Before introducing proteins from new or alternative dietary sources into the market, a compressive risk assessment including food allergic sensitization should be carried out in order to ensure their safety. We have recently proposed the adverse outcome pathway (AOP) concept to structure the current mechanistic understanding of the molecular and cellular pathways evidenced to drive IgE-mediated food allergies. This AOP framework offers the biological context to collect and structure existing in vitro methods and to identify missing assays to evaluate sensitizing potential of food proteins. Scope and approach: In this review, we provide a state-of-the-art overview of available in vitro approaches for assessing the sensitizing potential of food proteins, including their strengths and limitations. These approaches are structured by their potential to evaluate the molecular initiating and key events driving food sensitization. Key findings and conclusions: The application of the AOP framework offers the opportunity to anchor existing testing methods to specific building blocks of the AOP for food sensitization. In general, in vitro methods evaluating mechanisms involved in the innate immune response are easier to address than assays addressing the adaptive immune response due to the low precursor frequency of allergen-specific T and B cells. Novel ex vivo culture strategies may have the potential to become useful tools for investigating the sensitizing potential of food proteins. When applied in the context of an integrated testing strategy, the described approaches may reduce, if not replace, current animal testing approaches.

    Estimating the maximum attachment performance of tree frogs on rough substrates
    Langowski, Julian K.A. ; Rummenie, Anne ; Pieters, Remco P.M. ; Kovalev, Alexander ; Gorb, Stanislav N. ; Leeuwen, Johan L. van - \ 2019
    Bioinspiration & biomimetics 14 (2019)2. - ISSN 1748-3182

    Tree frogs can attach to smooth and rough substrates using their adhesive toe pads. We present the results of an experimental investigation of tree frog attachment to rough substrates, and of the role of mechanical interlocking between superficial toe pad structures and substrate asperities in the tree frog species Litoria caerulea and Hyla cinerea. Using a rotation platform setup, we quantified the adhesive and frictional attachment performance of whole frogs clinging to smooth, micro-, and macrorough substrates. The transparent substrates enabled quantification of the instantaneous contact area during detachment by using frustrated total internal reflection. A linear mixed-effects model shows that the adhesive performance of the pads does not differ significantly with roughness (for nominal roughness levels of 0-15 µm) in both species. This indicates that mechanical interlocking does not contribute to the attachment of whole animals. Our results show that the adhesion performance of tree frogs is higher than reported previously, emphasising the biomimetic potential of tree frog attachment. Overall, our findings contribute to a better understanding of the complex interplay of attachment mechanisms in the toe pads of tree frogs, which may promote future designs of tree-frog-inspired adhesives.

    Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment
    Tomotani, Barbara M. ; Bil, Wender ; Jeugd, Henk P. van der; Pieters, Remco P.M. ; Muijres, Florian T. - \ 2019
    Methods in Ecology and Evolution 10 (2019)1. - ISSN 2041-210X - p. 70 - 79.
    1. The recent boost in bird migration studies following the development of various tracking devices raised awareness of how detrimental attaching devices can be for animals. Such effects can occur during migration, but also immediately post‐release if the device impairs escape flight performance and, consequently, the bird's ability to evade predators. 2. In this study, we investigated the effect of carrying a device on the escape flight speed and aerodynamic force production in a migratory passerine. We recorded upward‐directed escape flights of 15 male blackcaps. Each individual was tested without a tag, and when equipped with three different leg‐loop dummy tags with masses representing around 3%, 5% and 7% of their body mass. The experiment was designed such that all individuals passed through all treatments in a randomized order. 3. We found that two factors affected flight speed in roughly equal amounts: first, tagged escape flights had lower flight speeds compared to the control flights, irrespective of tag mass. Second, we found an effect of the total mass, i.e. the sum of the masses of the individual bird and of the tag, with heavier birds being slower. In contrast, flight speed was not correlated with relative tag mass in percentage of body mass, the metric commonly used in ethical guidelines for tag attachment. Aerodynamic flight force production also depended on total mass, with heavier birds producing higher forces. But these flight forces did not differ between flights with or without a tag. 4. We conclude that, when tagging birds, it is misleading to choose heavy individuals for tagging in order to minimize the tag mass as a percentage of body mass. This is particularly relevant in species for which body mass is not necessarily related to size, like migratory birds that accumulate large fat reserves. The lower escape speed in “tagged” flights could not be explained by differences in net flight force production, because these did not differ between flights with and without a tag. This suggests that the tag also affected pre‐flight take‐off dynamics, possibly due to a leg harness‐induced reduction in leg push‐off performance.
    Light-dark rhythms during incubation of broiler chicken embryos and their effects on embryonic and post hatch leg bone development
    Pol, C.W. van der; Roovert-Reijrink, Inge Van; Maatjens, C.M. ; Gussekloo, S.W.S. ; Kranenbarg, S. ; Wijnen, H.J. ; Pieters, R.P.M. ; Schipper, H. ; Kemp, B. ; Brand, H. van den - \ 2019
    PLoS ONE (2019). - ISSN 1932-6203 - 17 p.
    There are indications that lighting schedules applied during incubation can affect leg health at hatching and during rearing. The current experiment studied effects of lighting schedule: continuous light (24L), 12 hours of light, followed by 12 hours of darkness (12L:12D), or continuous darkness (24D) throughout incubation of broiler chicken eggs on the development and strength of leg bones, and the role of selected hormones in bone development. In the tibiatarsus and femur, growth and ossification during incubation and size and microstructure at day (D)0, D21, and D35 post hatching were measured. Plasma melatonin, growth hormone, and IGF-I were determined perinatally. Incidence of tibial dyschondroplasia, a leg pathology resulting from poor ossification at the bone’s epiphyseal plates, was determined at slaughter on D35. 24L resulted in lower embryonic ossification at embryonic day (E)13 and E14, and lower femur length, and lower tibiatarsus weight, length, cortical area, second moment of area around the minor axis, and mean cortical thickness at hatching on D0 compared to 12L:12D especially. Results were long term, with lower femur weight and tibiatarsus length, cortical and medullary area of the tibiatarsus, and second moment of area around the minor axis, and a higher incidence of tibial dyschondroplasia for 24L. Growth hormone at D0 was higher for 24D than for 12L:12D, with 24L intermediate, but plasma melatonin and IGF-I did not differ between treatments, and the role of plasma melatonin, IGF-I, and growth hormone in this process was therefore not clear. To conclude, in the current experiment, 24L during incubation of chicken eggs had a detrimental effect on embryonic leg bone development and later life leg bone strength compared to 24D and 12L:12D, while the light-dark rhythm of 12L:12D may have a stimulating effect on leg health.
    Plasma citrulline concentration, a marker for intestinal functionality, reflects exercise intensity in healthy young men
    Kartaram, Shirley ; Mensink, Marco ; Teunis, Marc ; Schoen, Eric ; Witte, Gerrit ; Janssen Duijghuijsen, Lonneke ; Verschuren, Martie ; Mohrmann, Karin ; M'Rabet, Laura ; Knipping, Karen ; Wittink, Harriet ; Helvoort, Ardy van; Garssen, Johan ; Witkamp, Renger ; Pieters, Raymond ; Norren, Klaske van - \ 2019
    Clinical Nutrition 38 (2019)5. - ISSN 0261-5614 - p. 2251 - 2258.
    Citrulline - Exercise intensity - Glutamine - Intestinal fatty acid binding protein - Intestinal function

    Background & aims: Plasma citrulline concentration is considered to be a marker for enterocyte metabolic mass and to reflect its reduction as may occur during intestinal dysfunction. Strenuous exercise can act as a stressor to induce small intestinal injury. Our previous studies suggest that this comprises the intestinal ability to produce citrulline from a glutamine-rich protein bolus. In this study we investigated the effects of different exercise intensities and hydration state on citrulline and iFABP levels following a post-exercise glutamine bolus in healthy young men. Methods: Fifteen healthy young men (20–35 yrs, VO2 max 56.9 ± 3.9 ml kg−1 min−1) performed in a randomly assigned cross-over design, a rest (protocol 1) and four cycle ergometer protocols. The volunteers cycled submaximal at different percentages of their individual pre-assessed maximum workload (Wmax): 70% Wmax in hydrated (protocol 2) and dehydrated state (protocol 3), 50% Wmax (protocol 4) and intermittent 85/55% Wmax in blocks of 2 min (protocol 5). Immediately after 1 h exercise or rest, subjects were given a glutamine bolus with added alanine as an iso-caloric internal standard (7.5 g of each amino acid). Blood samples were collected before, during and after rest or exercise, up to 24 h post onset of the experiment. Amino acids and urea were analysed as metabolic markers, creatine phosphokinase and iFABP as markers of muscle and intestinal damage, respectively. Data were analysed using a multilevel mixed linear statistical model. p values were corrected for multiple testing. Results: Citrulline levels already increased before glutamine supplementation during normal hydrated exercise, while this was not observed in the dehydrated and rest protocols. The low intensity exercise protocol (50% Wmax) showed the highest increase in citrulline levels both during exercise (43.83 μmol/L ± 2.63 (p < 0.001)) and after glutamine consumption (50.54 μmol/L ± 2.62) compared to the rest protocol (28.97 μmol/L ± 1.503 and 41.65 μmol/L ± 1.96, respectively, p < 0.05). However, following strenuous exercise at 70% Wmax in the dehydrated state, citrulline levels did not increase during exercise and less after the glutamine consumption when compared to the resting condition and hydrated protocols. In line with this, serum iFABP levels were the highest with the strenuous dehydrated protocol (1443.72 μmol/L ± 249.9, p < 0.001), followed by the high intensity exercise at 70% Wmax in the hydrated condition. Conclusions: Exercise induces an increase in plasma citrulline, irrespective of a glutamine bolus. The extent to which this occurs is dependent on exercise intensity and the hydration state of the subjects. The same holds true for both the post-exercise increase in citrulline levels following glutamine supplementation and serum iFABP levels. These data indicate that citrulline release during exercise and after an oral glutamine bolus might be dependent on the intestinal health state and therefore on intestinal functionality. Glutamine is known to play a major role in intestinal physiology and the maintenance of gut health and barrier function. Together, this suggests that in clinical practice, a glutamine bolus to increase citrulline levels after exercise might be preferable compared to supplementing citrulline itself. To our knowledge this is the first time that exercise workload-related effects on plasma citrulline are reported in relation to intestinal damage.

    Europarlementariers willen pulsvisserij verbieden door fakenews
    Rijnsdorp, Adriaan ; Pieters, Remco ; Boute, Pim - \ 2018

    Het Europees Parlement benadeelt Nederlandse vissers op basis van foute, gemanipuleerde informatie. Dat stelt ondermeer visserijbioloog Adriaan Rijnsdorp, die deze week met verbijstering toekeek hoe een ruime meerderheid van het Europees Parlement voor een totaalverbod op de zogeheten pulsvisserij stemde. 'Als je met fakenews een politiek doel dient dan ben je smerig bezig', aldus de hoogleraar van de Wageningen Universiteit.

    Incentives, social learning and economic development : Experimental and quasi-experimental evidence from Uganda
    Shikuku, Kelvin Mashisia - \ 2018
    Wageningen University. Promotor(en): E.H. Bulte; K.E. Giller, co-promotor(en): J. Pieters. - Wageningen : Wageningen University - ISBN 9789463433303 - 210

    Informational constraints hinder successful adoption and scaling of potentially beneficial agricultural technologies. Social learning in the form of farmer-to-farmer technology transfer can help to address informational constraints. Without incentives, however, the first individuals in the target population to receive the technology may not “automatically” share the knowledge with their neighbours. This thesis examined the effect of private material rewards and social recognition on the diffusion of agricultural technologies through social learning. Secondly, it assessed the role of social distance in influencing information exchange, and the subsequent impacts on knowledge exposure and technology adoption. Thirdly, the mechanisms through which social networks influence technology diffusion were examined. Fourthly, the thesis quantified the impacts of adopting climate smart agricultural (CSA) technologies on productivity, downside risk, food security, and resilience of livelihoods in the post-conflict northern Uganda. The main results are summarized as follows: (1) rewarding disseminating farmers (DFs) with social recognition increased their effort to train their covillagers; (2) social distance influenced information exchange between DFs and their covillagers, but the direction of influence was inconclusive; (3) information exchange links increased awareness, knowledge, and adoption of drought-tolerant maize varieties by covillagers; (4) incentives changed both the DFs and neighbours’ networks subsequently increasing knowledge diffusion and adoption by co-villagers; (5) Adoption of CSA technologies boosted productivity, reduced production risk, and increased food security, but did not reduce downside risks. The thesis discusses policy implications of the findings and provides recommendations for future research.

    Data from: Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment
    Mizumo Tomotani, Barbara ; Bil, Wender ; Jeugd, Henk P. van der; Pieters, R.P.M. ; Muijres, F.T. - \ 2018
    Wageningen University & Research
    bird flight - experiment - Eurasian blackcap - geolocator - predation - Sylvia atricapilla
    1. The recent boost in bird migration studies following the development of various tracking devices raised awareness of how detrimental attaching devices can be for animals. Such effects can occur during migration, but also immediately post-release if the device impairs escape flight performance and, consequently, the bird’s ability to evade predators. 2. In this study, we investigated the effect of carrying a device on the escape flight speed and aerodynamic force production in a migratory passerine. We recorded upward-directed escape flights of 15 male blackcaps. Each individual was tested without a tag, and when equipped with three different leg-loop dummy tags with masses representing around 3%, 5% and 7% of their body mass. The experiment was designed such that all individuals passed through all treatments in a randomized order. 3. We found that two factors affected flight speed in roughly equal amounts: first, tagged escape flights had lower flight speeds compared to the control flights, irrespective of tag mass. Second, we found an effect of the total mass, i.e. the sum of the masses of the individual bird and of the tag, with heavier birds being slower. In contrast, flight speed was not correlated with relative tag mass in percentage of body mass, the metric commonly used in ethical guidelines for tag attachment. Aerodynamic flight force production also depended on total mass, with heavier birds producing higher forces. But these flight forces did not differ between flights with or without a tag. 4. We conclude that, when tagging birds, it is misleading to choose heavy individuals for tagging in order to minimize the tag mass as a percentage of body mass. This is particularly relevant in species for which body mass is not necessarily related to size, like migratory birds that accumulate large fat reserves. The lower escape speed in “tagged” flights could not be explained by differences in net flight force production, because these did not differ between flights with and without a tag. This suggests that the tag also affected pre-flight take-off dynamics, possibly due to a leg harness-induced reduction in leg push-off performance.
    Release of major peanut allergens from their matrix under various pH and simulated saliva conditions—Ara h2 and ara h6 are readily bio-accessible
    Koppelman, Stef J. ; Smits, Mieke ; Tomassen, Monic ; Jong, Govardus A.H. De; Baumert, Joe ; Taylor, Steve L. ; Witkamp, Renger ; Veldman, Robert Jan ; Pieters, Raymond ; Wichers, Harry - \ 2018
    Nutrients 10 (2018)9. - ISSN 2072-6643
    Allergen - Arachis hypogaea - Bio-accessibility - Peanut - Saliva

    The oral mucosa is the first immune tissue that encounters allergens upon ingestion of food. We hypothesized that the bio-accessibility of allergens at this stage may be a key determinant for sensitization. Light roasted peanut flour was suspended at various pH in buffers mimicking saliva. Protein concentrations and allergens profiles were determined in the supernatants. Peanut protein solubility was poor in the pH range between 3 and 6, while at a low pH (1.5) and at moderately high pHs (>8), it increased. In the pH range of saliva, between 6.5 and 8.5, the allergens Ara h2 and Ara h6 were readily released, whereas Ara h1 and Ara h3 were poorly released. Increasing the pH from 6.5 to 8.5 slightly increased the release of Ara h1 and Ara h3, but the recovery remained low (approximately 20%) compared to that of Ara h2 and Ara h6 (approximately 100% and 65%, respectively). This remarkable difference in the extraction kinetics suggests that Ara h2 and Ara h6 are the first allergens an individual is exposed to upon ingestion of peanut-containing food. We conclude that the peanut allergens Ara h2 and Ara h6 are quickly bio-accessible in the mouth, potentially explaining their extraordinary allergenicity.

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