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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    On the genetic mechanisms of nutrient-dependent lifespan and reproduction
    Zandveld, Jelle - \ 2017
    Wageningen University. Promotor(en): B.J. Zwaan, co-promotor(en): A.J.M. Debets. - Wageningen : Wageningen University - ISBN 9789463436861 - 209
    genetics - lifespan - reproduction - nutrients - drosophila melanogaster - fungi - diet - evolution - genetica - levensduur - voortplanting - voedingsstoffen - drosophila melanogaster - schimmels - dieet - evolutie

    Dietary restriction (DR), a moderate reduction in nutrient intake, improves health or extends lifespan across many species. Moreover, recent insights have shown that also the effects of specific nutrients are of importance for the beneficial effects of DR rather than intake alone. However, we still lack much insight through what mechanisms the lifespan increase through diet changes is exactly mediated.

    To further increase our understanding of the genetic mechanisms of nutrient-dependent lifespan, in Chapter 2, 3, 4, and 5 I employed different methods of genetic interventions (i.e. a genetic knockout, natural genetic variation and experimental evolution) using the model species Drosophila melanogaster and Podospora anserina. To test whether the genetic interventions affected the diet response, a broad range of diets was applied, thereby taking the recent insights of nutritional geometry into account. Furthermore, the response of the fly’s whole-genome transcription to different dietary treatments were assessed in Chapter 6 and 7 to identify and potentially disentangle genetic mechanisms for lifespan from those for reproduction.

    Chapter 2 addressed the effects of a triple knockout in the insulin-IGF signalling (IIS) pathway, namely for three genes encoding insulin-like peptides in Drosophila (dilp2-3,5). The mutant showed a strong elevation of lifespan that was irrespective of food type, but also a strong reduction of the female fly fecundity. In addition, this assay also revealed that the same knockout can yield different interpretations for its function in the fly’s diet response, which was strongly dependent per diet dimension under consideration (i.e. varying yeast, sugar, or its ratio in the diet). This observation set the stage for other experimental chapters in this thesis, where a broad range of diets was applied to depict the exact genotypic effects that are involved in the lifespan response to diet. For example, in Chapter 2, interactive effects were observed between dilp2-3,5 knockout and the lifespan response to dietary sugar, but however, not for the yeast component of the diet.

    In Chapter 3, for the same experimental diets, gene expression responses in dilp2-3,5 knockout flies were measured to describe the general dynamics on the pathway level. Interestingly, expression of the remaining fly head-expressed dilp, dilp6, was elevated on higher yeast levels upon dilp2-3,5 knockout. Therefore, compensatory mechanisms within IIS might still partly mediate the lifespan response to yeast.

    In Chapter 4 the natural genetic variation for the response to DR was explored in wild-derived strains of the fungus Podospora anserina. By applying a broad range of glucose concentrations in a synthetic medium, we constructed reaction norms for 62 natural occurring strains and showed considerable natural variation in the shape of the reaction norms, including the glucose concentration at which lifespan increased and how steeply the fungus’ lifespan responds to diet (the slope S). Furthermore, I identified a significant correlation between a strain’s general lifespan and both parameters, suggesting that the lifespan response to diet partly acts through a mechanism involved in the fungus’ lifespan determination under high nutrient, growth and reproduction permissive, conditions. On moderate glucose restriction levels we showed that a reduced reproduction was not always associated with lifespan extension, which indicates that decoupling of these traits (that often trade-off) can be achieved.

    An evolutionary perspective on diet response and the connection between reproduction and lifespan, two often interconnected traits in lifespan research, was provided in Chapter 5. Here, experimental evolution (EE) was performed in Drosophila melanogaster to test whether improved reproductive capacity (i.e. local adaptation) to three nutritionally distinct diets directly affected the lifespan response. Adaptation to the distinct nutritional conditions, had no consistent effect on the lifespan response to diet. Other life-history traits that I assessed could more consistently be associated with the evolutionary nutritional treatments, which together suggested that the adaptive genetic mechanisms increasing the fly’s reproduction were not necessarily interconnected singly with a change of lifespan, but rather with a change in the whole life-history strategy.

    By exploring the fly’s whole-genome transcription response in a continuously changing environ­ment, Chapter 6 continued on the evolutionary relevance of lifespan responses to diet. This type of fluctuations may better reflect the fly’s natural ecological setting than the continuous diets typically applied in whole-genome transcription laboratory studies. This revealed that flies were able to respond quickly to diet fluctuations throughout lifespan by drastically changing their transcription pattern and, moreover, my results indicated that a large part of the whole-genome transcription response could be attributed to the female fly’s reproduction. Because I measured the response of multiple life-history traits to the fluctuating diet changes, I was able to decouple groups of genes associated with lifespan from those associated with reproduction. This is an important step in the direction of unravelling the genetic architecture that specifically mediates the lifespan response to diet, which can be especially useful in whole-genome transcription studies.

    In Chapter 7, the consistencies between studies for their whole-genome transcription responses upon DR were investigated. This revealed large transcriptomic variations on different regulatory levels, i.e. the level of whole-genome transcription, most significant genes, and also gene ontology. To test whether the observed inconsistent whole-genome transcription responses were primarily a reflection of the fly’s reproduction, such as observed in Chapter 6, a new cohort of flies was subjected to different regimes that resulted in very different age-dependent reproduction patterns. By assessing whole-genome transcription in this cohort at two time points, the gene expression changes reflected the age-dependent reproduction patterns observed, rather than the lifespan phenotypes. Similar to Chapter 6, this again highlighted the importance of measuring multiple life-history traits for associating whole-genome transcription responses to lifespan effects of dietary restriction.

    In Chapter 8 the acquired insights across the experimental chapters were synthesized, discussing the importance of assessing a broad range of nutrients for the interpretation of any genotypic effect, and in addition discussing the value of measuring multiple life-history traits for genetic associations. In this chapter I also suggested directions for future research in Drosophila and Podospora that may be valuable for further unravelling and understanding the mechanisms of diet responses in other organisms, including in humans.

    The utility of sensor technology to support reproductive management on dairy farms
    Rutten, C.J. - \ 2017
    Wageningen University. Promotor(en): H. Hogeveen; M. Nielen, co-promotor(en): W. Steeneveld. - Wageningen : Wageningen University - ISBN 9789463431934 - 232
    dairy cattle - dairy farms - sensors - reproduction - reproductive behaviour - animal health - calving - activity - management - dairy farming - technology - agricultural economics - melkvee - melkveebedrijven - sensors - voortplanting - voortplantingsgedrag - diergezondheid - kalven - activiteit - bedrijfsvoering - melkveehouderij - technologie - agrarische economie

    Since the 1980s, efforts have been made to develop sensors that measure a parameter from an individual cow. The development started with individual cow recognition and was followed by sensors that measure the electrical conductivity of milk and pedometers that measure activity. Some sensors like activity meters, electrical conductivity, weight floors and somatic cell count sensors are commercially available. Adoption has in general been low and mainly driven by the AMS, with a clear exception for estrus detection. In practice, the economic benefits of using sensor systems has not been proven. So, to make sensors live up to their full potential there is a need for research to shift from technical development towards practical applications and integration with operational farm management. Estrus detection sensors can have a good detection performance and are currently applied by farmers in practice, therefore this thesis focusses on sensors that support reproductive management. The main objective of this thesis is to study the utility of sensor technology to support reproductive management on dairy farms. This main objective was split in five sub objectives that each study a part of the main objective and were discussed in the separate chapters of this thesis.

    We demonstrated that utility of sensors for reproductive management can be found in economic benefits (estrus and calving detection), reduction of labor (calving and estrus detection) and more detailed management information (prognosis of insemination success). So, automated estrus detection aids reproductive management.

    From this thesis the following conclusions can be drawn:

    The developed theoretical framework describes four levels of sensor development, which should all be included in proper development of sensor systems. The literature review showed that no studies developed sensor systems with regard to management and decision support.

    It was possible to improve the prediction of the start of calving compared to a model that only uses the expected calving date. However, predicting the start of calving within an hour was not possible with a high sensitivity and specificity.

    There was financial merit in the use of calving detection, because the sensor system enables more timely intervention by the farmer. The uncertainty about the positive effects was large, which caused a wide range in the simulated financial benefits.

    Investment in a sensor for estrus detection was on average profitable with a return on investment of 11%. Profitability was influenced most by the heuristic culling rules and the expected increase of the estrus detection rate between detection by visual observation and the sensor.

    Routinely collected farm data can be used to estimate a prognosis on insemination success and be used to determine whether an individual cow has a higher or lower than average likelihood of insemination success. Integration of this prognostic model with an estrus detection sensor has potential.

    Currently farmers only adopt sensors for estrus detection or because they were standard with an AMS. A reason for this is that sensor systems do not produce clear information for farmers. Sensor technology should be focused on management support of applications. Labor benefits of sensors are important for adoption of sensors by farmers, farmers value flexibility, increased family time and less physical workload as benefits. However, economic evaluations of technical solutions are unable to quantify these benefits. Sensor research should consider the preference of farmers regarding labor. For the appraisal of sensor technology new methods to value labor benefits of sensor are needed. Furthermore, in sensor development societal acceptance should be an important consideration. Animal rights activists may frame the use of sensors as a form of industrialized farming. Only using technical arguments and considerations to explain the benefits of sensors will hamper the societal acceptance of modern dairy farming. Application of sensors on dairy farms should be communicated smartly to society in terms that relate the values of citizens.

    Energy status and ovarian follicular development
    Meng, Li - \ 2016
    Wageningen University. Promotor(en): Jaap Keijer; Katja Teerds. - Wageningen : Wageningen University - ISBN 9789462579170 - 144
    ovarian development - energy - follicles - reproduction - atresia - development - ovaries - ovariumontwikkeling - energie - follikels - voortplanting - atresie - ontwikkeling - ovaria

    Female reproduction is tightly linked to body energy status and it has become increasingly clear that disturbed energy metabolism can negatively affect reproductive performance. Nevertheless, the way how a disturbed energy status affects ovarian follicular reserve as well as follicular recruitment and growth is little investigated and not fully elucidated. Therefore, the overall goal of this thesis was to investigate the effects of an altered metabolism, and particularly an altered energy status, on ovarian follicular development. To achieve this goal, the first aim was to establish the role of autophagy in follicular degeneration under normal physiological conditions, with focus on preantral and antral follicles; The second aim was to elucidate the effects of a diet-induced reduction in thyroid hormone concentrations, affecting whole body metabolism, on ovarian follicular development; The third aim was to investigate the effect of an increased nutrient flux towards skeletal muscle on ovarian follicular development and the possible underlying mechanism.

    It is well known that granulosa cell death via apoptosis is the main cause of atresia of antral follicles, however, whether preantral follicular attrition makes use of the same cell death pathway is not clear. Therefore, in chapter 2 I have investigated different cell death pathways in the adult rat ovary to examine whether they represent the reported histological differences between preantral and antral atretic follicles. Based on the results of studies in other organs, I used microtubule-associated light-chain protein 3 (LC3) and QSQTM1/p62 as markers of autophagy and cleaved caspase 3 (cCASP3) as marker of apoptosis, using immunohistochemistry, western blotting, and laser capture micro-dissection followed by qRT-PCR. The results showed that in the granulosa cells of atretic preantral follicles, p62 immunostaining was less intense compared to healthy preantral follicles, while no difference in LC3 immunostaining intensity was observed. In contrast, in antral follicles, no difference in both immunostaining and mRNA levels of LC3 and p62 were found between healthy and atretic follicles, indicating that autophagy was not responsible for attrition of antral follicles. cCASP3 immunostaining was scarce in the granulosa cells of atretic preantral follicles, whereas many cCASP3 positive apoptotic cells were present in atretic antral follicles, indicating that apoptosis is a major cell death pathway activated in antral follicle degeneration. Immunostaining for superoxide dismutase 2 (SOD2) was reduced in preantral and antral atretic follicles. This observation was confirmed by a concomitant down regulation of Sod2 mRNA levels. These findings suggest that preantral follicular atresia mainly makes use of autophagy as cell death pathway, while antral follicles degenerate mainly via apoptosis.

    In chapter 3, the consequences of prolonged exposure to reduced thyroid hormone concentrations in adulthood on the size of the ovarian follicle pool are investigated. Besides having a direct effect on the functioning of many cells, changes in thyroid hormone levels also influence metabolism. In this study female rats at the age of 10 weeks were given a control diet or an iodide deficient diet in combination with perchlorate supplementation to inhibit iodide uptake by the thyroid, resulting in a relatively mild chronic hypothyroid condition. At the age of 26 weeks animals were sacrificed and ovaries histologically evaluated. Plasma concentrations of relevant hormones (thyroid-stimulating hormone (TSH), tri-iodothyronine (T3), thyroxine (T4), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and anti-Müllerian hormone (AMH) were determined. Primordial, primary and preantral follicle numbers were significantly lower in the hypothyroid ovaries compared to the euthyroid controls, while a downward trend in antral follicle numbers and corpora lutea was observed. The percentage of atretic follicles was not different between the two groups. Plasma AMH concentrations showed a significant correlation with the growing follicle population represented by the total number of primary, preantral and antral follicles per ovary. The data indicate that prolonged mild hypothyroidism negatively affects ovarian follicular reserve as well as the size of the growing follicle population, which may impact fertility. AMH can serve, also under mild hypothyroid conditions, as a surrogate marker to assess the size of the growing ovarian follicle population, offering a non-invasive way to evaluate the correlation between female reproductive health and thyroid status.

    Subsequently, in chapter 4, the long-term effects of chronic hypothyroidism initiated already in the foetal/neonatal period on ovarian follicular development were investigated. In contrast to the experiments described in chapter 3, the rats in this experiment were exposed to reduced thyroid hormone levels from the moment of conception until necropsy. Effects on the ovarian follicular reserve and ovulation rate in prepubertal (12-day-old) and adult (64-day-old and 120-day-old) rats were studied. Besides, antioxidant gene expression, mitochondrial density and the occurrence of oxidative stress were analyzed. The results of this investigation showed that continuous fetal/postnatal hypothyroidism resulted in lower preantral and antral follicle numbers in adulthood, accompanied by a higher percentage of atretic follicles, when compared to euthyroid age-matched controls. Not surprisingly, ovulation rate was lower in the hypothyroid rats. At the age of 120 days, the mRNA and protein content of superoxide dismutase 1 (SOD1) was significantly increased, while catalase (CAT) mRNA and protein content was significantly decreased, suggesting a disturbed antioxidant defense capacity of ovarian cells in the hypothyroid animals. This was supported by a significant reduction in peroxiredoxin 3 (Prdx3), thioredoxin reductase 1 (Txnrd1), and uncoupling protein 2 (Ucp2) mRNA content and a downward trend in glutathione peroxidase 3 (Gpx3) and glutathione S-transferase mu 2 (Gstm2) mRNA content. These changes in gene expression were likely responsible for the increased immunostaining of the oxidative stress marker 4-hydroxynonenal. Together these results suggest that chronic hypothyroidism initiated in the foetal/neonatal period resulted in a decreased ovulation rate associated with a disturbance of the antioxidant defense system in the ovary. In contrast to hypothyroidism induced in adulthood (chapter 3), no reduction in primordial or primary follicle numbers was observed, suggesting that the ovarian reserve was not affected.

    Chapter 5 addressed the question what the consequences were of a change in nutrient flux on ovarian follicular development. In this chapter mice were employed that ectopically express uncoupling protein 1 (UCP1) in skeletal muscle (UCP1-TG). This did not affect adiposity, but led to a redistribution of energy sources away from the ovaries towards skeletal muscle tissue,; a model of skeletal muscle pseudo-starvation. The results showed that UCP1-TG female mice had increased energy expenditure, reduced body size, unchanged adiposity, increased plasma fibroblast growth factor 21 (FGF21) concentrations and reduced insulin-like growth factor 1 (IGF1) levels. UCP1-TG mice had a 30% lower number of healthy follicle compared to WT mice. Primary and preantral follicle numbers were decreased by 40%, while the number of atretic follicles was significantly increased and corpora lutea (CL) were absent in 40% of the ovaries of UCP1-TG mice. The latter suggested that these mice did not ovulate and thus were infertile. The elevated circulating FGF21 concentrations were not responsible for the ovarian phenotype, since UCP1-TG and UCP1-TG/FG21-/- mice show the same ovarian follicular phenotype. Significant correlation of circulating IGF1 levels with antral follicle, CL numbers and differentially activated AKT in healthy antral follicles and activated IRS2 in atretic follicles between WT and UCP1-TG mice shows, that IGF1 is, at least partly, responsible for the ovarian phenotype of these mice. Together, our data show that an energy drain towards skeletal muscle tissue negatively impacts growing pool of ovarian follicles and ovulation rate in female mice, which is, at least in part, mediated by IGF1, and not by FGF21.

    In conclusion, the results of my thesis research shows that preantral atresia occurs mainly through autophagy. Dietary induced chronic hypothyroidism, an intervention that reduces basal metabolic rate, initiated either during foetal/neonatal or adulthood impairs ovarian follicle development. The age at onset of hypothyroidism modified the effects of this condition on ovarian follicular development. A change in nutrient flux away from the ovaries towards skeletal muscle tissue negatively affects ovarian follicle development. Overall, the results of my thesis have provided new insights in the mechanisms of follicular attrition and shows that conditions that alter metabolic fuel use impact on ovarian follicular development.

    Puberende paling wil niet volwassen worden
    Palstra, Arjan - \ 2016
    eels - eel culture - captive animals - fish culture - reproduction

    In gevangenschap planten palingen zich nog niet voort. Wageningen UR kan al wel opgekweekte paling in de puberteit brengen.

    Non-genetic variance in pigs: genetic analysis of reproduction and production traits
    Sell-Kubiak, E.B. - \ 2015
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Piter Bijma; Herman Mulder. - Wageningen : Wageningen University - ISBN 9789462573291 - 186
    varkens - dierveredeling - voortplanting - dierlijke productie - genetische analyse - genotypische variatie - genomica - fenotypische variatie - pigs - animal breeding - reproduction - animal production - genetic analysis - genetic variance - genomics - phenotypic variation


    Sell-Kubiak, E. (2015). Non-genetic variance in pigs: genetic analysis of reproduction and production traits. PhD thesis, Wageningen University, The Netherlands

    The main objective of this thesis was to study the origin of random variance in reproduction and production traits of pigs. In pig breeding for many traits it is important not only to improve the reproduction and production trait itself, but also its variation. The variance of traits can be used to improve pigs’ productivity, and potentially also to improve uniformity of traits. Results presented in Chapters 2 and 3 show that the proposed approach to explore the origin of common litter variance was not successful. The impact of various sow features on growth rate and feed intake of grow-finish pigs was very small. More importantly, sow features did not explain the phenotypic variance due to common litter effects found in production traits of pigs. In Chapters 4 and 5 the residual variance of birth weight and litter size were found to have a genetic component. The genetic coefficient of variation at residual standard deviation level (GCVSDe) was proposed as a measure of expressing the potential response to selection (Chapter 4). For both traits the estimated GCVSDe was about 10%, indicating sufficient potential for response to selection. In Chapter 4 it was shown that analyzing variation in traits with Double Hierarchical Generalized Linear model (DHGLM) was highly comparable with the conventional analysis of standard deviation of a trait. The correlation between the additive genetic effects for birth weight and the residual variance was 0.6 (Chapter 4), whereas for litter size (TNB) and its residual variance (varTNB) this correlation was 0.5 (Chapter 5). Those moderate correlations are an important indication of the direction of correlated selection response in the mean of those traits. In Chapter 5 in a genome-wide association study for litter size variation, the significant SNPs explained 0.83% of total genetic variance in TNB and 1.44% in varTNB. The most significant SNP explained 0.4% of genetic variance in TNB (chromosome 11) and 0.5% in varTNB (chromosome 7). One of the possible candidate genes for varTNB on chromosome 7 is heat shock protein (HSPCB). Studying the residual variance of traits with DHGLM has a great potential to serve as an alternative to conventional analysis to study and to select for improved uniformity of various traits. Lastly, Chapter 6 focuses on discussion of the findings of this thesis and their overall importance for pig breeding, as well as highly relevant topics for breeding uniform and robust pigs (macro-micro sensitivity analysis and application of genomic selection).

    Mackerel winter spawning surveys 2014 - 2015 December survey
    Damme, C.J.G. van; O'Hea, B. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C043/15) - 12
    scomber scombrus - makrelen - kuitschieten - voortplanting - visbestand - pelagische visserij - mariene ecologie - monitoring - scomber scombrus - mackerels - spawning - reproduction - fishery resources - pelagic fishery - marine ecology - monitoring
    In recent years the western Atlantic mackerel stock has expanded, resulting in an earlier start of spawning and earlier occurrence of the mackerel peak of spawning. In 2014 and 2015, mackerel winter spawning surveys have been conducted to determine the start date of mackerel spawning in the western area. During the surveys both plankton sampling and trawl hauls are carried out. This report contains the results of the December 2014 survey, carried out on board the Nida.
    Mackerel winter spawning surveys 2014 - 2015 January survey: Survey report
    Damme, C.J.G. van; Holst, G. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C014/15) - 12
    scomber scombrus - makrelen - kuitschieten - voortplanting - visbestand - pelagische visserij - mariene ecologie - monitoring - scomber scombrus - mackerels - spawning - reproduction - fishery resources - pelagic fishery - marine ecology - monitoring
    In recent years the western Atlantic mackerel stock has expanded, resulting in an earlier start of spawning and earlier occurrence of the mackerel peak of spawning. In 2014 and 2015, mackerel winter spawning surveys have been conducted to determine the start date of mackerel spawning in the western area. During the surveys both plankton sampling and trawl hauls are carried out. This report contains the results of the January 2015 survey, carried out on board the CETON S205.
    The role of the starfish (Asterias rubens L.) predation in blue mussel (Mytilus edulis L.) seedbed stability
    Agüera García, A. - \ 2015
    Wageningen University. Promotor(en): Aad Smaal, co-promotor(en): Jeroen Jansen; Tim Schellekens. - Wageningen : Wageningen University - ISBN 9789462572164 - 170
    mytilus edulis - mossels - voortplanting - predatie - zaaibedden - predator prooi verhoudingen - waddenzee - aquacultuur - mytilus edulis - mussels - reproduction - predation - seedbeds - predator prey relationships - wadden sea - aquaculture


    Mussel beds are an important ecological component in the Wadden Sea. Mussels’ offspring settle massively in new suitable areas, forming seedbeds that may disappear again within months. The probability of a seedbed to survive the first winter is defined as seedbed stability; a definition that plays a very important role in the management of newly settled seedbeds. Many factors are important in the survival or extinction of seedbeds. Predation is thought to be particularly important during the first year after settlement and therefore key to survival. Many predators feed on mussel beds, but for most of them the potential to exterminate a seedbed is restricted by different factors such as prey selection or competition. Common starfish (Asterias rubens) are capable of concentrating/aggregating in high densities on mussel seedbeds making them an especially important factor limiting/affecting survival of mussel seedbeds. This study assesses the capacities of starfish as a mussel seed predator. It also provides tools and information to assess the risks of a seedbed being attacked and exterminated by starfish.

    In Chapter 2 the role of temperature and shading on winter predation was studied. The results showed that temperature limits feeding rate and feeding activity of starfish during winter. However, starfish feeding rate exhibited very high sensitivity to temperature changes. Light intensity affected both feeding rate and feeding activity. We conclude that starfish may not be an important factor destabilizing seedbeds during the average winter, but its importance may grow along with the increasing mean winter temperature due to climate change.

    In Chapter 3 the impact of salinity changes on predation performance and survival was assessed. Salinity is the main driver of species distributions in the Wadden Sea. Results show that salinity affected predation performance by reducing feeding activity and causing changes in prey selection. Moreover, as acclimation occurred, A. rubens predation performance improved in all treatments with survivors. We conclude that osmotic stress due to a salinity decreases determines A. rubens distribution, abundance and potential impact on the prey population. However this effect is influenced by the magnitude of the change in salinity and its timescale.

    In Chapter 4 the effect of tidal currents on predation rate was assessed, however, the chapter also tackles the role of hydrodynamic stress amelioration by mussels on the A. rubens population. The results suggest that mussels interact with their own predator beyond the role of food source, by ameliorating environmental stress, creating an additional dependence link between the foundation species and the predator, which potentially has major implications for ecosystem structure and stability.

    In Chapter 5, we assessed the role of mussel association with conspecifics at high densities on prey selection by A. rubens. We concluded that size selection does not always lead to an improvement in net profit. Size selection is a trade-off between energy yield and predation energy costs, which is affected by prey behaviour.

    The results of the prior chapters were integrated in Chapter 6 with field observations and literature to develop a simulation model. This model was designed to simulate growth of mussels and starfish, predation by starfish and mussel mortality. It can also be used to predict the likely effect of future environmental change scenarios on the potential impact of A. rubens on this important resource.

    In the general discussion, Chapter 7, previous literature, field data and the results from this thesis are summarised and reviewed to explain the spatial distribution of A. rubens in the Wadden Sea and the role of environmental conditions on A. rubens predation rate. Model simulations are used to answer the question: What is the role of A. rubens predation in mussel seedbed stability?

    Body composition and reproduction in broiler breeders: impact of feeding strategies
    Emous, R.A. van - \ 2015
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Rene Kwakkel; Marinus van Krimpen. - Wageningen : Wageningen University - ISBN 9789462572386 - 173
    vleeskuikenouderdieren - vleeskuikens - lichaamssamenstelling - gevogeltevoeding - voer - voedingseiwit - voeropname - diergedrag - corticosteron - voortplanting - vrouwelijke vruchtbaarheid - prestatieniveau - diervoeding - broiler breeders - broilers - body composition - fowl feeding - feeds - dietary protein - feed intake - animal behaviour - corticosterone - reproduction - female fertility - performance - animal nutrition


    Key words: broiler breeder, feeding strategies, body composition, reproduction, behavior

    Nowadays, welfare issues in broiler breeders associated with nutrition and reproductive characteristics, are becoming increasingly challenging. Due to genetic selection on broilers, body composition of breeders has changed dramatically during the last 50 years to less fat and more breast muscle. It is postulated that a certain amount of body fat in broiler breeders at the onset of lay is necessary for maximum performance and offspring quality. Body composition of breeders can be influenced by different feed allowances during rearing and lay, as well as by changes in nutrient composition of the diet. However, little is known about the effects of body composition on reproduction of broiler breeders. In this thesis, we investigated the effects of different feeding strategies during the rearing period on body composition at the end of rearing. Moreover, the effects of differences in body composition at the end of rearing, and feeding strategies during lay were evaluated on breeder performance, incubation traits, offspring performance, behavior and feather cover. From this study, it can be concluded that feeding a low protein diet during rearing decreased breast muscle and increased abdominal fat pad, whereas providing an increased feeding schedule, which resulted in a high growth pattern, only increased abdominal fat pad, at the end of rearing. The higher abdominal fat pad content resulted in an increased hatchability during the first phase of lay and a larger number of eggs during the second phase of lay. For maintaining growth pattern, broiler breeders had to provide a higher amount of feed with an increased energy to protein ratio compared to broiler breeders that were fed a diet with a standard energy to protein ratio. This resulted in an increased eating time and less stereotypic object pecking, which may indicate a reduced hunger and frustration. On the other hand, a low daily protein intake during the rearing and first phase of lay can lead to a poor feather cover. Feeding a high-energy diet during the second phase of lay resulted in increased hatchability, decreased embryonic mortality and more first grade chicks.

    Herring larvae surveys 2013 - 2014: Survey reports and results
    Damme, C.J.G. van; Bakker, C. - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR C107/14) - 33
    visbestand - noordzee - voortplanting - haringen - monitoring - fishery resources - north sea - reproduction - herrings - monitoring
    The international herring larvae surveys (IHLS) are carried out to sample larvae of the North Sea autumn and winter spawning herring populations. The abundance of larvae is used as an index for the estimation of North Sea herring spawning stock biomass.
    North Sea mackerel egg survey 2014
    Damme, C.J.G. van; Bakker, C. - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR C106/14) - 12
    visbestand - scomber scombrus - voortplanting - monitoring - noordzee - fishery resources - scomber scombrus - reproduction - monitoring - north sea
    IMARES was the only institute to carry out the North Sea mackerel egg survey and planned to cover the North Sea mackerel spawning area and season in four survey weeks.
    Don’t put all your eggs in one basket! : reproductive strategies and fecundity regulation in temperate marine teleosts
    Damme, C.J.G. van - \ 2013
    Wageningen University. Promotor(en): Adriaan Rijnsdorp, co-promotor(en): O.S. Kjesbu; Mark Dickey-Collas. - Wageningen : Wageningen UR - ISBN 9789461736253 - 183
    teleostei - zeevissen - voortplanting - voortplantingspotentieel - oöcytrijping - kuitschieten - biomassa - eierproductie - visstand - visserijbiologie - visserijbeheer - teleostei - marine fishes - reproduction - fecundity - oocyte maturation - spawning - biomass - egg production - fish stocks - fishery biology - fishery management

    In fisheries management the spawning stock biomass (SSB) is an important indicator of the status of exploited fish stocks. Knowledge on the reproductive biology is essential to estimate SSB. A large variety of reproductive strategies is found. In marine fish two extreme strategies are known, capital spawners which have a determinate fecundity (no de novo oocyte recruitment during spawning), and income spawners which have an indeterminate fecundity (de novo oocyte recruitment during spawning). In this thesis fecundity regulating mechanisms are studied in commercial fish species with contrasting life history.

    In capital spawning plaice Pleuronectes platessa and herring Clupea harengus , which spawn in autumn and/or winter, oocyte maturation starts around April when daylight length increases. Both species recruit a high number of oocytes which are down-regulated in the course of time in relation to the available energy. After the summer feeding period, when energy levels are highest, plaice shows a second recruitment phase. In herring, no difference was observed in the oocyte development between autumn and winter spawners, although winter spawners continue developing oocytes and spawn fewer but larger eggs. The income breeding horse mackerel Trachurus trachurus utilises food resources during spawning although the first batch of spawned eggs is developed on stored energy.

    Food availability, through the body condition, is the most important factor regulating fecundity. In situations where food is available during the spawning season traditional determinate spawners may switch to a pseudo-indeterminate fecundity style. In conclusion this thesis shows that fecundity type of marine fish females is not fixed at the species level but represents a plastic response to the environment through food availability and energy allocation.

    OYSTERECOVER: The Efficiency of Different Types of Oyster Spat Collectors for Ostrea edulis
    Brink, A.M. van den - \ 2012
    Yerseke : IMARES (Report / IMARES Wageningen UR C095/12) - 33
    mariene biologie - oesterschelpen - voortplanting - parasieten - marine biology - oyster shells - reproduction - parasites
    The aim of this task is to potentially identify a way to develop more efficient spat collecting techniques that may compensate for the lower survival rate of the oysters caused by the Bonamia ostreae parasite. As part of the project a review of the efficiency of different spat collectors was conducted with the intention of recommending three collector types to be tested in the field. The aim of this task is to potentially identify a way to develop more efficient spat collecting techniques that may compensate for the lower survival rate of the oysters caused by the Bonamia ostreae parasite.
    Glasaal Volendam - gaat het ze lukken? : Bedrijfsreportage
    Heijden, P.G.M. van der - \ 2012
    Aquacultuur 27 (2012)3. - ISSN 1382-2764 - p. 12 - 16.
    palingteelt - palingen - voortplanting - eel culture - eels - reproduction
    Bedrijfsreportage van Glasaal Volendam, een pootviskwekerij voor paling. Glasaal Volendam BV heeft zich tot doel gesteld paling voort te gaan planten en commercieel serieuze aantallen glasaal te gaan produceren.
    Vet als een Nederlandse aal: nieuwe inzichten over het vetgehalte van aal in relatie tot het trekgedrag
    Kotterman, M.J.J. ; Bierman, S.M. - \ 2012
    Visionair : het vakblad van sportvisserij Nederland 5 (2012)25. - ISSN 1569-7533 - p. 8 - 11.
    palingen - european eels - vismigratie - vetgehalte - monitoring - voortplanting - eels - european eels - fish migration - fat content - monitoring - reproduction
    De achteruitgang van de aalstand blijft de gemoederen bezighouden. Het dalende vetgehalte in deze bijzondere vissoort zou daarbij een negatief effect op de voortplanting hebben. Recent onderzoek van IMARES en RIKILT laat echter een ander beeld zien.
    All in good time : dynamics of the bovine estrous cycle investigated with a mathematical model
    Boer, H.M.T. - \ 2012
    Wageningen University. Promotor(en): Roel Veerkamp; Bas Kemp, co-promotor(en): Henri Woelders. - S.l. : s.n. - ISBN 9789461733559 - 192
    rundvee - dierveredeling - voortplanting - geslachtscyclus - wiskundige modellen - vruchtbaarheid - genomica - systeembiologie - cattle - animal breeding - reproduction - oestrous cycle - mathematical models - fertility - genomics - systems biology

    Bovine fertility is subject of extensive research in animal sciences, especially since a decline in dairy cow fertility has been observed during the last decades. One factor is reduced expression of estrous behavior. Fertility is a complex process, regulated by interactions between brain and reproductive organs. The objective of this thesis was to improve insight in the regulation of dairy cow fertility by developing and using a mechanistic mathematical model of the bovine estrous cycle. The model that was developed describes the dynamics of the bovine estrous cycle on individual cow level. It simulates follicle and CL development and the periodic changes in hormone levels that control these processes by a set of linked differential equations. The model captures a number of key physiological processes of the bovine estrous cycle, and serves as a starting point for further simulation studies, model validation, and extended models. The model was used to find candidate mechanisms that regulate follicular development. A normal estrous cycle contains 2 or 3 waves of follicular development, but why some cycles consist of 3 and others of 2 waves is unknown. Results showed that variation of (combinations of) model parameters regulating follicle growth rate or time point of CL regression can change the model output from 3 to 2 waves of follicular growth in a cycle. Several factors may perturb the regular oscillatory behavior of a normal estrous cycle. Such perturbations are likely the effect of simultaneous changes in multiple parameters. It was investigated how multiple parameter perturbation changes the behavior of the estrous cycle model, so as to identify biological mechanisms that could play a role in the development of cystic ovaries, a common reason for reproductive failure in dairy cows. Simulation results indicated that CL functioning, luteolytic signals, and GnRH synthesis are likely involved in the development of cystic ovaries. Empirical data of individual cows was used to identify mechanisms that explain individual differences in cycle characteristics by fitting the model to the data. Finding specific parameter configurations for individual cows shows the capability of the model to simulate ‘real’ data. Certain combinations of estimated parameter values induced a clear qualitative shift in model behavior (e.g. a different number of follicular waves), suggesting possible routes how environmental or genetic influences could affect estrous cycle characteristics. Experimental data to verify simulation results are not always available, but hypotheses based on the model predictions could be investigated in future animal experimen

    Seeing the water for the fish: building on perspectives of Lake Victoria
    Downing, A.S. - \ 2012
    Wageningen University. Promotor(en): Wolf Mooij; Marten Scheffer, co-promotor(en): Egbert van Nes. - S.l. : s.n. - ISBN 9789461733672 - 187
    waterkwaliteit - victoriameer - vissen - voedselwebben - aquatische ecosystemen - rivierbaars - groei - voortplanting - water quality - lake victoria - fishes - food webs - aquatic ecosystems - perch - growth - reproduction

    Over the past century, Lake Victoria, in East Africa, has been stage to the most dramatic social, economical and ecological changes: it saw a hundreds-rich diversity of fish species collapse; an introduced predator (Nile perch) invade and become the product of a valuable international fish export trade – a trade that invited an insurge of migrants to work on the lake’s shores.

    Since the 1990s, there has been an increase in dependence on the lake’s resources – including Nile perch and the other commercial fishes of the lake – and a decrease in the predictability and reliability of these resources.

    We here use a variety of ecological models to explore how changes in fishing and water quality influence changes in the lake’s food webs and Nile perch stocks. We describe the lake in its social-ecological perspective, and define the makers and breakers of the system’s resilience and recommend holistic and adaptive management policies.

    The second parity sow : causes and consequences of variation in reproductive performance
    Hoving, L.L. - \ 2012
    Wageningen University. Promotor(en): Bas Kemp, co-promotor(en): Nicoline Nieuwenhuizen-Soede. - S.l. : s.n. - ISBN 9789461731470 - 171
    varkens - zeugen - voortplanting - voortplantingsvermogen - adaptatiefysiologie - pigs - sows - reproduction - reproductive performance - adaptation physiology

    Many sows show reduced litter sizes in their second parity compared with their first parity. The aim of the current thesis was to describe causes and consequences of variation on second parity reproductive performance and to evaluate if feeding strategies during early gestation affect reproductive performance and sow body weight recovery after first lactation. In a first study, effects of sow weight development from first insemination up to first weaning on second parity reproductive performance were studied. Weight gain from first insemination up to first weaning showed a positive effect on non-pregnancy as well as on litter size, especially on a farm where gilts were relatively young and light at time of first insemination. In a second study, effects of weight loss during lactation were evaluated on embryonic survival and metabolic parameters during lactation and gestation in primiparous sows that were fed close to ad libitum. Sows with a high (>13.8%) weight loss showed a lower embryonic survival and fewer vital embryos at day 35 of gestation compared with sows with a lower weight loss, whilst no differences in metabolic parameters (IGF-1, NEFA, urea) were seen. The fact that the number of implantation sites was lower in high weight loss sows compared with low weight loss sows indicates that the negative effects of weight loss were already present during late lactation or early gestation. In a third study, a data-analysis using 46,500 sows was performed to assess relations between second parity performance and reproductive performance in later parities. Results showed that farrowing rate and litter size in parity 3 and up, as well as parity at culling, were related to second parity reproductive performance. These relations with second parity litter size were affected by first parity litter size. In practice, feed allowance during early gestation is often limited and might not be sufficient to support growth and recovery from lactation. The question was therefore raised if increased feed or protein intake during early pregnancy could improve litter size. In two experiments, the effects of an altered feeding strategy during the first month of gestation on farrowing rate and litter size (exp. 1) and embryonic survival and embryonic and placental development and metabolic parameters (exp. 2) were assessed. In Experiment 1, a 30% higher feeding level increased litter size with two piglets, without negatively affecting piglet birth weight. In Experiment 2, designed to find a physiological explanation for these results, an increased feeding level did not affect embryonic survival, embryonic development or placental development. Furthermore, no relations with metabolic parameters were found. From this thesis it can be concluded that second parity reproductive performance is related to reproductive performance in later parities. In order to improve second parity reproductive performance, weight loss during first lactation should be limited and gilts should be heavier at first weaning than at first insemination. Further, increased feeding levels during early gestation improve sow body weight recovery, without negatively affecting reproductive performance.

    Hatchery manual for broodstock management and larval production of tubrot (Psetta maxima)
    Rurangwa, E. ; Poelman, M. - \ 2011
    Yerseke : IMARES (Report / IMARES Wageningen UR C150/11) - 52
    tarbot - larven - broeddieren - bedrijfsvoering - visproductie - dierhouderij - voortplanting - broedinstallaties - kuitschieten - visziekten - visteelt - aquacultuur - turbot - larvae - broodstock - management - fish production - animal husbandry - reproduction - hatcheries - spawning - fish diseases - fish culture - aquaculture
    This hatchery manual is intended to provide detailed information from available published work and grey literature on turbot broodstock management and larval production. In reviewing larviculture techniques for turbot, it is notable that the major initial zoo technical advances were made in the 1980s. Subsequent refinements have been industry-led and are subject to commercial confidentiality. Some actors in the sector that have been approached either did not provide requested information or denied access to their sources of information. This manuscript therefore considers those aspects of commercial rearing techniques that are in the public domain, together with the applied scientific literature and information collected from different experts. With the aim to cover all aspects related to the production of turbot juveniles in Dutch farms from egg to fish of 10-15 g, the manual describes in details different steps. These have been grouped around the broodstock management, the hatchery/nursery period, the on growing and the grow out periods. A list of common diseases in turbot has been added at the end. The manual provides a link to the most update information available on live prey production and enrichment.
    Nascholing voor docenten biologie : voortplantingsstrategieën van planten; de evolutionele context
    Bouwman-Smits, L. - \ 2011
    bijscholing - docenten - voortplanting - planten - evolutie - onderwijsmethoden - continuing training - teachers - reproduction - plants - evolution - teaching methods
    Het resultaat van het project is een tweedaagse nascholingscursus voor docenten gericht op voortplantingsstrategieën van planten. De cursisten maken kennis met de seksualiteit van mossen tot zaadplanten. Ze doen hands-on ervaring op met practica en experimenten die ze rechtstreeks kunnen importeren in hun lessen en practica.
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