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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    Aanpassing rekenmodel "percentage aal onder de som-TEQ norm"
    Kotterman, M.J.J. ; Vries, P. de - \ 2015
    IJmuiden : IMARES (Rapport / IMARES Wageningen UR C104/15) - 27
    anguillidae - palingen - voedselveiligheid - normen - voedselkwaliteit - berekening - geslachtsverhouding - anguillidae - eels - food safety - standards - food quality - calculation - sex ratio
    Naast het bestaande rekenmodel voor de schatting van het deel van de aalvangst met gehalten som-TEQ onder de voedselveiligheidsnorm (“percentage aal onder de norm”) is nu een rekenmodel gemaakt zodat ook voor de som van niet-dioxine achtige PCBs (som-ndl-PCB) het percentage van de vangst onder de voedselveiligheidsnorm kan worden geschat. De gehalten som-TEQ en som-ndl-PCB in aal zijn aan elkaar gerelateerd, maar een eventuele overschrijding van de norm in aal kan van de som-TEQ, van de somndl-PCB óf van beide normen zijn. Dit kan per locatie verschillen. De norm voor som-ndl-PCBs wordt in de aal uit de onderzochte locaties het vaakst overschreden. Beide normen wegen wettelijk even zwaar; het laagste geschatte percentage aal onder de norm uit beide modellen wordt genomen als hét “percentage aal onder de norm”. Door het gebruik van de norm voor som-TEQ én som-ndl-PCBs wordt het geschatte percentage aal onder de norm in het gesloten gebied lager. Daarnaast zijn de beide modellen aangepast zodat de gemeten man-vrouw verhouding in het gebruikte mengmonster aal in de berekening wordt meegenomen.
    Offspring sex ratio bias and sex related characteristics of eggs in chicken
    Aslam, M.A. - \ 2014
    Wageningen University. Promotor(en): Mari Smits; T.G.G. Groothuis, co-promotor(en): Henri Woelders. - Wageningen : Wageningen University - ISBN 9789462570757 - 192
    kippen - eieren - geslachtsverhouding - karakteristieken - nageslacht - toewijzing - polymerase-kettingreactie - hormonen - voedselbeperking - dierveredeling - fowls - eggs - sex ratio - characteristics - progeny - allocation - polymerase chain reaction - hormones - food restriction - animal breeding

    Understanding the factors influencing sex of egg and sex ratio in laying chicken may lead to finding potential solutions for the problem of killing of day old male chicks, which is the current practice in breeding of laying hens. In studies described in this thesis, it was investigated if the sex of the chicken egg can be predicted by measurable differences in male and female eggs at unincubated stage and if the female primary sex ratio can be induced in laying chicken using different experimental conditions such as feed restriction and corticosterone feeding. The method of sex determination in unincubated chicken eggs using PCR targeted to CHD1 gene was first developed. This method was subsequently used to study the primary sex ratio bias as well as relationship between egg sex and yolk hormones. No significant relationship of the sex of egg with concentrations of several hormones (testosterone, estradiol, androstenedione, progesterone, dihydrotestosterone) and glucose in yolk as well as of egg parameters (mass, width and length) was found. Effect of feed availability on sex ratio was tested in two separate studies. In one study, the rate of change of hen body mass between day of laying and day of laying minus 2 days (encompass time of meiosis completion) was a significant predictor for the sex of that egg, suggesting meiotic drive as mechanism of sex ratio bias. This relationship was not found in the later study. The difference in results could be due to the reason that hens decreased in body mass much less in the later study as compared to earlier study. Blood corticosterone concentrations were associated with sex ratio per hen in the earlier study. Effect of egg mass on egg sex was studied during the later experiment of feed restriction. The egg sex ratio per hen was negatively associated with the average egg mass per hen in the feed restriction group. Two groups of hens were selected from the feed restriction group i.e. male biased hens with low egg mass and female biased hens with high egg mass for microarray analysis of gene expression in the germinal disc of collected F1 follicle. The results did not show differential expression of genes between the groups. However, gene set enrichment analysis showed that a number of processes related to cell cycle progression, mitotic/meiotic apparatus and chromosomal movement were differently enriched between the groups, supporting meiotic drive as potential mechanisms underlying sex ratio determination. In another experiment, blood circulating levels of corticosterone in hens were increased by feeding corticosterone mixed feed under ad libitum. The blood levels of corticosterone were significantly higher in treated hens but these levels were not associated with sex ratio. Treatment did not affect the overall sex ratio, but affected the sex ratio in interaction with hen body mass. In the corticosterone group, sex ratio, laying rate, and fertility rate per hen were decreased in heavy hens. These results suggest that three parameters (sex ratio, laying rate and fertility rate) are connected at the level of ovarian physiology. Interference with meiosis have been shown to affect these three parameters, suggesting the involvement of meiotic drive as mechanism of sex ratio bias.

    When to inseminate the cow? Insemination, ovulation and fertilization in dairy cattle
    Roelofs, J.B. - \ 2005
    Wageningen University. Promotor(en): Bas Kemp, co-promotor(en): Nicoline Nieuwenhuizen-Soede; F.J.C.M. van Eerdenburg. - Wageningen, The Netherlands : Wageningen University - ISBN 9789085042853 - 152
    melkvee - oestrus - kunstmatige inseminatie - ovulatie - bevruchting - diergedrag - gang - geslachtshormonen - geslachtsverhouding - dairy cattle - oestrus - artificial insemination - ovulation - fertilization - animal behaviour - gait - sex hormones - sex ratio
    Keywords: dairy cattle; oestrus; behaviour; pedometer; reproductive hormones; ovulation time; insemination strategy

    In dairy practice, calving rates after first insemination are often less than 50%. Part of this low percentage might be explained by wrongly timed inseminations. The aim was to establish the relationship between various oestrus characteristics and ovulation time in order to investigate whether these oestrus characteristics could predict ovulation time and to study the consequences of variation in the interval between insemination and ovulation on the success of fertilization and embryonic characteristics. The ultimate goal of the project was to come to an optimal insemination strategy that can be used in practice. The relationship between behavioural oestrous signs, changes in activity (measured by pedometers) and progesterone profiles and time of ovulation were. It was shown that monitoring progesterone profiles was not suitable to predict time of ovulation because of the large variation found in the decrease of progesterone relative to ovulation. Although the prediction of ovation time using behavioural oestrus signs was quite accurate, it seems not suitable for practice because of the high labour requirements. The increase in the number of steps measured by pedometers seems useful to predict time of ovulation accurately and could be easily implemented in practice. Effects of the interval between insemination and ovulation on success of fertilization and embryonic characteristics were also studied. It was shown that the insemination-ovulation interval in which high fertilization rates were observed was quite long (insemination from 36 to 12h before ovulation), while the interval in which the majority of fertilized ovum developed into a good quality embryo was considerably shorter (insemination from 24 to 12h before ovulation); the interval between insemination and ovulation did not affect the sex ratio of the embryos.

    In conclusion, the best chance to increase calving rates seems to be to use the insemination strategy, in which cows are inseminated between 5 to 17h after the first increase in the number of steps.
    Mode of action, origin and structure of the Paternal Sex Ratio chromosome in the parasitoid wasp Trichogramma kaykai
    Vugt, J.J.F.A. van - \ 2005
    Wageningen University. Promotor(en): Joop van Lenteren; Rolf Hoekstra, co-promotor(en): Hans de Jong; R. Stouthamer. - - 120
    trichogramma - chromosomen - geslachtsverhouding - geslachtsbepaling - parasitoïden - diploïdie - chromatine - transposons - trichogramma - parasitoids - chromosomes - sex ratio - sex determination - diploidy - chromatin - transposable elements
    Selfish genetic elements are defined as genetic elements that have a replication advantage relative to the rest of the genome. They are ubiquitous in nature and were extensively reported for almost all species studied so far. A special type of selfish genetic element, the sex ratio distorter, is most frequent in arthropods and changes the offspring sex ratio of its host. An example of an extremely selfish male biasing sex ratio distorter is the paternal sex ratio (PSR) chromosome in the parasitoid wasps Trichogramma kaykai and Nasonia vitripennis . These wasps have an arrhenotokous sex determination in which fertilized diploid eggs develop into females and males develop from unfertilized haploid eggs. Only part of the male wasps contains this additional B chromosome, which upon fertilizationeliminates the paternal genome, while keeping itself and the maternal chromosomes intact. The resulting haploid embryo develops into a B chromosome-carrying male. This extremely selfish B chromosome was first discovered in N. vitripennis . The recent discovery of a second PSR chromosome in the unrelated wasp T. kaykai provided an opportunity for a comparative study on PSR chromosomes. In this study I determined the mechanism, the origin and structure of the PSR chromosome in T. kaykai and compared my results with previous studies on the PSR chromosome in N. vitripennis .

    The mode of action of the Trichogramma PSR chromosome was revealed by examining microscopic preparations of freshly fertilized eggs. This chromosome modifies the paternal genome into a dense chromatin mass at the beginning of the first mitotic division, while the PSR chromosome itself escapes its own destructive effect and continues embryo development with the maternal chromosomes. Comparing the modes of action of the Trichogramma and Nasonia PSR chromosomes suggests that both systems are identical, except for the diameter of the paternal chromatin mass (PCM) and the occurrence of PCM-associated nuclei. However, their molecular mechanism remains unknown. Furthermore, both PSR chromosomes share the main structural characteristics of B chromosomes: They are much smaller than the normal chromosomes and contain high amounts of transposable elements and tandem repetitive DNA. B chromosomes are thought to accumulate transposable elements because they do not recombine meiotically with the normal chromosomes. Repeats have proven to be an important factor for the transmission efficiency of the Nasonia PSR chromosomes and are also thought to correlate with the B chromosome size in general. However, none of the DNA sequences found on the Trichogramma PSR chromosome were found on the Nasonia PSR chromosome or visa versa. About two thirds of the Trichogramma PSR chromosome comprises tandem arrays of 45S ribosomal DNA (rDNA), while on the Nasonia PSR chromosome three B chromosome specific repeat families are located and one repeat family that is also present on the Nasonia genome. 45S rDNA consists of three conserved genes essential for protein processing separated by three spacer sequences that are hypervariable between species but conserved within species. These spacer sequences are therefore often used for taxonomic purposes. One of the spacer sequences of the 45S rDNA on the Trichogramma PSR chromosome, i.e. ITS2, contains at least five different sequences that resemble either the ITS2 of T. kaykai or the related T. oleae . We therefore concluded that this B chromosome originated from T. oleae or a T. oleae -like species. Retrotransposon analysis revealed that the Nasonia PSR chromosome most likely originated from the Nasonia related wasp genus Trichomalopsis . Though both PSR chromosomes have a similar mode of action, the absence of any sequence homology between both chromosomes implies different PSR chromosome ancestors. This again makes it less likely that the molecular mechanism of paternal genome loss is identical. Future studies should focus on comparing the molecular mode of action and DNA sequence homology of both PSR chromosomes and revealing the incidence of more PSR chromosomes in other haplo-diploid organisms. This will not only provide more knowledge on the mechanism of early embryogenesis and in particular on the paternal chromosome processing following fertilization, but also on the origin and evolution of PSR chromosomes. Extending our knowledge on PSR chromosomes is expected most useful for the control of pest insects with haplo-diploid sex determination systems like the Argentine ant. Without females such insect populations will quickly perish.
    Evolutionary interactions between sex ratio distorters and their hosts
    Jeong, G.S. - \ 2004
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): R. Stouthamer. - [S.I.] : S.n. - ISBN 9789058089441 - 167
    hymenoptera - gastheren (dieren, mensen, planten) - wolbachia - geslachtsverhouding - gastheer parasiet relaties - parthenogenese - evolutie - hymenoptera - hosts - wolbachia - sex ratio - host parasite relationships - parthenogenesis - evolution
    On the evolution of Wolbachia-induced parthenogenesis in Trichogramma wasps
    Huigens, M.E. - \ 2003
    Wageningen University. Promotor(en): Joop van Lenteren. - [S.l.] : S.n. - ISBN 9789058088475 - 183
    wolbachia - parthenogenese - evolutie - geslachtsverhouding - trichogramma - trichogramma - wolbachia - parthenogenesis - evolution - sex ratio

    Organisms display a great variety of sex ratios (ratios of females vs. males), ranging from 100% females to a male bias. These sex ratios are not always only determined by the genes of the organism itself but may actually often be manipulated or distorted by "sex ratio distorters". One sex ratio distorter, the bacterium Wolbachia that lives in the cytoplasm of the cells of its host organism, has received much attention by biologists all over the world. This interest mainly arises from the fact that it manipulates arthropod or nematode reproduction in several ways - feminization, induction of cytoplasmic incompatibility, male-killing and parthenogenesis-induction - to enhance its own inheritance from mother to daughter. Because sperm cells do not contain enough cytoplasm, they cannot transmit Wolbachia and males are a dead end for the bacterium. Recent estimates of Wolbachia 's prevalence range from 17 to even 76% of the insect species.

    In many wasp, thrips and mite species Wolbachia has switched the mode of reproduction from sexuality to complete parthenogenesis (±100% females). However, in minute parasitoid wasps of the genus Trichogramma , which are used worldwide as natural enemies in biological control of lepidopteran pests, only a part of the females in a population is infected with Wolbachia and can therefore reproduce through parthenogenesis. My aim in this thesis is to gain more insight in the dynamics of parthenogenesis-inducing (PI) Wolbachia and to explain the coexistence of infected and uninfected forms in Trichogramma wasps. After first reviewing the literature on PI Wolbachia in chapter 2 , I tried to further our understanding of the coexistence of the two reproductive forms in natural Trichogramma kaykai and T. deion populations by combining fieldwork, molecular techniques, behavioural- and crossing experiments with model studies.

    Vertical transmission of Wolbachia from mother to daughter has been viewed as the main mode of transmission but in chapter 3 & 4 we show an unexpectedly frequent natural inter- and intraspecific horizontal transmission between and within Trichogrammakaykai and T. deion larvae sharing a common food source, a butterfly egg. Originally uninfected immature wasps could acquire Wolbachia inside the host egg but not all newly infected females exhibit parthenogenesis. In T. kaykai, intraspecific horizontal transfer was followed by complete parthenogenesis in future generations but when T. kaykai females received Wolbachia from T. deion , the infection tended to be lost several generations after interspecific horizontal transfer. Our results largely explain the discordance between Wolbachia - and (Trichogrammatid) host phylogenies. Frequent horizontal transfer might select for high virulence in these bacteria .

    Because of a nuclear-cytoplasmic conflict between Wolbachia and the nuclear genes of Trichogramma and the previously described horizontal transfer of Wolbachia , the infection is most likely associated with fitness costs in populations where infected and uninfected individuals coexist. In chapter 5 we show that infected T. kaykai suffer a reduced survival compared to uninfected conspecifics when they shared the same host. The survival rate of infected immatures was higher when they competed with other infected immatures from a different infected parent than in competition with uninfected immatures. This shows that PI Wolbachia -infected Trichogramma can suffer a substantial fitness cost. Because of this reduced competitive ability of infected larvae, horizontal transfer that occurs under the same superparasitism circumstances does not contribute much to an increase in the infection rate in the population.

    Previous work showed that the presence of another sex ratio distorter in males, a B chromosome called PSR (Paternal Sex Ratio) that destroys the paternal chromosomes after fertilization thereby causing an all-male or a male-biased offspring sex ratio, contributes to a low infection frequency in T. kaykai . In chapter 6 we determined if a PSR factor causes low infection frequencies in other species as well. Therefore, we studied natural populations of three Trichogramma species - T. kaykai , T. deion and T. pratti - from the Mojave Desert. Our data showed that all the male-biased and all-male Trichogramma broods collected from the butterfly Apodemia mormo deserti that contained males expressing the PSR phenotype, belonged to T. kaykai. In laboratory tests, 71.4% of the T. kaykaiPSR males horizontally transmitted the PSR phenotype to T. deion . This percentage is comparable to the transmission rate of PSR to T. kaykai females, namely 81.6%. Consequently, the PSR can be transmitted to T. deion and we expect this to happen in the field because T. kaykai and T. deion sometimes emerge from the same butterfly egg. Despite this, we cannot find PSR in T. deion . Modeling shows that low Wolbachia infection frequencies can only be attained when the PSR rates are very high. Therefore, other factors should keep the PI Wolbachia -infection from spreading to fixation in this species, e.g. nuclear suppressor genes.

    The mating structure in the host population plays a major role in the dynamics of PI Wolbachia and PSR . A PSR factor prevents the Wolbachia infection from spreading to all the females in T. kaykai because uninfected T. kaykai females show a high level of sib (brother-sister) mating. Sib mating is a barrier against the destructive effect of mating with a PSR -carrying male. Infected females do not have this advantage. Using a population genetic model with microsatellites as genetic markers in chapter 7 , we estimated high levels of sib-mating of 70% and an off-patch mating of 15%. Thirty-five percent of the patches were estimated to be parasitized by two T. kaykai females. Incorporating such levels of sib mating in a previously developed model describing the dynamics of PI Wolbachia and PSR in a Trichogramma population, resulted in stable low frequencies of infection, i.e., a coexistence between infected and uninfected individuals, and of the PSR chromosome. Our results show how mating structure allows the two sex ratio distorters to coexist in the population.

    The main conclusion from this thesis is that, despite the high vertical transmission and regular horizontal transfer of Wolbachia , a PI Wolbachia -infection can be attained at low frequencies in Trichogramma , due to the presence of a non-mendelian suppressor, like the male-biasing PSR factor in T. kaykai, but also due to other factors. In T. deion, for example, PSR does not keep the infection frequency at low levels but a nuclear mendelian suppressor against the PI Wolbachia might have evolved.

    Next to their significance for the understanding of the evolutionary pathways of Wolbachia -host interactions, the results reported in this thesis may also have important implications for future use of natural enemies, and more specifically Trichogramma wasps, in inundative biological control. We may now have a good method to render wasps parthenogenetic, via super- or multiparasitism by infected and uninfected females, thereby increasing the efficacy of parasitoid releases against lepidopteran pests.

    Sex ratio in pigs : geslachtsverhouding binnen een toom biggen
    Anonymous, - \ 1986
    [Wageningen] : Pudoc (Literatuurlijst / Pudoc nr. 4623)
    bibliografieën - vruchtbaarheid - varkens - voortplanting - geslacht (sex) - geslachtsverhouding - bibliographies - fertility - pigs - reproduction - sex - sex ratio
    Studies on intersexuality in pigs
    Breeuwsma, A.J. - \ 1970
    Rotterdam : [s.n.] - 127
    varkens - voortplanting - vruchtbaarheid - geslachtsverhouding - geslacht (sex) - embryologie - ontogenie - zoölogie - pigs - reproduction - fertility - sex ratio - sex - embryology - ontogeny - zoology
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