Usurped

A prose stor

Deadly combinations:Hybrid incompatibilities in the parasitic wasp genus <i>Nasonia</i>

Invloed man zijn en DNA-hoeveelheid bij soortvorming parasitaire wespen Sinds Darwin’s The Origin of Species is er veel onderzoek gedaan naar de processen die een rol spelen bij soortvorming. Het promotieonderzoek van Tosca Koevoets richt zich op het vroege stadium in het proces van soortvorming. Wanneer groepen niet meer in contact staan met elkaar, zullen ze langzaam ten gaan veranderen ten opzichte van elkaar, totdat zij verschillende soorten zijn geworden. Uiteindelijk zullen deze soorten genetisch zo veranderd zijn, dat het combineren van DNA van de verschillende soorten niet meer mogelijk is, wat tot uiting komt in allerlei problemen in de hybride nakomelingen. Deze problemen blijken in het beginstadium van soortvorming anders te zijn in mannen dan in vrouwen. Om te onderzoeken waar dit door komt, maakte Koevoets gebruik van parasitaire wespensoorten uit het geslacht Nasonia. Wespen hebben geen geslachtschromosomen, maar vrouwen ontstaan uit bevruchte eitjes en mannen uit onbevruchte eitjes. Vrouwen hebben dus twee keer zoveel DNA als mannen. Ook bij wespen bleken mannen kwetsbaarder voor hybridisatie dan vrouwen. Deze kwetsbaarheid werd zelfs nog groter onder stressomstandigheden. Dit werd veroorzaakt doordat mannen minder genetische variatie hebben, maar ook doordat ze überhaupt minder DNA hebben. Via een genetische techniek kunnen we er voor zorgen dat bevruchte eitjes (dus eigenlijk bestemd om vrouw te worden) zich tot man ontwikkelen. Daardoor kon onderzocht worden wat belangrijker is: man zijn of de hoeveelheid DNA. Natuurlijk lag het antwoord in het midden; beide facetten bleken belangrijk. Dit onderzoek toont aan dat genetische interacties, de hoeveelheid DNA en de genetische variatie belangrijke aspecten zijn bij het ontstaan van soorten

Perceptions of Early Childhood Educators Who Left the Field: A Case Study

Early childhood education (ECE) educators’ roles in promoting the positive development of children are consistently deemed essential in research. Research also presents the severe problems of burnout and turnover in the ECE field. Specific factors such as low compensation, lack of professional development opportunities, and high-stress environments are causing continued rates of burnout across the early education arena, resulting in ECE educators leaving the field. Therefore, it is important to understand the reasons ECE educators are leaving so these challenges are recognized and remedied. A qualitative descriptive case study was used to examine the issue of ECE educator turnover due to burnout. Participants in the study consisted of ECE educators who had previously worked in an ECE program in the Midwest, and recently left this employment of their own accord. Data collected through semistructured interviews gathered the participants’ perspectives to better understand what motivated them, what challenged them, and what influenced their decision to leave. This data provides identification of the factors that ECE leaders should recognize, understand, and address to increase ECE educator retention

The developing brain and pediatric brain cancer:in the context of genomic integrity, replication stress and DNA damage

During the early development of the embryo, brain development also begins. Because this must occur in a relatively short period of time, the cells experience a lot of stress due to the high speed of cell division. This can lead to mistakes in the DNA, which can lead to mutations. This can eventually develop into (brain) cancer. In this thesis, brain development and two different childhood brain cancers, medulloblastoma and high-grade glioma, are discussed. Medulloblastoma is a cancer that originates in the small brain, the cerebellum. High-grade gliomas can arise in different locations in the biggest part of the brain, the cerebrum. This depends on which mutation it contains. It is thought that these mutations and location in the brain are due to the point in the developmental phase that the brain was in when errors in the DNA developed, with certain phases perhaps more resistant to these errors than others. In addition, this thesis looks at the relationship of healthy cells during brain development and cancer formation by investigating the response to cell division stress and DNA damage of healthy cells. Here, too, cells from different developmental phases of the brain are examined and compared, and the difference in response between cells with and without a certain mutation in these mechanisms is examined. With the research in this thesis we try to gain moreknowledge about why these cancers behave in a certain way and develop

Experimental constraints on Mg isotope fractionation during clay formation: Implications for the global biogeochemical cycle of Mg

The direction and magnitude of magnesium (Mg) isotope fractionation attendant to the formation of clay minerals is fundamental to the use of Mg isotopes to decipher the biogeochemical cycling of Mg in the critical zone and for the oceanic Mg budget. This study provides experimental data on the Mg fractionation factor for two smectite- group minerals (stevensite and saponite) at temperatures relevant for Earth surface processes. The resultant solids were characterised by X-ray di↵raction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) to confirm the mineralogy and crystallinity of the product. A series of experiments were performed to asses the impact of temperature and pH on isotope fractionation. Bulk solid samples were treated with ammonium chloride to remove exchangeable Mg in order to distinguish the Mg isotopic fractionation between these sites and octahedral sites. All bulk and residual solids were enriched in 24Mg compared to the initial solution and 26Mg values of the exchangeable pool were lower than, or within error of, the initial solution. Final solutions were either within error of, or enriched in, 26Mg compared to the initial solution, depending on the fraction of Mg removed from solution (f Mg) For experiments with similar f Mg, increasing the pH resulted in a higher reaction rate and reduced fractionation from the initial solution. This could point to a kinetic effect, but we note composition of the residual solid (Li/Mg ratio) was also dependent on pH. The change in the Li/Mg ratio was reflected in the wavenumber of the Mg3- OH stretch in FT-IR data, which is a proxy for bond strength, and suggests an equilibrium control. An equilibrium control is further supported by the observation of reduced fractionation compared to the initial solution with increasing temperature. Rayleigh and batch fractionation models were fitted to the data giving fractionation factors of 0.9991 and 0.9990 respectively. We compare our results with existing field and experimental data and suggest that the apparent contradictions surrounding the direction of Mg isotope fractionation into phyllosilicate minerals could be due to the similarity of Mg bond lengths between clay octahedral sites and dissolved Mg. Thus small changes in mineral structure or initial solution conditions may result in a change in bond length suffcient to alter the direction of fractionation, implying that the magnitude and direction of Mg isotope fractionation into clay minerals could be dependent on local field conditions. Alternatively, if the precipitation of secondary clay minerals in the field preferentially incorporates light Mg, as observed in this experimental study, this implies the contribution of carbonate weathering to dissolved Mg fluxes has been underestimated, with major implications for the global biogeochemical cycle of Mg.NERC Standard Grant NE/M001865/1 NERC New Investigators Grants NE/K000705/1and NE/K000705/2 Marie Curie Intra-European Fellowship (PIEF-GA-2012-331501) Leverhulme Trust grant PLP-2015-28

Perceptions of Early Childhood Educators Who Left the Field: A Case Study

Early childhood education (ECE) educators’ roles in promoting the positive development of children are consistently deemed essential in research. Research also presents the severe problems of burnout and turnover in the ECE field. Specific factors such as low compensation, lack of professional development opportunities, and high-stress environments are causing continued rates of burnout across the early education arena, resulting in ECE educators leaving the field. Therefore, it is important to understand the reasons ECE educators are leaving so these challenges are recognized and remedied. A qualitative descriptive case study was used to examine the issue of ECE educator turnover due to burnout. Participants in the study consisted of ECE educators who had previously worked in an ECE program in the Midwest, and recently left this employment of their own accord. Data collected through semistructured interviews gathered the participants’ perspectives to better understand what motivated them, what challenged them, and what influenced their decision to leave. This data provides identification of the factors that ECE leaders should recognize, understand, and address to increase ECE educator retention

From Anonymous to Identifiable

A poe