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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    Genomics of Rapid Evolution in Field Crickets
    Pascoal, Sonia ; Risse, Judith ; Zhang, Xiao ; Blaxter, Mark ; Cezard, Timothee ; Challis, Richard J. ; Gharbi, Karim ; Hunt, John ; Kumar, Sujai ; Langan, Emma ; Liu, Xuan ; Rayner, Jack G. ; Ritchie, Michael G. ; Snoek, Basten ; Trivedi, Urmi ; Bailey, Nathan W. - \ 2020
    University of Edinburgh
    PRJEB24786 - ERP106639 - Teleogryllus oceanicus - cricket - genomics
    This study reveals the genomic architecture of a rapidly evolving mutation which segregates as a single-locus, X-linked trait -- flatwing -- in wild Hawaiian field crickets (Teleogryllus oceanicus). Flatwingsilences males by eliminating sound-producing structures on their forewings. Silence protects them from an acoustically-orienting parasitoid fly (Ormia ochracea), but interferes with their ability to attract and court females for mating. Silent crickets spread rapidly on several Hawaiian islands under pressure from the flies, representing one of the fastest rates of evoutionary change documented in the wild. Here we present an annotated genome sequence of T. oceanicus along with a linkage map and QTL analysis of the trait derived from RAD-sequencing of a backcrossed mapping population. RNA-seq was used to probe the functional pathways affected by the mutation during early development, and pleiotropic effects on another signaling trait, cuticular hydrocarbons, were assessed and genetically mapped.
    Field cricket genome reveals the footprint of recent, abrupt adaptation in the wild
    Pascoal, Sonia ; Risse, Judith E. ; Zhang, Xiao ; Blaxter, Mark ; Cezard, Timothee ; Challis, Richard J. ; Gharbi, Karim ; Hunt, John ; Kumar, Sujai ; Langan, Emma ; Liu, Xuan ; Rayner, Jack G. ; Ritchie, Michael G. ; Snoek, Basten L. ; Trivedi, Urmi ; Bailey, Nathan W. - \ 2020
    Evolution Letters 4 (2020)1. - ISSN 2056-3744 - p. 19 - 33.
    Evolutionary adaptation is generally thought to occur through incremental mutational steps, but large mutational leaps can occur during its early stages. These are challenging to study in nature due to the difficulty of observing new genetic variants as they arise and spread, but characterizing their genomic dynamics is important for understanding factors favoring rapid adaptation. Here, we report genomic consequences of recent, adaptive song loss in a Hawaiian population of field crickets (Teleogryllus oceanicus). A discrete genetic variant, flatwing, appeared and spread approximately 15 years ago. Flatwing erases sound‐producing veins on male wings. These silent flatwing males are protected from a lethal, eavesdropping parasitoid fly. We sequenced, assembled and annotated the cricket genome, produced a linkage map, and identified a flatwing quantitative trait locus covering a large region of the X chromosome. Gene expression profiling showed that flatwing is associated with extensive genome‐wide effects on embryonic gene expression. We found that flatwing male crickets express feminized chemical pheromones. This male feminizing effect, on a different sexual signaling modality, is genetically associated with the flatwing genotype. Our findings suggest that the early stages of evolutionary adaptation to extreme pressures can be accompanied by greater genomic and phenotypic disruption than previously appreciated, and highlight how abrupt adaptation might involve suites of traits that arise through pleiotropy or genomic hitchhiking.
    Organoid Models and Genome Editing to Investigate Fucosylation of Epithelial Receptors and Disease Resistance in Pigs
    Ritchie Martinez, Arabela - \ 2020
    In: Wias Annual Conference 2020. - WIAS - p. 55 - 55.
    Post-weaning diarrhoea (PWD) and oedema disease (OD) in piglets are a major cause of mortality and morbidity in the pig industry, and one of the main reasons for (preventative)antibiotic use worldwide. A leading cause of PWD and OD is infection by enterotoxigenic Escherichia coli (ETEC). It has been shown that a single nucleotide polymorphism in the pig genome of fucosyltransferase-1 (FUT1) decreases risk of intestinal ETEC-F18+ infection,possibly attributed to altered fucosylation patterns. The aim of our study is to elucidate links between epithelial glycoprotein fucosylation and disease resistance through hereditary polymorphisms. To further understand mechanisms on polymorphism-pathogen interactionswe aim to utilize intestinal and airway epithelium organoids. These provide genetically and phenotypically identical models to its host-derived tissue, which can be genetically modified using CRISPR-Cas technology to screen for genotype-to-phenotype susceptibility to pathogen infections. For example, we aim to determine the role of the MUC4-g.8227G>C polymorphism in susceptibility to ETEC-F4+ variants, identify which epithelial glycoproteins are expressed at different locations in the intestine, and determine which receptors are used for colonisation by ETEC. We anticipate that this innovative approach will greatly increase our understanding of infectious disease resistance mechanisms in pigs. Our research could provide important contributions towards breeding programmes aiming to increase disease resistance, reducing antibiotic use and possibly antibiotic resistance for the benefit of humans and animals. Furthermore, the advanced models and methodologies we are developing will benefit scientific research on pigs, while reducing the need for experimental animals
    Shifts in national land use and food production in Great Britain after a climate tipping point
    Ritchie, Paul D.L. ; Smith, Greg S. ; Davis, Katrina J. ; Fezzi, Carlo ; Halleck-Vega, Solmaria ; Harper, Anna B. ; Boulton, Chris A. ; Binner, Amy R. ; Day, Brett H. ; Gallego-Sala, Angela V. ; Mecking, Jennifer V. ; Sitch, Stephen A. ; Lenton, Timothy M. ; Bateman, Ian J. - \ 2020
    Nature Food 1 (2020)1. - ISSN 2662-1355 - p. 76 - 83.
    Climate change is expected to impact agricultural land use. Steadily accumulating changes in temperature and water availability can alter the relative profitability of different farming activities and promote land-use changes. There is also potential for high-impact ‘climate tipping points’, where abrupt, nonlinear change in climate occurs, such as the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC). Here, using data from Great Britain, we develop a methodology to analyse the impacts of a climate tipping point on land use and economic outcomes for agriculture. We show that economic and land-use impacts of such a tipping point are likely to include widespread cessation of arable farming with losses of agricultural output that are an order of magnitude larger than the impacts of climate change without an AMOC collapse. The agricultural effects of AMOC collapse could be ameliorated by technological adaptations such as widespread irrigation, but the amount of water required and the costs appear to be prohibitive in this instance.
    RNA-seq data from Teleogryllus oceanicus embryos of silent and singing morphs
    Pascoal, Sonia ; Risse, Judith ; Zhang, Xiao ; Blaxter, Mark ; Cezard, Timothee ; Challis, Richard J. ; Gharbi, Karim ; Hunt, John ; Kumar, Sujai ; Langan, Emma ; Liu, Xuan ; Rayner, Jack G. ; Ritchie, Michael G. ; Snoek, Basten ; Trivedi, Urmi ; Bailey, Nathan W. - \ 2019
    University of St Andrews
    PRJEB27235 - ERP109294 - Teleogryllus oceanicus
    RNA-seq data collected from Teleogryllus oceanicus of silent and singing morphs at embryonic stages
    SBfI RADseq of Teleogryllus oceanicus F3 cross between Daintree and Kailua flat-wing crickets
    Pascoal, Sonia ; Risse, Judith ; Zhang, Xiao ; Blaxter, Mark ; Cezard, Timothee ; Gharbi, Karim ; Hunt, John ; Kumar, Sujai ; Langan, Emma ; Liu, Xuan ; Rayner, Jack G. ; Ritchie, Michael G. ; Snoek, Basten ; Trivedi, Urmi ; Bailey, Nathan W. - \ 2019
    Wageningen University
    PRJEB29921 - ERP112280 - Teleogryllus oceanicus
    Large changes in Great Britain's vegetation and agricultural land-use predicted under unmitigated climate change
    Ritchie, P.D.L. ; Harper, Anna B. ; Smith, G.S. ; Kahana, R. ; Kendon, Elizabeth J. ; Lewis, Huw ; Fezzi, Carlo ; Halleck Vega, Sol Maria ; Boulton, C.A. ; Bateman, I.J. ; Lenton, T.M. - \ 2019
    Environmental Research Letters 14 (2019). - ISSN 1748-9326
    vegetation productivity - GB - arable production - unmitigated climate change - RCP8.5
    The impact of climate change on vegetation including agricultural production has been the focus of many studies. Climate change is expected to have heterogeneous effects across locations globally, and the diversity of land uses characterising Great Britain (GB) presents a unique opportunity to testmethods for assessing climate change effects and impacts. GB is a relatively cool and damp country, hence, the warmer and generally drier growing season conditions projected for the future are expected to increase arable production. Here we use state-of-the-art, kilometre-scale climate change scenarios to drive a land surface model (JULES; Joint UK Land Environment Simulator) and anECOnometricAGricultural land use model (ECO-AG). Under unmitigated climate change, by the end of the century, the growing season in GB is projected to get>5 °C warmer and 140 mm drier on average. Rising levels of atmospheric CO2 are predicted to counteract the generally negative impacts of climate change on vegetation productivity in JULES. Given sufficient precipitation, warming favours higher value arable production over grassland agriculture, causing a predicted westward expansion of arable farming in ECO-AG. However, drying in the East and Southeast, without any CO2 fertilisation effect, is severe enough to cause a predicted reversion from arable to grassland farming. Irrigation, if implemented, could maintain this land in arable production. However, the predicted irrigation demand of ∼200 mm (per growing season) in many locations is comparable to annual predicted runoff, potentially demanding large-scale redistribution of water between seasons and/or across the country. The strength of the CO2 fertilisation effect emerges as a crucial uncertainty in projecting the impact of climate change on GB vegetation, especially farming land-use decisions.
    Predicting the spatial dynamics of Wolbachia infections in Aedes aegypti arbovirus vector populations in heterogeneous landscapes
    Hancock, Penelope A. ; Ritchie, Scott A. ; Koenraadt, Constantianus J.M. ; Scott, Thomas W. ; Hoffmann, Ary A. ; Godfray, Charles - \ 2019
    Journal of Applied Ecology 56 (2019)7. - ISSN 0021-8901 - p. 1674 - 1686.
    arbovirus - dengue - gene drive - spatial spread - wAlbB - wMel - wMelPop - Zika

    A promising strategy for reducing the transmission of dengue and other arboviral human diseases by Aedes aegypti mosquito vector populations involves field introductions of the endosymbiotic bacteria Wolbachia. Wolbachia infections inhibit viral transmission by the mosquito, and can spread between mosquito hosts to reach high frequencies in the vector population. Wolbachia spreads by maternal transmission, and spread dynamics can be variable and highly dependent on natural mosquito population dynamics, population structure and fitness components. We develop a mathematical model of an A. aegypti metapopulation that incorporates empirically validated relationships describing density-dependent mosquito fitness components. We assume that density dependent relationships differ across subpopulations, and construct heterogeneous landscapes for which model-predicted patterns of variation in mosquito abundance and demography approximate those observed in field populations. We then simulate Wolbachia release strategies similar to that used in field trials. We show that our model can produce rates of spatial spread of Wolbachia similar to those observed following field releases. We then investigate how different types of spatio-temporal variation in mosquito habitat, as well as different fitness costs incurred by Wolbachia on the mosquito host, influence predicted spread rates. We find that fitness costs reduce spread rates more strongly when the habitat landscape varies temporally due to stochastic and seasonal processes. Synthesis and applications: Our empirically based modelling approach represents effects of environmental heterogeneity on the spatial spread of Wolbachia. The models can assist in interpreting observed spread patterns following field releases and in designing suitable release strategies for targeting spatially heterogeneous vector populations.

    Opposing patterns of intraspecific and interspecific differentiation in sex chromosomes and autosomes
    Moran, Peter A. ; Pascoal, Sonia ; Cezard, Timothee ; Risse, J.E. ; Ritchie, Michael G. ; Bailey, Nathan W. - \ 2018
    PRJEB26502 - ERP108494 - Teleogryllus commodus
    Comparing the geographic distribution of genome-wide variation at autosomal and X-loci among populations of two closely related field cricket species, Teleogryllus commodus and T. oceanicus.
    Data from: Opposing patterns of intraspecific and interspecific differentiation in sex chromosomes and autosomes
    Moran, Peter A. ; Pascoal, Sonia ; Cezard, Timothee ; Risse, J.E. ; Ritchie, Michael G. ; Bailey, Nathan W. - \ 2018
    hybridization - faster X effect - population genomics - sex chromosomes - RAD sequencing - Teleogryllus oceanicus - Teleogryllus commodus - Teleogryllus marini - Teleogryllus
    Linking intraspecific and interspecific divergence is an important challenge in speciation research. X chromosomes are expected to evolve faster than autosomes and disproportionately contribute to reproductive barriers, and comparing genetic variation on X and autosomal markers within and between species can elucidate evolutionary processes that shape genome variation. We performed RADseq on a 16-population transect of two closely-related Australian cricket species, Teleogryllus commodus and T. oceanicus, covering allopatry and sympatry. This classic study system for sexual selection provides a rare exception to Haldane’s rule, as hybrid females are sterile. We found no evidence of recent introgression, despite the fact that the species co-exist in overlapping habitats in the wild and interbreed in the laboratory. Putative X-linked loci showed greater differentiation between species compared to autosomal loci. However, population differentiation within species was unexpectedly lower on X-linked markers than autosomal markers, and relative X-to-autosomal genetic diversity was inflated above neutral expectations. Populations of both species showed genomic signatures of recent population expansions, but these were not strong enough to account for the inflated X/A diversity. Instead, most of the excess polymorphism on the X could better be explained by sex-biased processes that increase the relative effective population size of the X, such as interspecific variation in the strength of sexual selection among males. Taken together, the opposing patterns of diversity and differentiation at X versus autosomal loci implicate a greater role for sex-linked genes in maintaining species boundaries in this system.
    Opposing patterns of intraspecific and interspecific differentiation in sex chromosomes and autosomes
    Moran, Peter A. ; Pascoal, Sonia ; Cezard, Timothee ; Risse, Judith E. ; Ritchie, Michael G. ; Bailey, Nathan W. - \ 2018
    Molecular Ecology 27 (2018)19. - ISSN 0962-1083 - p. 3905 - 3924.
    faster-X effect - hybridization - population genomics - RAD sequencing - sex chromosomes - Teleogryllus

    Linking intraspecific and interspecific divergence is an important challenge in speciation research. X chromosomes are expected to evolve faster than autosomes and disproportionately contribute to reproductive barriers, and comparing genetic variation on X and autosomal markers within and between species can elucidate evolutionary processes that shape genome variation. We performed RADseq on a 16 population transect of two closely related Australian cricket species, Teleogryllus commodus and T. oceanicus, covering allopatry and sympatry. This classic study system for sexual selection provides a rare exception to Haldane's rule, as hybrid females are sterile. We found no evidence of recent introgression, despite the fact that the species coexist in overlapping habitats in the wild and interbreed in the laboratory. Putative X-linked loci showed greater differentiation between species compared with autosomal loci. However, population differentiation within species was unexpectedly lower on X-linked markers than autosomal markers, and relative X-to-autosomal genetic diversity was inflated above neutral expectations. Populations of both species showed genomic signatures of recent population expansions, but these were not strong enough to account for the inflated X/A diversity. Instead, most of the excess polymorphism on the X could better be explained by sex-biased processes that increase the relative effective population size of the X, such as interspecific variation in the strength of sexual selection among males. Taken together, the opposing patterns of diversity and differentiation at X versus autosomal loci implicate a greater role for sex-linked genes in maintaining species boundaries in this system.

    Differential gene expression is not required for facultative sex allocation : A transcriptome analysis of brain tissue in the parasitoid wasp nasonia vitripennis
    Cook, Nicola ; Boulton, Rebecca A. ; Green, Jade ; Trivedi, Urmi ; Tauber, Eran ; Pannebakker, Bart A. ; Ritchie, Michael G. ; Shuker, David M. - \ 2018
    Royal Society Open Science 5 (2018)2. - ISSN 2054-5703 - 8 p.
    Behavioural genetics - Local mate competition - Nasonia - Parasitoid - Sex allocation - Transcriptomics
    Whole-transcriptome technologies have been widely used in behavioural genetics to identify genes associated with the performance of a behaviour and provide clues to its mechanistic basis. Here, we consider the genetic basis of sex allocation behaviour in the parasitoid wasp Nasonia vitripennis. Female Nasonia facultatively vary their offspring sex ratio in line with Hamilton’s theory of local mate competition (LMC). A single female or ‘foundress’ laying eggs on a patch will lay just enough sons to fertilize her daughters. As the number of ‘foundresses’ laying eggs on a patch increases (and LMC declines), females produce increasingly male-biased sex ratios. Phenotypic studies have revealed the cues females use to estimate the level of LMC their sons will experience, but our understanding of the genetics underlying sex allocation is limited. Here, we exposed females to three foundress number conditions, i.e. three LMC conditions, and allowed them to oviposit. mRNA was extracted from only the heads of these females to target the brain tissue. The subsequent RNA-seq experiment confirmed that differential gene expression is not
    Winter distribution of plaice (Pleuronectes platessa) and lemon sole (Microstomus kitt) larvae in the English Channel and North Sea inferred from the 2016 IBTS sampling
    Pernak, M. ; Giraldo, C. ; Huwer, B. ; Damme, C.J.G. van; Nash, R. ; Klopmann, M. ; Ritchie, L. ; Loots, C. - \ 2017
    Although most fish species spawn during spring, ensuring a temporal coincidence of their larvae with the planktonic bloom, several spawn during winter. During the International Bottom Trawl Survey (IBTS), the MRN (Midwater Ring Net) sampling is performed each year during winter (January-February) all over the eastern English Channel (EEC) and North Sea. Until now, MRN data have been mainly used for stock assessment of North Sea Herring. Hence, the aim of the present study is to focus on others species (especially flatfishes) found in samples collected in 2016 and to determine spatial patterns in larval fish assemblages in relation to environmental conditions.
    Should the Lion Eat Straw Like the Ox? Animal Ethics and the Predation Problem
    Keulartz, Jozef - \ 2016
    Journal of Agricultural and Environmental Ethics (2016). - ISSN 1187-7863 - 22 p.
    Capability approach - Political theory of animal rights - Predation problem - Rights theories - Utilitarianism

    Stephen Clark’s article The Rights of Wild Things from 1979 was the starting point for the consideration in the animal ethics literature of the so-called ‘predation problem’. Clark examines the response of David George Ritchie to Henry Stephens Salt, the first writer who has argued explicitly in favor of animal rights. Ritchie attempts to demonstrate—via reductio ad absurdum—that animals cannot have rights, because granting them rights would oblige us to protect prey animals against predators that wrongly violate their rights. This article navigates the reader through the debate sparked off by Clarke’s article, with as final destination what I consider to be the best way to deal with the predation problem. I will successively discuss arguments against the predation reductio from Singer’s utilitarian approach, Regan’s deontological approach, Nussbaum’s capability approach, and Donadson and Kymlicka’s political theory of animal rights.

    Oviposition but not sex allocation is associated with transcriptomic changes in females of the parasitoid wasp Nasonia vitripennis
    Cook, Nicola ; Trivedi, Urmi ; Pannebakker, B.A. ; Blaxter, Mark ; Ritchie, Michael G. ; Tauber, Eran ; Sneddon, Tanya ; Shuker, David M. - \ 2015
    G3 : Genes Genomes Genetics 5 (2015)12. - ISSN 2160-1836 - p. 2885 - 2892.
    Behavior - Competition - Gene expression - Local mate - Sex allocation - Transcriptomics

    Linking the evolution of the phenotype to the underlying genotype is a key aim of evolutionary genetics and is crucial to our understanding of how natural selection shapes a trait. Here, we consider the genetic basis of sex allocation behavior in the parasitoid wasp Nasonia vitripennis using a transcriptomics approach. Females allocate offspring sex in line with the local mate competition (LMC) theory. Female-biased sex ratios are produced when one or a few females lay eggs on a patch. As the number of females contributing offspring to a patch increases, less female-biased sex ratios are favored. We contrasted the transcriptomic responses of females as they oviposit under conditions known to influence sex allocation: foundress number (a social cue) and the state of the host (parasitized or not). We found that when females encounter other females on a patch or assess host quality with their ovipositors, the resulting changes in sex allocation is not associated with significant changes in whole-body gene expression. We also found that the gene expression changes produced by females as they facultatively allocate sex in response to a host cue and a social cue are very closely correlated. We expanded the list of candidate genes associated with oviposition behavior in Nasonia, some of which may be involved in fundamental processes underlying the ability to facultatively allocate sex, including sperm storage and utilization.

    Variably protease-sensitive prionopathy in the UK: a retrospective review 1991-2008
    Head, M.W. ; Yull, H.M. ; Ritchie, D.L. ; Langeveld, J.P.M. ; Fletcher, N.A. ; Knight, R.S. ; Ironside, J.W. - \ 2013
    Brain 136 (2013)4. - ISSN 0006-8950 - p. 1102 - 1115.
    creutzfeldt-jakob-disease - abnormal prion protein - straussler-scheinker-disease - atypical scrapie - phenotype - patient - prp
    Variably protease-sensitive prionopathy is a newly described human prion disease of unknown aetiology lying out with the hitherto recognized phenotypic spectrum of Creutzfeldt-Jakob disease. Two cases that conform to the variably protease-sensitive prionopathy phenotype have been identified prospectively in the U.K. since the first description of the condition in 2008 in the U.S.A. To determine the incidence and phenotype of variably protease-sensitive prionopathy within a single well-defined cohort, we have conducted a retrospective review of patients referred to the National Creutzfeldt-Jakob Disease Research & Surveillance Unit during the period 1991-2008. The approach taken was to screen frozen brain tissue by western blotting for the form of protease-resistant prion protein that characterizes variably protease-sensitive prionopathy, followed by neuropathological and clinical review of candidate cases. Cases diagnosed as sporadic Creutzfeldt-Jakob disease with atypical neuropathology were also reviewed. Four hundred and sixty-five cases were screened biochemically, yielding four candidate cases of variably protease-sensitive prionopathy. One was discounted on pathological and clinical grounds, and one was a known case of variably protease-sensitive prionopathy previously reported, leaving two new cases, which were confirmed biochemically and neuropathologically as variably protease-sensitive prionopathy. A third new case that lacked frozen tissue was recognized retrospectively on neuropathological grounds alone. This means that five cases of variably protease-sensitive prionopathy have been identified (prospectively and retrospectively) during the surveillance period 1991-2011 in the U.K. Assuming ascertainment levels equivalent to that of other human prion diseases, these data indicate that variably protease-sensitive prionopathy is a rare phenotype within human prion diseases, which are themselves rare. Biochemical investigation indicates that the abnormal protease-resistant prion protein fragment that characterizes variably protease-sensitive prionopathy is detectable at low levels in some cases of sporadic Creutzfeldt-Jakob disease and conversely, that the form of abnormal prion protein that characterizes sporadic Creutzfeldt-Jakob disease can be found in certain brain regions of cases of variably protease-sensitive prionopathy, indicating molecular overlaps between these two disorders.
    Epidemiology and integrated control of Potato Late Blight in Europe
    Cooke, R.J. ; Schepers, H.T.A.M. ; Hermansen, A. ; Bain, R. ; Bradshaw, N. ; Ritchie, F. ; Shaw, D.S. ; Evenhuis, A. ; Kessel, G.J.T. ; Wander, J.G.N. ; Andersson, B. ; Hansen, J.G. ; Hannukkala, A. ; Naerstad, R. ; Nielsen, B. - \ 2011
    Potato Research 54 (2011)2. - ISSN 0014-3065 - p. 183 - 222.
    phytophthora-infestans population - a2 mating-type - genotypic diversity - northern-ireland - foliar aggressiveness - metalaxyl resistance - great-britain - r-genes - netherlands - cultivars
    Phytophthora infestans, the causal agent of late blight, is a major threat to potato production in northwestern Europe. Before 1980, the worldwide population of P. infestans outside Mexico appeared to be asexual and to consist of a single clonal lineage of A1 mating type characterized by a single genotype. It is widely believed that new strains migrated into Europe in 1976 and that this led to subsequent population changes including the introduction of the A2 mating type. The population characteristics of recently collected isolates in NW Europe show a diverse population including both mating types, sexual reproduction and oospores, although differences are observed between regions. Although it is difficult to find direct evidence that new strains are more aggressive, there are several indications from experiments and field epidemics that the aggressiveness of P. infestans has increased in the past 20 years. The relative importance of the different primary inoculum sources and specific measures for reducing their role, such as covering dumps with plastic and preventing seed tubers from becoming infected, is described for the different regions. In NW Europe, varieties with greater resistance tend not to be grown on a large scale. From the grower’s perspective, the savings in fungicide input that can be achieved with these varieties are not compensated by the higher (perceived) risk of blight. Fungicides play a crucial role in the integrated control of late blight. The spray strategies in NW Europe and a table of the specific attributes of the most important fungicides in Europe are presented. The development and use of decision support systems (DSSs) in NW Europe are described. In The Netherlands, it is estimated that almost 40% of potato growers use recommendations based on commercially available DSS. In the Nordic countries, a new DSS concept with a fixed 7-day spray interval and a variable dose rate is being tested. In the UK, commercially available DSSs are used for c. 8% of the area. The validity of Smith Periods for the new population of P. infestans in the UK is currently being evaluated.
    Detection of type 1 prion protein in variant Creutzfeldt-Jakob disease
    Yull, H.M. ; Ritchie, D.L. ; Langeveld, J.P.M. ; Zijderveld, F.G. van; Bruce, M.E. ; Ironside, J.W. ; Head, M.W. - \ 2006
    American Journal of Pathology 168 (2006)1. - ISSN 0002-9440 - p. 151 - 157.
    bovine spongiform encephalopathy - molecular classification - sheep scrapie - bse - cjd - prpsc - mice - transmissions - heterogeneity - phenotype
    Molecular typing of the abnormal form of the prion protein (PrPSc) has come to be regarded as a powerful tool in the investigation of the prion diseases. All evidence thus far presented indicates a single PrPSc molecular type in variant Creutzfeldt-Jakob disease (termed type 2B), presumably resulting from infection with a single strain of the agent (bovine spongiform encephalopathy). Here we show for the first time that the PrPSc that accumulates in the brain in variant Creutzfeldt-Jakob disease also contains a minority type 1 component. This minority type 1 PrPSc was found in all 21 cases of variant Creutzfeldt-Jakob disease tested, irrespective of brain region examined, and was also present in the variant Creutzfeldt-Jakob disease tonsil. The quantitative balance between PrPSc types was maintained when variant Creutzfeldt-Jakob disease was transmitted to wild-type mice and was also found in bovine spongiform encephalopathy cattle brain, indicating that the agent rather than the host specifies their relative representation. These results indicate that PrPSc molecular typing is based on quantitative rather than qualitative phenomena and point to a complex relationship between prion protein biochemistry, disease phenotype and agent strain
    Herbivore impact on grassland plant diversity depens on habitat productivity and herbivore size.
    Bakker, E.S. ; Ritchie, M.E. ; Olff, H. ; Milchunas, D.G. ; Knops, J.M.H. - \ 2006
    Ecology Letters 9 (2006)7. - ISSN 1461-023X - p. 780 - 788.
    species-richness - tallgrass prairie - community structure - establishment - recruitment - germination - disturbance - gradient - seed - environments
    Mammalian herbivores can have pronounced effects on plant diversity but are currently declining in many productive ecosystems through direct extirpation, habitat loss and fragmentation, while being simultaneously introduced as livestock in other, often unproductive, ecosystems that lacked such species during recent evolutionary times. The biodiversity consequences of these changes are still poorly understood. We experimentally separated the effects of primary productivity and herbivores of different body size on plant species richness across a 10-fold productivity gradient using a 7-year field experiment at seven grassland sites in North America and Europe. We show that assemblages including large herbivores increased plant diversity at higher productivity but decreased diversity at low productivity, while small herbivores did not have consistent effects along the productivity gradient. The recognition of these large-scale, cross-site patterns in herbivore effects is important for the development of appropriate biodiversity conservation strategies
    Small mammalian herbivores as mediators of plant community dynamics in the high-altitude arid rangelands of Trans-Himalaya
    Bagchi, S. ; Namgail, T. ; Ritchie, M.E. - \ 2006
    Biological Conservation 127 (2006)4. - ISSN 0006-3207 - p. 438 - 442.
    traditional pastoralism - ochotona-princeps - alpine meadow - vegetation - degradation - disturbance - competition - diversity - engineers - responses
    The high-altitude rangelands of the Trans-Himalaya represent a grazing ecosystem which has supported an indigenous pastoral community for millennia alongside a diverse assemblage of wild herbivores including burrowing mammals (pikas and voles). Pastoralists consider the small mammals to cause rangeland degradation and as competitors for their livestock, and actively eradicate them at many places. We present data on the ways in which small herbivores like pikas and voles mediate plant community dynamics. Vegetation cover and plant species richness were compared on and off both active and abandoned small mammal colonies. Plant species richness was higher inside colonies (about 4¿5 species/plot) than outside (about 3 species/plot) whereas vegetation cover was only marginally lower (52% compared to 60%). Soil disturbance due to small mammals is seen to be associated with higher plant diversity without causing dramatic decline in overall vegetation cover. Such disturbance-mediated dynamics and vegetation mosaics produce a rich array of testable hypotheses that can highlight how small mammals influence assembly processes, succession, and dominance hierarchies in plant communities in this arid ecosystem. So, eradicating small mammals may lead to declining levels of diversity in this ecosystem, and compromise ecosystem-functioning. Changes in traditional pastoral practices and overstocking are more likely to be responsible for degradation. We emphasize that eradicating small mammals can lead to loss of diversity in this ecosystem and it is not a solution for the degradation problems
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