Staff Publications

Staff Publications

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

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

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

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

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    The Price equation as a bridge between animal breeding and evolutionary biology
    Bijma, P. - \ 2020
    Philosophical Transactions of the Royal Society B. Biological sciences 375 (2020)1797. - ISSN 0962-8436 - 1 p.
    artificial selection - breeder's equation - genotype–environment covariance - indirect genetic effect - infectious disease prevalence

    The genetic response to selection is central to both evolutionary biology and animal and plant breeding. While Price's theorem (PT) is well-known in evolutionary biology, most breeders are unaware of it. Rather than using PT, breeders express response to selection as the product of the intensity of selection (i), the accuracy of selection (ρ) and the additive genetic standard deviation (σA); R = iρσA. In contrast to the univariate 'breeder's equation', this expression holds for multivariate selection on Gaussian traits. Here, I relate R = iρσA to PT, and present a generalized version, R = iwρA,wσA, valid irrespective of the trait distribution. Next, I consider genotype-environment covariance in relation to the breeder's equation and PT, showing that the breeder's equation may remain valid depending on whether the genotype-environment covariance works across generations. Finally, I consider the response to selection in the prevalence of an endemic infectious disease, as an example of an emergent trait. The result shows that disease prevalence has much greater heritable variation than currently believed. The example also illustrates that the indirect genetic effect approach moves elements of response to selection from the second to the first term of PT, so that changes acting via the social environment come within the reach of quantitative genetics. This article is part of the theme issue 'Fifty years of the Price equation'.

    Genetics and selective breeding of variation in wing truncation in a flightless aphid control agent
    Lommen, Suzanne T.E. ; Koops, Kees G. ; Cornelder, Bardo A. ; Jong, Peter W. de; Brakefield, Paul M. - \ 2019
    Entomologia Experimentalis et Applicata 167 (2019)7. - ISSN 0013-8703 - p. 636 - 645.
    Adalia bipunctata - artificial selection - augmentative pest control - biological control - Coccinellidae - Coleoptera - cryptic genetic variation - gene-by-environment interaction - ladybird - modifier genes - predator - winglessness

    Augmentative biological control by predaceous ladybird beetles can be improved by using flightless morphs, which have longer residence times on the host plants. The two-spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), is used for the biological control of aphids in greenhouses and on urban trees. Flightlessness due to truncated wings occurs at very low frequency in some natural populations of A. bipunctata. Pure-breeding strains of this 'wingless' genotype of A. bipunctata can easily be obtained in the laboratory. Such strains have not been commercialized yet due to concerns about their reduced fitness compared to wild-type strains, which renders mass production more expensive. Wingless strains exhibit, however, wide intra-population phenotypic variation in the extent of wing truncation which is related to fitness traits. We here use classical quantitative genetic techniques to study the heritability and genetic architecture of variation in wing truncation in a wingless strain of A. bipunctata. Split-families reared at one of two temperatures revealed strong family-by-temperature interaction: heritability was estimated as 0.64 ± 0.09 at 19 °C and 0.29 ± 0.06 at 29 °C. Artificial selection in opposite directions at 21 °C demonstrated that the degree of wing truncation can be altered within a few generations resulting in wingless phenotypes without any wing tissue (realized h2 = 0.72), as well as those with minimal truncations (realized h2 = 0.61) in two replicates. The latter lines produced more than twice as many individuals. This indicates that selective breeding of wing truncation may be exploited to improve mass rearing of flightless strains of A. bipunctata for commercial biological control. Our work illustrates that cryptic variation can also be a source for the selective breeding of natural enemies.

    Next generation biological control – an introduction
    Hesran, Sophie Le; Ras, Erica ; Wajnberg, Eric ; Beukeboom, Leo W. - \ 2019
    Entomologia Experimentalis et Applicata 167 (2019)7. - ISSN 0013-8703 - p. 579 - 583.
    antagonistic micro-organisms - artificial selection - biocontrol - efficacy improvement - experimental evolution - genetic variation - induced plant resistance - molecular tools - natural enemies - parasitoids - pathogens - predators
    Data from: No gains for bigger brains: functional and neuroanatomical consequences of relative brain size in a parasitic wasp
    Woude, E. van der; Groothuis, J. ; Smid, H.M. - \ 2019
    artificial selection - trade-offs - constraints - insects - host-parasite interaction - bidirectional artificial selection - brain-size - appetitive olfactory conditioning - brain scaling - parasitic wasp - parasitoid - longevity - Nasonia vitripennis
    Heritable genetic variation in relative brain size can underlie the relationship between brain performance and the relative size of the brain. We used bidirectional artificial selection to study the consequences of genetic variation in relative brain size on brain morphology, cognition and longevity in Nasonia vitripennis parasitoid wasps. Our results show a robust change in relative brain size after 26 generations of selection and 6 generations of relaxation. Total average neuropil volume of the brain was 16% larger in wasps selected for relatively large brains than in wasps selected for relatively small brains, whereas the body length of the large-brained wasps was smaller. Furthermore, the relative volume of the antennal lobes was larger in wasps with relatively large brains. Relative brain size did not influence olfactory memory retention, whereas wasps that were selected for larger relative brain size had a shorter longevity, which was even further reduced after a learning experience. These effects of genetic variation on neuropil composition and memory retention are different from previously described effects of phenotypic plasticity in absolute brain size. In conclusion, having relatively large brains may be costly for N. vitripennis, whereas no cognitive benefits were recorded.
    Data from: Selection for associative learning of color stimuli reveals correlated evolution of this learning ability across multiple stimuli and rewards.
    Liefting, Maartje ; Hoedjes, K.M. ; Lann, Cécile Le; Smid, H.M. ; Ellers, Jacintha - \ 2018
    Vrije Universiteit Amsterdam
    artificial selection - sensory modality - odour - colour - associative learning
    We are only starting to understand how variation in cognitive ability can result from local adaptations to environmental conditions. A major question in this regard is to what extent selection on cognitive ability in a specific context affects that ability in general through correlated evolution. To address this question we performed artificial selection on visual associative learning in female Nasonia vitripennis wasps. Using appetitive conditioning in which a visual stimulus was offered in association with a host reward, the ability to learn visual associations was enhanced within 10 generations of selection. To test for correlated evolution affecting this form of learning, the ability to readily form learned associations in females was also tested using an olfactory instead of a visual stimulus in the appetitive conditioning. Additionally, we assessed whether the improved associative learning ability was expressed across sexes by colour-conditioning males with a mating reward. Both females and males from the selected lines consistently demonstrated an increased associative learning ability compared to the control lines, independent of learning context or conditioned stimulus. No difference in relative volume of brain neuropils was detected between the selected and control lines.
    Camera vervangt ervaren selecteur
    Kamp, J.A.L.M. - \ 2015
    Boerderij 100 (2015)36. - ISSN 0006-5617 - p. 50 - 53.
    akkerbouw - aardappelen - vermeerderingsmateriaal - detectie - monitoring - diagnostische technieken - fotometrie - pootaardappelen - kwaliteit - kunstmatige selectie - gewasbescherming - precisielandbouw - arable farming - potatoes - propagation materials - detection - monitoring - diagnostic techniques - photometry - seed potatoes - quality - artificial selection - plant protection - precision agriculture
    Selecteren van pootaardappelen kost de teler veel tijd en vergt een hoge mate van vakmanschap. Wellicht kan een machine dat sneller en beter. Daarom start dit jaar het vierjarige project Smart Ziekzoeken Pootaardappelen om te testen of het automatisch opsporen van zieke aardappelplanten haalbaar is. Het project wordt uitgevoerd door Praktijkonderzoek Plant en Omgeving (PPO) en specialisten van Plant Research International (beide onderdeel van Wageningen UR)
    On the fate of seasonally plastic traits in a rainforest butterfly under relaxed selection
    Oostra, V. ; Brakefield, P.M. ; Hiltemann, Y. ; Zwaan, B.J. ; Brattström, O. - \ 2014
    Ecology and Evolution 4 (2014)13. - ISSN 2045-7758 - p. 2654 - 2667.
    sexual size dimorphism - bicyclus-anynana - phenotypic plasticity - reaction norms - life-history - evolutionary significance - artificial selection - geographic-variation - resource-allocation - thermal plasticity
    Many organisms display phenotypic plasticity as adaptation to seasonal environmental fluctuations. Often, such seasonal responses entails plasticity of a whole suite of morphological and life-history traits that together contribute to the adaptive phenotypes in the alternative environments. While phenotypic plasticity in general is a well-studied phenomenon, little is known about the evolutionary fate of plastic responses if natural selection on plasticity is relaxed. Here, we study whether the presumed ancestral seasonal plasticity of the rainforest butterfly Bicyclus sanaos (Fabricius, 1793) is still retained despite the fact that this species inhabits an environmentally stable habitat. Being exposed to an atypical range of temperatures in the laboratory revealed hidden reaction norms for several traits, including wing pattern. In contrast, reproductive body allocation has lost the plastic response. In the savannah butterfly, B. anynana (Butler, 1879), these traits show strong developmental plasticity as an adaptation to the contrasting environments of its seasonal habitat and they are coordinated via a common developmental hormonal system. Our results for B. sanaos indicate that such integration of plastic traits – as a result of past selection on expressing a coordinated environmental response – can be broken when the optimal reaction norms for those traits diverge in a new environment
    Signatures of Diversifying Selection in European Pig Breeds
    Wilkinson, S. ; Lu, Z.H. ; Megens, H.J.W.C. ; Archibald, A.L. ; Haley, C. ; Jackson, I.J. ; Groenen, M.A.M. ; Crooijmans, R.P.M.A. ; Ogden, R. ; Wiener, P. - \ 2013
    Plos Genetics 9 (2013)4. - ISSN 1553-7404
    quantitative trait loci - fatty-acid-composition - coat color - artificial selection - kit-ligand - skin pigmentation - complex traits - teat number - wild boar - ear size
    Following domestication, livestock breeds have experienced intense selection pressures for the development of desirable traits. This has resulted in a large diversity of breeds that display variation in many phenotypic traits, such as coat colour, muscle composition, early maturity, growth rate, body size, reproduction, and behaviour. To better understand the relationship between genomic composition and phenotypic diversity arising from breed development, the genomes of 13 traditional and commercial European pig breeds were scanned for signatures of diversifying selection using the Porcine60K SNP chip, applying a between-population (differentiation) approach. Signatures of diversifying selection between breeds were found in genomic regions associated with traits related to breed standard criteria, such as coat colour and ear morphology. Amino acid differences in the EDNRB gene appear to be associated with one of these signatures, and variation in the KITLG gene may be associated with another. Other selection signals were found in genomic regions including QTLs and genes associated with production traits such as reproduction, growth, and fat deposition. Some selection signatures were associated with regions showing evidence of introgression from Asian breeds. When the European breeds were compared with wild boar, genomic regions with high levels of differentiation harboured genes related to bone formation, growth, and fat deposition.
    Control of Pig Reproduction IX
    Rodriguez-Martinez, H. ; Soede, N.M. ; Flowers, W.L. - \ 2013
    Leicestershire, United Kingdom : Context Products Ltd (Society of Reproduction and Fertility volume 68) - ISBN 9781899043484 - 345
    varkens - geslachtelijke voortplanting - gameten - embryo's - kunstmatige inseminatie - embryotransplantatie - zwangerschap - partus - pasgeborenen - biggen - overleving - biotechnologie - metabolomica - eiwitexpressieanalyse - kunstmatige selectie - pigs - sexual reproduction - gametes - embryos - artificial insemination - embryo transfer - pregnancy - parturition - neonates - piglets - survival - biotechnology - metabolomics - proteomics - artificial selection
    Intrinsic Aerobic Capacity Sets a Divide for Aging and Longevity
    Koch, G. ; Kemi, O.J. ; Qi, N. ; Leng, S.X. ; Bijma, P. ; Gilligan, L.J. ; Wilkinson, J.E. ; Grevenhof, E.M. van - \ 2011
    Circulation Research 109 (2011)10. - ISSN 0009-7330 - p. 1162 - 1172.
    all-cause mortality - left-ventricular mass - exercise capacity - cardiorespiratory fitness - artificial selection - older-adults - risk-factors - cardiovascular-disease - physical-fitness - failing heart
    Rationale: Low aerobic exercise capacity is a powerful predictor of premature morbidity and mortality for healthy adults as well as those with cardiovascular disease. For aged populations, poor performance on treadmill or extended walking tests indicates closer proximity to future health declines. Together, these findings suggest a fundamental connection between aerobic capacity and longevity. Objectives: Through artificial selective breeding, we developed an animal model system to prospectively test the association between aerobic exercise capacity and survivability (aerobic hypothesis). Methods and Results: Laboratory rats of widely diverse genetic backgrounds (N:NIH stock) were selectively bred for low or high intrinsic (inborn) treadmill running capacity. Cohorts of male and female rats from generations 14, 15, and 17 of selection were followed for survivability and assessed for age-related declines in cardiovascular fitness including maximal oxygen uptake (VO2max), myocardial function, endurance performance, and change in body mass. Median lifespan for low exercise capacity rats was 28% to 45% shorter than high capacity rats (hazard ratio, 0.06; P
    Translating environmental gradients into discontinuous reaction norms via hormone signalling in a polyphenic butterfly
    Oostra, V. ; Jong, M.A. de; Invergo, B.M. ; Kesbeke, F. ; Wende, F. ; Brakefield, P.M. ; Zwaan, B.J. - \ 2011
    Proceedings of the Royal Society. B: Biological Sciences 278 (2011)1706. - ISSN 0962-8452 - p. 789 - 797.
    bicyclus-anynana - phenotypic plasticity - developmental plasticity - drosophila-melanogaster - starvation resistance - artificial selection - eyespot size - evolution - responses - canalization
    Polyphenisms—the expression of discrete phenotypic morphs in response to environmental variation—are examples of phenotypic plasticity that may potentially be adaptive in the face of predictable environmental heterogeneity. In the butterfly Bicyclus anynana, we examine the hormonal regulation of phenotypic plasticity that involves divergent developmental trajectories into distinct adult morphs for a suite of traits as an adaptation to contrasting seasonal environments. This polyphenism is induced by temperature during development and mediated by ecdysteroid hormones. We reared larvae at separate temperatures spanning the natural range of seasonal environments and measured reaction norms for ecdysteroids, juvenile hormones (JHs) and adult fitness traits. Timing of peak ecdysteroid, but not JH titres, showed a binary response to the linear temperature gradient. Several adult traits (e.g. relative abdomen mass) responded in a similar, dimorphic manner, while others (e.g. wing pattern) showed a linear response. This study demonstrates that hormone dynamics can translate a linear environmental gradient into a discrete signal and, thus, that polyphenic differences between adult morphs can already be programmed at the stage of hormone signalling during development. The range of phenotypic responses observed within the suite of traits indicates both shared regulation and independent, trait-specific sensitivity to the hormone signal.
    Innovations in the dairy chain: bio-economic analysis of novel breeding opportunities
    Demeter, R.M. - \ 2011
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Alfons Oude Lansink; Miranda Meuwissen; A.R. Kristensen. - [S.l.] : S.n. - ISBN 9789461732088 - 192
    dierveredeling - melkkoeien - zuivelindustrie - kunstmatige selectie - melkproducten - genomica - melkvetpercentage - melkeiwitpercentage - animal breeding - dairy cows - dairy industry - artificial selection - milk products - genomics - milk fat percentage - milk protein percentage
    In recent years, there has been a growing interest in the dairy sector to move from producing bulk dairy commodities towards producing specialized dairy products aimed at niche markets. Dairy farmers consider shifting from commodity milk to raw milk with specialized composition to meet consumer or industrial demands. In this context, the objectives of the thesis were 1) to assess qualitatively future scenarios to create value added in the dairy chain and 2) to ex-ante assess quantitatively the technical and economic implications at farm level of producing differentiated raw milk by using genetic selection. A two-step approach was applied, where the first step assessed qualitatively the strategic opportunities offered by a wide range of novel methods emerging at various stages in the production chain, whereas the second step assessed quantitatively the implications of specific strategies on farm level. The main findings indicate that creating value added is vital for the sustainable growth of the dairy industry, and producing raw milk with specialized characteristics by using novel breeding concepts can play an important role in this process. The ex-ante quantitative assessments have found no evidence that implementing novel genetic selection strategies to change fat or protein composition in milk would have large effects on herd production and profitability. The stakeholders of the dairy industry should initiate joint action plans to capitalize on the opportunities offered by recent milk genomics research.
    Genetic differences among populations in sexual dimorphism: evidence for selection on males in a dioecious plant
    Yu, Q. ; Ellen, E.D. ; Wade, M.J. ; Delph, L.F. - \ 2011
    Journal of Evolutionary Biology 24 (2011)5. - ISSN 1010-061X - p. 1120 - 1127.
    silene-latifolia caryophyllaceae - quantitative genetics - size dimorphism - artificial selection - phenotypic evolution - natural-selection - chloroplast dna - g-matrix - adaptation - traits
    Genetic variation among populations in the degree of sexual dimorphism may be a consequence of selection on one or both sexes. We analysed genetic parameters from crosses involving three populations of the dioecious plant Silene latifolia, which exhibits sexual dimorphism in flower size, to determine whether population differentiation was a result of selection on one or both sexes. We took the novel approach of comparing the ratio of population differentiation of a quantitative trait (QST) to that of neutral genetic markers (FST) for males vs. females. We attributed 72.6% of calyx width variation in males to differences among populations vs. only 6.9% in females. The QST/FST ratio was 4.2 for males vs. 0.4 for females, suggesting that selection on males is responsible for differentiation among populations in calyx width and its degree of sexual dimorphism. This selection may be indirect via genetic correlations with other morphological and physiological traits
    Locus-dependent selection in crop-wild hybrids of lettuce under field conditions and its implication for GM crop development
    Hooftman, D.A.P. ; Flavell, A.J. ; Jansen, J. ; Nijs, J.C.M. den; Syed, N.H. ; Sorensen, A.P. ; Wengel, P.O. ter; Wiel, C.C.M. van de - \ 2011
    Evolutionary Applications 4 (2011)5. - ISSN 1752-4563 - p. 648 - 659.
    sunflower helianthus-annuus - genetically-modified crops - linkage disequilibrium - gene flow - cultivated sunflower - artificial selection - disease resistance - lactuca-serriola - risk-assessment - transgene flow
    Gene escape from crops has gained much attention in the last two decades, as transgenes introgressing into wild populations could affect the latter’s ecological characteristics. However, different genes have different likelihoods of introgression. The mixture of selective forces provided by natural conditions creates an adaptive mosaic of alleles from both parental species. We investigated segregation patterns after hybridization between lettuce (Lactuca sativa) and its wild relative, L. serriola. Three generations of hybrids (S1, BC1, and BC1S1) were grown in habitats mimicking the wild parent’s habitat. As control, we harvested S1 seedlings grown under controlled conditions, providing very limited possibility for selection. We used 89 AFLP loci, as well as more recently developed dominant markers, 115 retrotransposon markers (SSAP), and 28 NBS loci linked to resistance genes. For many loci, allele frequencies were biased in plants exposed to natural field conditions, including over-representation of crop alleles for various loci. Furthermore, Linkage disequilibrium was locally changed, allegedly by selection caused by the natural field conditions, providing ample opportunity for genetic hitchhiking. Our study indicates that when developing genetically modified crops, a judicious selection of insertion sites, based on knowledge of selective (dis)advantages of the surrounding crop genome under field conditions, could diminish transgene persistence.
    Nucleotide variation and footprints of selection in the porcine and chicken genomes
    Amaral, A.J. - \ 2010
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Hendrik-Jan Megens; Henri Heuven. - [S.l. : S.n. - ISBN 9789085856559 - 160
    varkens - kippen - genomen - nucleotiden - genetische diversiteit - kunstmatige selectie - selectief fokken - rassen (dieren) - genetica - pigs - fowls - genomes - nucleotides - genetic diversity - artificial selection - selective breeding - breeds - genetics
    Exploring the effect of sex on empirical fitness landscapes
    Visser, J.A.G.M. de; Park, S.C. ; Krug, J. - \ 2009
    American Naturalist 174 (2009). - ISSN 0003-0147 - p. S15 - S30.
    shifting-balance process - artificial selection - recombination - evolution - populations - adaptation - epistasis - mutations - trajectories - advantage
    The nature of epistasis has important consequences for the evolutionary significance of sex and recombination. Recent efforts to find negative epistasis as a source of negative linkage disequilibrium and associated long-term advantage to sex have yielded little support. Sign epistasis, where the sign of the fitness effects of alleles varies across genetic backgrounds, is responsible for the ruggedness of the fitness landscape, with several unexplored implications for the evolution of sex. Here, we describe fitness landscapes for two sets of strains of the asexual fungus Aspergillus niger involving all combinations of five mutations. We find that 30% of the single-mutation fitness effects are positive despite their negative effect in the wild-type strain and that several local fitness maxima and minima are present. We then compare adaptation of sexual and asexual populations on these empirical fitness landscapes by using simulations. The results show a general disadvantage of sex on these rugged landscapes, caused by the breakdown by recombination of genotypes on fitness peaks. Sex facilitates movement to the global peak only for some parameter values on one landscape, indicating its dependence on the landscape’s topography. We discuss possible reasons for the discrepancy between our results and the reports of faster adaptation of sexual populations
    Genetics of survival in cannibalistic laying hens : the contribution of social effects
    Ellen, E.D. - \ 2009
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Piter Bijma; M.J. Wade. - [S.l. : S.n. - ISBN 9789085853664 - 168
    pluimvee - hennen - eierproductie - kannibalisme - dierveredeling - fokkerijmethoden - sociale interactie - lijnen - kunstmatige selectie - selectie - mortaliteit - overleving - pluimveehokken - diergenetica - poultry - hens - egg production - cannibalism - animal breeding - animal breeding methods - social interaction - lines - artificial selection - selection - mortality - survival - poultry housing - animal genetics
    Mortality due to cannibalism in laying hens is a worldwide economic and welfare problem occurring in all types of commercial poultry housing systems. Due to prohibition of beak-trimming and the traditional battery system in the European Union in the near future, mortality due to cannibalism in laying hens may increase. To reduce mortality in laying hens, it is possible to use genetic selection. Mortality due to cannibalism, however, depends on social interactions between group members. Traditional selection methods neglect these social interactions, meaning that they ignore the genetic effect an individual has on its group members. These methods are, therefore, not very effective. The main aim of this thesis is to investigate the effect of social interactions on the heritable variance in mortality due to cannibalism in laying hens and to develop a selection method that takes into account social interactions.
    To investigate the effect of social interactions on the heritable variance in mortality due to cannibalism, genetic parameters for direct and associative effects on survival time in three layer lines were estimated. For all three layer lines it was found that social interactions contribute approximately two-third of the heritable variation in survival time. The heritable variation in survival time is, therefore, substantially larger than suggested by the traditional methods currently used in poultry breeding.
    To improve traits affected by social interactions in laying hens, a solution is to select individually housed candidates based on the performance of their full sibs kept in family groups. Theoretical results suggest that this selection method offers good opportunities to improve traits affected by social interactions. A selection experiment was applied aiming to improve mortality due to cannibalism in laying hens using selection based on relatives. After one generation, mortality was 10% lower in the selection line compared to the control. In the second generation, no significant effect was found, which seemed to be related to environmental factors.
    Results in this thesis suggest that prospects for reducing mortality due to cannibalism by means of genetic selection are good. Using selection methods that incorporate social interactions may lead to substantial reduction of one of the major welfare problems in egg production. Further research is needed to investigate the effect of group size and kin recognition on social interactions.


    The quantitative genetics of phenotypic variation in animals
    Hill, W.G. ; Mulder, H.A. ; Zhang, X.S. - \ 2007
    Acta Agriculturae Scandinavica Section A-Animal Science 57 (2007)4. - ISSN 0906-4702 - p. 175 - 182.
    mutation-selection balance - environmental variance - drosophila-melanogaster - residual variance - stabilizing selection - directional selection - changing environments - artificial selection - plastic traits - heterogeneity
    Considerable attention has been paid to estimating genetic variability in quantitative traits and to how it is maintained and changed by selection in natural and domesticated populations, but rather little attention has been paid to how levels of environmental and phenotypic variance are influenced. We review recent estimates, showing there is substantial genetic variation in levels of environmental and phenotypic variation. We review evolutionary forces that can affect the level of environmental variation, and find that most models lead to a predicted reduction. We thus argue that its maintenance is a consequence of factors such as the intrinsic cost of homogeneity, phenotypic plasticity to variable environments, or mutants that increase variance. We show how to construct a selection index to predict the magnitude of changes in variance as a result of artificial selection, and consider the opportunities for artificial selection to increase uniformity
    Cold stress and immunity: Do chickens adapt to cold by trading-off immunity for thermoregulation?
    Hangalapura, B.N. - \ 2006
    Wageningen University. Promotor(en): Bas Kemp, co-promotor(en): Henk Parmentier; Henry van den Brand. - s.n. : S.n. - ISBN 9789085043584 - 160
    kippen - koudestress - voedselbeperking - immuniteit - immuniteitsreactie - kunstmatige selectie - genetica - adaptatie - diergezondheid - fowls - cold stress - food restriction - immunity - immune response - artificial selection - genetics - adaptation - animal health
    Future animal husbandry aims at enhanced animal welfare, with minimal use of preventive medical treatments. These husbandry conditions will resemble more natural or ecological conditions. Under such farming systems, animals will experience various kinds of stressors such as environmental (e.g. cold, heat, wind), and social stressors (e.g. pecking in chicken, competition for food). In Western Europe, environmental temperature can drop significantly below the optimal temperature needed for poultry farming during winter season. Apart from cold stress, competition for food could pose nutritional stress in future husbandry practices. Therefore, cold and nutritional stressors can pose a significant threat for poultry farming, as stressors are believed to affect health and welfare of animals. However, effects of cold and nutritional stress on health of poultry are not clearly understood. It has also been proposed that "artificial selection for a trait (e.g. growth, egg production) may program an individual to allocate a large portion of its resources to a demand, leaving it lacking the ability to respond to other demands". Therefore, the focus of this thesis was a) to understand the effects of cold and nutritional stressors on health status (immunocompetence) of two lines of chicken which have selectively been bred for high and low health status (antibody responses). b) to understand the effects of artificially selection on adaptive capacity of chickens to stressful conditions. Important findings of the present thesis are 1. both cold and nutritional stressors did not affect specific antibody responses. 2. both cold and moderate nutritional stressors have positive effect on innate immune component (e.g. phagocytic activity, natural antibody levels), both at cellular and gene levels. 3. cold stress suppresses plasma corticosterone levels in a dose dependent manner, whereas severe nutritional stress enhances plasma corticosterone levels. 4. inverse relation was found between cell mediate immune competence and plasma corticosterone levels. 5. genetic selection for a trait (e.g. selection for either high or low antibody levels) did not affect the immunological adaptive capacity of chickens to both cold and nutritional stressors. It was concluded that cold and nutritional stressors may not pose significant threat for the health of chickens in future farming conditions.
    A comparison of two methods for prediction of response and rates of inbreeding in selected populations with the results obtained in two selection experiments
    Loywyck, V. ; Bijma, P. ; Pinard-van der Laan, M.H. ; Arendonk, J.A.M. van; Verrier, E. - \ 2005
    Genetics, Selection, Evolution 37 (2005). - ISSN 0999-193X - p. 273 - 289.
    red-blood-cells - genetic-variability - mass selection - artificial selection - correlated responses - divergent selection - animal-model - responsiveness - generations - management
    Selection programmes are mainly concerned with increasing genetic gain. However, short-term progress should not be obtained at the expense of the within-population genetic variability. Different prediction models for the evolution within a small population of the genetic mean of a selected trait, its genetic variance and its inbreeding have been developed but have mainly been validated through Monte Carlo simulation studies. The purpose of this study was to compare theoretical predictions to experimental results. Two deterministic methods were considered, both grounded on a polygenic additive model. Differences between theoretical predictions and experimental results arise from differences between the true and the assumed genetic model, and from mathematical simplifications applied in the prediction methods. Two sets of experimental lines of chickens were used in this study: the Dutch lines undergoing true truncation mass selection, the other lines (French) undergoing mass selection with a restriction on the representation of the different families. This study confirmed, on an experimental basis, that modelling is an efficient approach to make useful predictions of the evolution of selected populations although the basic assumptions considered in the models (polygenic additive model, normality of the distribution, base population at the equilibrium, etc.) are not met in reality. The two deterministic methods compared yielded results that were close to those observed in real data, especially when the selection scheme followed the rules of strict mass selection: for instance, both predictions overestimated the genetic gain in the French experiment, whereas both predictions were close to the observed values in the Dutch experiment
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