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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    Interplay of robustness and plasticity of life history traits in habitats with different thermal regimes
    Liefting, M. ; Grunsven, R.H.A. van; Morrissey, M.B.M. ; Timmermans, M. ; Ellers, J. - \ 2015
    Journal of Evolutionary Biology 28 (2015)5. - ISSN 1010-061X - p. 1057 - 1066.
    orchesella-cincta collembola - wild bird population - phenotypic plasticity - reaction norms - genetic-structure - environmental canalization - drosophila-melanogaster - indeterminate growth - soil arthropod - evolution
    Phenotypic plasticity describes the ability of an individual to alter its phenotype in response to the environment and is potentially adaptive when dealing with environmental variation. However, robustness in the face of a changing environment may often be beneficial for traits that are tightly linked to fitness. We hypothesized that robustness of some traits may depend on specific patterns of plasticity within and among other traits. We used a reaction norm approach to study robustness and phenotypic plasticity of three life-history traits of the collembolan Orchesella cincta in environments with different thermal regimes. We measured adult mass, age at maturity and growth rate of males and females from heath and forest habitats at two temperatures (12 and 22 °C). We found evidence for ecotype-specific robustness of female adult mass to temperature, with a higher level of robustness in the heath ecotype. This robustness is facilitated by plastic adjustments of growth rate and age at maturity. Furthermore, female fecundity is strongly influenced by female adult mass, explaining the importance of realizing a high mass across temperatures for females. These findings indicate that different predicted outcomes of life-history theory can be combined within one species' ontogeny and that models describing life-history strategies should not assume that traits like growth rate are maximized under all conditions. On a methodological note, we report a systematic inflation of variation when standard deviations and correlation coefficients are calculated from family means as opposed to individual data within a family structure.
    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
    A bio-economic analysis of harvest control rules for the Northeast Arctic cod fishery
    Eikeset, A.M. ; Richter, A.P. ; Dankel, D.J. ; Dunlop, E.S. ; Heino, M. ; Dieckmann, U. ; Stenseth, N.C. - \ 2013
    Marine Policy 39 (2013). - ISSN 0308-597X - p. 172 - 181.
    reaction norms - gadus-morhua - management - stock - economics - model - recruitment - maturation - evolution - fecundity
    Harvest control rules (HCRs) have been implemented for many fisheries worldwide. However, in most instances, those HCRs are not based on the explicit feedbacks between stock properties and economic considerations. This paper develops a bio-economic model that evaluates the HCR adopted in 2004 by the Joint Norwegian-Russian Fishery Commission to manage the world's largest cod stock, Northeast Arctic cod (NEA). The model considered here is biologically and economically detailed, and is the first to compare the performance of the stock's current HCR with that of alternative HCRs derived with optimality criteria. In particular, HCRs are optimized for economic objectives including fleet profits, economic welfare, and total yield and the merging properties are analyzed. The performance of these optimal HCRs was compared with the currently used HCR. This paper show that the current HCR does in fact comes very close to maximizing profits. Furthermore, the results reveal that the HCR that maximizes profits is the most precautionary one among the considered HCRs. Finally, the HCR that maximizes yield leads to unprecautionary low levels of biomass. In these ways, the implementation of the HCR for NEA cod can be viewed as a success story that may provide valuable lessons for other fisheries
    Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment- and trait-specific effects
    Saastamoinen, M. ; Brommer, J.E. ; Brakefield, P.M. ; Zwaan, B.J. - \ 2013
    Ecology and Evolution 3 (2013)10. - ISSN 2045-7758 - p. 3576 - 3589.
    bicyclus-anynana - phenotypic plasticity - life-history - adaptive responses - reaction norms - evolution - growth - genotype - evolvability - canalization
    Different components of heritability, including genetic variance (VG), are influenced by environmental conditions. Here, we assessed phenotypic responses of life-history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full-sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype-by-environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental-specific heritabilities as well as some indication of cross-environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition-dependent gene expression
    Estimation of genetic variance for macro- and micro-environmental sensitivity using double hierarchical generalized linear models
    Mulder, H.A. ; Ronnegard, L. ; Veerkamp, R.F. ; Strandberg, E. - \ 2013
    Genetics, Selection, Evolution 45 (2013). - ISSN 0999-193X - 24 p.
    phenotypic plasticity - residual variance - dairy-cattle - environment interactions - developmental stability - breeding values - milk-production - reaction norms - selection - genotype
    Background Genetic variation for environmental sensitivity indicates that animals are genetically different in their response to environmental factors. Environmental factors are either identifiable (e.g. temperature) and called macro-environmental or unknown and called micro-environmental. The objectives of this study were to develop a statistical method to estimate genetic parameters for macro- and micro-environmental sensitivities simultaneously, to investigate bias and precision of resulting estimates of genetic parameters and to develop and evaluate use of Akaike?s information criterion using h-likelihood to select the best fitting model. Methods We assumed that genetic variation in macro- and micro-environmental sensitivities is expressed as genetic variance in the slope of a linear reaction norm and environmental variance, respectively. A reaction norm model to estimate genetic variance for macro-environmental sensitivity was combined with a structural model for residual variance to estimate genetic variance for micro-environmental sensitivity using a double hierarchical generalized linear model in ASReml. Akaike?s information criterion was constructed as model selection criterion using approximated h-likelihood. Populations of sires with large half-sib offspring groups were simulated to investigate bias and precision of estimated genetic parameters. Results Designs with 100 sires, each with at least 100 offspring, are required to have standard deviations of estimated variances lower than 50% of the true value. When the number of offspring increased, standard deviations of estimates across replicates decreased substantially, especially for genetic variances of macro- and micro-environmental sensitivities. Standard deviations of estimated genetic correlations across replicates were quite large (between 0.1 and 0.4), especially when sires had few offspring. Practically, no bias was observed for estimates of any of the parameters. Using Akaike?s information criterion the true genetic model was selected as the best statistical model in at least 90% of 100 replicates when the number of offspring per sire was 100. Application of the model to lactation milk yield in dairy cattle showed that genetic variance for micro- and macro-environmental sensitivities existed. Conclusion The algorithm and model selection criterion presented here can contribute to better understand genetic control of macro- and micro-environmental sensitivities. Designs or datasets should have at least 100 sires each with 100 offspring.
    Spatial variation in growth, maturation schedules and reproductive investment of female sole solea solea in the Northeast AtlanTic
    Mollet, F.M. ; Engelhard, G.H. ; Vainikka, A. ; Laugen, A.T. ; Rijnsdorp, A.D. ; Ernande, B. - \ 2013
    Journal of Sea Research 84 (2013). - ISSN 1385-1101 - p. 109 - 121.
    cod gadus-morhua - plaice pleuronectes-platessa - herring clupea-harengus - long-term changes - countergradient variation - reaction norms - bergmanns rule - rana-temporaria - sea plaice - evolutionary significance
    Latitudinal variation in life-history traits is often explained by phenotypically plastic responses or local adaptations to different thermal regimes. We compared growth, maturation schedules and reproductive investment of female sole Solea solea between 8 populations, covering much of the species' distribution in northern Europe, with respect to thermal gradients. An energy allocation model was fitted to size–age data, and probabilistic maturation reaction norms were estimated from size–age–maturity data. We found that northern populations from colder environments had higher rates of energy acquisition and reproductive investment, an intrinsic tendency to mature earlier, and had smaller asymptotic sizes than southern populations from warmer environments. Consequently, growth rate was higher before maturation but lower after maturation in the north compared to the south. This is opposite to Bergmann's rule according to which slower growth, delayed maturation and larger asymptotic sizes are usually observed at lower temperatures. The observed patterns could indicate strong countergradient thermal adaptation for rapid growth and development as well as sustained fecundity in the north, or indicate a response to other selection pressures correlated with the thermal gradient. Potentially higher mortality in northern populations during cold winters might be one of the key drivers of the observed geographical variation in growth and maturation of sole.
    Estimating age at maturation and energy-based life-history traits from individual growth trajectories with nonlinear mixed-effects models
    Brunel, T.P.A. ; Ernande, B. ; Mollet, F.M. ; Rijnsdorp, A.D. - \ 2013
    Oecologia 172 (2013)3. - ISSN 0029-8549 - p. 631 - 643.
    herring clupea-harengus - pleuronectes-platessa l - north-sea plaice - ontogenic growth - back-calculation - somatic growth - reaction norms - fish age - size - maturity
    A new method is presented to estimate individuals’ (1) age at maturation, (2) energy acquisition rate, (3) energy expenditure for body maintenance, and (4) reproductive investment, and the multivariate distribution of these traits in a population. The method relies on adjusting a conceptual energy allocation model to individual growth curves using nonlinear mixed-effects modelling. The method’s performance was tested using simulated growth curves for a range of life-history types. Individual age at maturation, energy acquisition rate and the sum of maintenance and reproductive investment rates, and their multivariate distribution, were accurately estimated. For the estimation of maintenance and reproductive investment rates separately, biases were observed for life-histories with a large imbalance between these traits. For low reproductive investment rates and high maintenance rates, reproductive investment rate estimates were strongly biased whereas maintenance rate estimates were not, the reverse holding in the opposite situation. The method was applied to individual growth curves back-calculated from otoliths of North Sea plaice (Pleuronectes platessa) and from scales of Norwegian spring spawning herring (Clupea harengus). For plaice, maturity ogives derived from our individual estimates of age at maturation were almost identical to the maturity ogives based on gonad observation in catch samples. For herring, we observed 51.5 % of agreement between our individual estimates and those directly obtained from scale reading, with a difference lower than 1 year in 97 % of cases. We conclude that the method is a powerful tool to estimate the distribution of correlated life-history traits for any species for which individual growth curves are available.
    Genotype-by-temperature interactions may help to maintain clonal diversity in asterionella formosa (Bacillariophyceae)
    Gsell, A.S. ; Domis, L.N.D. ; Przytulska-Bartosiewicz, A. ; Mooij, W.M. ; Donk, E. van; Ibelings, B.W. - \ 2012
    Journal of Phycology 48 (2012)5. - ISSN 0022-3646 - p. 1197 - 1208.
    diatom ditylum-brightwellii - fresh-water phytoplankton - reaction norms - phenotypic plasticity - genetic-variation - centric diatom - cell-size - environment interactions - marine-phytoplankton - skeletonema-costatum
    Marine and freshwater phytoplankton populations often show large clonal diversity, which is in disagreement with clonal selection of the most vigorous genotype(s). Temporal fluctuation in selection pressures in variable environments is a leading explanation for maintenance of such genetic diversity. To test the influence of temperature as a selection force in continually (seasonally) changing aquatic systems we carried out reaction norms experiments on co-occurring clonal genotypes of a ubiquitous diatom species, Asterionella formosa Hassall, across an environmentally relevant range of temperatures. We report within population genetic diversity and extensive diversity in genotype-specific reaction norms in growth rates and cell size traits. Our results showed genotype by environment interactions, indicating that no genotype could outgrow all others across all temperature environments. Subsequently, we constructed a model to simulate the relative proportion of each genotype in a hypothetical population based on genotype and temperature-specific population growth rates. This model was run with different seasonal temperature patterns. Our modeling exercise showed a succession of two to several genotypes becoming numerically dominant depending on the underlying temperature pattern. The results suggest that (temperature) context dependent fitness may contribute to the maintenance of genetic diversity in isolated populations of clonally reproducing microorganisms in temporally variable environments.
    Ecological and economic trade-offs in the management of mixed fisheries: a case study of spawning closures in flatfish fisheries
    Rijnsdorp, A.D. ; Overzee, H.M.J. van; Poos, J.J. - \ 2012
    Marine Ecology Progress Series 447 (2012). - ISSN 0171-8630 - p. 179 - 194.
    north-sea plaice - pleuronectes-platessa l - life-history evolution - evolving fish stocks - demersal fisheries - ecosystem approach - reaction norms - adult plaice - impact - communities
    As a contribution to the ecosystem approach to fisheries management, we estimated the effects of spawning closures on stock status, ecosystem impacts and economic performance. We focused on the flatfish fishery in the North Sea and explored how spawning closures for plaice and sole contribute to sustainable management of 4 target species (sole, plaice, turbot and brill). Seasonal patterns in fishing effort and catchability by age group and area were estimated to quantify the effect of different spawning closure scenarios on the selection pattern. The scenario performance was evaluated using indicators of stock status (spawning stock biomass), economic performance of the fishery (yield, revenue) and ecosystem impact (discards, bycatch of cod and rays, seabed integrity, fisheries-induced evolution). In a single-species context, spawning closures may be beneficial for the target species, while in a mixed fisheries and ecosystem context, negative effects may occur. A spawning closure for plaice combines positive effects on the plaice stock and the revenue with reductions of the negative impact for several ecosystem indicators and only a small negative effect on sea bed integrity. The effects did not differ when evaluated at current levels of effort or at maximum sustainable yield (MSY) effort. Tailor-made solutions are required that need to be developed in stakeholder consultation to trade-off the ecological and economic objectives. Mixed-species MSY was lower than the sum of the single-species MSYs.
    Genetic analysis of tolerance to infections using random regressions: a simulation study
    Kause, A. - \ 2011
    Genetics Research 93 (2011)4. - ISSN 0016-6723 - p. 291 - 302.
    environment interaction - rainbow-trout - oncorhynchus-mykiss - natural enemies - reaction norms - growth-rates - resistance - selection - genotype - parameters
    Tolerance to infections is the ability of a host to limit the impact of a given pathogen burden on host performance. This simulation study demonstrated the merit of using random regressions to estimate unbiased genetic variances for tolerance slope and its genetic correlations with other traits, which could not be obtained using the previously implemented statistical methods. Genetic variance in tolerance was estimated as genetic variance in regression slopes of host performance along an increasing pathogen burden level. Random regressions combined with covariance functions allowed genetic variance for host performance to be estimated at any point along the pathogen burden trajectory, providing a novel means to analyse infection-induced changes in genetic variation of host performance. Yet, the results implied that decreasing family size as well as a non-zero environmental or genetic correlation between initial host performance before infection and pathogen burden led to biased estimates for tolerance genetic variance. In both cases, genetic correlation between tolerance slope and host performance in a pathogen-free environment became artificially negative, implying a genetic trade-off when it did not exist. Moreover, recording a normally distributed pathogen burden as a threshold trait is not a realistic way of obtaining unbiased estimates for tolerance genetic variance. The results show that random regressions are suitable for the genetic analysis of tolerance, given suitable data structure collected either under field or experimental conditions.
    Harvest-induced maturation evolution under different life-history trade-offs and harvesting regimes
    Poos, J.J. ; Brannstrom, A. ; Dieckman, U. - \ 2011
    Journal of Theoretical Biology 279 (2011)1. - ISSN 0022-5193 - p. 102 - 112.
    north-sea plaice - fisheries-induced evolution - herring clupea-harengus - evolving fish stocks - cod gadus-morhua - reaction norms - population-dynamics - marine reserves - brook charr - arctic cod
    The potential of harvesting to induce adaptive changes in exploited populations is now increasingly recognized. While early studies predicted that elevated mortalities among larger individuals select for reduced maturation size, recent theoretical studies have shown conditions under which other, more complex evolutionary responses to size-selective mortality are expected. These new predictions are based on the assumption that, owing to the trade-off between growth and reproduction, early maturation implies reduced growth. Here we extend these findings by analyzing a model of a harvested size-structured population in continuous time, and by systematically exploring maturation evolution under all three traditionally acknowledged costs of early maturation: reduced fecundity, reduced growth, and/or increased natural mortality. We further extend this analysis to the two main types of harvest selectivity, with an individual's chance of getting harvested depending on its size and/or maturity stage. Surprisingly, we find that harvesting mature individuals not only favors late maturation when the costs of early maturation are low, but promotes early maturation when the costs of early maturation are high. To our knowledge, this study therefore is the first to show that harvesting mature individuals can induce early maturation.
    Simultaneous estimation of genotype by environment interaction accounting for discrete and continuous environmental descriptors in Irish dairy cattle
    Windig, J.J. ; Mulder, H.A. ; Bohte-Wilhelmus, D.I. ; Veerkamp, R.F. - \ 2011
    Journal of Dairy Science 94 (2011)6. - ISSN 0022-0302 - p. 3137 - 3147.
    milk-production traits - genetic correlations - herd environment - reaction norms - holstein cows - heat-stress - fertility - health - sensitivity - management
    Genotype by environment interaction can be analyzed by using a multi-trait model in which a trait measured in different environments is considered as separate traits. Alternatively, it can be analyzed by using a reaction norm model, in which the trait is considered a function of an environmental descriptor. Here, a model is developed where the 2 approaches are combined such that the effect of a continuous environmental descriptor can be analyzed in 2 or more discrete environments. The model is applied to somatic cell score (SCS) in relation to average herd milk production in 2 production environments: spring calving and year-round calving in Ireland. Heritabilities and additive genetic variances for SCS increased somewhat with increasing milk production and were higher in year-round calving. Under the combined model, the genetic correlation between spring and year-round calving was estimated at 0.82 to 0.84, clearly lower than obtained in a bivariate analysis ignoring effects of herd milk production. Thus, when estimating the genetic correlation between environments, effects of one environmental descriptor may be obscured by another, but can be disentangled in an analysis combining the reaction norm and the multi-trait approach. Such models will be especially useful for analyzing questions such as whether the effect of increasing production or temperature is more severe in different production systems or geographic regions.
    Temperature-induced plasticity in egg size and resistance of eggs to temperature stress in a soil arthropod
    Liefting, M. ; Weerenbeck, M. ; Dooremalen, C. van; Ellers, J. - \ 2010
    Functional Ecology 24 (2010)6. - ISSN 0269-8463 - p. 1291 - 1298.
    guttata-guttata lepidoptera - drosophila-melanogaster - orchesella-cincta - evolutionary genetics - adaptive significance - fitness consequences - thermal evolution - migrant skipper - reaction norms - seed beetle
    Keywords:acclimation;cold shock;development rate;egg hatching;heat shock;phenotypic plasticity;Orchesella cincta;oviposition temperature Summary 1. Temperature is considered one of the most important mediators of phenotypic plasticity in ectotherms, resulting in predictable changes in egg size. However, the fitness consequences of temperature-induced plasticity in egg size are not well understood and are often assessed at mild temperatures, whereas in the field, extreme temperatures will occur. 2. In this study we investigated egg size plasticity and fitness-linked traits of eggs in response to temperature in the springtail Orchesella cincta. Eggs were oviposited at two temperatures (16 and 20 °C), and transplanted to 10, 15 and 20 °C for rearing, or exposed to temperature shock (-6 and 38 °C) to measure survival, development rate and growth. 3. Eggs oviposited at 16 °C had a greater volume and dry weight than eggs oviposited at 20 °C but had similar lipid content. Eggs oviposited at 16 °C had high survival at all rearing temperatures, whereas survival of eggs oviposited at 20 °C declined at lower rearing temperatures and was significantly lower than survival of large eggs when reared at 10 and 15 °C. No difference in egg development rate was found between oviposition temperatures, although development rate increased with rearing temperature. Juveniles were 5–10% larger when hatching from eggs oviposited at 16 °C, independent of the temperature at which the eggs were reared. 4. Eggs oviposited at 16 °C were more resistant to thermal stress, as their survival after exposure to cold or heat shock was higher than survival of eggs oviposited at 20 °C. However, egg development rate of the eggs that survived temperature shock was not different from the control, independent of egg oviposition temperature. 5. Our results show that temperature-induced plasticity in O. cincta affects fitness-linked traits of offspring through increased hatchling size and increased thermal tolerance of eggs produced at lower temperatures. 6. The increased resistance to thermal stress of O. cincta eggs oviposited at lower temperatures may provide a protective strategy in uncertain thermal environments.
    Multiple growth-correlated life history traits estimated simultaneously in indivuals
    Mollet, F.M. ; Ernande, B. ; Brunel, T.P.A. ; Rijnsdorp, A.D. - \ 2010
    Oikos 119 (2010)1. - ISSN 0030-1299 - p. 10 - 26.
    north-sea plaice - pleuronectes-platessa l - herring clupea-harengus - evolving fish stocks - indeterminate growth - back-calculation - somatic growth - reaction norms - resource-allocation - arctica-islandica
    We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations
    Maximized PUFA measurements improve insight in changes in fatty acid composition in response to temperature
    Dooremalen, C. van; Pel, R. ; Ellers, J. - \ 2009
    Archives of Insect Biochemistry and Physiology 72 (2009)2. - ISSN 0739-4462 - p. 88 - 104.
    direct thermal-desorption - lipid-composition - biological significance - drought acclimation - orchesella-cincta - reaction norms - rapid method - collembola - cold - populations
    A general mechanism underlying the response of ectotherms to environmental changes often involves changes in fatty acid composition. Theory predicts that a decrease in temperature causes an increase in unsaturation of fatty acids, with an important role for long-chain poly-unsaturated fatty acids (PUFAs). However, PUFAs are particularly unstable and susceptible to peroxidation, hence subtle differences in fatty acid composition can be challenging to detect. We determined the fatty acid composition in springtail (Collembola) in response to two temperatures (5 degrees C and 25 degrees C). First, we tested different sample preparation methods to maximize PUFAs. Treatments consisted of different solvents for primary lipid extraction, mixing with antioxidant, flushing with inert gas, and using different temperature exposures during saponification. Especially slow saponification at low temperature (90 min at 70 degrees C) in combination with replacement of headspace air with nitrogen during saponification and methylation maximized PUFAs for GC analysis. Applying these methods to measure thermal responses in fatty acid composition, the data showed that the (maximized) proportion of C(20) PUFAs increased at low acclimation temperature. However, C(18) PUFAs increased at high acclimation temperature, which is contrary to expectations. Our study illustrates that PUFA levels in lipids may often be underestimated and this may hamper a correct interpretation of differential responses of fatty acid composition
    Genetic correlations between milk production and health and fertility dependent on herd environment
    Windig, J.J. ; Calus, M.P.L. ; Beerda, B. ; Veerkamp, R.F. - \ 2006
    Journal of Dairy Science 89 (2006)5. - ISSN 0022-0302 - p. 1765 - 1775.
    test-day records - dairy-cattle - reaction norms - covariance functions - production traits - farm-animals - genotype - yield - management - mastitis
    High milk production in dairy cattle can have negative side effects on health and fertility traits. This paper explores the genetic relationship of milk yield with health and fertility depending on herd environment. A total of 71,720 lactations from heifers calving in 1997 to 1999 in the Netherlands were analyzed. Herd environment was described by 4 principal components: intensity, average fertility, farm size, and relative performance indicating whether herds had good (poor) health and fertility despite a high (low) production. Fertility was evaluated by days to first service and number of inseminations (NINS); somatic cell score was used as a measure of udder health. Data were analyzed with a multitrait reaction norm model. Genetic correlation within traits across environments ranged from 0.84 to unity. Genetic correlations of the 3 traits with milk yield were antagonistic but varied over environments. Genetic correlation of milk yield with days to first service varied from 0.30 in small herds to 0.48 in herds with low average fertility. Correlations with NINS varied from 0.18 in large herds to 0.64 in high fertility herds, and with somatic cell score from 0.25 in herds with a high fertility relative to production to 0.47 in herds with a relative low fertility. Selection in environments of average value resulted in different predicted responses over environments. For example, selection for a decrease of NINS of 0.1 in an average production environment decreased milk yield by 35 kg in low production herds, but by 178 kg in high production herds.
    Population structure of the thornback ray (Raja clavata L.) in British waters
    Chevolot, M. ; Ellis, J.R. ; Hoarau, G. ; Rijnsdorp, A.D. ; Stam, W.T. ; Olsen, J.L. - \ 2006
    Journal of Sea Research 56 (2006)4. - ISSN 1385-1101 - p. 305 - 316.
    cod gadus-morhua - pleuronectes-platessa l. - southern north-sea - gulf-of-mexico - genetic-structure - atlantic cod - multilocus genotypes - microsatellite data - geographic scales - reaction norms
    Prior to the 1950s, thornback ray (Raja clavata L.) was common and widely distributed in the seas of Northwest Europe. Since then, it has decreased in abundance and geographic range due to over-fishing. The sustainability of ray populations is of concern to fisheries management because their slow growth rate, late maturity and low fecundity make them susceptible to exploitation as victims of by-catch. We investigated the population genetic structure of thornback rays from 14 locations in the southern North Sea, English Channel and Irish Sea. Adults comprised <4% of the total sampling despite heavy sampling effort over 47 hauls; thus our results apply mainly to sexually immature individuals. Using five microsatellite loci, weak but significant population differentiation was detected with a global FST = 0.013 (P <0.001). Pairwise Fst was significant for 75 out of 171 comparisons. Although earlier tagging studies suggest restricted foraging distances from home areas, the absence of genetic differentiation between some distant populations suggests that a substantial fraction of individuals migrate over wide areas. Autumn/winter locations appear to have a lower level of differentiation than spring/summer, which could be due to seasonal migration. Management and conservation of thornback ray populations will be challenging as population structure appears to be dynamic in space and time
    Fisheries-induced adaptive change in reproductive investment in North Sea plaice (Pleuronectes platessa)?
    Rijnsdorp, A.D. ; Grift, R.E. ; Kraak, S.B.M. - \ 2005
    Canadian Journal of Fisheries and Aquatic Sciences 62 (2005)4. - ISSN 0706-652X - p. 833 - 843.
    cod gadus-morhua - life-history evolution - beam-trawl effort - reaction norms - somatic growth - trade-offs - maturation - fecundity - size - age
    Life history theory predicts that fishing may select for increased reproductive investment. A model of the reaction norm for reproductive investment in a capital breeder was developed to disentangle changes in reproductive investment from changes in growth rate in North Sea plaice (Pleuronectes platessa). Trends in reproductive investment since 1960 were estimated as (i) the decrease in body weight of mature males and females between the start and end of the spawning period, (ii) the difference in weight of ripe and spent females, and (iii) the ovary weight of prespawning females. These estimates were related to somatic growth estimated by back-calculation of otoliths and temperature. The ovary weight and weight loss of females that had just started and just finished spawning did not reveal any trends. There was a significant increase in weight loss over the spawning season in both sexes, but much of this increase was likely due to changes in environmental conditions. Evidence for a fisheries-induced change in reproductive investment from our analyses thus remained inconclusive. However, fecundity and ovary-weight data from previous studies tentatively suggest that an increase in reproductive investment occurred between the late 1940s and the 1960s. Such an increase is consistent with a fisheries-induced evolutionary change
    Associations among descriptors of herd management and phenotypic and genetic levels of health and fertility
    Calus, M.P.L. ; Windig, J.J. ; Veerkamp, R.F. - \ 2005
    Journal of Dairy Science 88 (2005)6. - ISSN 0022-0302 - p. 2178 - 2189.
    somatic-cell count - dairy-cattle - environment interaction - milk-production - production diseases - clinical mastitis - reaction norms - genotype - selection - traits
    The objective of this paper was to investigate the association of descriptors of herd environment with phenotypic levels and breeding values of fertility and health traits. Analyses were performed for 82,080 first-lactation heifers and 173,787 multiparous cows. Fourteen environmental parameters were defined that described herd environment, such as average protein production, average somatic cell score (SCS), average calving interval, and average body condition score (BCS). Herds with lower average SCS had, in general, more desirable values for almost all analyzed traits (i.e., days to first service was 7 d shorter), as did herds with lower average calving interval (i.e., 2.8% lower incidence of predicted mastitis). Herds with higher average protein production had slightly poorer fertility but more desirable values for all other analyzed traits (i.e., 5.1% less predicted mastitis, 0.4 lower SCS, and 0.6 higher BCS). Variance components and breeding values of sires were estimated by applying a random regression on the environmental parameters. In general, genetic variances varied generally only slightly across environments. However, based on data exclusively for heifers, the genetic variance for number of inseminations was 4.1 times higher in herds with a higher number of inseminations, 1.9 times higher for survival in herds with higher fat to protein ratio, and 1.7 times higher for predicted mastitis in herds with higher number of inseminations. Based on the heifer data, the lowest estimated genetic correlation across environments was 0.76 (SE 0.21) for first-service conception between herds with differing average BCS. The minimum based on the cow data was 0.65 (SE 0.10) for survival between herds with differing average ages at calving. The relative importance of some fertility traits compared with yield traits doubled across environments. Possible reranking of individual animals within a population and the changes in genetic variance across environments suggests that environment-specific breeding values should be estimated for use in customized selection indices
    Quantitative genetic variation in an island population of the speckled wood butterfly (Pararge aegeria)
    Windig, J.J. ; Veerkamp, R.F. ; Nylin, S. - \ 2004
    Heredity 93 (2004)5. - ISSN 0018-067X - p. 450 - 454.
    sexual size dimorphism - bicyclus-anynana - fluctuating asymmetry - inbreeding depression - evolutionary genetics - natural-selection - reaction norms - wing pattern - trade-offs - inachis-io
    Evidence of changes in levels of genetic variation in the field is scarce. Theoretically, selection and a bottleneck may lead to the depletion of additive genetic variance (VA) but not of nonadditive, dominance variance (VD), although a bottleneck may converse VD to V A. Here we analyse quantitative genetic variation for the Speckled Wood butterfly Pararge aegeria on the island of Madeira about 120 generations after first colonisation. Colonisation of the island involved both a bottleneck and strong natural selection, changing the average value of traits. Several life history and morphological traits with varying levels of change since colonisation were analysed. In accordance with expectations, all traits except one showed relatively low levels of VA, with an average heritability (h2) of 0.078. Levels of VD for these traits were relatively high, 20-94% of total variance and on average 80% of VG. The exception was a morphological trait that probably had not experienced strong natural selection after colonisation, for which a h2 of 0.27 was found. Another interesting observation is that the population seems resistant to inbreeding effects, which may be the result of purging of deleterious alleles.
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