Source Of Natural Variation Research Articles

Genetic variability of milk fatty acids

The milk fatty acid (FA) profile is far from the optimal fat composition in regards to human health. The natural sources of variation, such as feeding or genetics, could be used to increase the concentrations of unsaturated fatty acids. The impact of feeding is well described. However, genetic effects on the milk FA composition begin to be extensively studied. This paper summarizes the available information about the genetic variability of FAs. The greatest breed differences in FA composition are observed between Holstein and Jersey milk. Milk fat of the latter breed contains higher concentrations of saturated FAs, especially short-chain FAs. The variation of the delta-9 desaturase activity estimated from specific FA ratios could explain partly these breed differences. The choice of a specific breed seems to be a possibility to improve the nutritional quality of milk fat. Generally, the proportions of FAs in milk are more heritable than the proportions of these same FAs in fat. Heritability estimates range from 0.00 to 0.54. The presence of some single nucleotide polymorphisms could explain partly the observed individual genetic variability. The polymorphisms detected on SCD1 and DGAT1 genes influence the milk FA composition. The SCD1 V allele increases the unsaturation of C16 and C18. The DGAT1 A allele is related to the unsaturation of C18. So, a combination of the molecular and quantitative approaches should be used to develop tools helping farmers in the selection of their animals to improve the nutritional quality of the produced milk fat.

Determinants of Lichen Diversity in a Rain Forest Understory

ABSTRACTChange in lichen diversity is often used as a bioindicator to estimate effects of atmospheric pollution, but natural variation in lichen cover and species richness can be very high. We examined the top‐down effects of spore‐consuming ants and the bottom‐up effects of nutrient and light availability on lichen diversity associated with the leaf surface of the rain forest understory plant, Piper cenocladum. Plots containing P. cenocladum were randomly assigned to treatments in factorial experiments that included high and low light levels, nutrient enrichment, and presence and absence of the ant mutualist, Pheidole bicornis. At the conclusion of the experiments, plants were harvested and size of leaves, secondary metabolite content (amides), epiphyll cover, and the species richness of the lichens (which comprised 85% of the epiphyll community) were quantified. Epiphyll cover (mosses, liverworts, and lichens) was greater on plants that had ant‐mutualists and balanced resources. Lichen species richness was greater for plants with balanced resources, particularly for those with high light availability. Relationships between toxins and lichen cover and richness were weak and unclear. In this system, natural sources of variation were reliable determinants of lichen diversity and both biotic and abiotic influences were important.

Biodiversity, ecosystem function and plant traits in mature and immature plant communities

Several studies of synthesized herbaceous plant communities have reported a positive relationship between vascular plant diversity and biomass production (Naeem et al. 1994; Tilman et al. 2001), and the European BIODEPTH experiment has been one of the most influential in this regard (Hector et al. 1999). Much, though not all, of the evidence for this relationship has come from experimental communities established from seed and harvested after only a year or two. It is not clear that such immature plant communities would be expected to provide reliable evidence of the relationship between diversity and ecosystem properties. Here we compare the relationship between diversity and biomass in BIODEPTH with that at the long-term monitoring site at Bibury in Gloucestershire, UK (Dunnett et al. 1998), a natural plant community that has much in common with BIODEPTH. The Bibury site offers a rare opportunity to address questions similar to those tackled by BIODEPTH, while avoiding some of the limitations of short-term experiments. If a positive relationship between vascular plant diversity and biomass production is an important phenomenon, one could argue that it should be detectable in natural vegetation. Previous attempts to explore the relationship between biodiversity and productivity in natural plant communities have been criticized on the grounds that both variables are frequently affected by additional (usually abiotic) variables (Lawton et al. 1998). For example, over a wide range of moderate-to-high biomass values, there is a well known negative relationship between biomass and species richness, driven by increasing competitive exclusion at higher productivity (Grime 1973; Grace 1999; Stevens et al. 2004). In experiments such as BIODEPTH, one aim is to exclude such natural sources of variation and create synthesized plant assemblages that vary only in artificially imposed levels of species richness. Of course, random environmental heterogeneity cannot be completely excluded, and Huston & McBride (2002) have shown how such heterogeneity can give rise to spurious diversity-function relationships. However, synthesized communities may also exhibit systematic variation in productivity equalling or exceeding that occurring in natural habitats, arising from the higher nitrogen availability in communities sown with N-fixing legumes. In BIODEPTH, addition of TriJolium pratense (nomenclature follows Stace 1997) increased biomass, on average, by 360 g m (Hector et al. 1999). As this increase was much larger than the effect of any other species, it is reasonable to attribute this effect to a direct result of the extra N fixed by Trifolium. The increase was also much larger than the effect of a change in diversity itself; doubling species richness increased biomass, on average, by only 80 g m-. The Bibury road verge lies on the north side of Akeman Street, originally a Roman road, in Gloucestershire, UK (National Grid reference SP 119048). The 700 m length of experimental verge was originally chosen

An Afterthought: Ecosystem Metrics and Pressure Indicators

Editing the symposium contributions has been an in-teresting and instructive experience, because they providea broad overview of the well-nigh unlimited creativity ofmarine scientists to try and find building blocks for anecosystem approach to fishery management. A wealth ofideas appears to be emerging on how different aspects of thestate of exploited marine ecosystems can be measured.Although the metrics produced are commonly referred to as‘‘ecosystem indicators’’, however, it is generally less clearwhat they actually indicate.The concept that management must take the widerranging effects of fisheries on the ecosystem into account iffisheries are to be sustainable without unduly affecting themarine environment is an important step forward. Also,these metrics may help to define management objectivesmore clearly. However, the contributions have not con-vinced me yet that the quantitative indicators developed areof much pragmatic use in controlling the fisheries. Part ofthe problem lies in the lack of rigour used in the definitionof what an indicator is, and what purpose it is supposed toserve. New metrics of ecosystem attributes appear to beadded to the list of potentially useful indicators for fisheriesmanagement, without a clear idea of what they actuallyindicate. Metrics, however, measure something specific,while indicators are supposed to tell us something differentfrom what they actually measure. The tacit inference isoften made that the metrics proposed provide an indicatorof the rate of overexploitation, but little if any evidence isprovided that they do. In fact, defining ecosystemexploitation rate is a problem in itself, because how maydifferent fisheries be combined in a single ‘‘pressureindicator’’ at an ecosystem level? Can we simply addcatches or average fishing mortalities of pelagic anddemersal species, or must weighting factors be applied?Can we use pressure indicators from modelling ap-proaches? The empirical correlation between ecosystemindicators and empirical pressure indicators has beenlargely neglected, and if it has been addressed, the resultshave not been unequivocal. Still, this is crucial if thecriteria defined for selecting a suite of appropriateindicators are to be applied rigorously.A comparison with traditional, single-species manage-ment may help to clarify the issue. The chance that a fish iscaught (fishing mortality) reflects the impact of the totalfishery on the stock and is on theoretical grounds a pressureindicator (of fishing effort). Changes in relative stockbiomass represent a measure of the ‘‘well-being’’ ofa population, encompassing all anthropogenic impacts(through fishing mortality) and natural sources of variation(through growth and recruitment, including competitionand predation effects). Stock assessment is aimed atelucidating the interactions between these two indicatorsso as to formulate best possible advice. This is important,because without a pressure indicator no-one could givequantitative advice on the extent to which effort should bereduced, and without a well-being indicator, we would notknow whether fishing would do any harm.I tend to believe that the indicator approach to take intoaccountecosystem effectsinfisheriesmanagementwillonlyhelp if we are able to go beyond the statement thatecosystems are overexploited and unhealthy, and insteadprovideadviceonquantitativemeasuresforspecificfisheriesto resolve a well-documented problem. In fact, many of theproblems encountered in an ecosystem context may besolved pragmatically from a single-species, community, orsingle-fishery perspective (as currently pursued in theAlaska region). For instance, bycatch rates of marinemammals, turtles, and elasmobranchs are effectively a sin-gle-species problem that may be resolved along traditionallines of single-species assessment and management, buttaking into account that specific fisheries are often causingthe problem. To control impact on benthic habitats, we donot necessarily require a full ecosystem approach, but againa fleet-orientated approach is essential. The remainingproblems that refer truly to the ecosystem level, but havetoberesolvedbymanagementandwhichcannotberesolvedby traditional management approaches, relate to the balancebetween the fisheries exploiting different components.Before metrics of ecosystem structure and functioning maybeappliedasecosystemindicators,however,wefirsthavetoestablish a clear relationship with suitable pressure indica-torsofecosystemexploitation.Thismaynotbeeasybecausegood ecosystem metrics should integrate all sources ofvariation over a range of time delays, and therefore areunlikely to meet important criteria for good indicators likeresponsiveness, sensitivity, and specificity (sensu Rice andRochet, 2005). Meeting these criteria probably would bereserved for good pressure indicators, but much more workappearstoberequiredtodefinethemandtounderstandtheirrelationship with indicators of ecosystem health. The

Statistical Analysis of Traction Measurements with Rolling, Sliding, and Spin

Traction measurements, like any other physical testing, contain variability associated with the test rig, test samples, and data acquisition systems. These natural sources of variation increased when simulating contacts with spin velocity in the most common rolling and sliding test conditions. Averaging the results within one test sequence with spinning, rolling, and sliding velocities did not always reflect the expected results from the entire population of possible measured values. To be confident in the conclusions that were drawn from the traction testing, it was important to repeat the test sequence several times and apply statistics for defining error bands around the expected traction values. To allow for easy application of error bands, simplified equations were curve fit to the data from the numerical routines. By making use of error bands, an easy determination of the test repeatability can be discerned, and quantified comparisons between data sets can be made with a higher degree of confidence.

Probabilistic programming for nitrate pollution control: Comparing different probabilistic constraint approximations

Agricultural nitrate emissions within a river catchment are, due to rainfall and other sources of natural variation, uncertain. A regulator aiming to reduce nitrate emissions into surface and groundwater faces a trade-off between reliability in achieving emission standards and the cost of compliance to agriculture. This paper explores this trade-off by comparing different assumptions about the probability distribution of nitrate emissions and thus the probabilistic constraint included in the catchment model. Three categories of probabilistic constraints are considered: (1) non-parametric, (2) normal and (3) lognormal. The results indicate that the restrictiveness of the non-parametric assumption could lead to a significant reduction in profit relative to the normal and lognormal. The lognormal assumption, although it is theoretically correct, cannot be generalised to the case of correlated emissions. However, ignoring the dependence between different sources of nitrate emissions introduces more bias than mis-specifying their distribution. Therefore a probabilistic constraint based on a correlated normal distribution of emissions gives the best approximation for nitrate emissions in this study.

Advances and challenges in predicting agricultural management effects on soil hydraulic properties

Agricultural management practices can significantly affect soil hydraulic properties and processes in space and time. These responses are coupled with the processes of infiltration, runoff, erosion, chemical movement, and crop growth. It is essential to quantify and predict management effects on soil properties in order to model their consequent effects on production and the environment. We present work done thus far on this topic area along with the challenges that lie ahead. The effects of tillage and reconsolidation, wheel-track soil compaction, crop residue management, macropore development and management interactions with natural sources of variability, such as topography, are addressed. Whether explicitly or implicitly, the available field studies include interactions between treatments, such as tillage, crop rotation and residue management. Controlled equipment traffic has been shown to have significant effects on soil compaction and related hydraulic properties in some soils and climates, but in others, landscape and temporal variability overwhelm any effects of wheel tracks. New research results on wheel-track effects in Colorado are highlighted along with initial attempts to predict their effects on hydraulic properties. The greatest challenge for the future is improved process-based prediction using a systems approach to include tightly coupled process interactions in space and time.

The sun's variable spectrum and its terrestrial effects

Abstract The solar radiation exhibits strong temporal variations not only in intensity but also in its spectrum which are linked to the evolution of the Sun through its magnetic activity cycle. The irradiance variability increases from longer to shorter wavelengths, with variations in the UV being orders of magnitude larger than those in the visible. While 99% of the total solar radiative output occurs at wavelengths longer than 300 nm, solar UV radiation accounts for up to 30% of the total variation. The continuous rise of the Earth's surface temperature over the last decades urgently raises a question about the physical origin of so-called global warming. A reliable estimate of the influence of human activity on the Earth's climate requires detailed knowledge about the natural sources of variability. One of the unknown boundary conditions for models of the evolution of the Earth's climate is the variation of the solar irradiance.

Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change

The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to Early Cretaceous) have been investigated to test whether these plant fossils provide evidence for CO(2)-rich atmosphere in the Mesozoic. We first assessed five sources of natural variation in the stomatal density and index of extant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. fully developed leaves, (3) short shoots vs. long shoots, (4) position in the canopy, and (5) male vs. female trees. Our analysis indicated that some significant differences in leaf stomatal density and index were evident arising from these considerations. However, this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples, with the stomatal index of four species of Mesozoic Ginkgo (G. coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower than the modern values recorded in this study for extant G. biloba. Calculated as stomatal ratios (the stomatal index of the fossil leaves relative to the modern value), the values generally tracked the CO(2) variations predicted by a long-term carbon cycle model confirming the utility of this plant group to provide a reasonable measure of ancient atmospheric CO(2) change.

Haematological health state indices of reproducing Great Tits: methodology and sources of natural variation

1. A cornerstone concept of ecological immunology is that immune function, interacting with various aspects of individual health state, plays a central role in the life‐history trade‐offs between conflicting demands of survival and reproduction. In order to develop this research, more knowledge about the applicability and usefulness of different health state assays is needed. 2. Eleven, mostly hemato‐serological, health state indices are described and their suitability for sensing the condition of breeding Great Tits (Parus major L.) in terms of measurement precision, constancy in time, diurnal variation, and sex‐ and site‐related differences, is examined. 3. Measurement errors for the plasma albumin content, residual body mass, heterophile/lymphocyte ratio and total plasma protein content were relatively small compared with the total variation, suggesting these indices to be most adequate for ecological research. Measurement precision was lowest for the heterophile count and ‘buffy coat’ layer height (relative amount of leucocytes in total blood volume). Buffy coat layer height correlated weakly (r=0·21) with total leucocyte count estimated from blood smears and therefore appeared inappropriate for estimation of the leucocyte number. 4. Body mass (residual in respect to size) and intensity of Haemoproteus blood parasite infection were the least variable state indices during the nestling period (for both, the correlation between the values measured on the 8th and 15th days of the nestling period=0·71). Haematocrit, heterophile count and albumin/globulin ratio showed no individual constancy across the nestling period, while other traits revealed moderate but statistically significant correlations between 8th‐ and 15th‐day values. 5. Leucocyte (both lymphocyte and heterophile) counts were higher among females captured at night compared with those captured during the day. 6. Females had higher intensities of Haemoproteus infection, higher heterophile counts and higher heterophile/lymphocyte ratios than males. Contrary to published information, females had higher haematocrits than males. 7. Haematocrit values in both sexes, as well as total plasma protein and albumin concentrations in males, differed significantly between Great Tits breeding in urban habitat and rural woodlands, respectively.

Heterokaryosis and vegetative incompatibility in Stagonospora nodorum

Heterokaryotic colonies of Stagonospora nodorum consist of a fine mosaic of individual cells of the two component genotypes that are linked by frequent hyphal anastomosis. The intimate mixing does not extend to the colony edge where 1 mm3 blocks of hyphae all of the same genotype occur. Colonies developed from single pycnidiospores from heterokaryons were homokaryotic and segregated into the two component genotypes, demonstrating that all the nuclei in a spore are of the same genotype. Spore progenies from single pycnidia produced by heterokaryons, however, were frequently genetically heterogeneous, indicating that these asexual fruiting structures are not uninucleate in origin. The nuclear ratio in heterokaryons was characteristic of the component genotypes and could deviate markedly from 1:1 with no reduction in growth. Only 1.6% of pairs of physiologically-different nitrate non-utilizing mutants from different strains showed complementation, indicating that vegetative incompatibility is widespread in S. nodorum. The few compatible strains had common origins and may be clonally related. Tests on a limited number of combinations suggested that vegetative incompatibility could not be overcome by protoplast fusion. Attempts to isolate somatic heterozygous diploids and parasexual recombinants were largely unsuccessful. Heterokaryosis and parasexuality do not appear to be significant sources of natural variation in this fungus.

Vitamin K1 (Phylloquinone) Content of Foods: A Provisional Table

A provisional table on the vitamin K1 (phylloquinone) content of foods was compiled in response to the expressed need for tabulated data by the public and professionals in medicine, nutrition, dietetics, and research. Data for vitamin K1 content in foods were evaluated according to criteria set for the analytical method, sampling, and quality control, with a confidence code assigned to each accepted value for each food item. Given the large analytical variation associated with the chick bioassays, only data obtained from methods using HPLC (high-performance liquid chromatography) were used. An effort was made to include vitamin K values that were representative of foods in the retail market. There are few food composition data for this nutrient. The available data do indicate that leafy, green vegetables, and certain legumes and vegetable oils are good dietary sources of vitamin K1. The distribution of vitamin K1 in plants is not uniform, with higher concentrations of the vitamin found in the outer leaves as compared to concentrations in the pale, inner leaves. The peels of fruits and vegetables appear to have higher concentrations of the vitamin than do the fleshy portions. Recent investigations indicate that season, climate, growing location, and soil fertility are sources of natural variation in the vitamin K1 concentration of foods. The limited data on the vitamin K1 content of foods need to be expanded to include other commonly-consumed foods, including prepared foods. One approach would be an improved database for simple foods, which could then be used in the U.S. Department of Agriculture recipe file of the USDA Survey Nutrient Database to calculate the vitamin K1 content of multicomponent foods. Furthermore, investigation is required to differentiate natural variation from that attributable to analytical methodology and sample preparation, such as homogenization and cooking.