Liming and reacidification reactions of a forest lake ecosystem,lake Lysevatten,in SW Sweden

Long-term monitoring, 1973 to 1987, of reactions to liming and reacidification of a forest lake ecosystem near the Swedish west coast is reported in this study. Treatment of Lake Lysevatten with a slag product of limestone in 1974 resulted in neutralization and a positive alkalinity. Prolonged dissolution proceeded for about 7 yr whereby 86% dissolved. During 1984–86 Lake Lysevatten approached maximum reacidification with high Al concentrations and an affected biota. Asellus aquaticus L. decreased and dominance within chironomid groups approached preliming conditions. However, the most obvious biological change was the development of the filamentous algal genus Mougeotia and increased growth of Sphagnum. Populations of both plants increased notably when pH declined to about 5. Our study suggests that extensive reacidification (pH < 6.0) of limed lakes should be avoided by successive treatments to prevent development of destabilized lake ecosystems.     

Somatic Chromosomes of the Cat

The number of chromosomes of the cat (Felis domestica) was determined at 38, and both the X and the Y chromosomes have submedially situated centromeres. X is of medium size while Y is one of the smallest chromosomes of the complement. For practical purposes, the chromosomes have been divided into groups according to their appearance.     

Growth of five landlocked Arctic charr stocks under hatchery conditions

Growth dynamics of five stocks of Arctic charr, were compared from the fry stage in June 1986 until December 1987. Each stock originated from a different lake in Sweden: Hornavan; Näckten; Torrön; Rensjön and Visjön. Hornavan charr reached the highest final mean weight (237 g), but they were not significantly heavier than Visjön charr (206 g). Growth of fish of the three remaining stocks was similar but less rapid. The superior growth performance of Hornavan charr was most pronounced during autumn. Coefficients of variation for individual size within stocks was between 30 and 54%, with Hornavan and Näckten charr displaying least variability. Charr from Lake Visjön had a significantly lower proportion of mature males (6%) than the other stocks (19–29%) at the end of the experiment. The results demonstrate that differences in growth potential exist between stocks of charr, and these differences may be related to differential seasonal rhythms in growth. Variations in early growth, size distributions and sexual maturation seemed to be subordinate factors affecting overall growth performance.     

Grazing by Steers at Different Sward Surface Heights on Extensive Pastures: A Study of Weight Gain and Fat Deposition

Live weight gain of steers grazing at three different target sward heights, Low (3-6 cm), Medium (6-10 cm) and High (>10 cm), together with carcass fat deposition, were studied during two grazing seasons. Sward height was measured with a sward stick. The grassland consisted of seminatural grazing areas mixed with previously cultivated areas. Animals grazed continuously with small adjustments in animal numbers (year 1) or pasture area (year 2) to maintain sward height within the target for each treatment. The recorded average sward heights were 4.7, 6.8 and 11.1 cm for pastures on treatments Low, Medium and High, respectively. The animals weighed approximately 440 kg at the start of the grazing season and went directly from pasture to slaughter at the end of the experiment. No differences between years were found and data from both years were thus pooled, giving a total of 50 steers of the Swedish Red and White breed in the data set. Over the whole grazing season, the average daily live weight gain of animals on treatment Low (0.43 kg day     

Characteristic Fly-ash Particles from Oil-shale Combustion Found in Lake Sediments

Fly-ash particles accumulate in sediments and can be used to assess spatial distribution and temporal trends of atmospheric deposition of pollutants derived from high temperature combustion of fossil fuels. Previous work has concerned fly-ash derived from oil and coal. Oil-shale is the main fossil fuel used in Estonia and a major source of atmospheric pollution in the Baltic states. To assess if oil-shale power plants produce specific fly-ash particles, we used scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) to compare fly-ash particles from oil-shale combustion with particles from oil and coal combustion. Two types were analysed, large black (10–30 μm) and small glassy (<5 μm) spheroidal particles. Although particle morphology to some extent is indicative of the fuel burnt, morphological characters are not sufficient to differentiate between particles of different origin. However, our results indicate that with EDX analysis the fly-ash from oil-shale can be distinguished from oil and coal derived particles in environmental samples. Concentrations of large black and small glassy spheroidal fly-ash particles in a sediment core from an Estonian lake showed similar trends to oil-shale combustion statistics from Estonian power plants.     

Variability in germination and in temperature and storage resistance among Paenibacillus larvae genotypes

There are several methods for cultivation of Paenibacillus larvae, the causative agent of American foulbrood (AFB) in honey bees. Protocols for detection of sub-clinical levels of the bacterium from honey and bee samples include heat treatment of samples. The main objective of this study was to investigate if there is variability in temperature resistance among P. larvae genotypes, potentially leading to biased diagnose and disease monitoring. The variation in germination and proliferation ability among type collection (N = 4) and field isolates (N = 4) of P. larvae representing four different genotypes was investigated. Results demonstrate a significant variability between P. larvae genotypes in germination rate on solid media as well as in endospore resistance to heat treatment and storage. It is concluded that strains of different genotypes should be included in evaluation of standard laboratory protocols for cultivation of P. larvae to avoid bias in disease monitoring and quantification of the pathogen.     

Vertical transmission of American foulbrood (Paenibacillus larvae) in honey bees (Apis mellifera)

The mode of transmission between hosts (horizontal versus vertical) of disease agents is important for determination of the evolution of virulence in pathogens. For disease management, it is imperative that the epidemiology of the disease is understood and pathogen transmission rates between hosts is a key factor for this understanding. Surprisingly little is known about transmission rates in honey bee pathology. We have studied the rate of vertical transmission of Paenibacillus larvae, the causative agent of American foulbrood (AFB) in honey bee colonies, as colonies reproduce by colony fission (swarming), by culturing for the spores from repetitive samples of adult bees. The results demonstrate vertical pathogen transmission to daughter swarms. The spore density declines over time in both mother colonies and daughter swarms if mother colonies do not exhibit clinical disease symptoms. Occasional positive samples more than a year post swarming, also in daughter swarms, indicate production of infectious spores from diseased larvae, without clinical disease observable by beekeepers, and/or maintenance of infective spores in the hive environment, allowing both horizontal and vertical transmission to be maintained. The results suggest that the virulence of AFB, being lethal at colony level in contrast to other bee diseases shaped by evolution, could be dependent on apicultural practices and that the pathogen probably would be maintained without causing frequent colony mortality in a natural system.     

Computational design of self-assembling protein nanomaterials with atomic level accuracy

We describe a general computational method for designing proteins that self-assemble to a desired symmetric architecture. Protein building blocks are docked together symmetrically to identify complementary packing arrangements, and low-energy protein-protein interfaces are then designed between the building blocks in order to drive self-assembly. We used trimeric protein building blocks to design a 24-subunit, 13-nm diameter complex with octahedral symmetry and a 12-subunit, 11-nm diameter complex with tetrahedral symmetry. The designed proteins assembled to the desired oligomeric states in solution, and the crystal structures of the complexes revealed that the resulting materials closely match the design models. The method can be used to design a wide variety of self-assembling protein nanomaterials.     

Occurrence of nematodes, tardigrades and rotifers on ice-free areas in East Antarctica

Nematodes, rotifers and tardigrades were collected on three nunataks (mountain peaks penetrating the ice sheet) in Vestfjella, on six nunataks in Heimefrontfjella and on the Schirmacher Oasis in East Antarctica in the austral summers of 1996/97 and 2001/02. Most samples were taken on the nunatak Basen in Vestfjella where the Swedish station Wasa is located. The microfauna was patchily distributed and the highest densities of animals were found on sites with visible vegetation of mosses, lichens or algae. Thirty-four taxa of nematodes and tardigrades were found. Only seven of these occurred regularly in apparently actively reproducing populations. Other occasional records of nematodes had very few specimens. The highest number of species was found on the nunatak Basen. Rotifers, found in 66% of the samples, were the most frequent animal group. Nematodes occurred in 37% of the samples and tardigrades in 42%. The most frequent nematodes were Plectus and Panagrolaimus, occurring in 26% and 5% of the samples, respectively. Macrobiotus, Hebesuncus and Acutuncus were the most frequent and abundant tardigrades. The pattern of animal distribution can be related to both habitat characteristics and to the geographic position of the nunatak. The communities are little organised and the distribution of the fauna has similarities with an early phase of colonisation.     

Sulphur deficiency in oilseed rape and cereals - Experience from Swedish field trials

Field trials in Sweden have shown responses to S-fertilizers by rapeseed, but not by barley. These responses varied from 0 to approximately 200 kg/ha seed. They are, however, hard to predict and the criteria of S availability have to be elucidated.