Relativitätstheorie als didaktische Herausforderung

The theory of relativity has been considered as one of the most abstract and most difficult theories at the turn of the century. Today relativity is taught at high schools. This process is explained here by the increased faith in this theory and by better verbal explanations of the twin paradox and other effects of relativity. The development of new audiovisual aides for the teaching of relativity and other fields of modern physics is seen here as one of the main didactical challenges for the future.     

Physiologische Anpassungen eines marinen insekts. II. Die Eigenschaften von schwimmenden und absinkenden Eigelegen

The gelatinous egg-masses of Clunio marinus (Diptera; Chironomidae) consist of a tube of jelly containing up to 175 eggs. The swimming egg-mass of the Atlantic populations (Race A) and the sinking egg-mass of the Baltic populations (Race B) have a higher density than the sea water, on which the female spawns; salinity is not important to the swimming or sinking of the egg-masses. Density and sinking velocity of gelatinous egg-masses from Atlantic midges are significantly higher than those from Baltic midges if the eggs are laid on water of the same salinity. The density of the eggs and the quantitative relation of eggs to jelly are the same in both races. The jelly of the egg-masses from the Baltic Sea race swells more than that from the Atlantic Sea race (increase of volume by absorption of water = 3-fold and 2.4-fold, respectively). During swelling the jelly alters from a trough-like shape into a tube-like from which closes around the eggs. If the surface tension of the spawning medium is lowered by use of detergents, the A-spawn will sink. A- and B-spawns occupy different positions at an oil-water interface. Interference contrast microscopy revealed that the A-jelly forms a well-defined outer line in relationship to the surrounding aqueous medium; this line is missing in the B-jelly. The morphological fine surface structures, as seen by the scanning electron microscope, do not explain the different properties of the A- and B-spawn. Extracts and hydrolysates of jelly material were separated by thin-layer chromatography. The results indicate that the spawn jelly of C. marinus consists of a polysaccharide-protein-complex, similar to the jellies of other invertebrates. It is rather probable that the chemical structure or the components of the jellies from A- and B-populations are not exactly the same; this would explain the different properties described. The ecological significance of swimming and sinking gelatinous egg-masses and the taxonomical position of both midge populations are discussed.     

Cadmium accumulation in Allium schoenoprasum L. grown in an aqueous medium

The ability of Allium schoenoprasum L. (chives) to accumulate and tolerate cadmium in aqueous Hoagland medium at 50microM and 250microM was tested under continuous growth or several successive harvests of shoots. After 28 days of continuous growth, chives accumulated the metal up to 0.2% and 0.5% of its dry weight, when grown in 50microM and 250microM, respectively. In experiments that the leaves were successively harvested every 16 days, there were no obvious stress symptoms after six harvests during a period of 96 days at 50microM Cd. At 250microM, after 64 days and four harvests, inhibition of growth occurred. In each treatment, a total of 1.2g kg(-1) DW and 2.4g kg(-1) DW was accumulated in the leaves, respectively. Total SH compounds concentration in leaf was found significantly higher by 3 and 7.4 times in plants treated with Cd at 50microM and 250microM in comparison to the control, respectively, while no difference in the concentration of glutathione (GSH+GSSG) was found. Thus, it is assumed that sulphur-containing compounds, yet unknown, are involved in defensive mechanisms against heavy metals in chives. The results presented, point to chives phytoremediation potential, but also on the potential risk in accumulation of heavy metals in a commonly edible plant.     

Accumulation and distribution of platinum and rhodium in the European eel Anguilla anguilla following aqueous exposure to metal salts

The platinum group metals (PGM) Pt and Rh are emitted into the environment mainly by catalytic exhaust gas converters of cars and by effluents of hospitals, which use Pt based anti-cancer drugs. However, there is still a lack of information on the availability of these precious metals to the biosphere. As PGM accumulate in sediments of aquatic ecosystems we focused our study on the uptake of the noble metals by European eels, Anguilla anguilla. Therefore, eels were exposed in tap water and humic water containing Pt(4+) and Rh(3+) at a concentration of 170 and 260 microg/l, respectively. After an exposure period of 6 weeks the mean Pt levels in bile, liver, kidney and intestine of the exposed eels ranged between 68 ng/g and 840 ng/g and the mean Rh levels between 35 ng/g and 155 ng/g whereas the PGM levels of the unexposed controls were below the detection limit of 50 ng/g for Pt and 5 ng/g for Rh. Rh was also taken up by gill and spleen. No PGM uptake was found for muscle and blood. The pattern of metal distribution within the eel differed between Pt and Rh and was dependent on the water type. Due to their accumulation capacity for PGM eels are suitable as accumulation indicators to detect PGM pollution in aquatic ecosystems.     

Female bushcrickets mated with parasitized males show rapid remating and reduced fecundity (Orthoptera: Phaneropteridae: Poecilimon mariannae)

 Following mating, female bushcrickets undergo a refractory period during which they are sexually unreceptive. The length of the refractory period correlates with the size of the spermatophylax. However, the size of the nuptial gift of acoustically signalling bushcrickets is often reduced as a result of infections by parasitoid flies. We examined the effect of male parasitoid infection on the induction of the refractory period and fecundity of females. We found a drastically reduced refractory period in females if the first mating partner was infected. During this shortened period fewer eggs were deposited, as an effect of the shorter refractory period, whereas the daily egg-laying rate remained the same regardless of whether the females were mated with a parasitized or an unparasitized male. Received: 17 July 2000 / Accepted in revised form: 4 August 2000     

Tissue distribution of 2,2',4,4'-tetrabromo[14C]diphenyl ether ([14C]-PBDE 47) in pike (Esox lucius) after dietary exposure--a time series study using whole body autoradiography

In the present study, the tissue distribution of [14C]-labelled 2,2',4,4'-tetrabrominated diphenyl ether (PBDE 47) and its possible metabolites was investigated after dietary exposure in pike (Esox lucius) using whole-body autoradiography. The study is a time series with pike examined 9, 18, 36 and 65 days after exposure. PBDE 47 was efficiently absorbed from the food (>90%) and radioactivity remained in the body in considerable amounts even after the longest period examined. The results indicate that PBDE 47 is not rapidly metabolised to hydrophilic, but possible to hydrophobic metabolites and that PBDE 47 and possible hydrophobic metabolites are accumulated in the lipid rich tissues of the pike. Melanin binding of PBDE 47 and possible metabolite(s) is suggested. The levels of PBDE 47 and/or metabolite(s) declines with time in most tissues except for the most lipid rich, where no decline in radioactivity is observed even after the longest period studied. Signs of irreversible incorporation of PBDE 47-derived radioactivity were detected but considered as too uncertain to conclude that covalent binding of PBDE 47-metabolites to macromolecules occurs.     

Determination of microcontaminants in sediments by on-line solid-phase extraction-gas chromatography-mass spectrometry

Two simple and straightforward analytical procedures for the screening of sediment samples are reported. They involve extraction with ethyl acetate or methanol and subsequent analysis by means of gas chromatography-mass spectrometry (GC-MS) using large-volume injection (LVI) or solid-phase extraction (SPE). The latter, which was originally developed for the analysis of aqueous samples, can be used without any modification. In general, 10 ml of organic solvent were added to 2 g of sediment, and the mixture was shaken and allowed to stand overnight. The methanolic extracts were then diluted in water and subjected to preconcentration and analysis using on-line SPE-GC-MS. The ethyl acetate extracts were injected directly into the GC using LVI. Both methods were used for the detection and identification of microcontaminants during a monitoring study of the river Nitra (Slovak Republic). They included polyaromatic hydrocarbons (PAHs), chlorofluorohydrocarbons, alkoxylated and alkylated phenols and benzothiazole derivatives. Semi-quantitative profiles of the contaminants were constructed and provisionally interpreted. The results indicate that SPE-GC-MS, and also LVI-GC-MS, have good potential for a rapid screening of sediment samples and the identification of microcontaminants. The analytical procedures pose no problems, and the on-line set-up is user-friendly.     

The vulnerability of Australian rural communities to climate variability and change: Part II—Integrating impacts with adaptive capacity

In the first paper in this series [Nelson, R., Kokic, P., Crimp, S., Martin, P., Meinke, H., Howden, S.M. (2010, this issue)], we concluded that hazard/impact modelling needs to be integrated with holistic measures of adaptive capacity in order to provide policy-relevant insights into the multiple and emergent dimensions of vulnerability. In this paper, we combine hazard/impact modelling with an holistic measure of adaptive capacity to analyse the vulnerability of Australian rural communities to climate variability and change. Bioeconomic modelling was used to model the exposure and sensitivity of Australian rural communities to climate variability and change. Rural livelihoods analysis was used as a conceptual framework to construct a composite index of adaptive capacity using farm survey data. We then show how this integrated measure of vulnerability provides policy-relevant insights into the constraints and options for building adaptive capacity in rural communities. In the process, we show that relying on hazard/impact modelling alone can lead to entirely erroneous conclusions about the vulnerability of rural communities, with potential to significantly misdirect policy intervention. We provide a preliminary assessment of which Australian rural communities are vulnerable to climate variability and change, and reveal a complex set of interacting environmental, economic and social factors contributing to vulnerability.     

Differential survival rates in a declining and an invasive farmland gastropod species

Individual marking by using transponders represents a promising tool to further investigate causes of population trends of farmland invertebrates and the dynamics of farmland biodiversity. Once common in agricultural fields the slug Arion rufus is now restricted to forests, whereas the closely related and similar Arion lusitanicus recently built up high populations. Here, it was tested whether (1) transponder tagging combined with artificial shelters for recapturing is a suitable approach for quantifying adult survival of farmland gastropods under real field conditions, (2) whether captive bred and wild A. lusitanicus differ in survival, and (3) whether in agricultural fields the declining slug A. rufus shows reduced survival rates compared to the invasive slug A. lusitanicus. One hundred and thirty transponder-tagged slugs were released and individual-based mark-recapture models were performed. Individual marking by using transponders proved to be a successful method for quantifying survival rates of the slugs. The favoured model showed no differences in survival or encounter rates between captive bred and wild A. lusitanicus. A. rufus showed significantly reduced survival rates compared to A. lusitanicus coinciding with their population trends in farmland areas. This might be due to differential susceptibility to habitat degradation, differential predation rates or promotion of the invasive competitor species. A further decrease of A. rufus in agricultural landscapes is expected.