Introduced reindeer and their effects on the vegetation and the epigeic invertebrate fauna of South Georgia (subantarctic)

Summary The introduced reindeer of South Georgia have had a serious impact on the vegetation throughout the range of three populations on the island. Exclosure experiments in areas where the reindeer were introduced have resulted in a dramatic change in the composition of the protected vegetation. Poa flabellata (the major winter food) and Acaena magellanica (a major summer food) have recovered to their former status inside the exclosures, while Deschampsia antarctia and the introduced grass Poa annua tolerate grazing and trampling and have spread over the grazed areas. Festuca contracta and Rostkovia magellanica are not eaten by the reindeer. Trampling has resulted in a high proportion of bare soil and peat in sites freely accessible to reindeer. However, the changes in the vegetation have not had such a significant effect on the associated invertebrate fauna. Thus in grazed and protected areas the faunistic composition is qualitatively similar, although there are quantitative differences, and some of the trends can probably be attributed to the presence of the reindeer. Compared with reindeer-free areas, the abundance of the perimylopid beetle Hydromedion sparsutum (a major primary decomposer) is reduced. The frequency of their egg parasite Notomymar aptenosoma (Hymenoptera, Mymaridae) increases. Consequently the ratio of perimylopoids to mymarids found in pitfall traps shifts from 1:0.01 (ungrazed areas) to 1:0.54 (grazed areas). Also the frequency of sciarids was found to be higher in reindeer areas. The larvae of these probably introduced gnats do not play a role in the natural terrestrial ecosystem of South Georgia, but in reindeer areas they appear to establish larger populations because they are able to live deeper in the soil and in hardened substrates. There is also a shift in the ratio between Collembola (major prey) to spiders from 1:1.3 (ungrazed areas) to 1:0.82 (grazed areas), for animals collected in pitfall traps. This may be a result of the trampling effect of the reindeer.     

Die Littorina-Arten: Kein Modell für die Entstehung der Landschnecken

Zusammenfassung Die europäischen Littorina-Arten verfügen über keinerlei Osmoregulation.Kleine Individuen (Arten) haben kleine Kiemen, die Kiemen wachsen positiv allometrisch.Die Fortpflanzung zeigt keine parallel dem spezifischen Habitat zunehmende Neigung zur direkten Entwicklung.Die Littorina-Arten stellen kein Modell für die Entwicklung der Landschnecken dar, sie zeigen lediglich typische Charaktere von Tieren der Gezeitenzone.

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The Littorina species of the European coasts: No model for the evolution of terrestrial gastropods

Summary The Littorina-species of the European coasts are completely isoosmotic with their environment.Small specimens (species) have very small gills; with increasing size the gills grow rapidly. The gills of different species of identical size show no difference. The reproduction does not trend towards direct development parallel to the habitat of the species.Therefore the Littorina species are no model for the evolution of terrestrial gastropods, their characteristics are merely those of intertidal animals.

     

Effects of decreased atmospheric deposition on the sulfur budgets of two Dutch moorland pools

The chemical composition of surface waters of two Dutch moorland pools and of incident precipitation, was monitored from 1982 to 1990. For this period, sulfur and water budgets were calculated using a hydrochemical model developed for well-mixed non-stratifying lakes. Total atmospheric deposition of S decreased significantly after 1986 at both locations. A model describing the sulfur budget in terms of input, output and reduction/oxidation processes predicted a fast decrease of pool water SO₄ ²⁻ concentrations after a decrease of atmospheric input. However, SO₄ ²⁻ concentrations in the surface water was lowered only slightly or remained constant. Apparently a source within the lake caused the unexpectedly high SO₄ ²⁻ concentrations. The possible supply of SO₄ ²⁻ from the sediment through regulation by (K-)Al-SO₄ containing minerals or desorption of SO₄ ²⁻ from positively charged surfaces in the sediment was evaluated. Solubility calculations of pore water with respect to alunite, basaluminite and jurbanite indicated that SO₄ ²⁻ concentration was not regulated by these minerals. It is suggested here (1) that desorption of SO₄ ²⁻ from peaty sediments may account for the estimated SO₄ ²⁻ supply provided that the adsorption complex is periodically recharged by partial oxidation of the upper bottom sediments and (2) that because of exposure of a part of the pool bottom to the atmosphere during dry summers and subsequent oxidation of reduced S, the amount of SO₄ ²⁻ may be provided which complements the decreasing depositional SO₄ ²⁻ input. In future research these two mechanisms need to be investigated.     

Untersuchungenüber Das tageszeitlich gebundene Schlüpfen yon Pseudosmittia Arenaria (Dipt. Chironomidae)

Zusammenfassung In einleitenden terminologischen Erwägungen wird vorgeschlagen, den Ausdruck Schlüpfrhythmus zugunsten von tageszeitlich gebundenem Schlüpfen aufzugeben. Pseudosmittia arenaria zeigt im normalen Tag-Nachtwechsel ein deutliches tageszeitlich gebundenes Schlüpfen mit einem Maximum 6–8h nach DL (Beginn der Beleuchtung).In Dauerdunkel schlüpfen keine Imagines. In Dauerlicht erscheinen die Tiere gleichmäßig über den ganzen Tag verteilt.Der ganze Bereich des sichtbaren Lichtes (geprüft von 476–641 m) ist wirksam. Auch die Lichtintensität in Licht-Dunkelbedingungen spielt im untersuchten Bereich (18–350 Lux) keine Rolle.Das Schlüpfmaximum von Ps. arenaria zeigt eine deutliche Beziehung zu DL. Es wandert bei konstanter Tageslänge um so dichter an DL heran, je kürzer die relative Länge der Lichtzeit ist.Bei kürzeren Tageslängen wandert das Maximum von DL fort, bei längeren an DL heran. Bei Tagen, die kürzer als 18h sind, liegt es in der folgenden Dunkelzeit, bei solchen, die länger als 36h sind, vor DL. Sein Weg beschreibt dabei eine kubische Parabel.Beim Eintritt des Gipfels in die folgende Dunkelzeit erscheint ein Maximum nur an jedem 2. Tag. Ein Maximum vor DL ruft ein zusätzliches Maximum in der gleichen Entfernung von LD (Beginn der Dunkelzeit) hervor. Bei extremen Tageslängen ist also dennoch ein Maximum ungefähr alle 24h zu beobachten. Dies ist exogen bedingt. Verlagert man durch schwache Beleuchtung während der Dunkelzeit das Maximum im 12h-Tag in die Lichtzeit, so erhält man ein Maximum an jedem Tag. Der Eintritt des Maximums in eine Dunkelzeit hat also das Umspringen auf einen Schlüpfgipfel an jedem 2. Tag bzw. auf 2 je Tag zur Folge.Im 12h-Tag mit absoluter Dunkelzeit während der Dunkelzeit kann man auch ein Maximum alle 12h erreichen, und zwar durch Umstimmung eines Teils der Population. Man hat dann 2 Gruppen, deren Maxima um 12h gegeneinander verschoben sind. Hemmend und fördernd auf den Einfluß des Lichtes wirken Temperatur und Substratfeuchtigkeit. Beide Faktoren können ohne Licht kein Schlüpfen hervorrufen. Beziehungen zwischen Lebensweise, Ökologie oder systematischer Stellung und tageszeitlich gebundenem Schlüpfen lassen sich bisher nicht feststellen.     

Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

Schriftenschau

Ohne Zusammenfassung     

The Active and the Inactive Form of the hAT1 Receptor Have an Identical Ligand-Binding Environment: An MPA Study on a Constitutively Active Angiotensin II Receptor Mutant

Several models of activation mechanisms were proposed for G protein-coupled receptors (GPCRs), yet no direct methods exist for their elucidation. The availability of constitutively active mutants has given an opportunity to study active receptor conformations within acceptable limits using models such as the angiotensin II type 1 (AT₁)¹ receptor mutant N111G-hAT₁ which displays an important constitutive activity. Recently, by using methionine proximity assay, we showed for the hAT₁ receptor that TMD III, VI, and VII form the ligand-binding pocket of the C-terminal amino acid of an antagonistic AngII analogue. In the present contribution, we investigated whether the same residues would also constitute the ligand-binding contacts in constitutively activated mutant (CAM) receptors. For this purpose, the same Met mutagenesis strategy was carried out on the N111G double mutants. Analysis of 43 receptors mutants in the N111G-hAT₁ series, photolabeled and CNBr digested, showed that there were only subtle structural changes between the wt-receptor and its constitutively active form.     

Multifactorial diversity sustains microbial community stability

Maintenance of a high degree of biodiversity in homogeneous environments is poorly understood. A complex cheese starter culture with a long history of use was characterized as a model system to study simple microbial communities. Eight distinct genetic lineages were identified, encompassing two species: Lactococcus lactis and Leuconostoc mesenteroides. The genetic lineages were found to be collections of strains with variable plasmid content and phage sensitivities. Kill-the-winner hypothesis explaining the suppression of the fittest strains by density-dependent phage predation was operational at the strain level. This prevents the eradication of entire genetic lineages from the community during propagation regimes (back-slopping), stabilizing the genetic heterogeneity in the starter culture against environmental uncertainty.     

Breast MRI in nonpalpable breast lesions: a randomized trial with diagnostic and therapeutic outcome – MONET – study

Background

In orthodontic treatment, anchorage control is a fundamental aspect. Usually conventional mechanism for orthodontic anchorage control can be either extraoral or intraoral that is headgear or intermaxillary elastics. Their use are combined with various side effects such as tipping of occlusal plane or undesirable movements of teeth. Especially in cases, where key-teeth are missing, conventional anchorage defined as tooth-borne anchorage will meet limitations. Therefore, the use of endosseous implants for anchorage purposes are increasingly used to achieve positional stability and maximum anchorage.

Methods/Design

The intended study is designed as a prospective, multicenter randomized controlled trial (RCT), comparing and contrasting the effect of early loading of palatal implant therapy versus implant loading after 12 weeks post implantation using the new ortho-implant type II anchor system device (Orthosystem Straumann, Basel, Switzerland). 124 participants, mainly adult males or females, whose diagnoses require temporary stationary implant-based anchorage treatment will be randomized 1:1 to one of two treatment groups: group 1 will receive a loading of implant standard therapy after a healing period of 12 week (gold standard), whereas group 2 will receive an early loading of orthodontic implants within 1 week after implant insertion. Participants will be at least followed for 12 months after implant placement. The primary endpoint is to investigate the behavior of early loaded palatal implants in order to find out if shorter healing periods might be justified to accelerate active orthodontic treatment. Secondary outcomes will focus e.g. on achievement of orthodontic treatment goals and quantity of direct implant-bone interface of removed bone specimens. As tertiary objective, a histologic and microtomography evaluation of all retrieved implants will be performed to obtain data on the performance of the SLA surface in human bone evaluation of all retrieved implants. Additionally, resonance frequency analysis (RFA, Osstell? mentor) will be used at different times for clinically monitoring the implant stability and for histological comparison in order to measure the reliability of the resonance frequency measuring device.

Trial registration

Current Controlled Trials ISRCTN97142521.