Die Regulation der Blutgerinnung

The patency of the vascular tree as well as thrombus formation are achieved by the interactions of several components of the circulating blood and the vessel wall. Circulating glycoproteins (coagulation factors), cellular elements of the blood (platelets), the fibrinolytic system, the endothelium of the vasculature and inhibitors that are present in the blood stream are involved in the maintainance of the subtle balance between anti-coagulant and pro-coagulant forces. Regulation of the activity of thrombin represents a key event in this process.     

Stable Isotopes of Nitrogen in Fossil Cladoceran Exoskeletons: Implications for Nitrogen Sources in the Central Baltic Sea During the Past Century

15  N of bulk sediment, organic carbon concentrations, and abundances of exoskeletons of Bosmina longispina maritima in the sediment, the data are used to evaluate significant sources of nitrogen in the food web over the past century. Nitrogen isotopic composition of bulk sediments ranges from 2.5 to 4.5?, that of exokeletons varies between 0.4 and 6.2?. The two are positively correlated. A marked increase in the abundance of Bosmina since 1965 (from less than 500 specimen to more than 5000 specimen cm³ of sediment) is correlated with a significant increase in sedimentary organic carbon concentrations (from 4% to more than 10%). The isotopic data do not identify increased land-derived nitrate as the dominant nitrogen source fuelling the increase. Instead, we postulate that nitrogen fixation by diazotrophic bacteria has been one of the larger sources of nitrogen in the Baltic Sea, as it is today. Received: 29 April 1998 / Accepted in revised form: 13 August 1998     

Levels of behavioral organization and the evolution of division of labor

The major features of insect societies that fascinate biologists are the self-sacrificing altruism expressed by colony members, the complex division of labor, and the tremendous plasticity demonstrated in the face of changing environments. The social behavior of insects is a result of complex interactions at different levels of biological organization. Genes give rise to proteins and peptides that build the nervous and muscular systems, regulate their own synthesis, interact with each other, and affect the behavior of individuals. Social behavior emerges from the complex interactions of individuals that are themselves far removed from the direct effects of the genes. In order to understand how social organization evolves, we must understand the mechanisms that link the different levels of organization. In this review, we discuss how behavior is influenced by genes and the neural system and how social behavior emerges from the behavioral activities of individuals. We show how different levels of organization share common features and are linked through common mechanisms. We focus on the behavior of the honey bee, the best studied of all social insects.     

A chemical view of the most ancient metazoa--biomarker chemotaxonomy of hexactinellid sponges

Hexactinellid sponges are often considered to be the most ancient metazoans. Lipid biomarkers from 23 species were studied for information on their phylogenetic properties, particularly their disputed relation to the two other sponge classes (Demospongiae, Calcarea). The most prominent lipid compounds in the Hexactinellida comprise C28 to C32 polyenoic fatty acids. Their structures parallel the unique patterns found in demosponge membrane fatty acids ('demospongic acids') and strongly support a close phylogenetic association of the Demospongiae and the Hexactinellida. Both taxa also show unusual mid-chain methylated fatty acids (C15-C25) and irregular C25- and C40-isoprenoid hydrocarbons, tracers for specific eubacteria and Archaea, respectively. These biomarkers indicate a similar, highly conservative symbiont community, although some shift in the abundance of the associated microbiota was observed. The lack of these features in calcareous sponges further contradicts the still common view that Calcarea and Demospongiae are more closely related to each other than either is to the Hexactinellida.     

Spatially resolved detection of luminescence: a unique tool for archaeochronometry

Archaeochronometry uses luminescence dating to reveal ages of sediments and artefacts. Uncertainties in luminescence ages are partly related to the dating procedure, which uses grain separates. This is particularly true for stone surfaces, which require an imaging method for luminescence detection. Here we present the development of a novel luminescence device with high spatial resolution as well as signal-to-noise ratio and data processing software that now allows us to determine palaeodoses and potentially the dose-rate for cut sections of rocks and artefacts. The determination of the luminescence age of single mineral grains within sections and even of selected zones within grains becomes feasible, opening up a wide field of new applications.