Untersuchungen über die Symbiose von Tieren mit Pilzen und Bakterien

Ohne ZusammenfassungEs ist mir eine angenehme Pflicht, auch an dieser Stelle der Deutschen Forschungsgemeinschaft, mit deren Unterstützung die vorliegenden Untersuchungen durchgeführt wurden, meinen besten Dank auszusprechen. Zu besonderem Dank fühle ich mich Herrn Prof. Dr. W. Schwartz für die Anregung zu dieser Arbeit, für viele Ratschläge und alle erhaltene Förderung verpflichtet.     

Striking phenotypic and functional differences in lamina propria lymphocytes from the large and small intestine of mice

Although intraepithelial T lymphocytes of the large intestine (LI) are known to differ from those of the small intestine (SI) in phenotype and function, differences in LI and SI lamina propria (LP) lymphocyte populations have not been clearly established. In this work we found striking phenotypic differences between SI and LI LP lymphocyte populations from Balb/c mice analyzed by flow cytometry. In the LI most lymphocytes were B cells and the predominant T cells were TCR-alpha beta+, CD8+. In contrast, in the SI most T lymphocytes were CD4+ expressing TCR-alpha beta+, although a higher proportion expressed TCR-gamma delta+ than in the LI. In T cells the expression of adhesion molecules and cytokines was also different between SI and LI. The proportion of LP T cells expressing alpha4beta7 and L-selectin was higher in the LI than in the SI; whereas a greater proportion of cells expressing alpha(E)beta7 were detected in the SI than in LI. Higher proportions of T cells expressing L-selectin and alpha4beta1 were detected in the intraepithelial compartment of the LI than that of the SI, whereas the number of T cells expressing alpha(E)beta7 was much higher in the SI than in the LI. The proportion of T cells spontaneously producing IL-2, IFN gamma, and IL-4 at the intraepithelial and lamina propria, in the small and large intestine, was different indicating that distinctive functional features exist in the lymphocyte populations residing at the different intestinal compartments.     

Modelling relationships between species spatial abundance patterns and climate

Aim To move towards modelling spatial abundance patterns and to evaluate the relative impacts of climatic change upon species abundances as opposed to range extents. Location Southern Africa, including Lesotho, Namibia, South Africa, Swaziland and Zimbabwe. Methods Quantitative response surface models were fitted for 78 bird species, mostly endemic (68) or near‐endemic to the region, to model relationships between species reporting rates (i.e. the proportion of checklists reporting a species for a particular grid cell), as recorded by the Southern African Bird Atlas Project, and four bioclimatic variables derived from climatic data for the period 1961–90. With caution, reporting rates can be used as a proxy for abundance. Models were used to project potential impacts of a series of projected climatic change scenarios upon species abundance patterns and range extents. Results Most models obtained were robust with good predictive power. Projections of potential future abundance patterns indicate that the magnitude of impacts upon a proxy for abundance are greater than those upon range extent for the majority of species (82% by 2071–2100). For most species (74%) both abundance and range extent are projected to decrease by 2100. Impacts are especially severe if species are unable to realize projected range changes; when only the area of a species' simulated present range is considered, overall abundance decreases of more than 80% are projected for 19 (24%) of species examined. Main conclusions Our results indicate that projected climatic changes are likely to elicit greater relative changes in species abundances than range extents. For most species examined changes were decreases, suggesting the impacts upon biodiversity are likely generally to be negative. These results also suggest that previous estimates of the proportion of species at increased risk of extinction as a result of climatic change may, in some cases, be under‐estimates.     

Pathological shear stress stimulates the tyrosine phosphorylation of alpha-actinin associated with the glycoprotein Ib-IX complex.

Shear-induced platelet responses are triggered by VWF binding to the platelet GpIb-IX complex, and there is evidence that this ligand-receptor coupling stimulates transmembranous signaling through the cytoplasmic tail of glycoprotein (Gp) Ib alpha. To investigate the mechanism by which signaling is effected, new molecular interactions involving GpIb-IX that develop in response to pathological shearing stress were examined in intact human platelets. Exposure to shear, but not alpha-thrombin, results in the co-immunoprecipitation of the actin cross-linking protein alpha-actinin with the GpIb-IX complex. Blockers of VWF binding to GpIb alpha or actin polymerization inhibit the association of alpha-actinin with the GpIb-IX complex, but the association of alpha-actinin with the GpIb-IX complex is not affected by inhibiting VWF binding to platelet integrin alpha IIb beta 3 (GpIIb-IIIa). alpha-Actinin becomes tyrosine phosphorylated in response to pathological shear stress, and phosphorylated alpha-actinin associates with GpIb-IX. In resting platelets, class IA heterodimeric phosphatidylinositol 3-kinase (PI 3-K) and protein kinase N (PKN) associate with nonphosphorylated alpha-actinin. Shear stress causes PI 3-K to disassociate from alpha-actinin, while it stimulates PKN binding to alpha-actinin. These results demonstrate that shear-induced VWF binding to GpIb alpha causes enhanced binding of cytoskeletal alpha-actinin to GpIb-IX and suggest that alpha-actinin, perhaps through tyrosine phosphorylation, serves as an adapter for a signaling complex that could regulate VWF-induced platelet aggregation.     

Hydratations- und Permeabilitätsstudien an unbefruchteten Fucus-Eiern (Fucus vesiculosus L.)

Ohne Zusammenfassung     

Age-specific fitness components and their temporal variation in the barn owl

Theory predicts that temporal variability plays an important role in the evolution of life histories, but empirical studies evaluating this prediction are rare. In constant environments, fitness can be measured by the population growth rate lambda, and the sensitivity of lambda to changes in fitness components estimates selection on these traits. In variable environments, fitness is measured by the stochastic growth rate lambda(S), and stochastic sensitivities estimate selection pressure. Here we examine age-specific schedules for reproduction and survival in a barn owl population (Tyto alba). We estimated how temporal variability affected fitness and selection, accounting for sampling variance. Despite large sample sizes of old individuals, we found no strong evidence for senescence. The most variable fitness components were associated with reproduction. Survival was less variable. Stochastic simulations showed that the observed variation decreased fitness by about 30%, but the sensitivities of lambda and lambda(S) to changes in all fitness components were almost equal, suggesting that temporal variation had negligible effects on selection. We obtained these results despite high observed variability in the fitness components and relatively short generation time of the study organism, a situation in which temporal variability should be particularly important for natural selection and early senescence is expected.     

The second Southern African Bird Atlas Project: Causes and consequences of geographical sampling bias

Using the Southern African Bird Atlas Project (SABAP2) as a case study, we examine the possible determinants of spatial bias in volunteer sampling effort and how well such biased data represent environmental gradients across the area covered by the atlas. For each province in South Africa, we used generalized linear mixed models to determine the combination of variables that explain spatial variation in sampling effort (number of visits per 5′ × 5′ grid cell, or “pentad”). The explanatory variables were distance to major road and exceptional birding locations or “sampling hubs,” percentage cover of protected, urban, and cultivated area, and the climate variables mean annual precipitation, winter temperatures, and summer temperatures. Further, we used the climate variables and plant biomes to define subsets of pentads representing environmental zones across South Africa, Lesotho, and Swaziland. For each environmental zone, we quantified sampling intensity, and we assessed sampling completeness with species accumulation curves fitted to the asymptotic Lomolino model. Sampling effort was highest close to sampling hubs, major roads, urban areas, and protected areas. Cultivated area and the climate variables were less important. Further, environmental zones were not evenly represented by current data and the zones varied in the amount of sampling required representing the species that are present. SABAP2 volunteers' preferences in birding locations cause spatial bias in the dataset that should be taken into account when analyzing these data. Large parts of South Africa remain underrepresented, which may restrict the kind of ecological questions that may be addressed. However, sampling bias may be improved by directing volunteers toward undersampled regions while taking into account volunteer preferences.     

Nestboxes and immigration drive the growth of an urban Peregrine Falcon Falco peregrinus population

Drivers of wildlife population dynamics are generally numerous and interacting. Some of these drivers may impact demographic processes that are difficult to estimate, such as immigration into the focal population. Populations may furthermore be small and subject to demographic stochasticity. All of these factors contribute to blur the causal relationship between past management action and current population trends. The urban Peregrine Falcon Falco peregrinus population in Cape Town, South Africa, increased from three pairs in 1997 to 18 pairs in 2010. Nestboxes were installed over this period to manage the interface between new urban pairs of Falcons and the human users of colonized buildings, and incidentally to improve breeding success. We used integrated population models (IPMs) formally to combine information from a capture–mark–recapture study, monitoring of reproductive success and counts of population size. As all local demographic processes were directly observed, the IPM approach also allowed us to estimate immigration by difference. The provision of nestboxes, as a possible stimulant of population growth, improved breeding success and accounted for an estimated 3–26% of the population increase. The most important driver of growth, however, was immigration. Despite low sample sizes, the IPM approach allowed us to obtain relatively precise estimates of the population‐level impact of nestbox deployment. The goal of conservation interventions is often to increase population size, so the effectiveness of such interventions should ideally be assessed at the population level. IPMs are powerful tools in this context for combining demographic information that may be limited due to small population size or practical constraints on monitoring. Our study quantitatively documented both the immigration process that led to growth of a small population and the effect of a management action that helped the process.     

Pathological shear stress directly regulates platelet alphaIIbbeta3 signaling

Integrin mechanotransduction is a ubiquitous biological process. Mechanical forces are transduced transmembranously by an integrin's ligand-bound extracellular domain through its -subunit's cytoplasmic domain connected to the cytoskeleton. This often culminates in the activation of tyrosine kinases directing cell responses. The delicate balance between hemostasis and thrombosis requires exquisitely fine-tuned integrin function, and balance is maintained in vivo despite that the major platelet integrin _IIb3 is continuously subjected to frictional or shearing forces generated by laminar blood flow. To test the hypothesis that platelet function is regulated by the direct effects of mechanical forces on _IIb3, we examined _IIb3/cytoskeletal interactions in human platelets exposed to shear stress in a cone-plate viscometer. We observed that -actinin, myosin heavy chain, and Syk coimmunoprecipitate with _IIb3 in resting platelets and that 120 dyn/cm² shear stress leads to their disassociation from _IIb3. Shear-induced disassociation of -actinin and myosin heavy chain from the ₃ tail is unaffected by blocking von Willebrand factor (VWF) binding to glycoprotein (Gp) Ib-IX-V but abolished by blocking VWF binding to _IIb3. Syk's disassociation from ₃ is inhibited when VWF binding to either GpIb-IX-V or _IIb3 is blocked. Shear stress-induced phosphorylation of SLP-76 and its association with tyrosine-phosphorylated adhesion and degranulation-promoting adapter protein are inhibited by blocking ligand binding to _IIb3 but not by blocking ligand binding to GpIb-IX-V. Chinese hamster ovary cells expressing _IIb3 with ₃ truncated of its cytoskeletal binding domains demonstrate diminished shear-dependent adhesion and cohesion. These results support the hypothesis that shear stress directly modulates _IIb3 function and suggest that shear-induced _IIb3-mediated signaling contributes to the regulation of platelet aggregation by directing the release of constraining cytoskeletal elements from the ₃-tail. platelets; mechanoreceptor; integrin; shear stress; signal transduction