ALBERT

Description: Questions What are the driving factors for the species richness of understorey herbs of isolated forest patches? How can the relative direct and indirect effects of patch area, site quality, habitat isolation and continuity be disentangled? What are the effects on different species groups? Location Eutrophic hardwood forest patches in northwestern Germany. The isolation of these patches results from extensive agricultural land use and prevailing poor soil conditions in the surrounding landscape. Thus, the patches are embedded within a matrix of both open habitats and species-poor acidic forests. Methods We surveyed 76 eutrophic forest patches and recorded all understorey herb species. Several measured site variables were divided into soil and structural components, and into variables describing mean site conditions and site heterogeneity. Partial least squares structural equation modelling (PLS-SEM) was employed to determine the direct and indirect effects of patch area, site heterogeneity, mean site conditions, isolation and habitat continuity on species richness of several species groups. Results The most important factor determining species richness was patch area, which showed the strongest direct effect on eutrophic forest specialist species. Richness of forest matrix species, which also occur in the surrounding forest areas, was not directly influenced by area. Soil heterogeneity as well as structural heterogeneity increased with area, but only soil heterogeneity was relevant for species richness. Soil heterogeneity was more important for forest species in general and stress tolerators than for generalist species, open habitat species, competitors and ruderals. Mean site conditions influenced species richness of generalists, open habitat species, competitors and nutrient-demanding species. Isolation had a (negative) effect only on habitat specialists. Conclusions The relative effects of driving factors varied considerably between species groups. From our results for eutrophic forest specialists, we conclude that large and well-connected habitat patches are especially important for the successful conservation of the unique and partly endangered flora of eutrophic hardwood forests. We determined the relative effects of driving factors on species richness of eutrophic forest patches and found considerable differences between different species groups. Richness of specialists was driven by soil heterogeneity, direct area effects and isolation whereas these factors hardly affected generalists and open habitat species. We conclude that large, well-connected habitat patches play an important role with respect to conservation.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print.

Description: Question: The eu-atlantic forest herb Ceratocapnos claviculata showed a recent increase in frequency within its native range and an eastward and northward range expansion in Central Europe. To gain deeper understanding of factors affecting the range expansion of the species, we analyzed vegetation relevés at three different scales and asked the following questions: As the species occurs in a wide range of vegetation types, is variation in community composition across the entire range related to climatic environmental zones and tree cover? Are there differences in species composition and habitat characteristics between the native range and the two invaded regions (S Sweden and NE Germany)? Did community composition and habitat characteristics within the native range (The Netherlands) change between ‘before 1970’ and ‘1990 to 2006’? Location: W, C and N Europe. Methods: We analysed vegetation-plot data with C. claviculata from various databases and own surveys using partial CCA, partial DCA, Indicator Species Analysis, MANCOVA and multiple regression. Results: Using vegetation plots from the entire distribution range, climatic environmental zones explained 68.9% of the total canonical Eigenvalue. Differences in floristic composition and habitat characteristics between the two invaded regions were as large as between native and invaded range sites. However, relevés from the invaded range were generally characterized by anthropogenic disturbance. Accordingly, abundance of C. claviculata was positively linked to silvicultural intensity. New relevés from 1990 to 2006 were characterized by higher Ellenberg nutrient indicator values, lower species diversity, higher proportions of neophytic and hemerobic species and showed a lower cover of the study species than old relevés from before 1970. Conclusions: Across the range of C. claviculata , climatic environmental zones determine vegetation composition. Accordingly, the species is characterized by a broad macroclimatic amplitude. Vegetation composition and structure differ significantly between the two regions of the new range. Thus, the species has successfully established under various biotic and abiotic environmental conditions. Beyond potential positive effects of soil eutrophication and mild winters, anthropogenic impact may directly facilitate seed dispersal and provide sites and resource conditions suitable for germination and establishment of C. claviculata , whereas a decrease of forest management may constrain the species.

Description: We present the first detailed 2D seismic tomographic image of the trench-outer rise, fore- and back-arc of the Tonga subduction zone. The study area is located approximately 100 km north of the collision between the Louisville hot spot track and the overriding Indo-Australian plate where ∼80 Ma old oceanic Pacific plate subducts at the Tonga Trench. In the outer rise region, the upper oceanic plate is pervasively fractured and most likely hydrated as demonstrated by extensional bending-related faults, anomalously large horst and graben structures, and a reduction of both crustal and mantle velocities. The 2D velocity model presented shows uppermost mantle velocities of ∼7.3 km/s, ∼10% lower than typical for mantle peridotite (∼30% mantle serpentinization). In the model, Tonga arc crust ranges between 7 and 20 km in thickness, and velocities are typical of arc-type igneous basement with uppermost and lowermost crustal velocities of ∼3.5 and ∼7.1 km/s, respectively. Beneath the inner trench slope, however, the presence of a low velocity zone (4.0–5.5 km/s) suggests that the outer fore-arc is probably fluid-saturated, metamorphosed and disaggregated by fracturing as a consequence of frontal and basal erosion. Tectonic erosion has, most likely, been accelerated by the subduction of the Louisville Ridge, causing crustal thinning and subsidence of the outer fore-arc. Extension in the outer fore-arc is evidenced by (1) trenchward-dipping normal faults and (2) the presence of a giant scarp (∼2 km offset and several hundred kilometers long) indicating gravitational collapse of the outermost fore-arc block. In addition, the contact between the subducting slab and the overriding arc crust is only 20 km wide, and the mantle wedge is characterized by low velocities of ∼7.5 km/s, suggesting upper mantle serpentinization or the presence of melts frozen in the mantle.

Description: Historically low temperatures have severely limited skeleton-breaking predation on the Antarctic shelf, facilitating the evolution of a benthic fauna poorly defended against durophagy. Now, rapid warming of the Southern Ocean is restructuring Antarctic marine ecosystems as conditions become favorable for range expansions. Populations of the lithodid crab Paralomis birsteini currently inhabit some areas of the continental slope off Antarctica. They could potentially expand along the slope and upward to the outer continental shelf, where temperatures are no longer prohibitively low. We identified two sites inhabited by different densities of lithodids in the slope environment along the western Antarctic Peninsula. Analysis of the gut contents of P. birsteini trapped on the slope revealed them to be opportunistic invertivores. The abundances of three commonly eaten, eurybathic taxa—ophiuroids, echinoids, and gastropods—were negatively associated with P. birsteini off Marguerite Bay, where lithodid densities averaged 4280 ind/km 2 at depths of 1100–1499 m (range 3440–5010 ind/km 2 ), but not off Anvers Island, where lithodid densities were lower, averaging 2060 ind/km 2 at these depths (range 660–3270 ind/km 2 ). Higher abundances of lithodids appear to exert a negative effect on invertebrate distribution on the slope. Lateral or vertical range expansions of P. birsteini at sufficient densities could substantially reduce populations of their benthic prey off Antarctica, potentially exacerbating the direct impacts of rising temperatures on the distribution and diversity of the contemporary shelf benthos.

Description: Gas seepage from marine sediments has implications for understanding feedbacks between the global carbon reservoir, seabed ecology and climate change. Although the relationship between hydrates, gas chimneys and seafloor seepage is well established, the nature of fluid sources and plumbing mechanisms controlling fluid escape into the hydrate zone and up to the seafloor remain one of the least understood components of fluid migration systems. In this study we present the analysis of new three-dimensional high-resolution seismic data acquired to investigate fluid migration systems sustaining active seafloor seepage at Omakere Ridge, on the Hikurangi subduction margin, New Zealand. The analysis reveals at high resolution, complex overprinting fault structures (i.e. protothrusts, normal faults from flexural extension, and shallow (〈1 km) arrays of oblique shear structures) implicated in fluid migration within the gas hydrate stability zone in an area of 2x7 km. In addition to fluid migration systems sustaining seafloor seepage on both sides of a central thrust fault, the data show seismic evidence for sub-seafloor gas-rich fluid accumulation associated with proto-thrusts and extensional faults. In these latter systems fluid pressure dissipation through time has been favored, hindering the development of gas chimneys. We discuss the elements of the distinct fluid migration systems and the influence that a complex partitioning of stress may have on the evolution of fluid flow systems in active subduction margins.

Description: Damage to the integrity of the vessel wall results in exposure of the subendothelial extracellular matrix (ECM), which triggers integrin-dependent adhesion and aggregation of platelets. The role of platelet β1 integrins in these processes remains mostly undefined. Here, we demonstrate by intravital fluorescence microscopy that platelet adhesion and thrombus growth on the exposed ECM of the injured carotid artery is not significantly altered in α2-null mice and even in mice with a Cre/loxP-mediated loss of all β1 integrins on their platelets. In contrast, inhibition of αIIbβ3 integrin on platelets in wild-type mice blocked aggregate formation and reduced platelet adhesion by 60.0%. Strikingly, αIIbβ3 inhibition had a comparable effect in α2-null mice, demonstrating that other receptors mediate shear-resistant adhesion in the absence of functional α2β1 and αIIbβ3. These were identified to be α5β1 and/or α6β1 as αIIbβ3 inhibition abrogated platelet adhesion in β1-null mice. We conclude that shear-resistant platelet adhesion on the injured vessel wall in vivo is a highly integrated process involving multiple integrin-ligand interactions, none of which by itself is essential. (Blood. 2003;102:4021-4027)

Description: Activated phagocytes express considerable amounts of MRP8 and MRP14, 2 calcium-binding S100 proteins forming stable heterodimers that are specifically secreted at inflammatory sites in many diseases. We previously reported that treatment of human microvascular endothelial cells with purified MRP8/MRP14 leads to loss of endothelial cell contacts. In this study, we demonstrate that MRP8/MRP14 complexes furthermore trigger cell death of endothelial cells after the onset of cell detachment. Morphologic analysis of dying endothelial cells revealed characteristic features of both apoptosis and necrosis. Furthermore, MRP8/MRP14 induced apoptotic caspase-9 and caspase-3 activation, DNA fragmentation, and membrane phosphatidylserine exposure in target cells. These events were independent of death receptor signaling and in part controlled by a mitochondrial pathway. Consistently, overexpression of antiapoptotic Bcl-2 abrogated caspase activation and externalization of phosphatidylserine; however, MRP8/MRP14 still induced plasma membrane damage and even DNA fragmentation. Thus, our results demonstrate that MRP8/MRP14 triggers cell death via caspase-dependent as well as -independent mechanisms. Excessive release of cytotoxic MRP8/MRP14 by activated phagocytes might therefore present an important molecular pathomechanism contributing to endothelial damage during vasculitis and other inflammatory diseases.

Description: Platelet activation at sites of vascular injury is crucial for hemostasis, but it may also cause myocardial infarction or stroke. Cytoskeletal reorganization is essential for platelet activation and secretion. The small GTPase Cdc42 has been implicated as an important mediator of filopodia formation and exocytosis in various cell types, but its exact function in platelets is not established. Here, we show that the megakaryocyte/platelet-specific loss of Cdc42 leads to mild thrombocytopenia and a small increase in platelet size in mice. Unexpectedly, Cdc42-deficient platelets were able to form normally shaped filopodia and spread fully on fibrinogen upon activation, whereas filopodia formation upon selective induction of GPIb signaling was reduced compared with wild-type platelets. Furthermore, Cdc42-deficient platelets showed enhanced secretion of α granules, a higher adenosine diphosphate (ADP)/adenosine triphosphate (ATP) content, increased aggregation at low agonist concentrations, and enhanced aggregate formation on collagen under flow. In vivo, lack of Cdc42 resulted in faster occlusion of ferric chloride–injured arterioles. The life span of Cdc42-deficient platelets was markedly reduced, suggesting increased clearing of the cells under physiologic conditions. These data point to novel multiple functions of Cdc42 in the regulation of platelet activation, granule organization, degranulation, and a specific role in GPIb signaling.