Wnt3a-mediated formation of phosphatidylinositol 4,5-bisphosphate regulates LRP6 phosphorylation

The canonical Wnt-beta-catenin signaling pathway is initiated by inducing phosphorylation of one of the Wnt receptors, low-density lipoprotein receptor-related protein 6 (LRP6), at threonine residue 1479 (Thr1479) and serine residue 1490 (Ser1490). By screening a human kinase small interfering RNA library, we identified phosphatidylinositol 4-kinase type II alpha and phosphatidylinositol-4-phosphate 5-kinase type I (PIP5KI) as required for Wnt3a-induced LRP6 phosphorylation at Ser1490 in mammalian cells and confirmed that these kinases are important for Wnt signaling in Xenopus embryos. Wnt3a stimulates the formation of phosphatidylinositol 4,5-bisphosphates [PtdIns (4,5)P2] through frizzled and dishevelled, the latter of which directly interacted with and activated PIP5KI. In turn, PtdIns (4,5)P2 regulated phosphorylation of LRP6 at Thr1479 and Ser1490. Therefore, our study reveals a signaling mechanism for Wnt to regulate LRP6 phosphorylation.     

A reversibly switching surface

We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.     

The historic influence of dams on diadromous fish habitat with a focus on river herring and hydrologic longitudinal connectivity

The erection of dams alters habitat and longitudinal stream connectivity for migratory diadromous and potamodromous fish species and interrupts much of organismal exchange between freshwater and marine ecosystems. In the US, this disruption began with colonial settlement in the seventeenth century but little quantitative assessment of historical impact on accessible habitat and population size has been conducted. We used published surveys, GIS layers and historical documents to create a database of 1356 dams, which was then analyzed to determine the historical timeline of construction, use and resultant fragmentation of watersheds in Maine, US. Historical information on the anadromous river herring was used to determine natural upstream boundaries to migration and establish total potential alewife spawning habitat in nine watersheds with historic populations. Dams in Maine were constructed beginning in 1634 and by 1850 had reduced accessible lake area to less than 5% of the virgin 892 km² habitat and 20% of virgin stream habitat. There is a near total loss of accessible habitat by 1860 that followed a west-east pattern of European migration and settlement. Understanding historic trends allows current restoration targets to be assessed and prioritized within an ecosystem-based perspective and may inform expectations for future management of oceanic and freshwater living resources.     

Estimated nitrogen use efficiency,surplus, and partitioning in young apple trees grown in varied organic production systems

A certified organic apple (Malus × domestica Borkh.) orchard was established to study the interaction of ground cover management systems (GMS) and nutrient sources (NS) on nitrogen (N) use efficiency and N surplus in the Southern U.S. for three years. Trees treated with green compost (GC) and wood chips (WC), regardless of the NS, had greater N accumulation and leaf N use efficiency compared to the shredded paper or mow-and-blow treated trees. The WC-treated trees had comparably low N surplus relative to the GC trees that induced more [NO₃⁻] in soil or soil solution in the rooting zone in September in year 3. GC trees had the highest [NO₃⁻] mineralization in the soil during winter. GMS had greater overall effects on the tree response variables than did the NS.     

Weak effect of edges on avian nesting success in fragmented and forested landscapes in Ontario,Canada

We studied the effects of anthropogenic edges on predation and parasitism of forest bird nests in an agriculturally fragmented landscape and a continuously forested landscape in Ontario, Canada. Nesting data were collected at 1937 nests across 10 species in the fragmented landscape from 2002–2008, and 464 nests across 4 species in the continuously forested landscape from 2006–2008. Brood parasitism only occurred in the fragmented landscape, and was positively related to the proportion of rural grassland and row crop habitats within 500-m of nests. Daily nest survival was negatively related to the density of roads within 500-m of nests in the fragmented landscape, but was not influenced by distance to anthropogenic edge in either landscape. Predation rates were higher in the fragmented landscape for Ovenbird and Rose-breasted Grosbeak nests, but did not differ between landscapes for Veery and American Redstart nests. Uniformly high predation in the fragmented landscape may be a result of (1) matrix predators that penetrate deep (>300 m) into the forest interior, or (2) the additive effect of forest-dependent and matrix-associated predators that results in high predation pressure in both edge and interior habitats. Further research focused on the identification of nest predators, their population dynamics, and habitat use is required to understand the underlying mechanisms leading to uniformly high nest predation in fragmented landscapes.     

Population genetic structure and landscape connectivity of the Eastern Yellowbelly Racer (<Emphasis Type="Italic">Coluber constrictor flaviventris</Emphasis>) in the contiguous tallgrass prairie of northeastern Kansas,USA

The tallgrass prairie of North America has undergone widespread habitat loss and fragmentation (<4% remains). The Flint Hills region of Kansas and Oklahoma is the largest tallgrass prairie remaining and therefore provides an opportunity to study the population genetic structure of grassland species in a relatively contiguous landscape and set a baseline for evaluating changes when the habitat is fragmented. We adopted a landscape genetics approach to identify how landscape structure affected dispersal, population genetic structure, and landscape connectivity of the Eastern Yellowbelly Racer (Coluber constrictor flaviventris) across a 13,500-km² landscape in northeastern Kansas, USA. The racer population had high allelic diversity, high heterozygosity, and was maintaining migration-drift equilibrium. Autocorrelation between genetic and geographic distance revealed that racers exhibited restricted dispersal within 3 km, and isolation-by-distance. Significant isolation-by-distance occurred at broad regional scales (>100 km), but because of sufficient gene flow between locations, we were unable to define discrete subpopulations using Bayesian clustering analyses. Resistance distance, which considers the permeability of habitats, did not explain significant variation in genetic distance beyond Euclidean distance alone, suggesting that racers are not currently influenced by landscape composition. In northeastern Kansas, racers appear to be an abundant and continuously distributed snake that perceives the landscape as well connected with no cover type currently impeding snake dispersal or gene flow.     

Relative importance of management vs. design for implementation of large-scale ecological networks

Ecological networks (ENs) are used to mitigate landscape-scale habitat loss, and are managed and designed to conserve regional biodiversity. In our study region in southern Africa, ENs of isolated grassland remnants are specifically set aside and managed for conservation, and are complemented by corridor-like power line servitudes which are maintained by regular mowing. Using grasshoppers, a sensitive and reliable bioindicator taxon, we determine whether ENs effectively conserve biodiversity. We used cluster analysis and variation partitioning to select the best subset of environmental variables which explained the patterns of species composition. We then compared the relative importance of environmental variables grouped by the scale of their influence: local-scale variables affected by management practices vs. landscape-scale variables affected by design of ENs. Management was consistently and significantly 2–5 times more influential than design in determining grasshopper assemblages within ENs and servitudes. Servitudes had a higher proportion of bare ground, lower proportion of tall grasses and higher abundance of grasshoppers relative to ENs. Three grasshopper species were strongly associated with servitudes and exhibited traits consistent with early colonizers. As management actions are primarily responsible for vegetation succession, the use of ENs for conservation efforts should first focus on appropriate management strategies, such as fire regime and grass height management before altering the landscape structure (e.g. increasing connectivity or enlarging patches). The conservation implications of these results are that, if ENs are managed and designed for heterogeneity and to simulate multiple successional stages, they may be beneficial for biodiversity conservation.     

Desertification and power laws

There is an ongoing controversy on the use of the patch-size distribution as an early warning signal for abrupt shifts to a desertified state in Mediterranean arid landscapes. This controversy started with Kéfi et al.’s suggestion that, when approaching the transition point to widespread desertification, vegetation patches would switch from a power-law (PL) to a truncated power-law (TPL) distribution. Here I show that, for fundamental reasons, no untruncated power law can be found in this context, irrespective of the level of degradation. This result does not deny the importance of the findings by Kéfi et al., but means that these have to be reinterpreted by moving from the PL/TPL dichotomy to other categorizations of the patch-size distribution. Physical constraints on patch-size distributions have general interest for landscape ecology.     

A GIS-based method for the reconstruction of the late eighteenth century forest vegetation in the Prignitz region (NE Germany)

Our goal was to reconstruct the late eighteenth century forest vegetation of the Prignitz region (NE Germany) at a scale of 1:50,000. We also wanted to relate the historical forest vegetation to the actual and potential natural vegetation. For these purposes, we selected 15 woody species and transferred relevant data found in historical records from various sources together with the recent localities of (very) old individuals belonging to these woody species into ArcView GIS. Following multi-step data processing including the generation of a point density layer using a moving window with kernel estimation and derivation of vegetation units applying Boolean algebra rules together with information on site conditions, we derived 17 forest communities corresponding to the potential natural vegetation. We were able to reconstruct the historical forest vegetation for 90% of the forest area ca. 1780. Only two of the 17 forest communities covered large parts of the forested area. The oak forest with Agrostis capillaris covered about 44% of the total forest area, and alder forests on fenland made up about 37%. Oak-hornbeam forests with Stellaria holostea comprised slightly less than 6% of the forest area, while all other forest communities comprised less than 1%. The historical forest vegetation is more similar to the potential forest vegetation and quite different from the actual forest vegetation because coniferous tree species currently cover approximately two-thirds of the actual forest area. The most beneficial result of this study is the map of high-resolution historical vegetation units that may serve as the basis for various further studies, e.g., modelling long-term changes in biodiversity at the landscape scale.