Patterns of island treeline elevation – a global perspective

Treeline research has strongly focused on mountain systems on the mainland. However, island treelines offer the opportunity to contribute to the global framework on treeline elevation due to their island‐specific attributes such as isolation, small area, low species richness and relative youth. We hypothesize that, similar to the mainland, latitude‐driven temperature variation is the most important determinant of island treeline elevation on a global scale. To test this hypothesis, we compared mainland with island treeline elevations. Then we focused 1) on the global effects of latitude, 2) on the regional effects of island type (continental vs oceanic islands) and 3) the local effects of several specific island characteristics (age, area, maximum island elevation, isolation and plant species richness). We collected a global dataset of islands (n = 86) by applying a stratified design using GoogleEarth and the Global Island Database. For each island we extracted data on latitude and local characteristics. Treeline elevation decreased from the mainland through continental to oceanic islands. Island treeline elevation followed a hump‐shaped latitudinal distribution, which is fundamentally different from the mainland double‐hump. Higher maximum island elevation generated higher treeline elevation and was found the best single predictor of island treeline elevation, even better than latitude. Lower island treeline elevation may be the result of a low mass elevation effect (MEE) influencing island climates and an increasingly impoverished species pool but also trade wind inversion‐associated aridity. The maximum island elevation effect possibly results from an increasing mass elevation effect (MEE) with increasing island elevation but also range shifts during climatic fluctuations and the summit syndrome (i.e. high wind speeds and poor soils in peak regions). Investigating islands in treeline research has enabled disentangling the global effect of latitude from regional and local effects and, at least for islands, a comprehensive quantification of the MEE.     

Boundaries of the wolf and the wild: a conceptual examination of the relationship between rewilding and animal reintroduction

Animal reintroduction and rewilding are two widely appealing and frequently connected forms of ecological restoration. However, the critical assumption that animal reintroduction automatically helps to restore formerly wild places is under‐theorized. To fill this void, we identified three common rewilding elements from the literature—ecological functioning, wilderness experience, and natural autonomy—and screened these against a hypothetical wolf reintroduction to Scotland. Each of the rewilding elements was likely to be positively impacted by a wolf reintroduction. Yet, there is a key conceptual difficulty in that the different rewilding elements do not necessarily enforce each other, and at times may even collide. Thus, a reintroduced species like the wolf may obfuscate the clear‐cut, purified nature category to which rewilding often aspires. As a way forward, we suggest that there is merit in actively engaging with the tensions created by rewilding and reintroductions. A reconceptualisation of the nature–culture spectrum as consisting of multiple layers (e.g. ecological functioning, wilderness experience, and natural autonomy) may help to interpret ecological restoration as a tentative, deliberative, and gradual enterprise. This bears some resemblance to the notion of approaching a landscape like a ‘palimpsest’ (i.e. a text built up of different layers written on top of each other), which may support the reconciliation of conflicting views without necessarily making those disappear. When viewed as feeding into a multilayered nature–culture spectrum, animal reintroduction and rewilding can be promoted as inspiring and essentially non‐controlling forms of ecological restoration and human interaction with nature.     

Nerve growth factor regulates endothelial cell survival and pathological retinal angiogenesis

The mechanism underlying vasoproliferative retinopathies like retinopathy of prematurity (ROP) is hypoxia‐triggered neovascularisation. Nerve growth factor (NGF), a neurotrophin supporting survival and differentiation of neuronal cells may also regulate endothelial cell functions. Here we studied the role of NGF in pathological retinal angiogenesis in the course of the ROP mouse model. Topical application of NGF enhanced while intraocular injections of anti‐NGF neutralizing antibody reduced pathological retinal vascularization in mice subjected to the ROP model. The pro‐angiogenic effect of NGF in the retina was mediated by inhibition of retinal endothelial cell apoptosis. In vitro, NGF decreased the intrinsic (mitochondria‐dependent) apoptosis in hypoxia‐treated human retinal microvascular endothelial cells and preserved the mitochondrial membrane potential. The anti‐apoptotic effect of NGF was associated with increased BCL2 and reduced BAX, as well as with enhanced ERK and AKT phosphorylation, and was abolished by inhibition of the AKT pathway. Our findings reveal an anti‐apoptotic role of NGF in the hypoxic retinal endothelium, which is involved in promoting pathological retinal vascularization, thereby pointing to NGF as a potential target for proliferative retinopathies.     

Genome wide association (GWA) study for early onset extreme obesity supports the role of fat mass and obesity associated gene (FTO) variants

Background

Obesity is a major health problem. Although heritability is substantial, genetic mechanisms predisposing to obesity are not very well understood. We have performed a genome wide association study (GWA) for early onset (extreme) obesity.

Methodology/Principal Findings

a) GWA (Genome-Wide Human SNP Array 5.0 comprising 440,794 single nucleotide polymorphisms) for early onset extreme obesity based on 487 extremely obese young German individuals and 442 healthy lean German controls; b) confirmatory analyses on 644 independent families with at least one obese offspring and both parents. We aimed to identify and subsequently confirm the 15 SNPs (minor allele frequency ≥10%) with the lowest p-values of the GWA by four genetic models: additive, recessive, dominant and allelic. Six single nucleotide polymorphisms (SNPs) in FTO (fat mass and obesity associated gene) within one linkage disequilibrium (LD) block including the GWA SNP rendering the lowest p-value (rs1121980; log-additive model: nominal p = 1.13×10⁻⁷, corrected p = 0.0494; odds ratio (OR)_CT 1.67, 95% confidence interval (CI) 1.22–2.27; OR_TT 2.76, 95% CI 1.88–4.03) belonged to the 15 SNPs showing the strongest evidence for association with obesity. For confirmation we genotyped 11 of these in the 644 independent families (of the six FTO SNPs we chose only two representing the LD bock). For both FTO SNPs the initial association was confirmed (both Bonferroni corrected p<0.01). However, none of the nine non-FTO SNPs revealed significant transmission disequilibrium.

Conclusions/Significance

Our GWA for extreme early onset obesity substantiates that variation in FTO strongly contributes to early onset obesity. This is a further proof of concept for GWA to detect genes relevant for highly complex phenotypes. We concurrently show that nine additional SNPs with initially low p-values in the GWA were not confirmed in our family study, thus suggesting that of the best 15 SNPs in the GWA only the FTO SNPs represent true positive findings.     

Enlightening energy parasitism by analysis of an ATP/ADP transporter from chlamydiae

Energy parasitism by ATP/ADP transport proteins is an essential, common feature of intracellular bacteria such as chlamydiae and rickettsiae, which are major pathogens of humans. Although several ATP/ADP transport proteins have so far been characterized, some fundamental questions regarding their function remained unaddressed. In this study, we focused on the detailed biochemical analysis of a representative ATP/ADP transporter (PamNTT1), from the amoeba symbiont Protochlamydia amoebophila (UWE25) to further clarify the principle of energy exploitation. We succeeded in the purification of the first bacterial nucleotide transporter (NTT) and its functional reconstitution into artificial lipid vesicles. Reconstituted PamNTT1 revealed high import velocities for ATP and an unexpected and previously unobserved stimulating effect of the luminal ADP on nucleotide import affinities. Latter preference of the nucleotide hetero-exchange is independent of the membrane potential, and therefore, PamNTT1 not only structurally but also functionally differs from the well-characterized mitochondrial ADP/ATP carriers. Reconstituted PamNTT1 exhibits a bidirectional orientation in lipid vesicles, but interestingly, only carriers inserted with the N-terminus directed to the proteoliposomal interior are functional. The data presented here comprehensively explain the functional basis of how the intracellular P. amoebophila manages to exploit the energy pool of its host cell effectively by using the nucleotide transporter PamNTT1. This membrane protein mediates a preferred import of ATP, which is additionally stimulated by a high internal (bacterial) ADP/ATP ratio, and the orientation-dependent functionality of the transporter ensures that it is not working in a mode that is detrimental to P. amoebophila. Heterologous expression and purification of high amounts of PamNTT1 provides the basis for its crystallization and detailed structure/function analyses. Furthermore, functional reconstitution of this essential chlamydial protein paves the way for high-throughput uptake studies in order to screen for specific inhibitors potentially suitable as anti-chlamydial drugs.     

Role of ischemia and deformation in the onset of compression-induced deep tissue injury: MRI-based studies in a rat model.

A rat model was used to distinguish between the different factors that contribute to muscle tissue damage related to deep pressure ulcers that develop after compressive loading. The separate and combined effects of ischemia and deformation were studied. Loading was applied to the hindlimb of rats for 2 h. Muscle tissue was examined using MR imaging (MRI) and histology. An MR-compatible loading device allowed simultaneous loading and measurement of tissue status. Two separate loading protocols incorporated uniaxial loading, resulting in tissue compression and ischemic loading. Uniaxial loading was applied to the tibialis anterior by means of an indenter, and ischemic loading was accomplished with an inflatable tourniquet. Deformation of the muscle tissue during uniaxial loading was measured using MR tagging. Compression of the tissues for 2 h led to increased T2 values, which were correlated to necrotic regions in the tibialis anterior. Perfusion measurements, by means of contrast-enhanced MRI, indicated a large ischemic region during indentation. Pure ischemic loading for 2 h led to reversible tissue changes. From the MR-tagging experiments, local strain fields were calculated. A 4.5-mm deformation, corresponding to a surface pressure of 150 kPa, resulted in maximum shear strain up to 1.0. There was a good correlation between the location of damage and the location of high shear strain. It was concluded that the large deformations, in conjunction with ischemia, provided the main trigger for irreversible muscle damage.     

Spatiotemporal modeling of first and second wave outbreak dynamics of COVID-19 in Germany

The COVID-19 pandemic has kept the world in suspense for the past year. In most federal countries such as Germany, locally varying conditions demand for state- or county-level decisions to adapt to the disease dynamics. However, this requires a deep understanding of the mesoscale outbreak dynamics between microscale agent models and macroscale global models. Here, we use a reparameterized SIQRD network model that accounts for local political decisions to predict the spatiotemporal evolution of the pandemic in Germany at county resolution. Our optimized model reproduces state-wise cumulative infections and deaths as reported by the Robert Koch Institute and predicts the development for individual counties at convincing accuracy during both waves in spring and fall of 2020. We demonstrate the dominating effect of local infection seeds and identify effective measures to attenuate the rapid spread. Our model has great potential to support decision makers on a state and community politics level to individually strategize their best way forward during the months to come.

     

Generalist Life Cycle Aids Persistence of Alexandrium ostenfeldii (Dinophyceae) in Seasonal Coastal Habitats of the Baltic Sea

In seasonal environments, strong gradients of environmental parameters can shape life cycles of phytoplankton. Depending on the rate of environmental fluctuation, specialist or generalist strategies may be favored, potentially affecting life cycle transitions. The present study examined life cycle transitions of the toxin producing Baltic dinoflagellate Alexandrium ostenfeldii and their regulation by environmental factors (temperature and nutrients). This investigation aimed to determine whether genetic recombination of different strains is required for resting cyst formation and whether newly formed cysts are dormant. Field data (temperature and salinity) and sediment surface samples were collected from a site with recurrent blooms and germination and encystment experiments were conducted under controlled laboratory conditions. Results indicate a lack of seasonal germination pattern, set by an endogenous rhythm, as commonly found with other dinoflagellates from the Baltic Sea. Germination of quiescent cysts was triggered by temperatures exceeding 10°C and combined nutrient limitation of nitrogen and phosphorus or a drop in temperature from 16 to 10°C triggered encystment most efficiently. Genetic recombination was not mandatory for the formation of resting cysts, but supported higher numbers of resistant cysts and enhanced germination capacity after a resting period. Findings from this study confirm that A. ostenfeldii follows a generalist germination and cyst formation strategy, driven by strong seasonality, which may support its persistence and possibly expansion in marginal environments in the future, if higher temperatures facilitate a longer growth season.