A few is enough: a low cover of a non-native seaweed reduces the resilience of Mediterranean macroalgal stands to disturbances of varying extent

There is increasing evidence that the severity of the ecological impact of non-native species does not necessarily scale linearly with their abundance in the introduced range. Nonetheless, the potential of low abundance invaders to alter the resilience of native communities to disturbance has been poorly explored. On Mediterranean rocky reefs, we tested the hypothesis that (1) a pulse disturbance opening gaps within canopy stands formed by the fucoid seaweed Cystoseira brachycarpa facilitates the establishment of the non-native seaweed Caulerpa cylindracea and that (2), once established, the seaweed can reduce the recovery of macroalgal canopies. In July 2011, C. cylindracea was experimentally transplanted in small and large plots that were either cleared of the canopy or left untouched. After 45 months, the cover of C. cylindracea was greatest in small canopy-removal plots, without, however, achieving values exceeding ~10%. Nonetheless, such a low abundance of C. cylindracea caused a threefold reduction in canopy recovery. The establishment of C. cylindracea in canopy-removal plots did not alter the structure of the understory assemblages or the cover of turf-forming, erect and encrusting algae and sessile invertebrates. Our results suggest that some non-native species may be stronger competitors than natives, despite their low abundance. This property has important implications for control programs since not achieving the total eradication of the targeted invader would make little progress towards the mitigation of its impacts. Finally, our results show that non-native species acting as passengers of change can ultimately promote the persistence of alternative degraded states.     

Cholesterol-rich microdomains as docking platforms for respiratory syncytial virus in normal human bronchial epithelial cells

Respiratory syncytial virus (RSV) is one of the major causes of respiratory infections in children, and it is the main pathogen causing bronchiolitis in infants. The binding and entry mechanism by which RSV infects respiratory epithelial cells has not yet been determined. In this study, the earliest stages of RSV infection in normal human bronchial epithelial cells were probed by tracking virions with fluorescent lipophilic dyes in their membranes. Virions colocalized with cholesterol-containing plasma membrane microdomains, identified by their ability to bind cholera toxin subunit B. Consistent with an important role for cholesterol in RSV infection, cholesterol depletion profoundly inhibited RSV infection, while cholesterol repletion reversed this inhibition. Merger of the outer leaflets of the viral envelope and the cell membrane appeared to be triggered at these sites. Using small-molecule inhibitors, RSV infection was found to be sensitive to Pak1 inhibition, suggesting the requirement of a subsequent step of cytoskeletal reorganization that could involve plasma membrane rearrangements or endocytosis. It appears that RSV entry depends on its ability to dock to cholesterol-rich microdomains (lipid rafts) in the plasma membrane where hemifusion events begin, assisted by a Pak1-dependent process.     

A Pseudomonas aeruginosa PAO1 acetylcholinesterase is encoded by the PA4921 gene and belongs to the SGNH hydrolase family

Through the use of molecular and biochemical experiments and bioinformatic tools, this work demonstrates that the PA4921 gene of the Pseudomonas aeruginosa PAO1 genome is a gene responsible for cholinesterase (ChoE) activity. Similar to the acetylcholinesterase (AchE) of Zea mays, this ChoE belongs to the SGNH hydrolase family. In mature ChoE, i.e., without a signal peptide, (18)Ser, (78)Gly, (127)N, and (268)H are conserved aminoacyl residues. Acetylthiocholine (ATC) and propionylthiocholine (PTC) are substrates of this enzyme, but butyrylcholine is an inhibitor. The enzyme also catalyzes the hydrolysis of the artificial esters p-nitrophenyl propionate (pNPP) and p-nitrophenyl butyrate (pNPB) but with lower catalytic efficiency with respect to ATC or PTC. The second difference is that pNPP and pNPB did not produce inhibition at high substrate concentrations, as occurred with ATC and PTC. These differences plus preliminary biochemical and kinetic studies with alkylammonium compounds led us to propose that this enzyme is an acetylcholinesterase (AchE) or propionylcholinesterase. Studies performed with the purified recombinant enzyme indicated that the substrate saturation curves and the catalytic mechanism are similar to those properties described for mammalian AchEs. Therefore, the results of this work suggest that the P. aeruginosa ChoE is an AchE that may also be found in Pseudomonas fluorescens.     

Avian responses to tourism in the biogeographically isolated high Córdoba Mountains,Argentina

Species do not respond identically to the presence of humans, and this may have consequences at higher-levels of ecological organization. We established bird transects on and off recreational trails in the high Córdoba Mountains of Argentina, a biogeographic island characterized by high levels of endemism, to examine the effect of human visitation at three different levels: (a) community (avian species richness and diversity), (b) guild (relative density of carnivores, granivores, insectivores, and omnivores), and (c) population (relative density of individual bird species). Human presence in the high Córdoba Mountains decreased avian species richness and diversity, and reduced insectivorous relative density, but we did not detect significant effects on granivores, omnivores, and carnivores. At the population level, 6 of 28 species were negatively affected by human visitation; four of these species are of conservation concern. Our results show negative responses to recreationists at multiple levels (e.g., reductions in density, displacement of species from highly visited areas), which may be related to spatial and temporal access to suitable resources, physical disturbance or species-specific tolerance thresholds. Our study area had lower levels of human visitation relative to other protected areas in the Northern Hemisphere, which raises the issue of whether this kind of biogeographically isolated habitat may be too fragile to sustain increasing levels of tourism.     

Higher Vulnerability and Stress Sensitivity of Neuronal Precursor Cells Carrying an Alpha-Synuclein Gene Triplication

Parkinson disease (PD) is a multi-factorial neurodegenerative disorder with loss of dopaminergic neurons in the substantia nigra and characteristic intracellular inclusions, called Lewy bodies. Genetic predisposition, such as point mutations and copy number variants of the SNCA gene locus can cause very similar PD-like neurodegeneration. The impact of altered α-synuclein protein expression on integrity and developmental potential of neuronal stem cells is largely unexplored, but may have wide ranging implications for PD manifestation and disease progression. Here, we investigated if induced pluripotent stem cell-derived neuronal precursor cells (NPCs) from a patient with Parkinson’s disease carrying a genomic triplication of the SNCA gene (SNCA-Tri). Our goal was to determine if these cells these neuronal precursor cells already display pathological changes and impaired cellular function that would likely predispose them when differentiated to neurodegeneration. To achieve this aim, we assessed viability and cellular physiology in human SNCA-Tri NPCs both under normal and environmentally stressed conditions to model in vitro gene-environment interactions which may play a role in the initiation and progression of PD. Human SNCA-Tri NPCs displayed overall normal cellular and mitochondrial morphology, but showed substantial changes in growth, viability, cellular energy metabolism and stress resistance especially when challenged by starvation or toxicant challenge. Knockdown of α-synuclein in the SNCA-Tri NPCs by stably expressed short hairpin RNA (shRNA) resulted in reversal of the observed phenotypic changes. These data show for the first time that genetic alterations such as the SNCA gene triplication set the stage for decreased developmental fitness, accelerated aging, and increased neuronal cell loss. The observation of this “stem cell pathology” could have a great impact on both quality and quantity of neuronal networks and could provide a powerful new tool for development of neuroprotective strategies for PD.     

GPGPU implementation of the BFECC algorithm for pure advection equations

In the present work an implementation of the Back and Forth Error Compensation and Correction (BFECC) algorithm specially suited for running on General-Purpose Graphics Processing Units (GPGPUs) through Nvidia’s Compute Unified Device Architecture (CUDA) is analyzed in order to solve transient pure advection equations. The objective is to compare it to a previous explicit version used in a Navier-Stokes solver fully written in CUDA. It turns out that BFECC could be implemented with unconditional stable stability using Semi-Lagrangian time integration allowing larger time steps than Eulerian ones.     

Unanticipated impacts of spatial variance of biodiversity on plant productivity

Experiments on biodiversity have shown that productivity is often a decelerating monotonic function of biodiversity. A property of nonlinear functions, known as Jensen's inequality, predicts negative effects of the variance of predictor variables on the mean of response variables. One implication of this relationship is that an increase in spatial variability of biodiversity can cause dramatic decreases in the mean productivity of the system. Here I quantify these effects by conducting a meta‐analysis of experimental data on biodiversity–productivity relationships in grasslands and using the empirically derived estimates of parameters to simulate various scenarios of levels of spatial variance and mean values of biodiversity. Jensen's inequality was estimated independently using Monte Carlo simulations and quadratic approximations. The median values of Jensen's inequality estimated with the first method ranged from 3.2 to 26.7%, whilst values obtained with the second method ranged from 5.0 to 45.0%. Meta‐analyses conducted separately for each combination of simulated values of mean and spatial variance of biodiversity indicated that effect sizes were significantly larger than zero in all cases. Because patterns of biodiversity are becoming increasingly variable under intense anthropogenic pressure, the impact of loss of biodiversity on productivity may be larger than current estimates indicate.     

Effects of fragments and landscape characteristics on the orchid bee richness (Apidae: Euglossini) in an urban matrix,southwestern Amazonia

Orchid bees are important pollinators in tropical forests. Although studies have already detected effects of habitat loss and forest fragmentation on bee assemblages, little is known about orchid bees in urban forest fragments. The aim of this study was to analyse the influence of forest fragments (size and edge index) and landscape features (forest cover area and built-up area around the forest fragments, connectivity and spatial distance from the urban center) on the abundance, richness and composition of orchid bees. Male bees were attracted by odoriferous baits and collected in ten forest fragments of different sizes. In total, we collected 3166 male bees belonging to 4 genera and 38 species. The increase of the built-up area and the reduction of the forest cover area around the forest fragments decreased the abundance and richness of bees. We recorded a smaller number of bees in areas closer to the urban center. We failed to find a significant relationship between abundance/richness of bees and forest fragment area, edge index, and connectivity. We observed that the faunistic dissimilarity was positively correlated with the geographic distance between forest fragments. The forest fragments that presented greater landscape dissimilarity also presented greater faunistic dissimilarity. Our results suggest that the matrix structure around the forest fragments is an important factor that influences the Euglossini bee assemblages inside these forest fragments. Based on our results, we believed that the conservation of fragments with a larger forest cover area and smaller built-up areas around them contribute to the maintenance of the diversity of orchid bees and their pollination services.     

Renal abscess due to Aspergillus fumigatus as the only sign of disseminated aspergillosis in a patient with AIDS

BackgroundAspergillus fumigatus can cause a wide variety of clinical syndromes, especially in the three largest immunocompromised groups, such as HIV-infected patients. Primary renal aspergillosis is an extremely rare entity.AimsWe report an unusual case of renal abscess due to Aspergillus fumigatus in a patient with AIDS.MethodsWe review clinical and laboratory records, and provide follow up of the patient.ResultsA 38-year-old man, HIV seropositive, was admitted to our hospital with fever, lumbar pain and respiratory symptoms. Abdominal ultrasound and computerised tomography showed a single and large lesion consistent with an abscess located in the left kidney. Aspergillus fumigatus was isolated from clinical sample obtained by ultrasound-guided needle aspiration. Despite a correct treatment based on amphotericin B and drainage of the abscess, surgery was necessary and nephrectomy was carried out. Histopathological examination of the surgical specimen confirmed the diagnosis of renal aspergillosis. Systemic antifungal therapy based on intravenous and oral voriconazole and highly active antiretroviral therapy was started after surgery. The patient had a good response to the established treatment and he remains in a good clinical condition at one year of follow up.ConclusionsCombined medical and surgical treatment is the elective therapy for renal abscesses due to Aspergillus when percutaneous drainage and the administration of systemic antifungal drugs, such as amphotericin B and/or oral voriconazole or itraconazole, fail. This case emphasizes renal fungal infections should be included in the differential diagnosis of kidney abscesses in AIDS patients.