Disturbances, elevation, topography and spatial proximity drive vegetation patterns along an altitudinal gradient of a top biodiversity hotspot

The correlation between vegetation patterns (species distribution and richness) and altitudinal variation has been widely reported for tropical forests, thereby providing theoretical basis for biodiversity conservation. However, this relationship may have been oversimplified, as many other factors may influence vegetation patterns, such as disturbances, topography and geographic distance. Considering these other factors, our primary question was: is there a vegetation pattern associated with substantial altitudinal variation (10–1,093 m a.s.l.) in the Atlantic Rainforest—a top hotspot for biodiversity conservation—and, if so, what are the main factors driving this pattern? We addressed this question by sampling 11 1-ha plots, applying multivariate methods, correlations and variance partitioning. The Restinga (forest on sandbanks along the coastal plains of Brazil) and a lowland area that was selectively logged 40 years ago were floristically isolated from the other plots. The maximum species richness (>200 spp. per hectare) occurred at approximately 350 m a.s.l. (submontane forest). Gaps, multiple stemmed trees, average elevation and the standard deviation of the slope significantly affected the vegetation pattern. Spatial proximity also influenced the vegetation pattern as a structuring environmental variable or via dispersal constraints. Our results clarify, for the first time, the key variables that drive species distribution and richness across a large altitudinal range within the Atlantic Rainforest.     

MAL regulates clathrin-mediated endocytosis at the apical surface of Madin-Darby canine kidney cells

MAL is an integral protein component of the machinery for apical transport in epithelial Madin-Darby canine kidney (MDCK) cells. To maintain its distribution, MAL cycles continuously between the plasma membrane and the Golgi complex. The clathrin-mediated route for apical internalization is known to differ from that at the basolateral surface. Herein, we report that MAL depends on the clathrin pathway for apical internalization. Apically internalized polymeric Ig receptor (pIgR), which uses clathrin for endocytosis, colocalized with internalized MAL in the same apical vesicles. Time-lapse confocal microscopic analysis revealed cotransport of pIgR and MAL in the same endocytic structures. Immunoelectron microscopic analysis evidenced colabeling of MAL with apically labeled pIgR in pits and clathrin-coated vesicles. Apical internalization of pIgR was abrogated in cells with reduced levels of MAL, whereas this did not occur either with its basolateral entry or the apical internalization of glycosylphosphatidylinositol-anchored proteins, which does not involve clathrin. Therefore, MAL is critical for efficient clathrin-mediated endocytosis at the apical surface in MDCK cells.     

Quantifying individual heterogeneity and its influence on life‐history trajectories: different methods for different questions and contexts

Heterogeneity among individuals influences the life‐history trajectories we observe at the population level because viability selection, selective immigration and emigration processes, and ontogeny change the proportion of individuals with specific trait values with increasing age. Here, we review the two main approaches that have been proposed to account for these processes in life‐history trajectories, contrasting how they quantify ontogeny and selection, and proposing ways to overcome some of their limitations. Nearly all existing approaches to model individual heterogeneity assume either a single normal distribution or a priori known groups of individuals. Ontogenetic processes, however, can vary across individuals through variation in life‐history tactics. We show the usefulness of describing ontogenetic processes by modelling trajectories with a mixture model that focuses on heterogeneity in life‐history tactics. Additionally, most methods examine individual heterogeneity in a single trait, ignoring potential correlations among multiple traits caused by latent common sources of individual heterogeneity. We illustrate the value of using a joint modelling approach to assess the presence of a shared latent correlation and its influence on life‐history trajectories. We contrast the strengths and limitations of different methods for different research questions, and we exemplify the differences among methods using empirical data from long‐term studies of ungulates.     

Spatial analysis of structural and tree‐ring related parameters in a timberline forest in the Italian Alps

Abstract. We investigated the variability in spatial pattern of some structural, dendrochronological and dendroclimatological features of a mixed Larix decidua‐Pinus cembra forest at the timberline in the eastern Italian Alps at fine geographical and temporal scales. Forest structure variables such as stem diameter, tree height, age and tree‐ring related parameters (yearly growth index, mean sensitivity, first order autocorrelation and some dendroclimatic variables) have been compared at various scale levels. We observed that most of the variables show positive autocorrelated structures due to both forest dynamics and fine‐scale driving forces, probably related to microrelief. Spatial structure of yearly indexed radial growth appears sensitive to extreme climatic events. Secondary succession after past disturbances drives the forest towards a structure governed by a gap regeneration dynamics that seems to ensure the different requirements of the two main tree species present. Small spatial scale studies of forest structures, especially if integrated to dendro‐ecological data, seem an efficient tool to assess the disturbance regime and species sensitivity to environmental change.     

Automatic Conversational Scene Analysis in Children with Asperger Syndrome/High-Functioning Autism and Typically Developing Peers

Individuals with Asperger syndrome/High Functioning Autism fail to spontaneously attribute mental states to the self and others, a life-long phenotypic characteristic known as mindblindness. We hypothesized that mindblindness would affect the dynamics of conversational interaction. Using generative models, in particular Gaussian mixture models and observed influence models, conversations were coded as interacting Markov processes, operating on novel speech/silence patterns, termed Steady Conversational Periods (SCPs). SCPs assume that whenever an agent''s process changes state (e.g., from silence to speech), it causes a general transition of the entire conversational process, forcing inter-actant synchronization. SCPs fed into observed influence models, which captured the conversational dynamics of children and adolescents with Asperger syndrome/High Functioning Autism, and age-matched typically developing participants. Analyzing the parameters of the models by means of discriminative classifiers, the dialogs of patients were successfully distinguished from those of control participants. We conclude that meaning-free speech/silence sequences, reflecting inter-actant synchronization, at least partially encode typical and atypical conversational dynamics. This suggests a direct influence of theory of mind abilities onto basic speech initiative behavior.     

It's not over until the FAT lady sings

The death receptors FAS, TRAIL‐Rs and TNFR1 play critical roles in programmed cell death, particularly in the immune system. Upon ligation of death receptors, caspase‐8 is activated within the so‐called ‘Death Induced Signalling Complex’ (DISC) but the mechanisms that mediate and modulate the activation of caspase‐8 are still not fully understood. This is an important issue because caspase‐8 is essential for apoptosis induced by death receptors. In this issue of The EMBO Journal, Kranz and Boutros ( 2014 ) describe their findings from a whole genome siRNA screen for the identification of novel regulators of death receptor induced apoptosis signalling. They identified the atypical cadherin FAT1 as a negative regulator of TRAIL‐R‐mediated caspase‐8 activation and consequent induction of apoptosis, although it had no impact on NF‐κB activation. The authors also show that FAT1 depletion substantially increased TRAIL‐induced killing of glioblastoma‐derived cell lines, suggesting a potential novel approach for treatment of this highly aggressive cancer.     

Scanning X-Ray Nanodiffraction on Dictyostelium discoideum

We have performed scanning x-ray nanobeam diffraction experiments on single cells of the amoeba Dictyostelium discoideum. Cells have been investigated in 1), freeze-dried, 2), frozen-hydrated (vitrified), and 3), initially alive states. The spatially resolved small-angle x-ray scattering signal shows characteristic streaklike patterns in reciprocal space, which we attribute to fiber bundles of the actomyosin network. From the intensity distributions, an anisotropy parameter can be derived that indicates pronounced local variations within the cell. In addition to nanobeam small-angle x-ray scattering, we have evaluated the x-ray differential phase contrast in view of the projected electron density. Different experimental aspects of the x-ray experiment, sample preparation, and data analysis are discussed. Finally, the x-ray results are correlated with optical microscopy (differential phase contrast and confocal microscopy of mutant strains with fluorescently labeled actin and myosin II), which have been carried out in live and fixed states, including optical microscopy under cryogenic conditions.     

Factors affecting subject-specific finite element models of implant-fitted rat bone specimens: critical analysis of a technical protocol

The authors propose a protocol to derive finite element (FE) models from micro computer tomography scans of implanted rat bone. A semi-automatic procedure allows segmenting the images using specimen-specific bone mineral density (BMD) thresholds. An open-source FE model generator processes the segmented images to a quality tetrahedral mesh. The material properties assigned to each element are integrated from the BMD field. Piecewise, threshold-dependent density–elasticity relationships are implemented to limit the effects of metal artefacts. A detailed sensitivity study highlights the coherence of the generated models and quantifies the influence of the modelling parameters on the results. Two applications of the protocol are proposed. The stiffness of bare and implanted rat tibiae specimens is predicted by simulating three-point bending and inter-implant displacement, respectively. Results are compared with experimental tests. The mean value and the variability between the specimens are well captured in both tests.     

Purification and characterization of an aminopeptidase from the chloroplast stroma of barley leaves by chromatographic and electrophoretic methods

Aminopeptidases catalyze the cleavage of amino acids from the amino terminus of protein or peptide substrates. Although some aminopeptidase activities have been found in plant chloroplasts, the identity of these proteins remains unclear. In this work, we report the purification to apparent homogeneity of a soluble aminopeptidase from isolated barley chloroplasts which preferentially degraded alanyl-p-nitroanilide (Ala-pNA). After organelle isolation in a density gradient and precipitation of soluble proteins with ammonium sulfate, the proteins were purified in three consecutive steps including hydrophobic interaction, gel permeation and ion-exchange chromatographies. The purified enzyme appeared as a single band with a M_r of 84 000 in sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis. The M_r of the native enzyme was estimated to be 93 000 by gel permeation chromatography, suggesting that the protein is a monomer. Mass spectrometry analysis of tryptic digests indicates that the primary structure of the protein has not been reported previously. The enzyme was characterized as a metalloprotease as it could be totally inhibited by 1,10-phenanthroline. Strong inhibition could also be observed using the specific aminopeptidase inhibitors amastatin and bestatin. Besides Ala-pNA, the purified protein could also cleave with decreasing activity glycyl-pNA, leucyl-pNA, lysyl-pNA, methionyl-pNA and arginyl-pNA. The possible physiological role of this enzyme in the chloroplast stroma is discussed.