Extreme weather events threaten biodiversity and functions of river ecosystems: evidence from a meta-analysis

Both gradual and extreme weather changes trigger complex ecological responses in river ecosystems. It is still unclear to what extent trend or event effects alter biodiversity and functioning in river ecosystems, adding considerable uncertainty to predictions of their future dynamics. Using a comprehensive database of 71 published studies, we show that event – but not trend – effects associated with extreme changes in water flow and temperature substantially reduce species richness. Furthermore, event effects – particularly those affecting hydrological dynamics – on biodiversity and primary productivity were twice as high as impacts due to gradual changes. The synthesis of the available evidence reveals that event effects induce regime shifts in river ecosystems, particularly affecting organisms such as invertebrates. Among extreme weather events, dryness associated with flow interruption caused the largest effects on biota and ecosystem functions in rivers. Effects on ecosystem functions (primary production, organic matter decomposition and respiration) were asymmetric, with only primary production exhibiting a negative response to extreme weather events. Our meta-analysis highlights the disproportionate impact of event effects on river biodiversity and ecosystem functions, with implications for the long-term conservation and management of river ecosystems. However, few studies were available from tropical areas, and our conclusions therefore remain largely limited to temperate river systems. Further efforts need to be directed to assemble evidence of extreme events on river biodiversity and functioning.     

Seasonal flexibility in organ size in the Andean lizard Liolaemus moradoensis

The understanding of animal functioning in fluctuating environments is a major goal of physiological and evolutionary ecology. In temperate terrestrial habitats, one of the most pervasive changes in environmental conditions is that associated with the seasonal change along the year. In this study, we describe the pattern of seasonal variation in the size of nine internal organs in the lizard Liolaemus moradoensis from the Andes Mountains of Central Chile. We observed that the size of digestive organs was greater during summer in comparison to other seasons. Dry masses of liver and fat bodies reached maximum values during summer and minimum during spring. We suspect that lowest spring values are related with build‐up costs of energetically expensive organs (e.g., digestive, muscle mass) at the end of the hibernation period. Dry mass of the heart and lungs did not show a clear pattern of variation, suggesting that cardiac and pulmonary performance were maintained throughout the year. The dry mass of kidneys was greater during winter than during summer, a result observed in other hibernating lizards but for which there is no clear explanation. Finally, the dry mass of testes showed a maximum value during autumn and a progressive reduction toward summer, indicating that reproduction occurs during autumn. When represented in a bivariate space, acquisition (digestive), distribution (heart, lungs and kidneys), storage (liver and fat bodies), and expenditure (testes) organs generate four clusters. In general terms, observed seasonal pattern of change in organ size is in agreement with those reported for other lizard species that inhabit highly fluctuating environments. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Availability of glucose and light modulates the structure and function of a microbial biofilm

We have studied the differences in the organic matter processing and biofilm composition and structure between autoheterotrophic and heterotrophic biofilm communities. Microbial communities grown on artificial biofilms were monitored, following incubation under light and dark conditions and with or without the addition of glucose as a labile organic compound. Glucose addition greatly affected the microbial biofilm composition as shown by differences in 16S rRNA gene fingerprints. A significant increase in β-glucosidase and peptidase enzyme activities were also observed in glucose-amended biofilms incubated in the dark, suggesting an active bacterial community. Light enhanced the algal and bacterial growth, as well as higher extracellular enzyme activity, thereby indicating a tight algal–bacterial coupling in biofilms incubated under illumination. In these biofilms, organic compounds excreted by photosynthetic microorganisms were readily available for bacterial heterotrophs. This algal–bacterial relationship weakened in glucose-amended biofilms grown in the light, probably because heterotrophic bacteria preferentially use external labile compounds. These results suggest that the availability of labile organic matter in the flowing water and the presence of light may alter the biofilm composition and function, therefore affecting the processing capacity of organic matter in the stream ecosystem.     

A model for the neuronal substrate of dead reckoning and memory in arthropods: a comparative computational and behavioral study

Returning to the point of departure after exploring the environment is a key capability for most animals. In the absence of landmarks, this task will be solved by integrating direction and distance traveled over time. This is referred to as path integration or dead reckoning. An important question is how the nervous systems of navigating animals such as the 1 mm³ brain of ants can integrate local information in order to make global decision. In this article we propose a neurobiologically plausible system of storing and retrieving direction and distance information. The path memory of our model builds on the well established concept of population codes, moreover our system does not rely on trigonometric functions or other complex non-linear operations such as multiplication, but only uses biologically plausible operations such as integration and thresholding. We test our model in two paradigms; in the first paradigm the system receives input from a simulated compass, in the second paradigm, the model is tested against behavioral data recorded from 17 ants. We were able to show that our path memory system was able to reliably encode and compute the angle of the vector pointing to the start location, and that the system stores the total length of the trajectory in a dependable way. From the structure and behavior of our model, we derive testable predictions both at the level of observable behavior as well as on the anatomy and physiology of its underlying neuronal substrate.     

Cooperation of two mRNA-binding proteins drives metabolic adaptation to iron deficiency

Iron (Fe) is an essential cofactor for a wide range of cellular processes. We have previously demonstrated in yeast that Cth2 is expressed during Fe deficiency and promotes degradation of a battery of mRNAs leading to reprogramming of Fe-dependent metabolism and Fe storage. We report here that the Cth2-homologous protein Cth1 is transiently expressed during Fe deprivation and participates in the response to Fe deficiency through the degradation of mRNAs primarily involved in mitochondrially localized activities including respiration and amino acid biosynthesis. In parallel, wild-type cells, but not cth1Deltacth2Delta cells, accumulate mRNAs encoding proteins that function in glucose import and storage and store high levels of glycogen. In addition, Fe deficiency leads to phosphorylation of Snf1, an AMP-activated protein kinase family member required for the cellular response to glucose starvation. These studies demonstrate a metabolic reprogramming as a consequence of Fe starvation that is dependent on the coordinated activities of two mRNA-binding proteins.     

Short‐Term Effects of Weight Loss on the Cardiovascular Risk Factors in Morbidly Obese Patients

Objective: To analyze the short‐term effects of weight loss on the cardiovascular risk factors in morbidly obese patients. Research Methods and Procedures: Five metabolic cardiovascular risk factors (blood glucose, blood pressure, total cholesterol, high‐density lipoprotein (HDL)‐cholesterol, and triglycerides) were determined before and 15.3 ± 2.1 months after laparoscopic gastric banding in 650 morbidly obese patients. Global cardiovascular risk was calculated according to the Prospective Cardiovascular Münster (PROCAM) scoring system. Results: Mean weight loss was 22.7 ± 20.4 kg. Normalization of the metabolic alteration was observed in 67.3% of patients with diabetes, 38.3% of patients with hypercholesterolemia, 72.5% of patients with low HDL‐cholesterol, 72.3% of patients with hypertriglyceridemia, and 46.7% of patients with hypertension. PROCAM score fell from 31.4 ± 11.6 to 28.0 ± 12.0 points (p < 0.001). The modifications of total cholesterol and blood pressure were unrelated to percentage weight loss. Percentage weight loss was significantly related to the reductions of fasting blood glucose, triglyceride level, and the PROCAM score and to the increase of HDL‐cholesterol concentrations observed after surgery. However, the strength of these four relationships was generally low. The variations of HDL‐cholesterol concentrations and blood pressure levels were more influenced by actual energy balance than by the extent of weight loss. Discussion: Weight loss observed in the first 12 to 18 months after gastric banding was associated with a significant improvement of single cardiovascular risk factors and global risk. On the other hand, the extent of weight loss was poorly related to the magnitude of improvement in cardiovascular risk.     

Lactobacillus uvarum sp. nov.--a new lactic acid bacterium isolated from Spanish Bobal grape must

Five strains isolated from grape musts in Spain in 1997, have been characterized by several molecular techniques, and three of them have been identified as pertaining to a new species. All strains are Gram-positive rods, aerotolerant and homofermentative bacteria that do not exhibit catalase activity. Phylogenetic analysis based on 16S rRNA gene sequences placed these strains within the genus Lactobacillus, closely related to Lactobacillus mali. DNA-DNA hybridization experiments confirmed that strain 71 belongs to the lately described species L. satsumensis, strain 88 belongs to L. mali and the other three isolates have an independent status at species level. Restriction analysis of the amplified 16S rRNA gene (16S-ARDRA), internal spacer region (ISR) analysis, random amplified polymorphism DNA (RAPD) and ribotyping were performed in order to establish genotypic similarities and differences between the new species and their closest species. The three isolates can be genetically differentiated from their closest relatives by RAPD analysis and ribotyping. Phenotypically, they can be distinguished by several traits such as their ability to grow at pH 3.3 and NaCl 5% (w/v) and by certain carbohydrate fermentations. The name L. uvarum sp. nov. is proposed. The type strain is 8T (=DSM 19971T = colección espa?ola de cultivos tipo (CECT) 7335T).     

Assessing the response of open-habitat bird species to landscape changes in Mediterranean mosaics

In Mediterranean landscapes, wildfires and land abandonment lead to major landscape modifications primarily by favouring the presence of open, shrub-like habitats. At present, we know very little of how these changes affect patterns of species occurrence at the landscape scale. In this work, we analyse the impact of these landscape changes on the occurrence patterns of eight open-habitat species by using presence/absence data collected in the Catalan Breeding Bird Atlas (NE Spain). We compared the species occurrence patterns along habitat gradients for three different landscape settings: a semi-permanent farmland–forest landscape (i.e. with variable proportions of farmland and forests) and two landscape settings which mimic those favoured by land abandonment and fire: farmland–shrubland landscapes and mosaic landscapes (i.e. variable proportions of farmland and forest coexisting with a shrubby matrix). In the forest–farmland landscape, we found a dominant negative effect of adjacent forest on species occurrence rates. This overall effect mostly disappeared in farmland–shrubland landscapes composed by two habitats with more similar vegetation structure. In mosaic landscapes, the general negative effect of forest habitats also appeared to be partially compensated by the presence of a shrubby matrix. Our results suggest that landscape gradients induced by fire and to some degree also land abandonment, mainly favouring availability of shrublands may potentially enhance the resilience of threatened open-habitat species at the landscape scale by increasing the range of potential habitats used. The analysis of species-occurrence patterns along predefined habitat gradients appears as a useful tool to predict potential species responses to land use change.     

Plasma membrane diffusion of G protein-coupled receptor oligomers

G protein-coupled receptors are known to form homo-and heteromers at the plasma membrane, but the molecular properties of these oligomers are relatively unknown. Here, we show a method that allows the diffusion of G protein-coupled receptors oligomers in the plasma membrane to be monitored in single cells by combining Bimolecular Fluorescence Complementation and Fluorescence Correlation Spectroscopy. With this approach we have measured, for the first time, the membrane diffusional characteristics of adenosine A(1) and A(2A) receptor homo-and heterodimers in Chinese Hamster Ovary cells. Interestingly, both homodimers display similar diffusion co-efficients (D) when expressed in living cells (D=5.0 and 4.8x10(-9) cm(2)/s, respectively) but the heterodimer formed by these receptors exhibit a significantly faster plasma membrane diffusion co-efficent (D=5.6x10(-9) cm(2)/s) when compared to the adenosine A(1) receptor tagged with the full-length yellow fluorescent protein (D=4.0x10(-9) cm(2)/s). Overall, these results demonstrate differences in plasma membrane diffusion between adenosine receptor homo-and heterodimers, providing new insights into the molecular plasticity of G protein-coupled receptor oligomerization.