How well does presence‐only‐based species distribution modelling predict assemblage diversity? A case study of the Tenerife flora

Prediction error is considered an important problem in species distribution models. To address this issue, we here examined the accuracy of overlays of presence‐only‐based models for many individual species in representing patterns of assemblage diversity. For this purpose, we used a database of 977 160 records of seed plant occurrences on an intensively surveyed, species‐rich island (Tenerife, Canary Islands) for modelling the distribution of all its 841 native plant species individually. The modelling was done using Maxent, one of the best‐performing presence‐only modelling techniques, using various thresholds to convert the estimated suitability values into predicted presence or absence. Distribution models for each individual species were overlaid to predict species richness and composition, which were then compared to the observed values for well‐surveyed grid cells. We found high levels of compositional error, when the best performing suitability threshold for predicting species richness was applied. Our best prediction had a mean species richness error of 24% and a mean compositional error of 60% relative to the observed values for the well‐surveyed cells; >50% of all species were included erroneously in >25% of the well‐surveyed cells. Hence, large quantities of data are not necessarily enough to obtain reliable predictions of assemblage diversity, limiting the usefulness of this methodology in conservation planning.     

CNF1 improves astrocytic ability to support neuronal growth and differentiation in vitro

Modulation of cerebral Rho GTPases activity in mice brain by intracerebral administration of Cytotoxic Necrotizing Factor 1 (CNF1) leads to enhanced neurotransmission and synaptic plasticity and improves learning and memory. To gain more insight into the interactions between CNF1 and neuronal cells, we used primary neuronal and astrocytic cultures from rat embryonic brain to study CNF1 effects on neuronal differentiation, focusing on dendritic tree growth and synapse formation, which are strictly modulated by Rho GTPases. CNF1 profoundly remodeled the cytoskeleton of hippocampal and cortical neurons, which showed philopodia-like, actin-positive projections, thickened and poorly branched dendrites, and a decrease in synapse number. CNF1 removal, however, restored dendritic tree development and synapse formation, suggesting that the toxin can reversibly block neuronal differentiation. On differentiated neurons, CNF1 had a similar effacing effect on synapses. Therefore, a direct interaction with CNF1 is apparently deleterious for neurons. Since astrocytes play a pivotal role in neuronal differentiation and synaptic regulation, we wondered if the beneficial in vivo effect could be mediated by astrocytes. Primary astrocytes from embryonic cortex were treated with CNF1 for 48 hours and used as a substrate for growing hippocampal neurons. Such neurons showed an increased development of neurites, in respect to age-matched controls, with a wider dendritic tree and a richer content in synapses. In CNF1-exposed astrocytes, the production of interleukin 1β, known to reduce dendrite development and complexity in neuronal cultures, was decreased. These results demonstrate that astrocytes, under the influence of CNF1, increase their supporting activity on neuronal growth and differentiation, possibly related to the diminished levels of interleukin 1β. These observations suggest that the enhanced synaptic plasticity and improved learning and memory described in CNF1-injected mice are probably mediated by astrocytes.     

Detection of Aeromonas hydrophila in food with an enzyme-linked immunosorbent assay

A microtitration plate, antibody capture, enzyme-linked immunosorbent assay was developed for the detection of Aeromonas hydrophila serotype O : 11 (highly virulent strains). The assay utilizes a detector antibody which shows no cross-reactions with Aeromonas strains other than serotype O : 11 or non- Aeromonas competing organisms. The detector antibody is mixed with the sample and incubated for 1 h, microcentrifuged and the supernatant fluid (unadsorbed antibody) titred in a microtitre plate coated with A. hydrophila cells from serotype O : 11. All the A. hydrophila strains from serotype O : 11 tested reacted strongly with the detector antibody. Also by culturing and performing the immunoassay with the detector antibody we established and quantified the presence of A. hydrophila O : 11 in different foods.     

Novel series of substituted biphenylmethyl urea derivatives as MCH-R1 antagonists for the treatment of obesity

We have designed and synthesized two novel series of MCH-R1 antagonists based on a substituted biphenylmethyl urea core. SAR was explored, suggesting that optimal binding with the receptor was achieved when the biphenylmethyl group and the linker were substituted on the same nitrogen of the urea moiety. Compound 1-(3'-cyano-4-biphenylmethyl)-3-(2-hydroxy-1,1-dimethylethyl)-1-{2-[1-(4-methylbenzyl)-4-piperidinyl]ethyl}urea 2t showed the best antagonist binding activity to the MCH-R1 with a 43 nM K(i).     

Temperature Dependence of Steady-State and Presteady-State Kinetics of a Type IIb Na+/Pi Cotransporter

The temperature dependence of the transport kinetics of flounder Na(+)-coupled inorganic phosphate (P(i)) cotransporters (NaPi-IIb) expressed in Xenopus oocytes was investigated using radiotracer and electrophysiological assays. (32)P(i) uptake was strongly temperature-dependent and decreased by approximately 80% at a temperature change from 25 degrees C to 5 degrees C. The corresponding activation energy (E (a)) was approximately 14 kcal mol(-1) for the cotransport mode. The temperature dependence of the cotransport and leak modes was determined from electrogenic responses to 1 mM P(i) and phosphonoformic acid (PFA), respectively, under voltage clamp. The magnitude of the P(i)- and PFA-induced changes in holding current decreased with temperature. E (a) at -100 mV for the cotransport and leak modes was approximately 16 kcal mol(-1) and approximately 11 kcal mol(-1), respectively, which suggested that the leak is mediated by a carrier, rather than a channel, mechanism. Moreover, E (a) for cotransport was voltage-independent, suggesting that a major conformational change in the transport cycle is electroneutral. To identify partial reactions that confer temperature dependence, we acquired presteady-state currents at different temperatures with 0 mM P(i) over a range of external Na(+). The relaxation time constants increased, and the peak time constant shifted toward more positive potentials with decreasing temperature. Likewise, there was a depolarizing shift of the charge distribution, whereas the total available charge and apparent valency predicted from single Boltzmann fits were temperature-independent. These effects were explained by an increased temperature sensitivity of the Na(+)-debinding rate compared with the other voltage-dependent rate constants.     

Priming xylem for stress recovery depends on coordinated activity of sugar metabolic pathways and changes in xylem sap pH

Some plant species are capable of significant reduction of xylem embolism during recovery from drought despite stem water potential remains negative. However, the functional biology underlying this process is elusive. We subjected poplar trees to drought stress followed by a period of recovery. Water potential, hydraulic conductivity, gas exchange, xylem sap pH, and carbohydrate content in sap and woody stems were monitored in combination with an analysis of carbohydrate metabolism, enzyme activity, and expression of genes involved in sugar metabolic and transport pathways. Drought resulted in an alteration of differential partitioning between starch and soluble sugars. Upon stress, an increase in the starch degradation rate and the overexpression of sugar symporter genes promoted the efflux of disaccharides (mostly maltose and sucrose) to the apoplast. In turn, the efflux activity of the sugar‐proton cotransporters caused a drop in xylem pH. The newly acidic environment induced the activity of apoplastic invertases leading to the accumulation of monosaccharides in the apoplast, thus providing the main osmoticum necessary for recovery. During drought and recovery, a complex network of coordinated molecular and biochemical signals was activated at the interface between xylem and parenchyma cells that appeared to prime the xylem for hydraulic recovery.     

Synaptic dendritic activity modulates the single synaptic event

Synaptic transmission is the key system for the information transfer and elaboration among neurons. Nevertheless, a synapse is not a standing alone structure but it is a part of a population of synapses inputting the information from several neurons on a specific area of the dendritic tree of a single neuron. This population consists of excitatory and inhibitory synapses the inputs of which drive the postsynaptic membrane potential in the depolarizing (excitatory synapses) or depolarizing (inhibitory synapses) direction modulating in such a way the postsynaptic membrane potential. The postsynaptic response of a single synapse depends on several biophysical factors the most important of which is the value of the membrane potential at which the response occurs. The concurrence in a specific time window of inputs by several synapses located in a specific area of the dendritic tree can, consequently, modulate the membrane potential such to severely influence the single postsynaptic response. The degree of modulation operated by the synaptic population depends on the number of synapses active, on the relative proportion between excitatory and inbibitory synapses belonging to the population and on their specific mean firing frequencies. In the present paper we show results obtained by the simulation of the activity of a single Glutamatergic excitatory synapse under the influence of two different populations composed of the same proportion of excitatory and inhibitory synapses but having two different sizes (total number of synapses). The most relevant conclusion of the present simulations is that the information transferred by the single synapse is not and independent simple transition between a pre- and a postsynaptic neuron but is the result of the cooperation of all the synapses which concurrently try to transfer the information to the postsynaptic neuron in a given time window. This cooperativeness is mainly operated by a simple mechanism of modulation of the postsynaptic membrane potential which influences the amplitude of the different components forming the postsynaptic excitatory response.     

Floristic studies on freshwater algae of Lake Gondwana,Northern Victoria Land (Antarctica)

Benthic algal mats and phytoplankton of Lake Gondwana (Northern Victoria Land, Antarctica) were investigated. Biomass, chlorophyll content and floristic analyses were carried out on algal mats. The mats are composed of two layers different in colour, floristic composition and chlorophyll content. The algal flora of the mats amount to 34 taxa (19 Cyanophyta, 7 Bacillariophyta, 8 Chlorophyta). The phytoplankton community is species-poor (only 5 taxa). Crytophyta account for about 98% of total algal density.