Activité migratoire des tétranyques: Mise en évidence d'un rythme

Résumé L'étude en différentes conditions de la migration verticale deTetranychus urticae dans de fortes infestations, a permis de mettre en éviduence un rythme circadien caractérisé par un mouvement alterné de montée et de descente, la population migrant vers le haut des plantes en début d'après-midi. Ce rythme est en partie endogène puisqu'il se maintient plusieurs jours dans des conditions constantes.      

Influence des basses températures sur les potentialités biologiques d'Orius laevigatus et d'Orius majusculus (Het.: Anthocoridae)

Résumé Des expérimentations ont permis de comparer l'influence de deux conditions de conservation au froid et de leur durée sur la longévité et la fécondité de deux cspèces d'anthocorides,Orius majusculus (Reuter) etOrius laevigatus (Fieber). La survie des adultes est meilleure dans les conditions thermopériodiques 13°C/3°C qu'à la température constante de 9°C. La longévité des femelles après passage au froid est d'autant plus grande que la durée d'exposition a été courte. La fécondité d'O. laevigatus ne subit pas de réduction significative après 50 jours de conservation en thermopériode alors que celle d'O. majusculus est fortement réduite après 20 jours dans les mêmes conditions.

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Summary Laboratory studies were done to compare the effect of two cold storage conditions on longevity and fecundity of two anthocorids,Orius majusculus (Reuter) andOrius laevigatus (Fieber). Survival of adults is better at a thermoperiodic condition of 13°C/3°C than at a constant temperature of 9°C. Female longevity decreases as the duration of exposure to cold conditions increases. Fecundity ofO. laevigatus is not significantly reduced after 50 days of exposure to thermoperiodic conditions even though those ofO. majusculus is strongly reduced after 20 days.

     

The OLA major histocompatibility complex of sheep. Genetic frequencies compared in Prélpe sheep with and without scrapie

The OLA genic frequencies were studied in both normal "Préalpe" Sheep and those affected with Scrapie. In the non-affected Sheep of contaminated flocks, frequencies were generally decreased, compared with frequencies of the same factors in sick Sheep or in non-infected controls. Three OLA-A genes significantly decreased; at this locus, results in "Préalpe" and "Ile-de-France" Sheep were inversed. This observation excludes OLA genes being involved in pathogeny or resistance to the disease, but suggests the existence of a linkage between the OLA loci and at least one resistance or susceptibility locus.     

Breathing space: deoxygenation of aquatic environments can drive differential ecological impacts across biological invasion stages

The influence of climate change on the ecological impacts of invasive alien species (IAS) remains understudied, with deoxygenation of aquatic environments often-overlooked as a consequence of climate change. Here, we therefore assessed how oxygen saturation affects the ecological impact of a predatory invasive fish, the Ponto-Caspian round goby (Neogobius melanostomus), relative to a co-occurring endangered European native analogue, the bullhead (Cottus gobio) experiencing decline in the presence of the IAS. In individual trials and mesocosms, we assessed the effect of high, medium and low (90%, 60% and 30%) oxygen saturation on: (1) functional responses (FRs) of the IAS and native, i.e. per capita feeding rates; (2) the impact on prey populations exerted; and (3) how combined impacts of both fishes change over invasion stages (Pre-invasion, Arrival, Replacement, Proliferation). Both species showed Type II potentially destabilising FRs, but at low oxygen saturation, the invader had a significantly higher feeding rate than the native. Relative Impact Potential, combining fish per capita effects and population abundances, revealed that low oxygen saturation exacerbates the high relative impact of the invader. The Relative Total Impact Potential (RTIP), modelling both consumer species’ impacts on prey populations in a system, was consistently higher at low oxygen saturation and especially high during invader Proliferation. In the mesocosm experiment, low oxygen lowered RTIP where both species were present, but again the IAS retained high relative impact during Replacement and Proliferation stages at low oxygen. We also found evidence of multiple predator effects, principally antagonism. We highlight the threat posed to native communities by IAS alongside climate-related stressors, but note that solutions may be available to remedy hypoxia and potentially mitigate impacts across invasion stages.

     

Usnic acid derivatives from Leprocaulon microscopicum

In addition to known dibenzofuran derivatives such as (?)-usnic acid, (?)-isousnic acid and (?)-placodiolic acid, a Leprocaulon microscopicum acetone extract yielded a new compound, (±)-9-O-methylplacodiolic acid in a keto-enol equilibrium focused on the C-ring. Structures were established using mass spectrometry and combination of 1D and 2D NMR spectral data. ¹³C assignments of placodiolic acid were revised. Tautomers of the (±)-9-O-methylplacodiolic acid were only separated by GC and a thorough fragmentation study confirmed the structural features. To complete the study, evaluation of antiproliferative effects on HT-29 human colorectal cancer cells showed moderate activity for (?)-usnic acid only.     

First report of Culicoides boyi (Diptera: Ceratopogonidae) in France

Culicoides boyi Nielsen, Kristensen & Pape 2015 (Diptera: Ceratopogonidae), described in Denmark in 2015, is reported in France. This species is closely related to Culicoides pulicaris (Linnaeus 1758) and can only be distinguished from this species by a subtle variation in spot wing pattern and by calculation of maxillary palpal ratio.     

Differential signalling of NH2-terminal flag-labelled thrombopoietin receptor activated by TPO or anti-FLAG antibodies

In this report, we compared activation of NH2-terminal FLAG-labelled thrombopoietin receptor (Mpl) by anti-FLAG antibodies and by thrombopoietin (TPO). We found that anti-FLAG monoclonal antibodies M1 dimerize FLAG-labelled receptor and trigger proliferation of BaF3/FLAG-Mpl cells. In UT7/FLAG-Mpl cells, activation of the FLAG-Mpl receptor by low TPO concentrations triggered proliferation, while high concentrations triggered differentiation. Activation of FLAG-Mpl receptors in these cells by all tested concentrations of M1 antibodies induced proliferation but not differentiation. Low TPO concentrations induced similar to M1 antibodies level of Jak2, Stat3, Stat5 and Akt phosphorylation. In contrast, only TPO and not M1 antibodies activated Erks phosphorylation. Since the anti-FLAG antibodies do not react with the TPO binding site of the receptor, we hypothesize that they can trigger a distinct signal by dimerizing Mpl in a manner different from that induced by TPO.     

Confined diffusion without fences of a g-protein-coupled receptor as revealed by single particle tracking

Single particle tracking is a powerful tool for probing the organization and dynamics of the plasma membrane constituents. We used this technique to study the micro -opioid receptor belonging to the large family of the G-protein-coupled receptors involved with other partners in a signal transduction pathway. The specific labeling of the receptor coupled to a T7-tag at its N-terminus, stably expressed in fibroblastic cells, was achieved by colloidal gold coupled to a monoclonal anti T7-tag antibody. The lateral movements of the particles were followed by nanovideomicroscopy at 40 ms time resolution during 2 min with a spatial precision of 15 nm. The receptors were found to have either a slow or directed diffusion mode (10%) or a walking confined diffusion mode (90%) composed of a long-term random diffusion and a short-term confined diffusion, and corresponding to a diffusion confined within a domain that itself diffuses. The results indicate that the confinement is due to an effective harmonic potential generated by long-range attraction between the membrane proteins. A simple model for interacting membrane proteins diffusion is proposed that explains the variations with the domain size of the short-term and long-term diffusion coefficients.     

Comparison of progesterone concentration determination by 12 non-isotopic immunoassays and gas chromatography/mass spectrometry in 99 human serum samples

A single serum progesterone determination may be highly predictive for early pregnancy and in vitro fertilisation and embryo-transfer outcomes. We therefore compared 12 direct non-isotopic progesterone immunoassays with gas-chromatography/mass spectrometry (GC/MS). For each assay, data from the analysis of 99 individual sera were compared with data obtained by GC/MS, using regression and bias plot analyses and the ratio method. We observed a larger difference in concentration between high and low values and a broader distribution of results for immunoassays than for GC/MS. All immunoassays displayed bias in the calibration process and a lack of specificity and/or sensitivity, to various degrees. We tried to identify the parameters of the assay procedure that might contribute to these discrepancies. None of the criteria investigated (antibodies, control and preparation of calibrators, blocking agents and choice of tracer) had a significant effect when studied alone.     

Probing functionalized gold colloids for single particle tracking experiments

Functionalized submicroscopic particles are currently used to label proteins or lipids at the surface of living cells for single particle tracking experiments. In many cases, it can be of crucial importance for the particle to be anchored to a single molecule. We have addressed this question for the labeling at the plasma membrane of NRK cells of the mu-opioid receptor bearing a T7 epitope at the N-terminus. Using biophysical methods we were able to prepare quasi-monovalent anti-T7 antibody conjugated gold colloids (40 nm diameter) leading to stable and specific binding to the receptor. The rational method, we report here, can be extended to design customized probes for the labeling of various tagged molecules.