Comparison of primer sets for the study of Planctomycetes communities in lentic freshwater ecosystems

International audienceIn search of a primer set that could be used to study Planctomycetes dynamics in lakes and especially via fingerprinting methods, e.g. denaturing gradient gel electrophoresis (DGGE), three existing specific primer sets, developed for marine and soil systems, have been tested on water samples from four freshwater ecosystems. The first primer set (PLA46F/ PLA886R) allowed PCR amplification of Planctomycetes sequences in only one of the four ecosystems, whereas the second primer set (PLA40F/ P518R) amplified Planctomycetes sequences in all the studied ecosystems but with a low specificity, since sequences belonging to Verrucomicrobiales and Chlamydiales clades were also amplified. Finally, the third primer set (PLA352F/PLA920R) allowed amplification of Planctomycetes sequences in the four ecosystems with a very high specificity. It amplified all known Planctomycetes genera and yielded the highest Operational Taxonomic Unit (OTU) richness and diversity estimates. In silico analyses supported these results. Further experiments comparing PLA352F/PLA920R to PLA46F/P1390R (a primer set generating a longer PCR fragment, also used to study Planctomycetes) yielded very similar results. Our findings suggest that the primer set PLA352F/ PLA920R provides good estimates of Planctomycetes richness and diversity compared with other, and can thus be used to study Planctomycetes dynamics in lentic freshwater ecosystems

Landscape woody features, local management and vegetation composition shape moth communities in extensively managed grasslands

1. Agricultural intensification has led to a dramatic impoverishment of biodiversity. Moths are not an exception: rapid declines of common and widespread species have been reported and it is still not clear which conservation measures should be applied to restore their populations. 2. We investigated how much of the variation in moth assemblages inhabiting extensively managed meadows in a region of high-intensity agriculture is explained by surrounding woody landscape features, meadow management and vegetation composition, and which specific variables are the most influential. 3. Results show that the percentage of forest and the length of hedgerows within a 250 m radius were especially important for forest macromoths, explaining 42% of variation in abundance and 23% of species richness, whereas meadow management played a relatively marginal role. The abundance of grassland macromoths was also positively influenced by the length of hedgerows in the landscape (combined with elevation it explained 10% of the variance), while it responded negatively to uncut refuge and to delayed mowing (7%). Regarding grassland macromoth species richness, the annual harvesting frequency was the main predictor (4%). In contrast, micromoth abundance was more influenced by meadow management, notably the date of the first cut (4%) and vegetation composition (8%, though not conclusive due to a single outlier), whereas landscape features explained nothing. 4. Altogether, these results demonstrate the importance of both woody features within farmed landscapes and biodiversity-friendly meadow management for the maintenance of integral moth communities

Grassland intensification dramatically impacts grasshoppers: Experimental evidence for direct and indirect effects of fertilisation and irrigation

European mountain hay meadows are hosting an exceptionally rich biodiversity. They are currently threatened by both land abandonment and farming intensification via aerial irrigation and slurry application. The consequences of mountain grassland intensification on arthropods are still poorly documented, which is a serious handicap to proposing ecologically-friendly management guidance. Six experimental treatments mimicking a gradient of management intensity (including irrigation, fertilisation and various combinations thereof) were initiated in 2010 at twelve montane and subalpine Swiss meadow sites. In 2013, we sampled orthopterans to assess the influence of management practice on that taxonomic group. In parallel, the changes in vegetation height and ambient temperature (at 10 cm above ground level) induced by the intensification process were quantified in order to better appraise the underlying mechanisms. Intensification had a negative impact on Caelifera (grasshoppers), with decreases in densities and species richness reaching as much as 70% and 50%, respectively, in the most intensively managed treatment plots. Intensification furthermore led to a marked increase in mean vegetation height and a cooling of ambient temperature by up to 4.2 ◦C. Such microhabitat and microclimate alterations are likely to affect Caelifera development, in particular thermophilous species. In contrast, Ensifera (bushcrickets) densities and species richness showed no significant response to our experimental manipulations. Finally, the application of irrigation by sprinklers alone had limited impact on both orthopterans and meadow microclimate. We conclude that orthopterans, in particular Caelifera, are fairly sensitive to grassland management intensification: fertilisation should be avoided in focal areas for biodiversity conservation

Spatiotemporal Changes in the Structure and Composition of a Less-Abundant Bacterial Phylum (Planctomycetes) in Two Perialpine Lakes

International audienceWe used fingerprinting and cloning-sequencing to study the spatiotemporal dynamics and diversity of Planctomycetes in two perialpine lakes with contrasting environmental conditions. Planctomycetes, which are less-abundant bacteria in freshwater ecosystems, appeared to be structured in the same way as the entire bacterial community in these ecosystems. They were more diversified and displayed fewer temporal variations in the hypolimnia than in the epilimnia. Like the more-abundant bacterial groups in aquatic systems, Planctomycetes communities seem to be composed of a very small number of abundant and widespread operational taxonomic units (OTUs) and a large number of OTUs that are present at low abundance. This indicates that the concept of "abundant or core" and "rare" bacterial phylotypes could also be applied to less-abundant freshwater bacterial phyla. The richness and diversity of Planctomycetes were mainly driven by pH and were similar in both of the lakes studied, whereas the composition of the Planctomycetes community seemed to be determined by a combination of factors including temperature, pH, and nutrients. The relative abundances of the dominant OTUs varied over time and were differently associated with abiotic factors. Our findings demonstrate that less-abundant bacterial phyla, such as Planctomycetes, can display strong spatial and seasonal variations linked to environmental conditions and suggest that their functional role in the lakes studied might be attributable mainly to a small number of phylotypes and vary over space and time in the water column

Le palais de l’Égypte à l’Exposition universelle de 1900

L’Exposition universelle de 1900, à Paris, fut certainement l’une des plus importantes dans le monde. Elle proposa à ses quelque 52 millions de visiteurs quantité d’édifices évoquant des sujets variés, mais également des pavillons nationaux. En ce tournant de siècle, l’Égypte se devait d’être présente malgré les difficultés qu’elle connaissait : un palais « pharaonique » allait permettre de montrer au grand public les diverses facettes historiques, culturelles et artisanales du pays vues par ..