Drought-Adaptation Potential in Fagus sylvatica: Linking Moisture Availability with Genetic Diversity and Dendrochronology

<div><h3>Background</h3><p>Microevolution is essential for species persistence especially under anticipated climate change scenarios. Species distribution projection models suggested that the dominant tree species of lowland forests in Switzerland, European beech (<em>Fagus sylvatica</em> L.), might disappear from most areas due to expected longer dry periods. However, if genotypes at the moisture boundary of the species climatic envelope are adapted to lower moisture availability, they can serve as seed source for the continuation of beech forests under changing climates.</p> <h3>Methodology/Principal Findings</h3><p>With an AFLP genome scan approach, we studied neutral and potentially adaptive genetic variation in <em>Fagus sylvatica</em> in three regions containing a dry and a mesic site each (<em>n</em>_ind. = 241, <em>n</em>_markers = 517). We linked this dataset with dendrochronological growth measures and local moisture availabilities based on precipitation and soil characteristics. Genetic diversity decreased slightly at dry sites. Overall genetic differentiation was low (<em>F</em>_st = 0.028) and Bayesian cluster analysis grouped all populations together suggesting high (historical) gene flow. The Bayesian outlier analyses indicated 13 markers with three markers differing between all dry and mesic sites and the others between the contrasting sites within individual regions. A total of 41 markers, including seven outlier loci, changed their frequency with local moisture availability. Tree height and median basal growth increments were reduced at dry sites, but marker presence/absence was not related to dendrochronological characteristics.</p> <h3>Conclusion and Their Significance</h3><p>The outlier alleles and the makers with changing frequencies in relation to moisture availability indicate microevolutionary processes occurring within short geographic distances. The general genetic similarity among sites suggests that ‘preadaptive’ genes can easily spread across the landscape. Yet, due to the long live span of trees, fostering saplings originating from dry sites and grown within mesic sites might increase resistance of beech forests during the anticipated longer dry periods.</p> </div

Wikipedia Arabe et la construction collective du savoir (Wikipedia Arabic and the collective construction of knowledge)

Cette recherche part du constat d’une faible participation à, et d’un maigre contenu dans Wikipedia Arabe et questionne les obstacles à un contenu plus riche. La problématique de la recherche est double: d’abord proposer une cartographie numérique de Wikipedia dans la région du Moyen-Orient et Afrique du Nord. Cette cartographie informe d’une part sur la représentation des participants à Wikipedia Arabe, et d’autre part, sur la contribution à la distribution du savoir arabe et de son étendue. Deuxièmement, la recherche s’intéresse au contenu de Wikipedia arabe et de son mode de production. Plus particulièrement, les questions de recherche portent sur la participation à la production de contenu de Wikipedia Arabe, les barrières à l’entrée dans Wikipedia Arabe, les dynamiques de négociation et de consensus entre éditeurs et administrateurs Wikipediens de la région et les solutions envisagées pour améliorer et encourager la production de contenu. La démarche méthodologique est principalement qualitative.So far Arabic content on Wikipedia Arabic is very weak; this paper questions the barriers that prevent contributors to Wikipedia Arabic from being more active in content production on Wikipedia Arabic. The research problematic is twofold: first, it suggests a digital cartography of Wikipedia in the MENA region that informs about those who represent Wikipedia Arabic and thus, contribute to the Arab knowledge distribution. Second, while adopting a qualitative approach, the research looks at the content of Arabic Wikipedia. It questions its production methods, contribution barriers, dynamics of negotiation between Wikipedians, and strategies of consensus between editors and admins, as well as the envisioned solutions to improve and promote Wikipedia Arabic content production.</p

Experimental evidence for homoclinic chaos in an electrochemical growth process

Experimental investigations of galvanostatic electrochemical growth processes in steady thin layer electrolytes are reported. For some control parameter values, the measurement of the cell potential versus time provides periodic and aperiodic oscillations. The deterministic character of these potential signals is demonstrated using standard dynamical systems theory tools such as time-delay phase portrait reconstructions, Poincar6 maps and one-dimensional maps. A transient period-doubling transition is described. The homoclinic nature of the chaotic behavior is emphasized. The origin of the spatio-temporal behavior is discussed in terms of the competition between the electrochemical process (reduction of metallic ions) and the transport processes (migration, diffusion and convection). Analysis of video images shows that the oscillations in growth rate are in phase across the entire cell width (up to 40 mm) and are in phase with the oscillations in the cell potential

When capacitive transduction meets the thermomechanical limit: Towards femto-newton force sensors at very high frequency

International audienceWe show that the capacitive transduction of a MEMS device using a setup based on a microwave detection scheme achieves the measurement of the thermomechanical noise spectrum of a high-frequency (>10 MHz) high-stiffness (>10 5 N/m) resonator, reaching the outstanding displacement resolution of 1 fm/√Hz. This result paves the way for vibrating sensors with exquisite force resolution in the fN/vHz range, enabling large-bandwidth measurements of mechanical interactions at small scale and rheology of fluids at very high frequency. An example of application is given and concerns atomic force microscopy images of biomolecular assemblies

Range wide versus local patterns of genetic diversity in hornbeam (Carpinus betulus L.)

A study based on AFLP markers was conducted to characterise the present population genetic structure of Carpinus betulus in Europe and to formulate guidelines for the use of this species in plantations on a local scale in Flanders. High within-population diversity and little (but significant) genetic differentiation were detected at both Flemish and European scales. However, there was a pattern of isolation by distance only at the European scale. Within-population gene diversity, a new rarefaction-based measure of number of genotypes (lsquoband richnessrsquo) and percentage of polymorphic loci are lower north of major mountain chains, suggesting that the mountain ranges formed a second bottleneck for the hornbeam during postglacial recolonisation. In Flanders, despite lower gene diversity, there were more polymorphic loci than in other European populations, a pattern that might have been caused by the mixing of material through planting, e.g. in hedges. In view of these findings, it is advised to create a single Flemish seed zone and to use preferentially reproductive material from this seed zone for new plantations in Flander

Genetic diversity and spatial structure within a natural stand of a tropical forest tree species, Carapa procera (Meliaceae), in French Guiana

Isozyme markers were used to characterize levels of diversity, genotypic structure and spatial genetic structure for the low-density tree species, #Carapa procera# (five adults per ha), within 300 ha of a continuous tropical rain forest stand. Both seed and adult stages were investigated, a high level of genetic diversity being found in both. Fixation indices showed excess homozygosity in seeds, and excess heterozygosity in adults, which might be caused by selection in favour of heterozygotes. Autocorrelation analysis of the spatial distribution of genotypes revealed no significant pattern in adults or in seeds before dispersal, and there was a high variability in correlogram shapes among alleles. This suggests that gene flow is extensive in #C procera#, probably mainly through long-distance pollen dispersal, as seed dispersal is expected to be rather limited in this species (maximum distances of about 50 m). No clear-cut spatial pattern was observed in pollen allele frequencies, which supports the hypothesis of extensive pollen flow. This overall lack of structure is consistent with the data already available on the mating system of this predominantly outcrossing species. (Résumé d'auteur