Crystallographic structure of ultrathin Fe films on Cu(100)

We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.Comment: 4 pages, 3 figures, RevTeX/LaTeX2.0

Stressful conditions reveal decrease in size, modification of shape but relatively stable asymmetry in bumblebee wings

Human activities can generate a wide variety of direct and indirect effects on animals, which can manifest as environmental and genetic stressors. Several phenotypic markers have been proposed as indicators of these stressful conditions but have displayed contrasting results, depending, among others, on the phenotypic trait measured. Knowing the worldwide decline of multiple bumblebee species, it is important to understand these stressors and link them with the drivers of decline. We assessed the impact of several stressors (i.e. natural toxin-, parasite-, thermic- and inbreeding-stress) on both wing shape and size and their variability as well as their directional and fluctuating asymmetries. The total data set includes 650 individuals of Bombus terrestris (Hymenoptera: Apidae). Overall wing size and shape were affected by all the tested stressors. Except for the sinigrin (e.g. glucosinolate) stress, each stress implies a decrease of wing size. Size variance was affected by several stressors, contrary to shape variance that was affected by none of them. Although wing size directional and fluctuating asymmetries were significantly affected by sinigrin, parasites and high temperatures, neither directional nor fluctuating shape asymmetry was significantly affected by any tested stressor. Parasites and high temperatures led to the strongest phenotype modifications. Overall size and shape were the most sensitive morphological traits, which contrasts with the common view that fluctuating asymmetry is the major phenotypic marker of stress

Standardized protocol to evaluate pollen polypeptides as bee food source

International audienceBees mainly rely on pollen for their protein resources. As these molecules are essential for numerous aspects of bee physiology like ovary development and larval growth, their quantification and determination are crucial to evaluate diet quality. However, the term “protein” has been used to mention crude protein, total amino acids, or protein sensu stricto (i.e., polypeptides of molecular weight >10,000 Da). In addition to this ambiguity, current methods for protein quantification suffer from bias due to nonprotein nitrogen and protein-to-protein variations. A reliable and nondestructive method to quantify the pollen polypeptides is then essential to estimate bee food source. The present paper aims (a) to detail such a protocol, (b) to evaluate its efficiency, and (c) to confront its results to those returned by traditional methods of protein estimation. Our protocol clearly overrides some bias of previous methods and is highly reliable. Results show the high variability in content of pollen polypeptides and suggest that the main part of the proteinaceous nitrogen is from oligopeptides. They also highlight that hand-collected pollen is a better matrice than pollen loads to estimate the polypeptides of pollen as bee food source