Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology

Convergent plate margins typically experience a transition from subduction to collision dynamics as massive continental blocks enter the subduction channel. Studies of high-pressure rocks indicate that tectonic fragments are rapidly exhumed from eclogite facies to midcrustal levels, but the details of such dynamics are controversial.To understand the dynamics of a subduction channel we report the results of a petrochronological study from the central Sesia Zone, a key element of the internalWestern Alps.This comprises two polymetamorphic basement complexes (Eclogitic Micaschist Complex and Gneiss Minuti Complex) and a thin, dismembered cover sequence (Scalaro Unit) associated with pre-Alpine metagabbros and metasediments (Bonze Unit). Structurally controlled samples from three of these units (Eclogitic Micaschist Complex and Scalaro-Bonze Units) yield unequivocal petrological and geochronological evidence of two distinct high-pressure stages. Ages (U-Th-Pb) of growth zones in accessory allanite and zircon, combined with inclusion and textural relationships, can be tied to the multi-stage evolution of single samples.Two independent tectono-metamorphic ‘slices’ showing a coherent metamorphic evolution during a given time interval have been recognized: the Fondo slice (which includes Scalaro and Bonze rocks) and the Druer slice (belonging to the Eclogitic Micaschist Complex).The new data indicate separate stages of deformation at eclogite-facies conditions for each recognized independent kilometer-sized tectono-metamorphic slice, between ~85 and 60 Ma, with evidence of intermittent decompression (∆P~0.5 GPa) within only the Fondo slice. The evolution path of the Druer slice indicates a different P-T-time evolution with prolonged eclogite-facies metamorphism between ~85 and 75Ma. Our approach, combining structural, petrological and geochronological techniques, yields field-based constraints on the duration and rates of dynamics within a subduction channel.

Structure and dynamics of hybrid zones at different stages of speciation in the common vole (Microtus arvalis)

The genetic structure and dynamics of hybrid zones provide crucial information for understanding the processes and mechanisms of evolutionary divergence and speciation. In general, higher levels of evolutionary divergence between taxa are more likely to be associated with reproductive isolation and may result in suppressed or strongly restricted hybridization. In this study, we examined two secondary contact zones between three deep evolutionary lineages in the common vole (Microtus arvalis). Differences in divergence times between the lineages can shed light on different stages of reproductive isolation and thus provide information on the ongoing speciation process in M. arvalis. We examined more than 800 individuals for mitochondrial (mtDNA), Y-chromosome and autosomal markers and used assignment and cline analysis methods to characterize the extent and direction of gene flow in the contact zones. Introgression of both autosomal and mtDNA markers in a relatively broad area of admixture indicates selectively neutral hybridization between the least-divergent lineages (Central and Eastern) without evidence for partial reproductive isolation. In contrast, a very narrow area of hybridization, shifts in marker clines and the quasi-absence of Y-chromosome introgression support a moving hybrid zone and unidirectional selection against male hybrids between the lineages with older divergence (Central and Western). Data from a replicate transect further support non-neutral processes in this hybrid zone and also suggest a role for landscape history in the movement and shaping of geneflow profiles.

The Plasmodium Class XIV Myosin, MyoB, Has a Distinct Subcellular Location in Invasive and Motile Stages of the Malaria Parasite and an Unusual Light Chain

Myosin B (MyoB) is one of the two short class XIV myosins encoded in the Plasmodium genome. Class XIV myosins are characterized by a catalytic "head," a modified "neck," and the absence of a "tail" region. Myosin A (MyoA), the other class XIV myosin in Plasmodium, has been established as a component of the glideosome complex important in motility and cell invasion, but MyoB is not well characterized. We analyzed the properties of MyoB using three parasite species as follows: Plasmodium falciparum, Plasmodium berghei, and Plasmodium knowlesi. MyoB is expressed in all invasive stages (merozoites, ookinetes, and sporozoites) of the life cycle, and the protein is found in a discrete apical location in these polarized cells. In P. falciparum, MyoB is synthesized very late in schizogony/merogony, and its location in merozoites is distinct from, and anterior to, that of a range of known proteins present in the rhoptries, rhoptry neck or micronemes. Unlike MyoA, MyoB is not associated with glideosome complex proteins, including the MyoA light chain, myosin A tail domain-interacting protein (MTIP). A unique MyoB light chain (MLC-B) was identified that contains a calmodulin-like domain at the C terminus and an extended N-terminal region. MLC-B localizes to the same extreme apical pole in the cell as MyoB, and the two proteins form a complex. We propose that MLC-B is a MyoB-specific light chain, and for the short class XIV myosins that lack a tail region, the atypical myosin light chains may fulfill that role.

Multivalency effects in Pseudomonas aeruginosa biofilm inhibition and dispersal by glycopeptide dendrimers targeting lectin LecA

The galactose specific lectin LecA partly mediates the formation of antibiotic resistant biofilms by Pseudomonas aeruginosa, an opportunistic pathogen causing lethal airways infections in immunocompromised and cystic fibrosis patients, suggesting that preventing LecA binding to natural saccharides might provide new opportunities for treatment. Here 8-fold (G3) and 16-fold (G4) galactosylated analogs of GalAG2, a tetravalent G2 glycopeptide dendrimer LecA ligand and P. aeruginosa biofilm inhibitor, were obtained by convergent chloroacetyl thioether (ClAc) ligation between 4-fold or 8-fold chloroacetylated dendrimer cores and digalactosylated dendritic arms. Hemagglutination inhibition, isothermal titration calorimetry and biofilm inhibition assays showed that G3 dendrimers bind LecA slightly better than their parent G2 dendrimers and induce complete biofilm inhibition and dispersal of P. aeruginosa biofilms, while G4 dendrimers show reduced binding and no biofilm inhibition. A binding model accounting for the observed saturation of glycopeptide dendrimer galactosyl groups and LecA binding sites is proposed based on the crystal structure of a G3 dendrimer LecA complex.

Long distance dispersal shaped patterns of human genetic diversity in Eurasia

Most previous attempts at reconstructing the past history of human populations did not explicitly take geography into account, or considered very simple scenarios of migration and ignored environmental information. However, it is likely that the Last Glacial Maximum (LGM) affected the demography and the range of many species, including our own. Moreover, long-distance dispersal (LDD) may have been an important component of human migrations, allowing fast colonization of new territories and preserving high levels of genetic diversity. Here, we use a high-quality microsatellite dataset genotyped in 22 populations to estimate the posterior probabilities of several scenarios for the settlement of the Old World by modern humans. We considered models ranging from a simple spatial expansion to others including LDD and a LGM-induced range contraction, as well as Neolithic demographic expansions. We find that scenarios with LDD are much better supported by data than models without LDD. Nevertheless, we show evidence that LDD events to empty habitats were strongly prevented during the settlement of Eurasia. This unexpected absence of LDD ahead of the colonization wave front could have been caused by an Allee effect, either due to intrinsic causes such as an inbreeding depression built during the expansion, or to extrinsic causes such as direct competition with archaic humans. Overall, our results suggest only a relatively limited effect of the LGM-contraction on current patterns of human diversity. This is in clear contrast with the major role of LDD migrations, which have potentially contributed to the intermingled genetic structure of Eurasian populations.

Polydnavirus DNA of the braconid wasp Chelonus inanitus is integrated in the wasp's genome and excised only in later pupal and adult stages of the female

Many endoparasitic wasps inject, along with the egg, polydnavirus into their insect hosts, the virus being a prerequisite for successful parasitoid development. The genome of polydnaviruses consists of multiple circular dsDNA molecules of variable size. We show for a 12 kbp segment of the braconid Chelonus inanitus (CiV12) that it is integrated into the wasp genome. This is the first direct demonstration of integration for a bracovirus. PCR data indicated that the integrated form of CiV12 was present in all male and female stages investigated while the excised circular virus DNA only appeared in females after a specific stage in pupal-adult development. The data also indicated that after excision of virus DNA the genomic DNA was rejoined. This has not yet been reported for any polydnavirus. Sequence analyses in the junction regions revealed the presence of an imperfect consensus sequence of 15 nucleotides in CiV12, in each terminus of the integrated virus DNA and in the rejoined genomic DNA. Within these repeats two sequence types (ATA, TAC) were observed in the various virus clones and in the clones encompassing the rejoined genomic DNA; they corresponded to the sequence type in the right and left junction, respectively. To explain this, we propose a model of virus DNA replication in which the genomic DNA is folded to juxtapose the direct repeat of the left with that of the right junction; recombination at specific sites would then yield the two types of virus and rejoined genomic DNA.

Sleep-Wake Cycle Dysfunction in the TgCRND8 Mouse Model of Alzheimer's Disease: From Early to Advanced Pathological Stages.

In addition to cognitive decline, individuals affected by Alzheimer's disease (AD) can experience important neuropsychiatric symptoms including sleep disturbances. We characterized the sleep-wake cycle in the TgCRND8 mouse model of AD, which overexpresses a mutant human form of amyloid precursor protein resulting in high levels of β-amyloid and plaque formation by 3 months of age. Polysomnographic recordings in freely-moving mice were conducted to study sleep-wake cycle architecture at 3, 7 and 11 months of age and corresponding levels of β-amyloid in brain regions regulating sleep-wake states were measured. At all ages, TgCRND8 mice showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep during the resting and active phases. Increased wakefulness in TgCRND8 mice was accompanied by a shift in the waking power spectrum towards fast frequency oscillations in the beta (14-20 Hz) and low gamma range (20-50 Hz). Given the phenotype of hyperarousal observed in TgCRND8 mice, the role of noradrenergic transmission in the promotion of arousal, and previous work reporting an early disruption of the noradrenergic system in TgCRND8, we tested the effects of the alpha-1-adrenoreceptor antagonist, prazosin, on sleep-wake patterns in TgCRND8 and non-transgenic (NTg) mice. We found that a lower dose (2 mg/kg) of prazosin increased NREM sleep in NTg but not in TgCRND8 mice, whereas a higher dose (5 mg/kg) increased NREM sleep in both genotypes, suggesting altered sensitivity to noradrenergic blockade in TgCRND8 mice. Collectively our results demonstrate that amyloidosis in TgCRND8 mice is associated with sleep-wake cycle dysfunction, characterized by hyperarousal, validating this model as a tool towards understanding the relationship between β-amyloid overproduction and disrupted sleep-wake patterns in AD.

Long-distance spore dispersal in wood-inhabiting Basidiomycetes

Eight species of wood-inhabiting basidiomycetes (Laurilia sulcata, Peniophora aurantiaca, Resinicium bicolor, Scytinostroma galactinum, Terana caerulea, Trichaptum abietinum, T. biforme and T. fuscoviolaceum) were used in a spore-trapping test to evaluate their individual ability for long-distance spore dispersal. Petri dishes with single spore mycelia were used as baits. In the experiment, carried out at the Botanical Institute in Göteborg, spores from the air were regularly captured. Surprisingly, spores were captured from species whose nearest known natural occurrence was located quite far from Göteborg. The closest population of Peniophora aurantiaca is about 1000 km south of Göteborg. The results from this experiment support the hypothesis that fungal spores are widely and efficiently dispersed. Such a broad and extensive dispersal ability is of vital importance, especially for wood-inhabiting species which are highly dependent on a substrate which is onlv temporarily available.

Dispersal and microsite limitation in an abandoned calcareous grassland of the southern prealps

Dispersal limitation is often involved when the species composition of a dry abandoned grassland shows a slow response to resumed regular mowing. A seed-addition experiment, using 32 species which do not belong to the local species pool, was performed on Monte San Giorgio (southern Switzerland) to test whether the low recruitment success was due to dispersal limitation or due to unfavourable microsite conditions. In October 1997, 20 species were individually sown in six 3 × 4 m blocks of a 2 × 2 factorial “partial” split-plot design with treatments of abandonment vs. mowing and undisturbed vs. root-removed soil, this last being applied in small naturally-degradable pots. Moreover, 12 species were sown only in the treatments on undisturbed soil. Seedlings of sown and spontaneously germinating seeds were observed on 16 occasions over one 12-month period. Seeds of 31 out of the 32 species germinated. Twenty-four species showed germination rates higher than 5% and different seasonal germination patterns. Established vegetation, especially the tussocks ofMolinia arundinacea, reduced the quality of microsites for germination. Whereas a few species germinated better under the litter ofMolinia arundinacea, many more germinated better under the more variable microsite conditions of a mown grassland. Only a few seedlings of 25 species out of the 31 germinated species survived until October 1998. Seedling survival was negatively affected by litter, unfavourable weather conditions (frost and dry periods followed by heavy rains) and herbivory (slugs and grasshoppers). Tussocks ofMolinia arundinacea, however, tended to protect seedlings. The poor establishment success of “new” species observed in abandoned meadows on Monte San Giorgio after resumed mowing is due to dispersal and microsite limitations.

Morphomechanical Innovation Drives Explosive Seed Dispersal

How mechanical and biological processes are coordinated across cells, tissues, and organs to produce complex traits is a key question in biology. Cardamine hirsuta, a relative of Arabidopsis thaliana, uses an explosive mechanism to disperse its seeds. We show that this trait evolved through morphomechanical innovations at different spatial scales. At the organ scale, tension within the fruit wall generates the elastic energy required for explosion. This tension is produced by differential contraction of fruit wall tissues through an active mechanism involving turgor pressure, cell geometry, and wall properties of the epidermis. Explosive release of this tension is controlled at the cellular scale by asymmetric lignin deposition within endocarp b cells-a striking pattern that is strictly associated with explosive pod shatter across the Brassicaceae plant family. By bridging these different scales, we present an integrated mechanism for explosive seed dispersal that links evolutionary novelty with complex trait innovation.