Mapping the onshore/offshore crustal transition at the Westernmost Mediterranean from seismic profiling

Cembrowski, Marcel... et. al.-- European Geosciences Union General Assembly 2013, 7-12 April, Vienna, Austria.-- 1 pageThe evolution of theWesternMediterranean is strongly affected by the collision of the African and Eurasian plates. The plate boundary as seen from earthquakes is diffuse over a wide area extending north and south of Gibraltar strait. The Western end of the Mediterranean is delineated by the Gibraltar Arc System, comprising the arcuate Spanish Betic and Moroccan Rif Mountain Belts, together with the Alboran-Sea Basin in-between. The extension of the Alboran Basin which started from Late Eocene and which coexisted with the Africa -Europe conversion is still under debate and is one of the key points to constrain the evolution of the Western Mediterranean. This motivated our interest to map the still unknown crustal transition from the Betic-Rif chain into the Alboran Sea, taking advantage of the coincidence in time (October 2011) of two seismic experiments in the area, on land (Rifsis project) and at sea (Gassis-WestMed project). For this purpose we deployed several tens of seismic stations, both in Morocco and Spain, to record the air-gun shooting (every 50 m) of the Sarmiento de Gamboa Spanish vessel performing multichannel reflection profiles at the Alboran sea, and hence to extend these marine lines to wide-angle distances in-land. The airguns were calibrated for the near zero-offset marine reflection study and it turns out to be difficult to observe clear signals on the records in-land at offsets larger than about 70 km. The data has therefore been processed with a frequency-dependent lateral coherence filter to enhance coherent reflection/refraction signals through the frequency-dependent attenuation of incoherent noise and signals. This processing has permitted to track signals (seismic energy) up to more than 200 km on some profiles. Hence, a classical procedure of forward modeling (ray tracing approach) to fit the travel times of the identified wide-angle phases is now underway, taking advantage of the sedimentary/basement sequences inferred from the multichannel sections to constrain the upper part of the velocity-depth model. The first structural results delineate significant lateral variations in crustal depths, particularly at the Rif-Alboran transition. In our presentation we will show and discuss data processing examples which enabled signal detection to large offsets, the signal identification and their interpretation, and the different 2-D cross sections which image the crustal transition to the Alboran BasinPeer Reviewe

Why do herbivorous mites suppress plant defenses?

Plants have evolved numerous defensive traits that enable them to resist herbivores. In turn, this resistance has selected for herbivores that can cope with defenses by either avoiding, resisting or suppressing them. Several species of herbivorous mites, such as the spider mites Tetranychus urticae and Tetranychus evansi, were found to maximize their performance by suppressing inducible plant defenses. At first glimpse it seems obvious why such a trait will be favored by natural selection. However, defense suppression appeared to readily backfire since mites that do so also make their host plant more suitable for competitors and their offspring more attractive for natural enemies. This, together with the fact that spider mites are infamous for their ability to resist (plant) toxins directly, justifies the question as to why traits that allow mites to suppress defenses nonetheless seem to be relatively common? We argue that this trait may facilitate generalist herbivores, like T. urticae, to colonize new host species. While specific detoxification mechanisms may, on average, be suitable only on a narrow range of similar hosts, defense suppression may be more broadly effective, provided it operates by targeting conserved plant signaling components. If so, resistance and suppression may be under frequency-dependent selection and be maintained as a polymorphism in generalist mite populations. In that case, the defense suppression trait may be under rapid positive selection in subpopulations that have recently colonized a new host but may erode in relatively isolated populations in which host-specific detoxification mechanisms emerge. Although there is empirical evidence to support these scenarios, it contradicts the observation that several of the mite species found to suppress plant defenses actually are relatively specialized. We argue that in these cases buffering traits may enable such mites to mitigate the negative side effects of suppression in natural communities and thus shield this trait from natural selection

Small tandem DNA duplications result from CST-guided Pol alpha-primase action at DNA break termini

Error-prone repair of DNA double-strand breaks have been implied to cause cancer-associated genome alterations, but the mechanism of their formation remains unclear. Here the authors find that DNA polymerase alpha primase plays part in tandem duplication formation at CRISPR/Cas9-induced complementary 3 ' ssDNA protrusions.Small tandem duplications of DNA occur frequently in the human genome and are implicated in the aetiology of certain human cancers. Recent studies have suggested that DNA double-strand breaks are causal to this mutational class, but the underlying mechanism remains elusive. Here, we identify a crucial role for DNA polymerase alpha (Pol alpha)-primase in tandem duplication formation at breaks having complementary 3 ' ssDNA protrusions. By including so-called primase deserts in CRISPR/Cas9-induced DNA break configurations, we reveal that fill-in synthesis preferentially starts at the 3 ' tip, and find this activity to be dependent on 53BP1, and the CTC1-STN1-TEN1 (CST) and Shieldin complexes. This axis generates near-blunt ends specifically at DNA breaks with 3 ' overhangs, which are subsequently repaired by non-homologous end-joining. Our study provides a mechanistic explanation for a mutational signature abundantly observed in the genomes of species and cancer cells.Genome Instability and Cance

The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy

Donor-acceptor co-doped SiC is a promising light converter for novel monolithic all-semiconductor white LEDs due to its broad-band donor-acceptor pair luminescence and potentially high internal quantum efficiency. Besides sufficiently high doping concentrations in an appropriate ratio yielding short radiative lifetimes, long nonradiative lifetimes are crucial for efficient light conversion. The impact of different types of defects is studied by characterizing fluorescent silicon carbide layers with regard to photoluminescence intensity, homogeneity and efficiency taking into account dislocation density and distribution. Different doping concentrations and variations in gas phase composition and pressure are investigated