Does heterogeneity spoil the basket? The role of productivity and feedback information on public good provision

In a circular neighborhood of eight, each member contributes repeatedly to two local public goods, one with the left and one with the right neighbor. All eight two-person games provide only local feedback information and are structurally independent in spite of their overlapping player sets. Heterogeneity is induced intra-personally by asymmetric productivity in left and right games and inter-personally by two randomly selected group members who are less privileged (LP) by being either less productive or excluded from end-of-period feedback information about their payoffs and neighbors’ contributions. Although both LP-types let the neighborhood as a whole evolve less cooperatively, their spillover dynamics differ. While less productive LPs initiate “spoiling the basket” via their low contributions, LPs with no-end-of-round information are exploited by their neighbors. Furthermore, LP-positioning, closest versus most distant, affects how the neighborhood evolves

Phylogenetic Analyses Reveal Monophyletic Origin of the Ergot Alkaloid Gene dmaW in Fungi

Ergot alkaloids are indole-derived mycotoxins that are important in agriculture and medicine. Ergot alkaloids are produced by a few representatives of two distantly related fungal lineages, the Clavicipitaceae and the Trichocomaceae. Comparison of the ergot alkaloid gene clusters from these two lineages revealed differences in the relative positions and orientations of several genes. The question arose: is ergot alkaloid biosynthetic capability from a common origin? We used a molecular phylogenetic approach to gain insights into the evolution of ergot alkaloid biosynthesis. The 4-γ,γ-dimethylallyltryptophan synthase gene, dmaW, encodes the first step in the pathway. Amino acid sequences deduced from dmaW and homologs were submitted to phylogenetic analysis, and the results indicated that dmaW of Aspergillus fumigatus (mitosporic Trichocomaceae) has the same origin as corresponding genes from clavicipitaceous fungi. Relationships of authentic dmaW genes suggest that they originated from multiple gene duplications with subsequent losses of original or duplicate versions in some lineages

Phylogenetic Analyses Reveal Monophyletic Origin of the Ergot Alkaloid Gene \u3cem\u3edmaW\u3c/em\u3e in Fungi

Ergot alkaloids are indole-derived mycotoxins that are important in agriculture and medicine. Ergot alkaloids are produced by a few representatives of two distantly related fungal lineages, the Clavicipitaceae and the Trichocomaceae. Comparison of the ergot alkaloid gene clusters from these two lineages revealed differences in the relative positions and orientations of several genes. The question arose: is ergot alkaloid biosynthetic capability from a common origin? We used a molecular phylogenetic approach to gain insights into the evolution of ergot alkaloid biosynthesis. The 4-γ,γ-dimethylallyltryptophan synthase gene, dmaW, encodes the first step in the pathway. Amino acid sequences deduced from dmaW and homologs were submitted to phylogenetic analysis, and the results indicated that dmaW of Aspergillus fumigatus (mitosporic Trichocomaceae) has the same origin as corresponding genes from clavicipitaceous fungi. Relationships of authentic dmaW genes suggest that they originated from multiple gene duplications with subsequent losses of original or duplicate versions in some lineages

Behavioral spillovers in local public good provision: an experimental study

In a circular neighborhood, each member has a left and a right neighbor with whom(s) he interacts repeatedly. From their two separate endowment amounts individuals can contribute to each of their two structurally independent public goods, either shared only with their left, respectively right, neighbor. If most group members are discrimination averse and conditionally cooperating with their neighbors, this implies intra- as well as inter personal spillovers which link all neighbors. Investigating individual adaptations in one’s two games with differing freeriding incentives confirms, through behavioral spillovers, that both individual contributions anchor on the local public good with the smaller free-riding incentive. Therefore asymmetry in gaining from local public goods allows to establish a higher level of voluntary cooperation

Partial Reconstruction of the Ergot Alkaloid Pathway by Heterologous Gene Expression in Aspergillus nidulans

Ergot alkaloids are pharmaceutically and agriculturally important secondary metabolites produced by several species of fungi. Ergot alkaloid pathways vary among different fungal lineages, but the pathway intermediate chanoclavine-I is evolutionarily conserved among ergot alkaloid producers. At least four genes, dmaW, easF, easE, and easC, are necessary for pathway steps prior to chanoclavine-I; however, the sufficiency of these genes for chanoclavine-I synthesis has not been established. A fragment of genomic DNA containing dmaW, easF, easE, and easC was amplified from the human-pathogenic, ergot alkaloid-producing fungus Aspergillus fumigatus and transformed into Aspergillus nidulans, a model fungus that does not contain any of the ergot alkaloid synthesis genes. HPLC and LC-MS analyses demonstrated that transformed A. nidulans strains produced chanoclavine-I and an earlier pathway intermediate. Aspergillus nidulans transformants containing dmaW, easF, and either easE or easC did not produce chanoclavine-I but did produce an early pathway intermediate and, in the case of the easC transformant, an additional ergot alkaloid-like compound. We conclude that dmaW, easF, easE, and easC are sufficient for the synthesis of chanoclavine-I in A. nidulans and expressing ergot alkaloid pathway genes in A. nidulans provides a novel approach to understanding the early steps in ergot alkaloid synthesis

Chromosome-End Knockoff Strategy to Reshape Alkaloid Profiles of a Fungal Endophyte

Molecular genetic techniques to precisely eliminate genes in asexual filamentous fungi require the introduction of a marker gene into the target genome. We developed a novel strategy to eliminate genes or gene clusters located in subterminal regions of chromosomes, and then eliminate the marker gene and vector backbone used in the transformation procedure. Because many toxin gene clusters are subterminal, this method is particularly suited to generating nontoxic fungal strains. We tested this technique on Epichloë coenophiala, a seed-transmissible symbiotic fungus (endophyte) of the important forage grass, tall fescue (Lolium arundinaceum). The endophyte is necessary for maximal productivity and sustainability of this grass but can produce ergot alkaloids such as ergovaline, which are toxic to livestock. The genome sequence of E. coenophiala strain e19 revealed two paralogous ergot alkaloid biosynthesis gene clusters, designated EAS1 and EAS2. EAS1 was apparently subterminal, and the lpsB copy in EAS2 had a frame-shift mutation. We designed a vector with a fungal-active hygromycin phosphotransferase gene (hph), an lpsA1 gene fragment for homologous recombination at the telomere-distal end of EAS1, and a telomere repeat array positioned to drive spontaneous loss of hph and other vector sequences, and to stabilize the new chromosome end. We transformed E. coenophiala with this vector, then selected “knockoff” endophyte strains, confirmed by genome sequencing to lack 162 kb of a chromosome end including most of EAS1, and also to lack vector sequences. These ∆EAS1 knockoff strains produced no detectable ergovaline, whereas complementation with functional lpsB restored ergovaline production

Enhanced Production of Runaway Electrons during a Disruptive Termination of Discharges Heated with Lower Hybrid Power in the Frascati Tokamak Upgrade

4 pages, 4 figures.-- PACS nrs.: 52.55.Fa, 52.35.Py, 52.50.Sw, 52.55.Pi.We report on the observation of a large production of runaway electrons during a disruptive termination of discharges heated with lower-hybrid waves at the Frascati Tokamak Upgrade. The runaway current plateaus, which can carry up to 80% of the predisruptive current, are observed more often than in normal Ohmic disruptions. The largest runaway currents correspond to the slowest plasma current decay rates. This trend is opposite to what is observed in most tokamaks. We attribute this anomalous behavior to the acceleration of the preexistent wave-resonant suprathermal electrons during the disruption decay phase. These results could be relevant for the operation of the ITER tokamak whenever a sizeable amount of lower-hybrid power is made available.Research supported in part by Spanish DGES Project No. FTN2003-04587. This work was also supported by the Euratom Communities under the contract of association between EURATOM and ENEA.Publicad

Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letter

Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe2 heterostructures

Among transition-metal dichalcogenides, mono and few-layers thick VSe2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe/VSe2 heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe2 do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe/VSe2 interface and its relation with interfacial magnetic coupling