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Volume 464 Issue 7290, 8 April 2010

The availability of miniature 'backpack-style' GPS loggers means it is now possible to track individual birds in a flock, and to answer the long-standing question of how birds fly in formation. Experiments on flocks of homing pigeons reveal that a bird's position in the flight depends on its place in a well-defined social hierarchy - an airborne 'pecking order'. The cover composite represents the birds' actual trajectories coloured according to leadership rank: those near the red end of the spectrum at the top of the hierarchy and those near the violet at the bottom. Cover graphics: Mate Nagy/images: Simon Walker.

Postdoc Journal

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Editorial

  • Government influence favouring enhanced openness is rightly diversifying practices in science publishing.

    Editorial
  • Much of what people know about science is learned informally. Education policy-makers should take note.

    Editorial
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Research Highlights

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Journal Club

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News

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Correction

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News Feature

  • The explosion in commercial archaeology has brought a flood of information. The problem now is figuring out how to find and use this unpublished literature, reports Matt Ford.

    • Matt Ford
    News Feature
  • Almost every human protein has segments that can form amyloids, the sticky aggregates known for their role in disease. Yet cells have evolved some elaborate defences, finds Jim Schnabel.

    • Jim Schnabel
    News Feature
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Correspondence

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Opinion

  • China and South Korea have invested heavily in environmental stimulus projects. Other G20 countries need to deliver on their sustainability promises to save both the planet and the economy, says Edward Barbier.

    • Edward Barbier
    Opinion
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Correction

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Books & Arts

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Correction

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News & Views

  • Without the trillions of microbes that inhabit our gut, we can't fully benefit from the components of our diet. But cultural differences in diet may, in part, dictate what food our gut microbiota can digest.

    • Justin L. Sonnenburg
    News & Views
  • The sequencing of ancient DNA is generating dramatic results. The sequence from a bone fragment has revealed the existence of an unknown type of extinct human ancestor that lived in Asia 40,000 years ago.

    • Terence A. Brown

    Collection:

    News & Views
  • Microfluidic devices have many applications in chemistry and biology, but practical hitches associated with their use are often overlooked. One such device that optimizes catalysts tackles these issues head-on.

    • Robert C. R. Wootton
    • Andrew J. deMello
    News & Views
  • According to an innovative exercise in 'morphospace analysis', modern fish owe their stunning diversity in part to an ecological cleaning of the slate by the mass extinction at the end of the Cretaceous.

    • Michael Alfaro
    • Francesco Santini
    News & Views
  • For more than a century, the binary star system ε Aurigae has been a riddle, wrapped in a mystery, inside an enigma. But no more — the system's previously inferred but unseen disk of dust has been detected.

    • Edward Guinan
    News & Views
  • Most emissions of nitrous oxide from semi-arid, temperate grasslands usually occur during the spring thaw. The effects that grazing has on plant litter and snow cover dramatically reduce these seasonal emissions.

    • Stephen J. Del Grosso
    News & Views
  • Some cancer cells that become tolerant to a drug remain resistant even after its withdrawal, yet these cells eventually become sensitive to the drug again. The underlying molecular mechanism is unusual.

    • Paul Workman
    • Jon Travers
    News & Views
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Article

  • A quantum spin liquid is a hypothetical system of spins (such as those carried by electrons), the orientations of which continue to fluctuate even at absolute zero. Theoretical and experimental evidence for the existence of such states at the microscopic level is elusive, but these authors have modelled correlated electrons arranged on a honeycomb lattice (such as in graphene), and identified the conditions under which a microscopic quantum spin liquid would be realized in two dimensions.

    • Z. Y. Meng
    • T. C. Lang
    • A. Muramatsu
    Article
  • A new mouse model is developed in which haematopoietic malignancies are caused by genetic changes in the microenvironment of blood cells. Deletion in bone progenitor cells of Dicer1, a gene involved in microRNA processing, leads to a myelodysplastic syndrome-like phenotype which can progress to leukaemia. Deregulation of Sbds, which is mutated in human Schwachman–Bodian–Diamond syndrome, may be involved in this process.

    • Marc H. G. P. Raaijmakers
    • Siddhartha Mukherjee
    • David. T. Scadden
    Article
  • Zscan4 is shown to be involved in maintaining telomeres in embryonic stem (ES) cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once within nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis–specific homologous recombination genes. Knocking down Zscan4 shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages.

    • Michal Zalzman
    • Geppino Falco
    • Minoru S. H. Ko
    Article
  • Here, multivesicular body (MVB) biogenesis is reconstituted using giant unilamellar vesicles and all of the ESCRT complexes. ESCRT-0 is required for clustering of cargo proteins, whereas ESCRT-I and -II in combination deform the membrane into buds, in which cargo is confined. ESCRT-III subunits localize to the bud neck and are required for scission of the membrane to form intraluminal vesicles. These results explain how ESCRT complexes sequester cargo proteins into MVBs.

    • Thomas Wollert
    • James H. Hurley
    Article
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Letter

  • ε Aurigae is a bright, eclipsing binary star system but the cause of each 18-month-long eclipse has been unknown for nearly 190 years, because the companion was, until recently, undetectable. The preferred explanation has been a tilted disk of opaque material and here the authors report interferometric images that do indeed show an opaque disk of very low mass, tilted as expected, crossing the disk of the F star.

    • Brian Kloppenborg
    • Robert Stencel
    • Sean M. Carroll
    Letter
  • A challenge in the semiconductor industry is to create integrated circuits that use new physical state variables — other than charge or voltage — to offer memory and logic functions. Memristive devices, which combine the electrical properties of a memory element and a resistor, use resistance instead, and here such 'memristors' are shown to perform logic operations as well.

    • Julien Borghetti
    • Gregory S. Snider
    • R. Stanley Williams
    Letter
  • The strength of conventional metals is determined by the interaction of dislocations with obstacles such as grain boundaries. Molecular dynamics simulations reveal that the strength of ultrafine-grained copper containing twin boundaries can be controlled by a dislocation nucleation mechanism activated below a critical twin thickness. Below this thickness the material becomes softer. The smaller the grains, the smaller the critical twin boundary spacing, and the higher the metal's maximum strength.

    • Xiaoyan Li
    • Yujie Wei
    • Huajian Gao
    Letter
  • To examine the effect of increased livestock numbers on nitrous oxide emissions the authors report year-round nitrous oxide flux measurements at ten steppe grassland sites in Inner Mongolia. They find that nitrous oxide emission is much higher during spring thaw and is highest in ungrazed steppe, decreasing with increasing stocking rate, which suggests that grazing decreases rather than increases nitrous oxide emissions.

    • Benjamin Wolf
    • Xunhua Zheng
    • Klaus Butterbach-Bahl
    Letter
  • Here a method of seismic wave imaging known as 'ambient noise' tomography is used to generate high-resolution images of seismic wave speeds in the crust and uppermost mantle. The observations reveal strong and uniform anisotropy — where waves travel through rock at different speeds depending on direction — in the deep crust in areas of the western United States that have undergone significant extension during the past 65 million years.

    • M. P. Moschetti
    • M. H. Ritzwoller
    • Y. Yang
    Letter
  • How large groups of animals move in a coordinated way has defied complete explanation. Inability to track each member of a flock has hampered understanding of the behavioural rules governing flocks of birds. This, however, has been achieved for a small group of homing pigeons fitted with lightweight GPS loggers. A well–defined hierarchy is revealed — the average position of a pigeon within the flock strongly correlates with is position in the social hierarchy (a kind of airborne pecking order).

    • Máté Nagy
    • Zsuzsa Ákos
    • Tamás Vicsek
    Letter
  • Ancient mitochondrial DNA from a hominin individual who lived in the mountains of Central Asia between 48,000–30,000 years ago has been sequenced. Comparative genomics suggest that this mitochondrial DNA derives from an out-of-Africa migration distinct from the ones that gave rise to Neanderthals and modern humans. It also seems that this hominin lived in close spatio-temporal proximity to Neanderthals and modern humans.

    • Johannes Krause
    • Qiaomei Fu
    • Svante Pääbo
    Letter Open Access
  • An extensive genome-wide survey of over 48,000 single nucleotide polymorphisms in dogs and their wild progenitor, the grey wolf, was conducted to shed light on the process of dog diversification. The results reveal that much of genome diversity came from Middle Eastern progenitors, combined with interbreeding with local wolf populations, and that recent evolution involved limited genetic variation to create the phenotypic diversity of modern dogs.

    • Bridgett M. vonHoldt
    • John P. Pollinger
    • Robert K. Wayne
    Letter
  • Although explored in the rodent, the relationship between single neuron activity, oscillations and behavioural learning is unknown in humans. Here, successful memory formation in humans was predicted by the coordination of spike timing relative to the local theta oscillation. These data provide a direct connection between the behavioural modulation of oscillations and plasticity within specific circuits.

    • Ueli Rutishauser
    • Ian B. Ross
    • Erin M. Schuman
    Letter
  • One of the roles of the human gut microbiota is to break down nutrients using bacterial enzymes that are lacking from the human genome. It is now shown that the gut microbiota of Japanese, but not American, individuals contains porphyranases, enzymes that digest sulphated polysaccharides which are present in the marine environment only. These findings indicate that diet can select for gene content of the human microbiota.

    • Jan-Hendrik Hehemann
    • Gaëlle Correc
    • Gurvan Michel
    Letter
  • During Arabidopsis embryogenesis, a single cell is specified to become the founder cell of the root meristem — the hypophysis — in response to signals from adjacent cells. Hypophysis specification requires an auxin-responsive transcription factor, MONOPTEROS (MP), which promotes transport of auxin from the embryo to the hypophysis precursor. Here, MP target genes are identified and the means by which they mediate root formation is shown.

    • Alexandra Schlereth
    • Barbara Möller
    • Dolf Weijers
    Letter
  • VEGF–B is shown to have an unexpected role in targeting lipids to peripheral tissues. VEGF–B controls endothelial uptake of fatty acids via transcriptional regulation of vascular fatty acid transport proteins. Bioinformatic analyses suggest that the uptake of these lipids is tightly coupled with lipid use by mitochondria. Mice that do not have VEGF–B accumulate less lipids in muscle, heart and brown adipose tissue, and instead shunt them to white adipose tissue.

    • Carolina E. Hagberg
    • Annelie Falkevall
    • Ulf Eriksson
    Letter
  • To study the changes in chromatin structure that accompany zygotic genome activation and pluripotency during the maternal–zygotic transition (MZT), the genomic locations of histone H3 modifications and RNA polymerase II have been mapped during this transition in zebrafish embryos. H3 lysine 27 trimethylation and H3 lysine 4 trimethylation are only detected after MZT; evidence is provided that the bivalent chromatin domains found in cultured embryonic stem cells also exist in embryos.

    • Nadine L. Vastenhouw
    • Yong Zhang
    • Alexander F. Schier
    Letter
  • Endogenous retroviruses (ERVs) are widely dispersed in mammalian genomes, and are silenced in somatic cells by DNA methylation. Here, an ERV silencing pathway independent of DNA methylation is shown to operate in embryonic stem cells. The pathway involves the histone H3K9 methyltransferase ESET and might be important for ERV silencing during the stages in embryogenesis when DNA methylation is reprogrammed.

    • Toshiyuki Matsui
    • Danny Leung
    • Yoichi Shinkai
    Letter
  • In meiotic cells paired homologues are joined by a set of crossovers known as a double Holliday junction (DHJ). Whether DHJs form during mitotic recombination has been unclear, as mitotic cells possess alternative repair pathways that would not require DHJ formation. Here it is demonstrated that mitotic and meiotic cells form similar DHJs, but that the levels in mitotic cells are approximately 10–fold lower, and show a preference for joints between sister chromatids rather than homologues. Consequently, in mitotic cells non–crossover outcomes are favoured.

    • Malgorzata Bzymek
    • Nathaniel H. Thayer
    • Neil Hunter
    Letter
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Corrigendum

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Erratum

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Retraction

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Careers and Recruitment

  • Bangalore and the south may be India's main information-technology centre, but the country's science hub arguably lies within the state of Maharashtra, home to the cities of Mumbai and Pune.

    • K. S. Jayaraman
    Careers and Recruitment
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Careers Q&A

  • Sanjay Singh, chief executive of Gennova Biopharmaceuticals in Pune and former head of malaria-vaccine antigen research for the US National Institutes of Health, talks of Maharashtra's research potential.

    • K. S. Jayaraman
    Careers Q&A
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Prospects

  • The academic track is riddled with risks, yet most still believe it to be the safest career route for the devoted scientist. Andrea Schweitzer suggests a different way.

    • Andrea Schweitzer
    Prospects
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Futures

  • Total recall.

    • Steve Longworth
    Futures
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