The latest news from Nature 25 April 2012
This press release contains:
---Summaries of newsworthy papers:
Astrophysics: Galaxy formation is written in the stars
Geoscience: Determining the drivers of ice-sheet loss
Immunology: Natural defences may boost antibiotic treatments
Correspondence: Scrap bear necessities
Immunology: Scratching out allergy misconceptions
Ecology: Invasive forest species alter growing season
Astrophysics: A Later Heavier Bombardment
Cardiovascular biology: An inflammatory trigger for heart failure
Geoscience: Ironing out iron deposition anomalies
Quantum physics: Scaling up quantum simulation
And finally… Cultivating a better understanding of organic and conventional yields
--- Geographical listing of authors
 Astrophysics: Galaxy formation is written in the stars (pp 485-488; N&V)
Observations of variations in a measure called the stellar initial mass function, which gives clues about the star formation process, could challenge existing galaxy formation models. The findings are published in this week’s Nature.
Much of our knowledge of galaxies comes from analysing radiation from their stars, which is strongly dependent on the mass distribution of a population of stars. This distribution can be described by the stellar initial mass function, which had been considered to be the same in different types of galaxies. However, Michele Cappellari and colleagues report a strong variation of the initial mass function of stars in early-type galaxies, indicating that the stellar initial mass function is not universal.
The authors suggest that models assuming a constant initial mass function need to be revised to explain how stars seem to 'know' what kind of galaxy they will end up inside.
Michele Cappellari (University of Oxford, UK)
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Nate Bastian (Technische Universität München, Garching, Germany) N&V author
 Geoscience: Determining the drivers of ice-sheet loss (pp 502-505)
A survey of Antarctic ice-shelf thinning between 2003 and 2008 reveals loss rates of up to 7 metres per year. The research, which is published in this week’s Nature, provides insights into the causes of this accelerated ice-sheet mass loss. Observed patterns of Antarctic ice-shelf thinning are strongly regional, which enables identification of the major contributing factor to this loss. The authors suggest that the melting is triggered by warm water beneath the ice shelves rather than changes in atmospheric conditions at the surface.
Ice shelves (the portion of ice sheets extending over the ocean) provide a buttressing effect that limits the flow of upstream glaciers and ice streams. Loss of this buttressing effect caused by ice sheet thinning may contribute to rapid loss of ice mass. Hamish Pritchard and colleagues use satellite data to measure changes in Antarctic ice-shelf thickness and identify the cause of ice mass loss. The most dramatic losses are observed on the coast of West Antarctica, where warm waters lie beneath the ice shelves. This melting reduces the buttressing effect of the ice shelves, leading to accelerated mass loss.
The authors’ data indicate that changing winds drive warm waters through deep troughs cutting across the continental shelf. These findings indicate that wind-driven movement of warm water may influence Antarctic ice-sheet loss, and consequently sea-level changes.
Hamish Pritchard (British Antarctic Survey, Cambridge, UK)
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 Immunology: Natural defences may boost antibiotic treatments (pp 524-528)
A method for enhancing antibiotic treatments is described in this week’s Nature. Specific factors produced by mice that regulate their response to infection are shown to work with antibiotics to shorten the time and effects of bacterial infection. These findings imply that targeting host infection-resolving programs could lower antibiotic requirements and may have implications in addressing antibiotic resistance.
Charles Serhan and co-workers identify new infection-resolving factors, known as specialized pro-resolving mediators (SPM), which are directly involved in resolving Escherichia coli infection in mice. These mediators, which are anti-inflammatory lipid derivatives, improve infection-related symptoms, increase clearance of infectious bacteria and increase survival. The authors find that administering antibiotics together with SPMs resulted in accelerated resolution of infection compared with that seen with either SPMs or antibiotics alone. In addition, they show that SPMs enhance antibiotic clearance of the skin-infecting bacterium Staphylococcus aureus.
Bacterial infections such as E. coli are a worldwide health concern, and antibiotic-resistant bacteria have a serious impact on treatment options, increasing health-care costs. The work by Serhan and colleagues illustrates new opportunities to address these problems by using specialized infection-resolving mediators produced by hosts to enhance the effects of antibiotics.
Charles Serhan (Harvard Medical School, Boston, MA, USA)
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Correspondence: Scrap bear necessities (p. 455)
Animal welfare has suddenly become an issue in China, with bear farming in the spotlight. A Correspondence by Qiang Weng and colleagues in this week’s Nature reports on the swell of public opinion against the cruel and widespread practice of extracting bile from live bears.
The demand for rare ingredients for traditional Chinese medicines has long been in conflict with conservation and animal-rights movements outside China. But a recent stock-market move by a Chinese pharmaceutical company to cash in on the bears’ ‘liquid gold’ has fuelled anger internally as well.
The desired component of bear bile can be made in the lab and has been readily available for years, but many customers want the real thing and are prepared to pay handsomely for it.
A 10-year fight to ban bear farming, led by the Animals Asia Foundation, has at last caught on and is backed by government officials, scientists and celebrities such as actor Jackie Chan and former basketball player Yao Ming. Qiang Weng and his co-signatories are calling for legislation through an animal welfare bill.
Qiang Weng (Beijing Forestry University, China)
 Immunology: Scratching out allergy misconceptions (pp 465-472; N&V)
A Perspective article on the origin of allergic responses, published in Nature this week, challenges conventional views that allergy is due to a misdirected immune response. Instead, the authors argue that allergic responses are excessive or exaggerated responses to protect from environmental toxins.
Two types of adaptive immune responses have important roles in protecting mammals from a range of infectious agents, from viruses (type 1) to tapeworms (type 2). Type 2 immunity is also implicated in allergic reactions, and is therefore considered a misdirected immune response to parasites such as worms. However, most allergy-inducing substances bear no obvious similarities to parasites and the response to allergens is far more rapid and severe, sometimes leading to anaphylactic shock. Thus, Ruslan Medzhitov and colleagues contend that type 2 immunity protects against more than just macroparasites.
The authors propose that allergic immunity evolved as a defence mechanism against noxious environmental factors such as venoms, natural toxins and irritants. They note that reactions such as sneezing and itching seem to be used to reduce exposure and promote expulsion of unwanted substances, although these actions can become detrimental when excessive.
Ruslan Medzhitov (Yale University, New Haven, CT, USA)
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David Artis (University of Pennsylvania, Philadelphia, PA, USA) N&V author
Fred Finkelman (Cincinnati Veterans Affairs Medical Center, OH, USA) N&V author
 Ecology: Invasive forest species alter growing season (AOP)
A study of plant species in forests in the Eastern United States shows that invasive forest species seem to have extended growing seasons relative to native species. The findings, published in Nature this week, suggest that the effects of invasive species may be as important as the effects of climate change in determining forest nutrient dynamics.
The timing of various stages in plant life-cycles has a profound effect on nutrient uptake and productivity within ecosystems. Differences have been noted in the timing of transformation of atmospheric carbon into organic molecules in the leaves of native and non-native species. To determine whether these changes are widespread and when they occur, Jason Fridley performed a three-year study of 73 species of shrubs and vines in the Eastern US. He finds that non-native species are extending the autumn growing season by an average of four weeks compared to natives.
No differences between the species in their spring growth patterns were observed, and non-natives species did not seem to be more able to track temperature changes than native species. Fridley concludes that invaders are driving a seasonal redistribution of forest productivity that may rival climate change in its effect on forest processes.
Jason Fridley (Syracuse University, NY, USA)
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 &  Astrophysics: A Later Heavier Bombardment (AOP; N&V)
Two studies investigating the timing, frequency and origin of historic asteroid impacts on the Earth, such as happened during the Late Heavy Bombardment, are published in Nature this week. The Late Heavy Bombardment is a period, thought to have been 4.1 to 3.8 billion years ago, when asteroids and comets pummelled the inner planets of our Solar System.
Impact craters provide the most obvious indication for asteroid impact and are well preserved on the Moon, but disappear quickly on Earth due to tectonic processes and erosion. Brandon Johnson and Jay Melosh determine the properties of asteroids crashing into Earth by looking at layers of debris that are ejected during the impact, known as spherule beds. Their estimates are made on the basis that the thickness of spherule layers are expected to vary according to the size of the asteroid and the speed at which it hits the Earth. This historical record of asteroid impacts indicates that the number of projectiles colliding with Earth was substantially higher 3.5 billion years ago than it is today, with a gradual decline in the number of strikes.
In a separate article, William Bottke and colleagues find that the Late Heavy Bombardment may have taken place over a longer period than previously predicted. The authors propose that most of the late impacting objects came from an extended and now largely extinct extension of the Solar System’s asteroid belt towards Mars, the E belt.
Brandon Johnson (Purdue University, West Lafayette, IN, USA) Author paper 
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William Bottke (Southwest Research Institute, Boulder, CO, USA) Author paper 
Please note this author is travelling.
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Frank Kyte (University of California, Los Angeles, CA, USA) N&V author
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 Cardiovascular biology: An inflammatory trigger for heart failure (AOP)
A possible cause of inflammation implicated in the development of heart failure is reported in Nature. The study demonstrates that mitochondrial DNA that escapes from a degradation pathway in stressed mouse heart cells triggers an inflammatory response, leading to abnormalities in cardiac structure and function and increased risk of death.
Heart cells respond to stress by breaking down damaged components, such as mitochondria (the energy factories of cells that originally derived from bacteria). Kinya Otsu and colleagues show that if mitochondrial DNA escapes from this degradation pathway it triggers inflammation as would bacterial DNA. When the mice are subjected to stress, the mitochondrial DNA activates an inflammatory response that induces heart problems and increases risk of death.
These findings highlight the important role mitochondrial DNA has in inducing and maintaining inflammation in the heart, the authors conclude.
Kinya Otsu (King’s College London, UK)
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 Geoscience: Ironing out iron deposition anomalies (pp 498-501)
Iron formations deposited around 1.88 billion years ago provide a record of changing global ocean conditions during this period, according to a study in Nature this week. These formations are rocks comprising layers of iron-rich and silica-rich minerals. Re-dating of iron formations in Australia shows that they coincide with similar deposits in North America, which indicates that there was a global event responsible for these formations.
Deposits of iron formations mark a time when the oceans were lacking oxygen and were rich in iron; these deposits disappeared following a rise in atmospheric oxygen around 2.32 billion years ago. The sudden re-appearance of these layers in an oxygenated atmospheric environment around 500 million years later was thought to have happened at different times in Australia and North America. However, Birger Rasmussen and colleagues show that these formations were deposited at the same time, 1.88 billion years ago. These findings challenge previous theories that local marine conditions were responsible for these events. The authors suggest that enhanced submarine volcanism and hydrothermal activity caused changes in seawater conditions that favoured the deposition of iron formations, and decoupled atmospheric and seawater redox states.
Birger Rasmussen (Curtin University, Bentley, Australia)
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 Quantum physics: Scaling up quantum simulation (pp 489-492; N&V)
An advance in quantum simulation, which could help scientists understand the properties of complex electronic and magnetic materials, is reported in this week’s Nature. The work represents a step towards simulation of currently intractable problems in quantum magnetism.
Technical challenges have limited quantum simulations so far to systems that are too small to be computationally relevant — just a few tens of quantum bits (qubits). Joseph Britton and colleagues manage to produce a system much larger than achieved in previous experiments. Their triangular crystal lattice of a few hundred beryllium ions held in an electromagnetic trap can be used to simulate tunable antiferromagnetic interactions (in magnetic materials, these arise from correlations among electron spins).
This demonstration, coupled with the high spin-count, excellent quantum control and low technical complexity of the trap, brings within reach the simulation of interesting problems, such as exotic quantum phases.
Joseph Britton (National Institute of Standards and Technology, Boulder, CO, USA)
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Christian Roos (Austrian Academy of Sciences, Innsbruck, Austria) N&V author
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 And finally… Cultivating a better understanding of organic and conventional yields (AOP)
Under certain conditions organic farming systems can nearly match conventional yields, according to an analysis in Nature. Although, overall, organic farming produces a lower yield compared with conventional agriculture, the performance varies substantially according to crop type, growing conditions and management practices.
The question of the merits of organic versus conventional farming has sparked much debate. Whereas conventional farming has a greater environmental impact on the land it uses, organic farming may require greater land use for the same yield. In a meta-analysis comparing the yields of organic and conventional agriculture, Verena Seufert and colleagues find that the difference is contextual. For some combinations of crops, environment and specific practices (such as perennials grown on favourable soils) the difference is small, sometimes only 5% lower than conventional yields.
These findings demonstrate that there are many factors to consider when weighing up the benefits of organic or conventional agriculture. The authors conclude that a variety of farming techniques may be needed to meet rising demands for affordable food while reducing environmental costs.
Verena Seufert (McGill University, Montreal, Canada)
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ALSO IN THIS ISSUE:
 Multiple dynamic representations in the motor cortex during sensorimotor learning (pp 473-478)
 Clonally dominant cardiomyocytes direct heart morphogenesis (pp 479-484; N&V)
 Thermal and electrical transport across a magnetic quantum critical point (pp 493-497)
 NLRP10 is a NOD-like receptor essential to initiate adaptive immunity by dendritic cells (pp 510-513)
 Molecular mechanism of ATP binding and ion channel activation in P2X receptors
GEOGRAPHICAL LISTING OF AUTHORS:
The following list of places refers to the whereabouts of authors on the papers numbered in this release. For example, London: 4 - this means that on paper number four, there will be at least one author affiliated to an institute or company in London. The listing may be for an author's main affiliation, or for a place where they are working temporarily. Please see the PDF of the paper for full details.
East Perth: 9
Saint-Genis Laval: 1
Cambridge: 2, 14
UNITED STATES OF AMERICA
La Jolla: 2
Los Angeles: 14
Boulder: 7, 10
New Haven: 4, 15
District of Columbia
West Lafayette: 6, 7
Iowa City: 15
St. Paul: 11
From North America and Canada
Neda Afsarmanesh, Nature New York
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From Japan, Korea, China, Singapore and Taiwan
Eiji Matsuda, Nature Tokyo
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From the UK
Rebecca Walton, Nature London
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