This Week in Science

Science  12 Sep 2014:
Vol. 345, Issue 6202, pp. 1306
  1. Viral Evolution

    Evolution of Ebola virus over time

    1. Laura M. Zahn

    Whole-genome sequencing of Ebola

    PHOTO: NIAID

    The high rate of mortality in the current Ebola epidemic has made it difficult for researchers to collect samples of the virus and study its evolution. Gire et al. describe Ebola epidemiology on the basis of 99 whole-genome sequences, including samples from 78 affected individuals. The authors analyzed changes in the viral sequence and conclude that the current outbreak probably resulted from the spread of the virus from central Africa in the past decade. The outbreak started from a single transmission event from an unknown animal reservoir into the human population. Two viral lineages from Guinea then spread from person to person into Sierra Leone.

    Science, this issue p. 1369

  2. Planetary Dynamics

    Orbits don't forget their chaotic pasts

    1. Margaret M. Moerchen

    Many exoplanets orbit in planes that don't correspond to their star's spin axis. This phenomenon may be the fossil record of a dynamical history. Storch et al. demonstrate in simulations that the evolution of a star's spin is key in determining how its planets' orbits are eventually oriented. A binary companion body can drive a hot Jupiter to migrate inward, which induces chaotic behavior in the stellar spin axis and feedback down the line. If we can accurately replicate the statistics observed in planetary surveys, we may understand better how planets form.

    Science, this issue p. 1317

  3. Water Splitting

    Scheduling hydrogen release from water

    1. Jake Yeston

    Photosynthesis splits water to provide protons and electrons for plant growth; oxygen is a by-product. When chemists split water, they're also more interested in making fuel, and the simplest product is hydrogen (a combination of protons and electrons). One challenge is keeping the reactive hydrogen and oxygen product streams separate. Rausch et al. present a scheme that captures the protons and electrons in a molecular cluster of silico-tungstic acid. Later, they expose the cluster to platinum, coaxing the acid into releasing hydrogen. Eliminating the mixing risk increases the potential for household use.

    Science, this issue p. 1326

  4. Physiology

    Regulating nitric oxide production

    1. Wei Wong

    Blood vessels relax and enable increased blood flow when the enzyme eNOS produces nitric oxide (NO) in the endothelial cells lining the vessels. The activity of eNOS varies with modifications to specific sites in the enzyme, such as S-sulfhydration, a process that is triggered by the gas hydrogen sulfide (H2S). Altaany et al. found that S-sulfhydration of eNOS increased its activity by affecting other modifications to the enzyme. Endothelial cells from mice that could not produce H2S also produced less NO than those from normal mice. Enhancing the S-sulfhydration of eNOS may be an effective strategy to increase blood flow in patients.

    Sci. Signal. 7, ra87 (2014).

  5. Low-Density Materials

    Compressive, ductile ceramic nanolattices

    1. Marc S. Lavine

    A compressible ceramic lattice

    PHOTO: MEZA ET AL.

    Ceramics are strong and stiff, but their limited ability to stretch like putty or steels makes them unsuitable for many engineering applications. Meza et al. constructed ceramic nanolattices from aluminum oxide, in which the beams are designed to stretch rather than bend. A key parameter in lattice design is the ratio of the wall thickness to the beam radius. When that ratio is small enough, compressing the beams does not break them. That way, the nanolattices can be highly compressed and recover to something close to their original shape when the stress is removed.

    Science, this issue p. 1322

  6. Social Psychology

    Moral homeostasis in real life vs. the lab

    1. Gilbert Chin

    Individuals who witnessed a moral deed are more likely than nonwitnesses to perform a moral deed themselves and are also more likely to allow themselves to act immorally. Hofmann et al. asked smartphone users to report their encounters with morality (see the Perspective by Graham). Most moral judgment experiments are lab-based and don't allow for conclusions based on what people experience in their daily lives. This field experiment revealed that people experience moral events frequently in daily life. A respondent's ideology influenced the kind of event reported and the frequency, which is consistent with moral foundations theory.

    Science, this issue p. 1340; see also p. 1242

  7. Microbial Ecology

    Patterns of life in the ocean wave

    1. Caroline Ash

    The open ocean is not uniform. The seas teem with unseen life that has evolved distinctive patterns of species distribution, much as the land-bound world contains a spectrum of biological provinces. Taking data from genome studies, Hellweger et al. devised a model showing how marine bacteria diversified throughout the world's oceans into stable geographic provinces independently of natural selection (see the Perspective by Giovannoni and Nemergut). All that is needed to create these distributions are mutations and ocean currents.

    Science, this issue p. 1346; see also p. 1246

  8. Error Memory

    Practice makes perfect — or does it?

    1. Peter Stern

    How do we learn from past errors? Herzfeld et al. found that when we practice a movement, the human brain has a memory for errors that is then used to learn faster in new conditions. This memory for error exists in parallel with motor memory's two traditional forms: memory of actions and memory of external perturbations. They also proposed a mathematical model for learning from errors. This model explained previous experimental results and predicted other major findings that they later verified experimentally.

    Science, this issue p. 1349

  9. Magnetism

    All-optical magnetic state switching

    1. Ian S. Osborne

    Magneto-optical memory storage media, such as hard drives, use magnetic fields to change the magnetization of memory bits, but the process is slow. Light can often reveal information about the magnetization state of a sample, such as its field direction. Lambert et al. show that under the right circumstances, light can also switch the magnetization state of a thin ferromagnetic film. Using light pulses instead of magnetic fields led to ultrafast data memory and data storage.

    Science, this issue p. 1337

  10. Ice Sheets

    Top-down rather than bottom-up change

    1. H. Jesse Smith

    The Larsen-B Ice Shelf in Antarctica collapsed in 2002 because of a regional increase in surface temperature. This finding, reported by Rebesco et al., will surprise many who supposed that the shelf's disintegration probably occurred because of thinning of the ice shelf and the resulting loss of support by the sea floor beneath it. The authors mapped the sea floor beneath the ice shelf before it fell apart, which revealed that the modern ice sheet grounding line was established around 12,000 years ago and has since remained unchanged. If the ice shelf did not collapse because of thinning from below, then it must have been caused by warming from above.

    Science, this issue p. 1354

  11. Quantum Information

    Manipulating a defect in diamond

    1. Jelena Stajic

    Like magnetic storage in today's classical computers, tiny “magnets” associated with electronic and nuclear states—spins—are promising qubits (quantum bits) for the future. Electronic spins in special defects in diamond called nitrogen-vacancy (NV) centers are one example. Whereas most applications focus on the least energetic (ground) state of an NV center, Bassett et al. explored the properties of the higher-energy (excited) state (see the Perspective by Childress). They used light pulses to bring the system into the excited state and to vary the time it stayed there. In this way, they could both deduce the electronic structure of the excited state and manipulate the ground state spin. Similar methods may be applicable to other quantum information systems.

    Science, this issue p. 1333; see also p. 1247

  12. Making Stripes

    Origin of fish pigment cell for pattern

    1. Beverly A. Purnell

    Zebrafish stripes arise from the interactions of pigment cells: black melanophores, iridescent iridophores, and yellow-orange xanthophores. Melanophores and iridophores develop from nerve-associated stem cells, but the origin of xanthophores is unclear. Two studies now reveal that adult xanthophores originate from xanthophores in embryonic and larval fish, when they proliferate to cover the skin before the arrival of black and silver cells in a striped arrangement. Mahalwar et al. show that xanthophores change their final shape and color depending on their location. In black cells, xanthophores appear faint and stellate, but in silver cells, they are bright and compact. Precise superposition creates the blue and golden colors. McMenamin et al. observe the loss of pigment in embryonic xanthophores and the later reappearance in the adult. They show that redifferentiation depends on the thyroid hormone that also limits melanophore population expansion.

    Science, this issue p. 1362 and p. 1358

    PHOTO: LARISSA B. PATTERSON AND DAVID M. PARICHY
  13. Black Hole Physics

    Sheltered black hole seeds grow faster

    1. Margaret M. Moerchen

    Astrophysicists have struggled to find a way to grow supermassive black holes within the first billion years of the universe, in the first 6% of its current age. These objects power the extremely bright and distant quasars whose light from that era has finally reached us. To grow a black hole so massive so quickly seemed to violate the expected balance of both radiation pressure and angular momentum. Alexander and Natarajan report that the predicted accretion rate can be exceeded with the help of a protective gas cloud at the heart of a star cluster. There, the radiation from accretion is reverted back onto the black hole, enabling a phase of supraexponential growth for a brief 10 million years.

    Science, this issue p. 1330

  14. Mucosal Immunology

    Immune cells and bugs make a sugary coat

    1. Kristen L. Mueller

    Epithelial cells line the intestinal tract and help to keep the peace between our immune system and our trillions of gut microbes. Such peacekeeping requires glycosylated proteins (proteins with attached carbohydrate chains) present on the epithelial cell surface, but how glycosylation occurs is unclear. Goto et al. find that fucosylation (a type of glycosylation) of gut epithelial cells in mice requires gut microbes (see the Perspective by Hooper). This process also requires innate lymphoid cells there, which produce the cytokines interleukin-22 and lymphotoxin, presumably in response to microbial signals. These cytokines signal epithelial cells to add fucose to membrane proteins, which allows the détente between microbes and immune cells to continue.

    Science, this issue 10.1126/science.1254009; see also p. 1248

  15. Origin of Notochord

    Origin of the spine lies in a worm

    1. Beverly A. Purnell

    The notochord, the developmental backbone precursor, defines chordates—the group of animals to which humans belong. The origin of the notochord remains mysterious. Lauri et al. report the identification of a longitudinal muscle in an annelid worm that displays striking similarities to the notochord regarding position, developmental origin, and expression profile. Similar muscles, termed axochords, are found in various invertebrate phyla. These data suggest that the last common ancestor of bilaterians already possessed contractile midline tissue that, via stiffening, developed into a cartilaginous rod in the chordate line.

    Science, this issue p. 1365

  16. Immunogenetics

    Response to pathogens is in the genes

    1. Laura M. Zahn

    T cells are important in mounting immune responses to a host of pathogens, and they have also been implicated in autoimmune disease. By examining the variability in gene expression in stimulated T cells over time from a multi-ethnic cohort of healthy humans, Ye et al. identified specific genetic polymorphisms that explain differences among individuals in response to pathogens. Furthermore, a candidate gene approach led to the identification of a single-nucleotide polymorphism that controls the response of the autoimmune-associated IL2RA gene. This study helps us understand the degree to which immune responses are driven by the environment or by an individual's physiological or genetic factors.

    Science, this issue p. 10.1126/science.1254665

  17. Biodiversity Loss

    Costa Rican birds of a feather lost together

    1. Andrew M. Sugden

    Evolutionary history is lost when land is converted for farming, and recently evolved species may cope better with changing land use. Frishkoff et al. compared bird diversity over 12 years in three different kinds of landscape in tropical Central America. They mapped their data onto the bird evolutionary tree and found that more evolutionary branches were lost in intensive agricultural landscapes than in mixed landscapes. In turn, mixed landscapes lost more evolutionary branches than forest reserves. This is not just because of species loss; in fact, mixed agricultural landscapes contained similar numbers of species to those in forest reserves. Evolutionary history is lost because the more evolutionarily distinct species—those with fewer extant relatives and a longer evolutionary history—are more likely to become extinct in agricultural land.

    Science, this issue p. 1343

  18. Photoacclimation

    Making sure leftover light gets in

    1. Caroline Ash

    Bacteria that harvest sunlight through photosynthesis are everywhere and are vital for absorbing carbon dioxide. Like plants in a jungle, these cells have to compete for access to light. Gan et al. found that one species of such cyanobacteria, Leptolyngbya, survives on the scraps of leftover light that other photosynthetic cells can't use. When the light is crowded out by competing organisms, Leptolyngbya changes the pathways in its cells that make the light-harvesting molecules and remodels them into structures that can use redder light at longer wavelengths that is unused by other cells.

    Science, this issue p. 1312