Editors' Choice

Science  01 Nov 2013:
Vol. 342, Issue 6158, pp. 535
  1. Ecology

    Caribbean Coral

    1. Caroline Ash
    CREDIT: © JESSE CANCELMO/ALAMY

    Coral reefs occupy a vanishingly small proportion of the oceans yet are home to 25% of marine diversity, nurture important fisheries, provide vital coastal protection, and offer a variety of economic benefits from tourism and associated activities. Predictions of how well and how rapidly reefs can recover from damage due to extreme weather events or disease are often highly uncertain, largely because of the lack of long-term, systematically collected data. Manfrino et al. established transects and quadrats around Little Cayman Island in the Caribbean, a region that is notorious for the generally degraded state of its reef systems. Half of the coastline of this small island is marine protected area, which includes zones of no-take fisheries. Between 1999 and 2004, thermal stress led to coral bleaching and infectious disease that reduced coral cover by more than 40%, yet 7 years later, the coral cover, the density of juvenile colonies, and the overall size structure of the coral assemblages all had returned to the pre-1999 state. The ability of this reef to recover was attributed to limited human disturbance, its relative isolation, and the recruitment of juvenile herbivorous fish, which help to keep competing seaweeds at bay.

    PLOS ONE 8, e75432 (2013).

  2. Microbiology

    From Drowning to Dried Up

    1. Nicholas S. Wigginton
    CREDIT: © PETE OXFORD/MINDEN PICTURES/CORBIS

    Anthropogenic methane emitted into the atmosphere is a concern because of its behavior as a greenhouse gas. However, naturally abundant anaerobic microorganisms in soils and sediments also produce methane. In lake sediments, this occurs at depths in the sediment column where oxygen is no longer present and when the sediments are constantly submerged in water. To understand how methanogenic microbial communities respond to periods of desiccation and exposure to oxygen, Conrad et al. compared the rates of methanogenesis, gene abundance, and microbial community structure of anoxic sediments from nine oxbow lakes in the Brazilian Amazon region, before and after a cycle of drying and rewetting. In lakes where water was clear or contained a high concentration of organic matter, archaeal and bacterial diversity decreased, but methane production rates increased. If extreme drying events in oxbow lakes become more common as a result of climate change, the balance of microbial methane production relative to consumption this may become unbalanced, and may have unknown consequences for the carbon cycle.

    Environ. Microbiol. 10.1111/1462-2920.12267 (2013).

  3. Genetics

    Double Dealing

    1. Laura M. Zahn

    Many plants are polyploid, that is, they carry an n-fold excess, often two, of entire sets of chromosomes relative to their ancestors. Some species exhibit variation in chromosome number within populations. One such plant is Arabidopsis arenosa, a close relative of the model system plant A. thaliana; however, it is not known how these plants can avoid missegregation after chromosome doubling. Yant et al. examined meiotic chromosomes in natural tetraploid (resulting from a single doubling of chromosome number) and diploid A. arenosa and observed that the number of chiasmata (a measure of recombination) was reduced in the polyploid individuals. Induced polyploids, however, showed cytological abnormalities and significantly reduced fertility, suggesting that diploid A. arenosa are not adapted for the polyploid condition and that polyploids are subject to selection that acts to maintain proper meiosis and gamete formation. Genome-wide scans identified regions of the genome enriched in eight meiosis-related genes, suggesting that the transition to polyploidy resulted in selection for genes that function in ways that mitigate the potentially deleterious consequences.

    Curr. Biol. 23, 10.1016/j.cub.2013.08.059 (2013).

  4. Neuroscience

    Better Together

    1. L. Bryan Ray

    G protein (heterotrimeric guanine nucleotide–binding protein)–coupled receptors (GPCRs) are one of the most abundant and most important families of integral membrane proteins, and evidence continues to accumulate showing that they can function as heterodimers. These have been especially promising findings because GPCRs are common drug targets, and heteromers could offer an additional means of tuning drug specificity. Baba et al. show that in mice, type 1 and type 2 melatonin receptors function together in the retina to produce physiological increases in the sensitivity of photoreceptors to light during the night. Tagged receptors were localized in complexes in the retina, and the loss of one receptor subtype or the other prevented melatonin's effects in the retina. Furthermore, the heteromeric receptors coupled to a signaling pathway distinct from that activated by the monomeric receptors, increasing the efficacy and potency of the receptor complex in the activation of phospholipase C and protein kinase C. An ability to replenish such melatonin signaling could be useful in limiting age-related loss of retinal function, as can occur in macular degeneration.

    Sci. Signal. 6, ra89 (2013).

  5. Neuroscience

    Selective Delivery

    1. Pamela J. Hines
    CREDIT: MARION BARABAN

    In an extremely elongated nerve cell, the nucleus is a considerable distance from the growing tip of the axon. Baraban et al. have used zebrafish embryos to show that some messenger RNAs (mRNAs) manage to find their way to the axon tip and that the machinery that transports them there is selective. The authors focused on zebrafish mRNAs that are orthologous to mRNAs that had previously been identified in axons of neurons cultured from rat, mouse, and frog. Of the three mRNAs studied, the one encoding a tubulin variant was the mRNA most effectively delivered into axons of the optic, cranial, and posterior lateral-line nerves in the developing zebrafish embryo. Transport into axons depended on an intact microtubule system and was discriminatory; some mRNA types were transported with more variability, whereas others were not transported at all. Using a reporter system with a membrane-bound fluorescent protein, the authors narrowed down the element required for transport of the tubulin mRNA to a 37-nucleotide portion of the 3′ untranslated region. This selective delivery of mRNA molecules to the axon could facilitate axon guidance in response to changing developmental conditions.

    J. Neurosci. 33, 15726 (2013).

  6. Physics

    Periodic Ions

    1. Jelena Stajic

    Cold gases of both charged and neutral atoms have been used to simulate more complex quantum systems. Whereas neutral atoms are relatively easy to trap in optical lattices (which mimic the periodic potentials found in solids), ions present a bigger challenge because stray electric fields may cause them to escape the trap. Thus, the typical trapping time of an ion in an optical lattice has been on the order of 10 to 100 µs. Karpa et al. trapped an ion in a combined electrostatic and one-dimensional optical lattice potential and cooled it by manipulating its energy levels with an external magnetic field and by using optical pumping. The ion was cooled to the lowest vibrational level of the lattice potential; similar results were obtained with a three-ion system. By periodically driving an ion and measuring its position, the authors found that it remained localized to a single lattice site for up to 10 ms: four orders of magnitude longer than the vibrational period. With an increase in the number of trapped ions, it is expected that the technique will enable the quantum simulation of many-body systems with long-range interactions.

    Phys. Rev. Lett. 111, 163002 (2013).

  7. Chemistry

    Bacterial Pockets

    1. Marc S. Lavine

    Just like their sometimes human hosts, bacteria need to eat, migrate, communicate, reproduce, and interact with their neighbors. Thus, to study bacterial behavior, it is necessary to create a three-dimensional host environment that allows for these processes to occur—and ideally in a way where one can position different bacteria at will. Connell et al. tackle these challenges using a microscopic three-dimensional printing strategy. Bacteria of interest are trapped by mixing them with a warm solution of gelatin that is then allowed to cool. By including a photoexcitable molecule in the solution, the gel can be selectively cross-linked to form pockets of bacteria that form free-floating, adjacent, or nested communities. Removal of the unreacted gel creates a set of porous channels that can be used for the transportation of food, waste, or signaling molecules. The mechanical properties of the gel can be tuned through the addition of bovine serum albumin, which cross-links with the gelatin. The authors fabricated a range of gels with mixtures of Staphylococcus aureus and Pseudomonas aeruginosa, which often form coinfections in human patients, to determine how bacterial concentration and location affected each of the populations. When a dense shell of P. aeruginosa was fabricated around a core of S. aureus, the former enhanced the survival of the latter when exposed to the antibiotic β-lactam.

    Proc. Natl. Acad. Sci. U.S.A. 110, 10.1073/pnas.1309729110 (2013).

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