This Week in Science

Science  28 Aug 2015:
Vol. 349, Issue 6251, pp. 939
  1. Sexual Selection

    A third option leads to poor mates

    1. Sacha Vignieri

    Túngara frogs are subject to a “decoy” effect when choosing potential mates

    PHOTO: © DANITA DELIMONT/ALAMY;

    A “decoy” effect decreases rational decision-making in humans. Irrational decisions in this case are a result of a choice between two options being affected by the introduction of a suboptimal third choice. Lea and Ryan show that tungara frogs are also subject to a decoy effect, choosing a male with a less appealing call when presented with a third, inferior calling male. These results suggest that the choice of mates by animals may be context dependent. It appears that rational choice may not always drive sexual selection.

    Science, this issue p. 964

  2. Quantum Mechanics

    Manipulation of a quantum squeeze

    1. Ian S. Osborne

    The uncertainty principle of quantum mechanics dictates that even when a system is cooled to its ground state, there are still fluctuations. This zero-point motion is unavoidable but can be manipulated. Wollman et al. demonstrate such manipulation with the motion of a micrometer-sized mechanical system. By driving up the fluctuations in one of the variables of the system, they are able to squeeze the other related variable below the expected zero-point limit. Quantum squeezing will be important for realizing ultrasensitive sensors and detectors.

    Science, this issue p. 952

  3. Topological Matter

    Magnetizing a topological insulator

    1. Jelena Stajic

    Edge current (blue) flows at the boundaries of magnetic domains on a topological insulator

    PHOTO: SLAC NATIONAL ACCELERATOR LABORATORY

    Inducing magnetism in a topological insulator can lead to exotic effects. The usual experimental route is to introduce magnetic dopants into the material, but that approach is intricate and creates unwanted disorder. Wang et al. used a simpler technique: They fabricated a bilayer consisting of Bi2Se3, a topological insulator, and EuS, a magnet. The physical proximity of EuS induced magnetism on the surface of Bi2Se3. This approach allowed for the creation of magnetic domains at will and the detection of characteristic current flowing along the domains' edges.

    Science, this issue p. 948

  4. Synthetic Biology

    Engineering cell population behavior

    1. L. Bryan Ray

    Attaining the full promise of synthetic biology will require designing population-level behaviors of multiple interacting cell types. As a start, Chen et al. engineered two strains of the bacterium Escherichia coli to produce signaling molecules that regulate transcription in the complementary strain (see the Perspective by Teague and Weiss). The signaling circuit was successfully designed to produce feedback loops that produce synchronous oscillations in transcription between the two strains. A mathematical model helped determine how to modulate the oscillations and control their robustness to perturbations.

    Science, this issue p. 986; see also p. 924

  5. Nanoparticles

    Crystal nuclei beaten to the punch

    1. Phil Szuromi

    Amorphous nanoparticles often dissolve more rapidly than their crystalline counterparts, which can be useful in applications such as drug delivery. Amstad et al. made amorphous nanoparticles from organic and inorganic compounds—even table salt—using droplets of dissolved compounds created with a microfluidic nebulator. The solvent evaporates fast enough that nanoparticles form before crystal nuclei can develop. The small particle size inhibits crystallization for periods of months

    Science, this issue p. 956

  6. Fungal Symbionts

    Cosmopolitan plant root symbionts

    1. Caroline Ash

    The aboveground lives of plants are only sustainable because of the symbiotic soil fungi that encase their roots. These fungi swap nutrients with plants, defend them from attack, and help them withstand abrupt environmental changes. Out of necessity, fungal symbionts in the soil would appear to be restricted and local to certain plant species. Davison et al., however, discovered that some taxa are globally distributed. How these underground fungi have dispersed so widely remains a mystery; perhaps human farmers have had something to do with it.

    Science, this issue p. 970

  7. Mucosal Immunology

    Gut microbes make T cells keep the peace

    1. Kristen L. Mueller

    Our guts harbor trillions of microbial inhabitants, some of which regulate the types of immune cells that are present in the gut. For instance, Clostridium species of bacteria induce a type of T cell that promotes tolerance between the host and its microbial contents. Ohnmacht et al. and Sefik et al. characterized a population of gut regulatory T cells in mice, which required gut microbiota to survive. Multiple bacterial species of the microbiota could induce transcription factor–expressing regulatory T cells that helped maintain immune homeostasis. Mice engineered to lack these transcription factors exhibited enhanced susceptibility to colonic inflammation and had elevated amounts of proinflammatory molecules associated with allergies (see the Perspective by Hegazy and Powrie).

    Science, this issue pp. 989 and 993

  8. Climate Science

    How to melt the Antarctic Ice Sheet

    1. Kip Hodges

    Computer simulations suggest that it is possible to entirely eliminate the Antarctic Ice Sheet, Earth's largest reservoir of fresh water. Winkelmann et al. explored the fate of the Antarctic Ice Sheet over 10,000 years into the future, showing that global warming related to massive carbon emissions would not only lead to complete melting of the ice sheet, but a global sea-level rise of more than 50 m. The global demand for energy derived from fossil fuels, if left unchecked, is likely to have devastating impacts on coastal populations and polar ecosystems.

    Sci. Adv. 10.1126/sciadv.1500589 (2015).

  9. Cancer

    Not just another Notch for treatment

    1. Yevgeniya Nusinovich

    Pulmonary neuroendocrine tumors, such as small-cell lung cancer, are among the most difficult cancers to treat. The healing effects of standard chemotherapy regimens are only transient, and the tumors typically acquire drug resistance quickly. Saunders et al. discovered that DLL3, a ligand in the Notch signaling pathway, is associated with the neuroendocrine cancer phenotype. An antibody conjugated to a cytotoxic drug targeted DLL3, which proved to be much more effective than standard chemotherapy for treating patient-derived tumor xenografts. Unlike chemotherapy, the anti-DLL3 treatment was particularly effective against tumor-initiating cells.

    Sci. Transl. Med. 7, 302ra136 (2015).

  10. Colloids

    Learning from the packing of particles

    1. Marc S. Lavine

    Colloidal particles, which consist of clusters of hundreds or thousands of atoms, can still resemble atomic systems. In particular, colloids have been used to study the packing of spheres and the influence of short-range interactions on crystallization and melting. Manoharan reviews these similarities, as well as the cases in which colloidal particles show behavior not seen in atomic systems. For example, the packing of nonspherical objects, where geometry or topology may matter, can give insights into the role of entropy in packing.

    Science, this issue 10.1126/science.1253751

  11. Psychology

    Empirically analyzing empirical evidence

    1. Gilbert Chin

    One of the central goals in any scientific endeavor is to understand causality. Experiments that seek to demonstrate a cause/effect relation most often manipulate the postulated causal factor. Aarts et al. describe the replication of 100 experiments reported in papers published in 2008 in three high-ranking psychology journals. Assessing whether the replication and the original experiment yielded the same result according to several criteria, they find that about one-third to one-half of the original findings were also observed in the replication study.

    Science, this issue 10.1126/science.aac4716

  12. Advanced Imaging

    Adding to the super-resolution arsenal

    1. Stella M. Hurtley

    Structured illumination microscopy (SIM) uses light intensities that are orders of magnitude lower than other super-resolution methods. SIM is also far faster over cellular-sized fields of view. Li et al. used two approaches to improve the resolution of SIM to allow live cell imaging of dynamic cellular processes, including endocytosis and cytoskeleton remodeling. The contrast in performance between SIM and other techniques is due to a few key differences. Defining the practical resolution at the limited signal-to-noise ratios necessary for live cell imaging will require better imaging metrics.

    Science, this issue 10.1126/science.aab3500

  13. Organic Chemistry

    Iron plays matchmaker to pair up olefins

    1. Jake Yeston

    In theory, shining the right wavelength of light onto carbon-carbon double bonds should pair them up into four-membered cyclobutane rings. In practice, however, this route can prove finicky and inefficient, particularly if the necessary wavelength lies deep in the ultraviolet region. Hoyt et al. report an iron catalyst that coaxes a wide variety of simple olefins into such rings without the need for photoexcitation (see the Perspective by Smith and Baran). Systematic optimization of the ligand coordinated to iron effectively eliminated competing pathways to alternative products.

    Science, this issue p. 960; see also p. 925

  14. Life History

    Wing growth drives songbird selection

    1. Sacha Vignieri

    Nestling birds are particularly vulnerable to predation, providing pressure for individuals to grow and leave the nest as quickly as possible. In contrast to temperate songbirds, tropical birds appear to grow more slowly despite high rates of nest predation. Martin shows that overall rates of growth are similar across this latitudinal gradient, but tropical birds become mobile more rapidly due to faster wing growth. This trajectory is facilitated by higher provisioning of fewer offspring, providing an example of how life history responds to divergent selection pressures.

    Science, this issue p. 966

  15. Immunology

    New targets to treat inflammation

    1. John F. Foley

    Some members of the mitogen-activated protein kinase (MAPK) family promote the production of proinflammatory cytokines. As such, these kinases have been targeted for the treatment of inflammatory diseases. Disappointing clinical trials with such drugs, however, have spurred the search for other candidate targets. Wilhelmsen et al. found that MAPK family member ERK5 promoted inflammatory responses to microbial products in human endothelial and immune cells. Inhibitors of ERK5 and its upstream activating kinase reduced systemic inflammation in mice with microbial infections or tissue injury.

    Sci. Signal. 8, ra86 (2015).

  16. Paleontology

    Species diversity in human evolution

    1. Julia Fahrenkamp-Uppenbrink

    Early Homo species were long thought to have evolved from one into the next, culminating in Homo sapiens. In a Perspective, Schwartz and Tattersall highlight recent studies that argue against this linear transformative view. Many studies do not pay enough attention to morphological differences, shoehorning fossils into Homo without properly defining what characterizes the genus or the species within it. Recent research suggests that in the past, Homo was as diverse as other mammals. Acknowledging this diversity will help us better understand how humans evolved.

    Science, this issue p. 931

  17. Neuronal Development

    Axon paths in developing spinal cords

    1. Pamela J. Hines

    Sensory neurons entering the spinal cord take different paths as inputs for pain and proprioception diverge. Working with chick and mouse embryos, Guy et al. found that glycerophospholipids produced by radial glial cells guide these neural fibers, or axons, in the developing spinal cord. A soluble glycerophospholipid released by the cells provided an inhibitory signal to the pain-sensitive axons, keeping them on their own unique pathway.

    Science, this issue p. 974

  18. Heart Disease

    A giant disruption of the heart

    1. Paula A. Kiberstis

    Certain forms of heart failure originate from genetic mutations. Understanding how the culprit mutant proteins alter normal heart function could lead to more effective treatments. One candidate is the giant protein tintin, which is mutated in a subset of patients with dilated cardiomyopathy. Through a combination of patient-derived stem cells, tissue engineering, and gene editing, Hinson et al. found that disease-associated titin mutations disrupt the function of the contractile unit in heart muscle. As a result, the heart does not respond properly to mechanical and other forms of stress.

    Science, this issue p. 982

  19. DNA Recombination

    Matching DNA three bases at a time

    1. Guy Riddihough

    The exchange of genetic information between DNA strands is vital for accurate DNA repair and effective meiotic cell division. Using single-molecule methods and molecular dynamics simulations, Lee et al. show that members of the family of recombinase enzymes responsible for these strand exchange reactions search for and recognize matching DNA strands three bases at a time. A single mismatch abolishes triplet recognition, except for the meiosis-specific recombinase. This enzyme can stabilize a partially mismatched triplet, reflecting the partial homology of the DNA substrates in meiosis.

    Science, this issue p. 977

  20. Solid-State Physics

    Trying to break a stubborn law

    1. Jelena Stajic

    The electrical resistivity of most metals at low temperatures has a characteristic quadratic dependence on temperature. This law is typically ascribed to the scattering of electrons off each other in the presence of a crystal lattice. By measuring the resistivity of SrTiO3 with varying dopant concentrations, Lin et al. test the applicability of the law for metals with low carrier densities. The law persists down to the lowest carrier concentrations, into the regime where the conditions for this behavior were previously thought to break down.

    Science, this issue p. 945