Editors' Choice

Science  03 Jul 2015:
Vol. 349, Issue 6243, pp. 43
  1. Evolution

    Trench warfare keeps cheaters rare

    1. Guy Riddihough

    Many Dictyostelium discoideum band together to form a stalk and fruiting body


    When starving, thousands of normally solitary Dictyostelium discoideum amoebae band together to form a slug, which then differentiates into a stalk and fruiting body. The cells of the stalk die, allowing the cells at the top of the fruiting body to form spores and disperse. “Cheater” amoebae avoid forming the stalk and dying. To determine whether cheating provides amoebae with a selective advantage in nature, Ostrowski et al. studied ∼150 positions in amoebae genomes that influence cheating. The genomes maintained a balanced mixture of sequence variation at many of these positions. This indicates that cheaters remain rare because they are engaged in a form of evolutionary “trench warfare” with cooperator amoebae, which results in a stalemate between the two.

    Curr. Biol. 10.1016/j.cub.2015.04.059 (2015).

  2. Physics

    Probing beyond the Standard Model

    1. Ian S. Osborne

    The Standard Model of physics presents an inventory of the known fundamental particles and how they interact in order to describe the world around us. But observations, such as that of the preponderance of matter over antimatter, suggest that the Standard Model is incomplete. Experiments with large particle colliders and measurements using smaller-scale precision atom-based techniques are under way in attempts to fill in the holes of the picture. Parker et al. describe one such cold atom experiment, the search for an elusive permanent electric dipole moment in a cloud of laser-trapped radium atoms. Their initial results show promise for detecting such an effect, which should then provide constraints on establishing new physics beyond the Standard Model.

    Phys. Rev. Lett. 114, 233002 (2015).

  3. Mineralogy

    The shocking history of the Moon

    1. Brent Grocholski

    A lunar silica grain including stishovite


    The mineral stishovite helps us determine the size of past meteorite impacts, because it forms only at the high pressure and temperature possible only in the most energetic meteorite strikes. Silica also needs to be present for it to form, which helps constrain what type of rock the meteorite hit. This rare mineral was first discovered in Arizona's Meteor Crater in 1962. Now, Kaneko et al. have found a small grain of stishovite in a Moon rock collected by the Apollo 15 mission. A more complete search for stishovite in lunar samples will provide a new path for reconstructing the impact history of the Moon.

    Am. Mineral. 10.2138/am-2015-5290 (2015)

  4. Human Anatomy

    How agriculture shaped our bones

    1. Andrew M. Sugden

    The rise of agriculture fundamentally changed human mobility


    Human mobility declined after the Pleistocene, affecting human health and social organization—but what caused this decline? To find out, Ruff et al. examined skeletal remains from nearly 2000 individuals spanning a 33,000-year period from the Upper Paleolithic to the 20th century. They found that a decrease in the bending strength of leg bones accompanied the shift to an increasingly sedentary lifestyle that occurred in Europe during the Neolithic to Roman eras (approx. 7000 to 2000 years before the present). This implies a decline of mobility as agriculture came to dominate how people produced food. The remains did not reveal any further declines in the past 2000 years, even after agriculture became more mechanized.

    Proc. Natl. Acad. Sci. U.S.A. 112, 7147 (2015).

  5. Cell Signaling

    Protein kinase C shapes calcium signals

    1. L. Bryan Ray

    The activation of hormone receptors on cells causes the concentration of free calcium in the cytoplasm to oscillate. Cells can encode information in the frequency, amplitude, and duration of such calcium oscillations, which may modulate the activation of downstream signaling pathways. Bartlett et al. compared calcium signals generated by hormone receptors or by a simpler mechanism that bypasses these receptors in rat hepatocytes, a type of liver cell. This allowed the authors to isolate the effects of the enzyme protein kinase C (PKC) on calcium oscillations, because PKC is only activated downstream of the receptor. PKC regulated both the shape and propagation rates of calcium waves

    J. Biol. Chem. 10.1074/jbc.M115.657767 (2015).

  6. T Cell Metabolism

    Complementing metabolic demands

    1. Kristen L. Mueller

    For T cells, fighting infections is taxing work. T cells must proliferate and produce inflammatory mediators that help rid the body of infection. Doing so requires that they change their metabolism; for instance, by increasing their glycolytic capacity. How T cells do this at a molecular level, however, remains incompletely understood. Kolev et al. studied how this occurs in human T helper 1 (TH1) cells, which are important for clearing intracellular infections. When activated, TH1 cells produced complement C3b, an ancient innate immune mediator, which signaled in an autocrine manner to drive increases in nutrient uptake, glycolysis, and oxidative phosphorylation. These data highlight how the immune system can repurpose its components for evolutionary advantage.

    Immunity 42, 1033 (2015).

  7. Materials Science

    From solution to a solid bright idea

    1. Marc S. Lavine

    Semiconducting quantum dots are ideal for down-converting light, so that a single blue source can be partly changed into other colors to give an overall white emission. Hanson et al. note that the conversion efficiency seen for quantum dots in solution is rarely matched when they are put into solid-state devices. This is particularly true for the red part of the spectrum, for which the best converters depend on expensive rare earth materials. Using low-cost materials, they grew CdSe/CdS core/shell particles so that the particles were mostly shell material. Conversion efficiencies in solid-state devices approached unity. At high driving currents, thermal quenching was a problem but was partly solved by adding a spacer between the light source and quantum dot layer.

    ACS Appl. Mat. Inter. 10.1021/acsami.5b02818 (2015).