Editors' Choice

Science  02 Jun 2017:
Vol. 356, Issue 6341, pp. 919
  1. Animal Communication

    Flexible geckos

    1. Sacha Vignieri

    Tokay geckos alter their calls to be better heard in noisy environments.

    PHOTO: REINHARD DIRSCHERL/ALAMY STOCK PHOTO

    In noisy environments, mammals (including humans) and birds alter the amplitude of their calls, a phenomenon termed the Lombard effect. Brumm and Zollinger tested whether such an effect also occurs in reptiles—specifically, the noisy tokay gecko (Gekko gecko). They found no evidence of amplitude alteration, consistent with its absence in other herpetiles. However, they did find that the lizards modulated their calls to be better heard. The lizards both increased the length of each call type and varied the percentages of call types made, with calling in noisy environments including more loud “geck-o” calls. These results suggest that reptile call flexibility may be higher than thought and suggests that the Lombard effect evolved independently in the bird and mammal lineages.

    Proc. R. Soc. B 10.1098/rspb.2017.0451 (2017).

  2. Plant Evolution

    Arabidopsis out of Africa

    1. Laura M. Zahn

    Arabidopsis thaliana is one of the most studied plant species, and, as a model organism, there is a need to understand its origin and genetic diversity. Durvasula et al. investigated the genetic diversity of Arabidopsis populations from Africa. Contrary to previous hypotheses suggesting that Arabidopsis was introduced recently to Africa, the samples examined did not derive from other continents. Furthermore, Arabidopsis samples examined from sub-Saharan Africa were native and exhibited more variation and ancient diversity than Eurasian samples, suggesting an African origin. Interestingly, the spread of Arabidopsis out of Africa reflects the patterns of genetic diversity seen in other species, including humans, suggesting a common response to the climate among disparate organisms.

    Proc. Natl. Acad. U.S.A. 10.1073/pnas.1616736114 (2017).

  3. Climate Change

    Greening the Antarctic

    1. Andrew M. Sugden

    Antarctic moss banks show increased biological activity consistent with the effects of warming temperatures.

    PHOTO: CARLOS FAIRBAIRN

    The ecological consequences of climate change in the polar regions are becoming increasingly evident. A study in the Antarctic now shows how terrestrial vegetation may be responding to rising temperatures. Amesbury et al. analyzed peat cores spanning the past 150 years from moss banks in the western Antarctic Peninsula. Multiple proxies in the cores—including carbon isotope discrimination, populations of testate amoebae, and the balance of moss growth and decomposition—are indicative of an increase in biological activity over the past 50 years, coinciding with the increasing rate of temperature rise. This activity is likely to lead to further greening in the Antarctic, as is already evident in Arctic landscapes.

    Curr. Biol. 27, 1 (2017).

  4. Immunology

    Orchestrating pathogen defenses in the skin

    1. Stella M. Hurtley

    In the tropics, the single-celled parasite Leishmania major transmitted by biting sandflies causes cutaneous leishmaniasis. This difficult-to-treat infection causes disfiguring lesions, and there is no protective vaccine. Glennie et al. studied a population of skin-resident CD4+ memory T cells that can promote a protective immune response in mice. They found that within 3 days of infection, these cells recruited inflammatory monocytes to the infection site. The monocytes helped to kill the parasites by releasing nitric oxide and reactive oxygen species. The skin-resident T cells were key to protection; circulating T cells could not substitute for their protective role within the skin. Thus, the barrier function of the skin is fortified by the presence of these immunological sentinels.

    PLOS Path. 10.1371/journal.ppat.1006349 (2017).

  5. Near-Field Cosmology

    Milky Way satellites going in circles

    1. Keith T. Smith

    The Large Magellanic Cloud, a dwarf galaxy orbiting our Milky Way Galaxy

    PHOTO: PATRICK J ENDRES - ALASKAPHOTOGRAPHICS/GETTY IMAGES

    The satellite dwarf galaxies that orbit our Milky Way can be used to constrain models of cosmology. Cautun and Frenk examined the 10 Milky Way satellites whose three-dimensional velocities have been measured precisely and compared them with a cosmological simulation. They find that the observed velocities are mostly tangential (i.e., favoring circular orbits), whereas the simulation predicts that radial motions should dominate. That difference is unlikely but not impossible: Only a few percent of simulated galaxies are as extreme as the Milky Way. Either the observations or models are biased, the Milky Way is a statistical outlier, or our understanding of cosmology is incomplete.

    Mon. Not. R. Astron. Soc. 468, L41 (2017).

  6. Physics

    A quantum-well magnetic tunnel junction

    1. Jelena Stajic

    Magnetic tunnel junctions, which are essential to the function of hard drive read heads in modern computers, allow current to pass when the spins of their two ferromagnetic layers are pointing in the same direction. Eisenstein et al. built a magnetic tunnel junction out of much more exotic components: a bilayer of GaAs quantum wells, each hosting a two-dimensional electron gas. A perpendicular external magnetic field caused the electrons in each well to group into the so-called Landau energy levels. When the filling fraction was 5/2 in one layer and 7/2 in the other, the junction acted as a diode, allowing the tunneling of current in essentially only one direction. This suggests that each layer acted like a ferromagnet, with full spin polarization.

    Phys. Rev. Lett. 118, 186801 (2017).

  7. Ocean Oxygen

    Less oxygen in a warmer ocean

    1. H. Jesse Smith

    Climate warming should decrease the concentration of dissolved oxygen (O2) in the surface ocean, for a variety of reasons. This trend, predicted on theoretical grounds and by ocean models, has been difficult to detect within the much greater range of natural variability, though. Ito et al. analyzed existing measurements of O2 in the ocean collected from 1958 to 2015, and they report that a widespread negative O2 trend has begun to emerge. Further work will be needed to understand which mechanisms are responsible for the global and regional trends, however.

    Geophys. Res. Lett. 10.1002/2017GL073613 (2017).