RESEARCH NEWS & VIEWS

50 Years Ago In a written answer in the House of Commons on June 24, the Minister of Technology, Mr. F. Cousins, gave the names of 17 research associations which actively encouraged the use of computers in their respective industries; of 18 research associations which had access to computers on their premises, at universities or at member firms … In another written answer on June 24, Mr. Cousins stated that of 4,064 non-industrial Civil Servants employed by his Department … 1,400 had university degrees or equivalent qualifications in scientific or technological subjects, and about another 1,400 had other scientific or technological qualifications. In a third written answer, Mr Cousins stated … action was in hand … to promote the greater use of technological subjects in television and radio programmes, and to produce special booklets and films for wide distribution among young people. From Nature 10 July 1965

100 Years Ago Among the recent additions to the zoological department at South Kensington are some specimens which are surely destined to possess historical interest for posterity. They consist only of two or three examples of harvest-mice and one housemouse, but they were caught in the trenches in northern France, in that part of the trenches, in fact, occupied by some of our Indian troops. These specimens were collected and presented to the museum by one of the officers of an Indian regiment, whose keenness for his favourite pursuit of natural history allowed him in the intervals of being heavily shelled by the enemy a little relaxation in the way of trapping and skinning any animals for the national museum in London. From Nature 8 July 1915

factors such as spatial scale, logging-practice terminology, disturbance history, hunting pressure, road-building activity, survey intensity and observer experience. Moreover, although the total species list seems extensive, it contains numerous open-country or garden birds (such as the common bulbul Pycnonotus barbatus and the house wren Troglodytes aedon), along with highly conspicuous dispersive taxa (such as parrots and raptors) that may have been observed flying between primary forest patches rather than using logged forests. Inclusion of these categories may obscure the key impacts of logging on populations of forest-dependent species. Similar issues arise with species traits, which Burivalova et al. treat in a simplified form. For example, the authors assigned bird species to one of seven feeding groups (carnivores, insectivores, granivores, nectarivores, frugivores, omnivores or herbivores), but many species belong in multiple categories, and shift between categories over space and time9. Many of these issues can be addressed by expanding or refining the underlying environmental and biological data. Attempts should be made to coordinate and standardize methods across the current spate of long-term initiatives that monitor the effects of selective logging at the local and landscape scale in tropical and temperate forests. In addition, the immediate prospects for improving information on species traits are good, particularly for birds. For instance, comprehensive data sets that describe the diet, habitat use and biometrics of birds are available (see ref. 9, for example). These offer a more nuanced assessment of key attributes such as dietary niche and dispersal ability,

which are relevant to ecosystem processes such as seed dispersal. Incorporating these advances into global models will shed further light on the role of species traits in predicting responses to landuse change, as well as the broader implications for ecosystem function and services10,11. Thus, although Burivalova and colleagues’ efforts may fall short of providing a workable model for sustainable forestry, they point the way to more-sophisticated approaches that can help us to understand the impacts of selective logging on biodiversity, and to develop guidelines for logging practices that balance the needs of people with biodiversity across the tropics and beyond. ■ Joseph A. Tobias is in the Department of Life Sciences, Imperial College London, Silwood Park, Ascot SL5 7PY, UK. e-mail: [email protected] 1. Asner, G. P., Rudel, T. K., Aide, T. M., Defries, R. & Emerson, R. Conserv. Biol. 23, 1386–1395 (2009). 2. Burivalova, Z. et al. Proc. R. Soc. B 282, 20150164 (2015). 3. Bregman, T. P., Şekercioğlu, C. H. & Tobias, J. A. Biol. Conserv. 169, 372–383 (2014). 4. Burivalova, Z., Şekercioğlu, C. H. & Koh, L. P. Curr. Biol. 24, 1–6 (2014). 5. Bicknell, J. E., Struebig, M. J., Edwards, D. P. & Davies, Z. G. Curr. Biol. 24, 1119–1120 (2014). 6. Newbold, T. et al. Proc. R. Soc. B 280, 20122131 (2013). 7. Cleary, D. F. R. et al. Ecol. Appl. 17, 1184–1197 (2007). 8. Hamer, K. C. et al. Biol. Conserv. 188, 82–88 (2015). 9. Wilman, H. et al. Ecology 95, 2027 (2014).
 10. Edwards, D. P., Tobias, J. A., Sheil, D., Meijaard, E. & Laurance, W. F. Trends Ecol. Evol. 29, 511–520 (2014). 11. Ewers, R. M. et al. Nature Commun. 6, 6836 (2015).

ASTR O PH YSI CS

A twist in the tale of γ-ray bursts An unusually long burst of γ-rays zapped Earth in December 2011, lasting 4 hours. The cause of this burst is now proposed to be a peculiar supernova produced by a spinning magnetic neutron star. See Letter p.189 STEPHEN J. SMARTT

T

he story of γ-ray bursts (GRBs) originates in nuclear-weapons monitoring during the cold war, and has been elaborated by subsequent technological developments and scientific detective work. GRBs were discovered by the Vela satellites launched in the late 1960s by the US Air Force. The spacecraft carried sensitive γ-ray detectors to monitor the Soviet Union’s compliance with the Nuclear Test Ban Treaty. No nuclear

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explosions on Earth were seen. Instead, mysterious γ-ray flashes were detected, randomly distributed on the sky1. On page 189 of this issue, Greiner et al.2 present data for a γ-ray flash that suggest an association with a rare type of supernova, similar to an unusual type of stellar explosion that has been recognized only in the past few years3. Nearly 50 years after the end of the cold war, following several space missions dedicated to high-energy astronomy and the harnessing of the most powerful ground-based telescopes,

NEWS & VIEWS RESEARCH

log average luminosity (erg s–1)

we have a clearer picture of the from a rapidly spinning neutron 55 cause of GRBs. They fall into two star9. Neutron stars are formed SGRBs main types, defined simply by the when massive stars collapse, and LGRBs duration of the γ-ray emission. the release of gravitational potenUltra-long GRBs Short GRBs last between about 0.1 tial energy is what causes a normal 50 and 1 second, whereas long GRBs supernova. Neutron stars that are last from about 2 seconds to sevborn with spin periods of less than 111209A eral minutes. The leading model about 10–20 milliseconds have 45 for the production of short GRBs enough energy to power the emisLLGRBs is the merger of a black hole and sion observed by the authors. a neutron star (the dense nucleus The physical mechanism SGRs of a dead massive star), or of a through which rotational energy 40 pair of neutron stars. It is thought can be extracted from a rapidly that these mergers might also spinning neutron star is the emisGalactic sources produce bursts of gravitational sion of radiation from the object’s waves. If these can be recorded by magnetic-field poles (magnetic 35 10–2 1 10 102 103 104 105 106 10–1 future detectors4, it would directly dipole radiation); neutron stars Time (s) validate one of general relativity’s known as magnetars, which tenets and revolutionize physics. have magnetic fields of around Long GRBs are the more Figure 1 | Energetics and duration of γ-ray bursts.  The astrophysical 1014 gauss, can lose10,11 rotational commonly detected, and make phenomena known as γ-ray bursts (GRBs) can be grouped according to energy through this mechanism up about 70% of all the events their luminosity (energy emitted per second) and duration. The lowest-energy on the timescales required to detected by the Swift satellite, phenomena are located in our Galaxy and fall in the shaded region at the explain the authors’ observations. which is dedicated to the discovery bottom of this diagram. Soft γ-ray repeaters (SGRs) are magnetic neutron stars These are extreme, but physically also found in the Milky Way. Low-luminosity GRBs (LLGRBs) are probably of GRBs. The nearest known long a distinct class of extragalactic source. Most of the transient γ-ray flashes plausible, field strengths, and it has GRB was located 40 million par- observed in the sky are the massively energetic short or long GRBs (SGRBs been shown that simple models of secs away, far beyond the local and LGRBs, respectively) located at huge cosmological distances. Their magnetic dipole radiation from group of galaxies that contains the duration ranges from about a fraction of a second to many minutes, magnetars do match the data Milky Way. Relatively close events respectively. The ultra-long GRBs, which include the 4-hour-long GRB from super-luminous supernovae such as this tend to be accom- 111209A discussed by Greiner et al.2, are distinctly different from the quite well12. panied by a particular type of bulk of the population. (Adapted from ref. 5.) Greiner et al. have reached the supernova explosion. The leading secure conclusion that an unuhypothesis for their origin involves the collapse the supernova was emitted. The unusual sual and luminous supernova accompanied of a massive star followed by the formation of a properties of 111209A have been studied the ultra-long GRB 111209A. Their deducblack hole, which is surrounded by a spinning by several groups5,7,8, but Greiner and col- tion stretches the standard physical model disk of gas assembled from the star’s remains. leagues’ deep optical and near-infrared imag- invoked to explain supernova luminosities As material from the disk falls onto the black ing now provide a superior data set suitable to breaking point. Although, in this case too, hole, a jet is launched that accelerates particles for a study of the decaying emission from the the simple magnetar models fit the light curve close to the speed of light. The relativistic jet is explosion. quite well, they contain several free paramfocused in a beam and creates γ-ray emission, After forensically detailed examination of eters that are unconstrained. The magneticfollowed by X-ray and optical radiation. The the GRB’s light curve — which depicts the field strength, spin period and ejecta mass signature of the supernova emerges days later, evolution of its luminosity over time — the can be chosen to fit many shapes of supernova when the emission from the beam, known as authors observed a distinct bump. This bump light curves, not just this one. The models the afterglow, fades rapidly. is the signature of a luminous supernova, cor- have therefore been criticized for being too In the past few years, a rare type of GRB has responding to an explosion that is several flexible. The current analysis cannot conbeen discovered5, known as an ultra-long GRB. times brighter than those typically associ- firm that a magnetar is indeed the powering As the name suggests, the duration of the γ-ray ated with long GRBs. The spectrum of this mechanism of the supernova. Also, the low emission from these can be several thousand supernova is also atypical: it does not show signal-to-noise ratio of the spectrum obtained seconds, but the events seem to be of similar the strong absorption features due to iron does not lend itself to an unambiguous power (energy emitted per second) to the bulk that are prominent in the spectra of events conclusion. of the known long and short GRBs (Fig. 1). The associated with long GRBs. The authors sugThis possible link between super-luminous most likely cause for one of the detected ultra- gest that this spectrum is similar to those of supernovae and GRBs requires further inveslong GRBs — which lasted several days — was a new class of super-luminous supernova dis- tigation, but the quest is hampered by the the tidal (gravitational) disruption of a star as covered in 2011 (ref. 3). Never before has the rarity of both phenomena. Greiner and colit was being consumed by a supermassive black super-luminous class been directly associated leagues’ supernova is only one example, and hole at the centre of a galaxy6. However, there with GRBs. although its light curve and spectrum bear are three recorded GRBs for which neither the Super-luminous supernovae are some some resemblance to those of super-luminous supernova link nor the cause of the tidal dis- 10–100 times brighter than all other types, and supernovae, they are certainly not a perfect ruption could be established5. evolve slowly. Most of them cannot be powered match. It is also intriguing that most GRBs Greiner and colleagues studied the nearest by the radioactive decay of the nickel isotope and super-luminous supernovae have been of these, known as GRB 111209A. Its γ-ray 56Ni, which is the standard physical model found in low-mass dwarf galaxies13. Dwarf emission lasted about 4 hours, and an after- invoked to explain the light emitted from galaxies are likely to have lower abundances of glow detected at optical wavelengths allowed supernovae previously associated with GRBs. elements heavier than helium than the galaxies an accurate determination of its redshift However, the light curves of super-luminous in which the bulk of star formation occurs in (0.677). This tells us that the Universe was supernovae can be quantitatively modelled the Universe14. The similarity of the birthplaces about half its current age when the light from if extra energy is injected into the explosion of GRBs and super-luminous supernovae has 9 J U LY 2 0 1 5 | V O L 5 2 3 | N AT U R E | 1 6 5

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RESEARCH NEWS & VIEWS also suggested13 a link between them. Fifty years after a military mission unexpect­ edly made one of the most remarkable discoveries in high-energy astronomy, we are still struggling to unify the physical models of GRBs. Greiner and co-workers’ findings add another twist to the tale of γ-ray astronomy, which will undoubtedly be followed by others in the next few years, when gravi­ tational-wave detectors start surveying highenergy phenomena in the sky. ■

Stephen J. Smartt is at the Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK. e-mail: [email protected]

6. Burrows, D. N. et al. Nature 476, 421–424 (2011). 7. Gendre, B. et al. Astrophys. J. 766, 30 (2013). 8. Stratta, G. et al. Astrophys. J. 779, 66 (2013). 9. Inserra, C. et al. Astrophys. J. 770, 128 (2013). 10. Kasen, D. & Bildsten, L. Astrophys. J. 717, 245 (2010). 11. Woosley, S. E. Astrophys. J. 719, L204 (2010). 12. Nicholl, M. et al. Mon. Not. R. Astron. Soc. 444, 2096–2113 (2014). 13. Lunnan, R. et al. Astrophys. J. 787, 138 (2014). 14. Chen, T.-W. et al. Astrophys. J. 763, L28 (2013).

1. Klebesadel, R. W., Strong, I. B. & Olson R. A. Astrophys. J. 182, L85 (1973). 2. Greiner, J. et al. Nature 523, 189–192 (2015). 3. Quimby, R. M. et al. Nature 474, 487–489 (2011). 4. Aasi, J. et al. Astrophys. J. Suppl. Ser. 211, 7(2014). 5. Levan, A. J. et al. Astrophys. J. 781, 13 (2014).

P ROT ISTO LO GY

How to build a microbial eye Dissection of the subcellular eye of microorganisms called warnowiid dinoflagellates reveals that this structure is composed of elements of two cellular organelles — the plastid and the mitochondrion. See Letter p.204 T H O M A S A . R I C H A R D S & S U E LY L . G O M E S

T

he ancient Greek physician Galen described the key anatomical features of the eye1, including the retina, lens, cornea and iris. Yet arguably the first true understanding of how the vertebrate eye works came in the early seventeenth century, with mathematician Johannes Kepler’s demonstration that vision occurs as an image projected on to the surface of the retina2. As such, an eye can be defined as a cornea and/or a lens that forms an aperture allowing

light arising from a specific direction to pass on to a sensory surface that processes this signal into a chemical message. But animals were not the only organisms to evolve such systems — analogous structures and biochemical responses exist in cells of several eukaryotic microorganisms (cells that package most of their DNA in a nucleus), allowing these microbes to move in response to light3. On page 204 of this issue, Gavelis et al.4 describe the subcellular features that make up the eye-like structures of warno­wiid dinoflagellates, which in anatomical terms are

a Warnowiid dinoflagellate Plastid network (retinal body)

remarkably similar to vertebrate eyes. Warnowiid dinoflagellates are unicellular plankton that have not been cultured in the laboratory, but that are known to possess a remarkably complex eye-like structure, called the ocelloid. Ocelloids consist of distinct components similar to key parts of vertebrate ‘camera-type’ eyes: a cornea, a lens (called a hyalosome) and a pigmented cup or retinalike structure. Gavelis et al. studied warno­ wiids isolated from marine waters in Japan and Canada, and demonstrate that the anatomy of ocelloids is built from reconfigured plastids and mitochondria (Fig. 1a). These are sub­c ellular compartments seen in many eukaryotic groups that formed in the distant past through the intracellular incorporation of symbiotic bacteria; these organelles usually contain their own genomes and typically function in energy transformation. Specifically, Gavelis and colleagues show that the retinal body of ocelloids arises from a membrane network derived from plastids, and that multiple mitochondria form a cornea-like surface across a lens structure. To test these microscopy-based observations, the authors microdissected the warnowiid

b Chlamydomonas

c Blastocladiella

Nucleus

Lipid vesicles Pigment-rich lipid stacks

Rhodopsin

Lens

Mitochondrial layer (cornea)

Mitochondrion

Figure 1 | Eyes across the tree of life.  a,  The eye-like ocelloids found in unicellular organisms known as warnowiid dinoflagellates have a ‘camera-like’ complexity that resembles that of animal eyes. Gavelis et al.4 show that two of these components in warnowiids have arisen through the reconfiguration of membrane-bound organelles that are usually used for cellular energy transformation: the cornea is formed from a layer of mitochondria and the retinal body is derived from a network of plastids.

b, c, Microorganisms from other branches of the tree of life also contain eye-like structures, although these are anatomically simpler. b, The eyespots of Chlamydomonas algae comprise stacks of pigment-rich lipid molecules, located inside the cell’s plastid, which shades light from one side of lightsensitive rhodopsin proteins. c, The eyespots of Blastocladiella fungi are lipid-filled vesicles close to the cell’s main mitochondrion that are overlaid with rhodopsin proteins.

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Astrophysics: A twist in the tale of γ-ray bursts.

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