Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public. http://www.nature.com/nature/current_issue/ Nature Publishing Group en © 2004 Nature Publishing Group Nature 0028-0836 1476-4679 © 2004 Nature Publishing Group permissions@nature.com http://www.nature.com/includes/rj_globnavimages/nature_logo.gif http://www.nature.com/nature/ http://dx.doi.org/10.1038/4311023a The shortages of flu vaccine in the United States this autumn have laid bare some troubling weaknesses in the nation's public-health system. Struggling with the flu doi:10.1038/4311023a Nature 431, 1023 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Editorial 1023 1023 http://dx.doi.org/10.1038/4311023b The message from researchers about the state of European fish stocks is consistent, but its delivery could be improved. Fishing for excuses doi:10.1038/4311023b Nature 431, 1023 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Editorial 1023 1023 http://dx.doi.org/10.1038/4311025a US presidential candidates cover everything from nuclear waste to the flu vaccine. Science shares the limelight as election battle enters final phase Erika Check Geoff Brumfiel doi:10.1038/4311025a Nature 431, 1025 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1025 1025 http://dx.doi.org/10.1038/4311026a $3 million study to test effects of scans on monkeys. Ultrasound scans accused of disrupting brain development Jim Giles doi:10.1038/4311026a Nature 431, 1026 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1026 1026 http://dx.doi.org/10.1038/4311026b Meeting will look at importance of ethnicity in medical research. Geneticists struggle towards consensus on place for ‘race’ Meredith Wadman doi:10.1038/4311026b Nature 431, 1026 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1026 1026 http://dx.doi.org/10.1038/4311027a Study starts to investigate cause of mass extinction 250 million years ago. Comet impact theory faces repeat analysis Rex Dalton doi:10.1038/4311027a Nature 431, 1027 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1027 1027 http://dx.doi.org/10.1038/4311027b New government accused of breaking funding promises. Spain's budget fails basic science, researchers charge Monica Salamone doi:10.1038/4311027b Nature 431, 1027 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1027 1027 http://dx.doi.org/10.1038/4311028a Japan's ‘super-abnormal’ storms bring buckets of data. Deluge of typhoons may aid forecast models David Cyranoski doi:10.1038/4311028a Nature 431, 1028 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1028 1028 http://dx.doi.org/10.1038/4311028b US National Institutes of Health accepts generics into giant drug trial. Generic drugs allowed in global trial of AIDS therapy Erika Check doi:10.1038/4311028b Nature 431, 1028 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1028 1028 http://dx.doi.org/10.1038/4311029a A new human-like species — a dwarfed relative who lived just 18,000 years ago in the company of pygmy elephants and giant lizards — has been discovered in Indonesia.Skeletal remains show that the hominins, nicknamed ‘hobbits’ by some of their discoverers, were only one Little lady of Flores forces rethink of human evolution Rex Dalton doi:10.1038/4311029a Nature 431, 1029 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1029 1029 http://dx.doi.org/10.1038/4311029b Private-public partnership should help hunt for disease genes. Novartis goes public with DNA data in bid to tackle diabetes Jonathan Knight doi:10.1038/4311029b Nature 431, 1029 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News 1029 1029 http://dx.doi.org/10.1038/4311030a Warning system for quakes still on track, say Japanese expertsTokyoAn earthquake of magnitude 6.8 tore up the western coastal region of Niigata in Japan on the weekend of 23 October. The tremor claimed at least 25 lives, and demonstrated its power by throwing News in Brief doi:10.1038/4311030a Nature 431, 1030 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News in Brief 1030 1030 http://dx.doi.org/10.1038/4311032a Earthquake researchers in the United States have long shunned the word ‘prediction’. But, thanks to improved data and a change in public perception, cracks are beginning to appear in their resolve. David Cyranoski tracks the debate. Earthquake prediction: A seismic shift in thinking David Cyranoski doi:10.1038/4311032a Nature 431, 1032 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News Feature 1032 1032 http://dx.doi.org/10.1038/4311035a The gamma rays spat out by dying stars last an instant. Tony Reichhardt reports on the fast-response satellite that hopes to capture them. Astronomy: Bagging bursts, swiftly Tony Reichhardt doi:10.1038/4311035a Nature 431, 1035 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News Feature 1035 1035 http://dx.doi.org/10.1038/4311036a When science is under political assault, keeping a dignified silence is counterproductive. Scientists must conquer reluctance to speak out Stephen Porder Kai M. A. Chan Paul A. T. Higgins doi:10.1038/4311036a Nature 431, 1036 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Correspondence 1036 1036 http://dx.doi.org/10.1038/4311036b SirYour correspondents M. J. Hsu and G. Agoramoorthy (Nature431, 627; 200410.1038/431627c), seem to deny to scientists a right that lawyers, financiers, writers and even movie stars claim for themselves, which is direct involvement in political processes.If this Why leave it to others to speak up about science? Ian Flintoff doi:10.1038/4311036b Nature 431, 1036 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Correspondence 1036 1036 http://dx.doi.org/10.1038/4311036c SirM. J. Hsu and G. Agoramoorthy in Correspondence (Nature431, 627; 200410.1038/431627c) imply that anybody choosing a career in science or education should disenfranchise themselves, and that a Nobel prize in a field other than peace equals a ban Knowledge is a good base to campaign from Kaihsu Tai doi:10.1038/4311036c Nature 431, 1036 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Correspondence 1036 1036 http://dx.doi.org/10.1038/4311037a How Lawrence Bragg and his father used X-rays to solve crystal structures. Driven to diffraction Kenneth C. Holmes doi:10.1038/4311037a Nature 431, 1037 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Books and Arts 1037 1038 http://dx.doi.org/10.1038/4311038a In the winter of 1811–12, three major earthquakes struck an area of the North American mid-continent in rapid succession. According to eye-witnesses, the ground ruptured profoundly in numerous locations, lakes appeared where there had been none, and the mighty Mississippi River flowed backwards. The earthquakes, Shaking up seismology Naomi Oreskes doi:10.1038/4311038a Nature 431, 1038 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Books and Arts 1038 1040 http://dx.doi.org/10.1038/4311039a From art to environment Betty Beaumont's Ocean Landmark is in deep water. Martin Kemp doi:10.1038/4311039a Nature 431, 1039 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Books and Arts 1039 1039 http://dx.doi.org/10.1038/4311040a Extinction is the single irreversible feature that lies at the heart of the biotic crisis overtaking the planet. But it is not the extinction of species that counts most, even though we are in the opening phase of a species extinction spasm to surpass anything Population biology on the wing Norman Myers doi:10.1038/4311040a Nature 431, 1040 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Books and Arts 1040 1040 http://dx.doi.org/10.1038/4311040b In Benno Müller-Hill's review of the book on Adolf Butenandt (Nature431, 246; 2004), it was wrongly claimed that Otmar von Verschuer told colleagues in 1946 of his and Gunter Hillman's involvement in the analysis of blood samples from Auschwitz. In Correction doi:10.1038/4311040b Nature 431, 1040 (2004) Nature 431 7012 Books and Arts 1040 1040 http://dx.doi.org/10.1038/4311041a How failing a PhD led to a strategy for a successful scientific career. A wake-up call Bruce Alberts doi:10.1038/4311041a Nature 431, 1041 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Essay 1041 1041 http://dx.doi.org/10.1038/4311043a We are the only living species of the genus Homo. Given the startling results of a cave excavation in Southeast Asia, it seems that we coexisted with another species until much more recently than had been thought. Palaeoanthropology: Human evolution writ small Marta Mirazón Lahr Robert Foley doi:10.1038/4311043a Nature 431, 1043 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1043 1044 http://dx.doi.org/10.1038/4311044a A famous sixteenth-century supernova, seen by Tycho Brahe, is still a hot topic. The stellar explosion might have been initiated by a companion star — and modern astronomers have at last identified it. Astronomy: Tycho's mystery companion David Branch doi:10.1038/4311044a Nature 431, 1044 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1044 1046 http://dx.doi.org/10.1038/4311045a 100 YEARS AGOIs his letter of last week detailing his most interesting experiments on cross-bred maize, Mr. R. H. Lock makes the following statement:– “I see from the published account of a recent discussion at the Cambridge meeting of the British Association that the 100 and 50 years ago doi:10.1038/4311045a Nature 431, 1045 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1045 1045 http://dx.doi.org/10.1038/4311046a The Red List Index is a new indicator of species' extinction risk. It will make a major contribution in measuring the success of an internationally agreed aim to slow biodiversity loss by 2010. Conservation biology: Biodiversity barometers Thomas Brooks Elizabeth Kennedy doi:10.1038/4311046a Nature 431, 1046 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1046 1047 http://dx.doi.org/10.1038/4311047a An ingeniously constructed record of sunspot activity shows that the current episode is the most intense for several thousand years. But that does not let us off the anthropogenic hook of global warming. Solar physics: Spots from rings Paula J. Reimer doi:10.1038/4311047a Nature 431, 1047 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1047 1048 http://dx.doi.org/10.1038/4311047b Bacteria such as Salmonella typhimurium move by the action of their flagella. Depending on the direction of rotation, flagella either act singly, causing uncoordinated tumbling, or clump together into a single helical propeller for straight-line swimming. The 60-nm-long hook that joins the flagellar filament Molecular motors: Smooth coupling in Salmonella Christopher Surridge doi:10.1038/4311047b Nature 431, 1047 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1047 1047 http://dx.doi.org/10.1038/4311048a How does natural selection affect lifespan? The question has exercised biologists for some years. The latest twist comes from ingenious experiments on tropical fish from different ecological backgrounds. Evolutionary biology: Mortality and lifespan Peter A. Abrams doi:10.1038/4311048a Nature 431, 1048 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1048 1048 http://dx.doi.org/10.1038/4311049a In Yi Zhang's News and Views article “Molecular biology: No exception to reversibility” (Nature431, 637–639; 2004), there were errors in Fig. 1b. In the side chain of citrulline, a double bond should have been shown between NH and Correction doi:10.1038/4311049a Nature 431, 1049 (2004) 2004-10-27 Nature 2004-10-27 431 7012 News and Views 1049 1049 http://dx.doi.org/10.1038/4311051a Neuroscience: Depression and gene expressionProc. Natl Acad. Sci. USA101, 15506–15511 (2004)Major depressive disorder is a serious affliction for all too many people. Using microarray technology, S. J. Evans et al. show that changes in certain gene transcripts could help to Research Highlights doi:10.1038/4311051a Nature 431, 1051 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Research Highlights 1051 1051 http://dx.doi.org/10.1038/4311053a This tree's genetic uniformity may have helped to fell entire European populations.The outbreak of Dutch elm disease in the 1970s ravaged European elm populations, killing more than 25 million trees in Britain alone; the greatest impact was on Ulmus procera, otherwise known as the English elm. Here we use molecular and historical information to show that this elm derives from a single clone that the Romans transported from Italy to the Iberian peninsula, and from there to Britain, for the purpose of supporting and training vines. Its highly efficient vegetative reproduction and its inability to set seeds have preserved this clone unaltered for 2,000 years as the core of the English elm population — and the preponderance of this susceptible variety may have favoured a rapid spread of the disease. Phylogeography: English elm is a 2,000-year-old Roman clone Luis Gil Pablo Fuentes-Utrilla Álvaro Soto M. Teresa Cervera Carmen Collada doi:10.1038/4311053a Nature 431, 1053 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Brief Communications 1053 1053 http://dx.doi.org/10.1038/nature02999 Currently, it is widely accepted that only one hominin genus, Homo, was present in Pleistocene Asia, represented by two species, Homo erectus and Homo sapiens. Both species are characterized by greater brain size, increased body height and smaller teeth relative to Pliocene A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia P. Brown T. Sutikna M. J. Morwood R. P. Soejono Jatmiko E. Wayhu Saptomo Rokus Awe Due doi:10.1038/nature02999 Nature 431, 1055 (2004) Nature 431 7012 Article 1055 1061 http://dx.doi.org/10.1038/nature02997 The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism Fadel A. Samatey Hideyuki Matsunami Katsumi Imada Shigehiro Nagashima Tanvir R. Shaikh Dennis R. Thomas James Z. Chen David J. DeRosier Akio Kitao Keiichi Namba doi:10.1038/nature02997 Nature 431, 1062 (2004) Nature 431 7012 Article 1062 1068 http://dx.doi.org/10.1038/nature03006 The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0–G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova. The binary progenitor of Tycho Brahe's 1572 supernova Pilar Ruiz-Lapuente Fernando Comeron Javier Méndez Ramon Canal Stephen J. Smartt Alexei V. Filippenko Robert L. Kurucz Ryan Chornock Ryan J. Foley Vallery Stanishev Rodrigo Ibata doi:10.1038/nature03006 Nature 431, 1069 (2004) Nature 431 7012 Letter 1069 1072 http://dx.doi.org/10.1038/nature03055 Observations from the gamma-ray spectrometer instrument suite on the Mars Odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near-surface ice in high latitudes of both martian hemispheres. Ice concentrations are estimated to range from 70 per cent at 60° latitude to 100 per cent near the poles, possibly overlain by a few centimetres of ice-free material in most places. This result is supported by morphological evidence of metres-thick layered deposits that are rich in water-ice and periglacial-like features found only at high latitudes. Diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution, but such a degree of concentration is difficult to accommodate with such processes. Alternatively, there are suggestions that ice-rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity, but these results have been difficult to reproduce with other models. Here we propose instead that, during periods of low obliquity (less than 25°), high-latitude ice deposits form in both hemispheres by direct deposition of ice, as a result of sublimation from an equatorial ice reservoir that formed earlier, during a prolonged high-obliquity excursion. Using the ice accumulation rates estimated from global climate model simulations we show that, over the past ten million years, large variations of Mars' obliquity have allowed the formation of such metres-thick, sedimentary layered deposits in high latitude and polar regions. Recent ice-rich deposits formed at high latitudes on Mars by sublimation of unstable equatorial ice during low obliquity Benjamin Levrard François Forget Franck Montmessin Jacques Laskar doi:10.1038/nature03055 Nature 431, 1072 (2004) Nature 431 7012 Letter 1072 1075 http://dx.doi.org/10.1038/nature02961 The controlled production of single photons is of fundamental and practical interest; they represent the lowest excited quantum states of the radiation field, and have applications in quantum cryptography and quantum information processing. Common approaches use the fluorescence of single ions, single molecules, colour centres and semiconductor quantum dots. However, the lack of control over such irreversible emission processes precludes the use of these sources in applications (such as quantum networks) that require coherent exchange of quantum states between atoms and photons. The necessary control may be achieved in principle in cavity quantum electrodynamics. Although this approach has been used for the production of single photons from atoms, such experiments are compromised by limited trapping times, fluctuating atom–field coupling and multi-atom effects. Here we demonstrate a single-photon source based on a strongly localized single ion in an optical cavity. The ion is optimally coupled to a well-defined field mode, resulting in the generation of single-photon pulses with precisely defined shape and timing. We have confirmed the suppression of two-photon events up to the limit imposed by fluctuations in the rate of detector dark counts. The stream of emitted photons is uninterrupted over the storage time of the ion, as demonstrated by a measurement of photon correlations over 90 min. Continuous generation of single photons with controlled waveform in an ion-trap cavity system Matthias Keller Birgit Lange Kazuhiro Hayasaka Wolfgang Lange Herbert Walther doi:10.1038/nature02961 Nature 431, 1075 (2004) Nature 431 7012 Letter 1075 1078 http://dx.doi.org/10.1038/nature02925 Determining the nature of the electronic phases that compete with superconductivity in high-transition-temperature (high-Tc) superconductors is one of the deepest problems in condensed matter physics. One candidate is the ‘stripe’ phase, in which the charge carriers (holes) condense into rivers of charge that separate regions of antiferromagnetism. A related but lesser known system is the ‘spin ladder’, which consists of two coupled chains of magnetic ions forming an array of rungs. A doped ladder can be thought of as a high-Tc material with lower dimensionality, and has been predicted to exhibit both superconductivity and an insulating ‘hole crystal’ phase in which the carriers are localized through many-body interactions. The competition between the two resembles that believed to operate between stripes and superconductivity in high-Tc materials. Here we report the existence of a hole crystal in the doped spin ladder of Sr14Cu24O41 using a resonant X-ray scattering technique. This phase exists without a detectable distortion in the structural lattice, indicating that it arises from many-body electronic effects. Our measurements confirm theoretical predictions, and support the picture that proximity to charge ordered states is a general property of superconductivity in copper oxides. Crystallization of charge holes in the spin ladder of Sr14Cu24O41 P. Abbamonte G. Blumberg A. Rusydi A. Gozar P. G. Evans T. Siegrist L. Venema H. Eisaki E. D. Isaacs G. A. Sawatzky doi:10.1038/nature02925 Nature 431, 1078 (2004) Nature 431 7012 Letter 1078 1081 http://dx.doi.org/10.1038/nature02921 Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components. Furthermore, it is highly desirable to use silicon—the dominant material in the microelectronic industry—as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon, but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III–V compound semiconductors, but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction of efficient optical switching in silicon using resonant structures. All-optical control of light on a silicon chip Vilson R. Almeida Carlos A. Barrios Roberto R. Panepucci Michal Lipson doi:10.1038/nature02921 Nature 431, 1081 (2004) Nature 431 7012 Letter 1081 1084 http://dx.doi.org/10.1038/nature02995 Direct observations of sunspot numbers are available for the past four centuries, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades. Unusual activity of the Sun during recent decades compared to the previous 11,000 years S. K. Solanki I. G. Usoskin B. Kromer M. Schüssler J. Beer doi:10.1038/nature02995 Nature 431, 1084 (2004) Nature 431 7012 Letter 1084 1087 http://dx.doi.org/10.1038/nature02956 Excavations at Liang Bua, a large limestone cave on the island of Flores in eastern Indonesia, have yielded evidence for a population of tiny hominins, sufficiently distinct anatomically to be assigned to a new species, Homo floresiensis. The finds comprise the cranial and some post-cranial remains of one individual, as well as a premolar from another individual in older deposits. Here we describe their context, implications and the remaining archaeological uncertainties. Dating by radiocarbon (14C), luminescence, uranium-series and electron spin resonance (ESR) methods indicates that H. floresiensis existed from before 38,000 years ago (kyr) until at least 18 kyr. Associated deposits contain stone artefacts and animal remains, including Komodo dragon and an endemic, dwarfed species of Stegodon. H. floresiensis originated from an early dispersal of Homo erectus (including specimens referred to as Homo ergaster and Homo georgicus) that reached Flores, and then survived on this island refuge until relatively recently. It overlapped significantly in time with Homo sapiens in the region, but we do not know if or how the two species interacted. Archaeology and age of a new hominin from Flores in eastern Indonesia M. J. Morwood R. P. Soejono R. G. Roberts T. Sutikna C. S. M. Turney K. E. Westaway W. J. Rink J.- x. Zhao G. D. van den Bergh Rokus Awe Due D. R. Hobbs M. W. Moore M. I. Bird L. K. Fifield doi:10.1038/nature02956 Nature 431, 1087 (2004) Nature 431 7012 Letter 1087 1091 http://dx.doi.org/10.1038/nature03042 Predicting the consequences of species loss is critically important, given present threats to biological diversity such as habitat destruction, overharvesting and climate change. Several empirical studies have reported decreased ecosystem performance (for example, primary productivity) coincident with decreased biodiversity, although the relative influence of biotic effects and confounding abiotic factors has been vigorously debated. Whereas several investigations focused on single trophic levels (for example, grassland plants), studies of whole systems have revealed multiple layers of feedbacks, hidden drivers and emergent properties, making the consequences of species loss more difficult to predict. Here we report functionally important organisms and considerable biocomplexity in a sedimentary seafloor habitat, one of Earth's most widespread ecosystems. Experimental field measurements demonstrate how the abundance of spatangoid urchins—infaunal (in seafloor sediment) grazers / deposit feeders—is positively related to primary production, as their activities change nutrient fluxes and improve conditions for production by microphytobenthos (sedimentatry microbes and unicellular algae). Declines of spatangoid urchins after trawling are well documented, and our research linking these bioturbators to important benthic–pelagic fluxes highlights potential ramifications for productivity in coastal oceans. Bioturbators enhance ecosystem function through complex biogeochemical interactions Andrew M. Lohrer Simon F. Thrush Max M. Gibbs doi:10.1038/nature03042 Nature 431, 1092 (2004) 2004-10-06 Nature 2004-10-06 431 7012 Letter 1092 1095 http://dx.doi.org/10.1038/nature02936 Classical theories for the evolution of senescence predict that organisms that experience low mortality rates attributable to external factors, such as disease or predation, will evolve a later onset of senescence. Here we use patterns of senescence in guppies derived from natural populations that differ in mortality risk to evaluate the generality of these predictions. We have previously found that populations experiencing higher mortality rates evolve earlier maturity and invest more in reproduction, as predicted by evolutionary theory. We report here that these same populations do not have an earlier onset of senescence with respect to either mortality or reproduction but do with respect to swimming performance, which assesses neuromuscular function. This mosaic pattern of senescence challenges the generality of the association between decreased extrinsic mortality and delayed senescence and invites consideration of more derived theories for the evolution of senescence. Effect of extrinsic mortality on the evolution of senescence in guppies David N. Reznick Michael J. Bryant Derek Roff Cameron K. Ghalambor Dionna E. Ghalambor doi:10.1038/nature02936 Nature 431, 1095 (2004) Nature 431 7012 Letter 1095 1099 http://dx.doi.org/10.1038/nature02918 Evolution can favour more than one reproductive tactic among conspecifics of the same sex. Under the conditional evolutionarily stable strategy, individuals adopt the tactic that generates the highest fitness return for their status: large males guard females, whereas small males sneak copulations. Tactics change at the status at which fitness benefits switch from favouring one tactic to favouring the alternative. This ‘switchpoint’ is expressed in many species as a threshold between divergent morphologies. Environmental and demographic parameters that influence the relative fitness of male tactics are predicted to determine a population's switchpoint and consequently whether the population is monomorphic or dimorphic. Here we show threshold evolution in the forceps dimorphism of the European earwig Forficula auricularia and document the transition from completely monomorphic to classical male-dimorphic populations over a distance of only 40 km. Because the superior fighting ability of the dominant morph will be more frequently rewarded at high encounter rates, population density is likely to be a key determinant of the relative fitness of the alternative tactics, and consequently the threshold. We show that, as predicted, population density correlates strongly with the shift in threshold, and that this factor drives the local evolution of the male dimorphism in these island populations. Our data provide evidence for the origin of phenotypic diversity within populations, through the evolution of a switchpoint in a conditional strategy that has responded to local population density. Population density drives the local evolution of a threshold dimorphism Joseph L. Tomkins Gordon S. Brown doi:10.1038/nature02918 Nature 431, 1099 (2004) Nature 431 7012 Letter 1099 1103 http://dx.doi.org/10.1038/nature02990 Trichomonas vaginalis is a unicellular microaerophilic eukaryote that lacks mitochondria yet contains an alternative organelle, the hydrogenosome, involved in pyruvate metabolism. Pathways between the two organelles differ substantially: in hydrogenosomes, pyruvate oxidation is catalysed by pyruvate:ferredoxin oxidoreductase (PFOR), with electrons donated to an [Fe]-hydrogenase which produces hydrogen. ATP is generated exclusively by substrate-level phosphorylation in hydrogenosomes, as opposed to oxidative phosphorylation in mitochondria. PFOR and hydrogenase are found in eubacteria and amitochondriate eukaryotes, but not in typical mitochondria. Analyses of mitochondrial genomes indicate that mitochondria have a single endosymbiotic origin from an α-proteobacterial-type progenitor. The absence of a genome in trichomonad hydrogenosomes precludes such comparisons, leaving the endosymbiotic history of this organelle unclear. Although phylogenetic reconstructions of a few proteins indicate that trichomonad hydrogenosomes share a common origin with mitochondria, others do not. Here we describe a novel NADH dehydrogenase module of respiratory complex I that is coupled to the central hydrogenosomal fermentative pathway to form a hydrogenosomal oxidoreductase complex that seems to function independently of quinones. Phylogenetic analyses of hydrogenosomal complex I-like proteins Ndh51 and Ndh24 reveal that neither has a common origin with mitochondrial homologues. These studies argue against a vertical origin of trichomonad hydrogenosomes from the proto-mitochondrial endosymbiont. Non-mitochondrial complex I proteins in a hydrogenosomal oxidoreductase complex Sabrina D. Dyall Weihong Yan Maria G. Delgadillo-Correa Adam Lunceford Joseph A. Loo Catherine F. Clarke Patricia J. Johnson doi:10.1038/nature02990 Nature 431, 1103 (2004) Nature 431 7012 Letter 1103 1107 http://dx.doi.org/10.1038/nature02977 Cryptosporidium species cause acute gastroenteritis and diarrhoea worldwide. They are members of the Apicomplexa—protozoan pathogens that invade host cells by using a specialized apical complex and are usually transmitted by an invertebrate vector or intermediate host. In contrast to other Apicomplexans, Cryptosporidium is transmitted by ingestion of oocysts and completes its life cycle in a single host. No therapy is available, and control focuses on eliminating oocysts in water supplies. Two species, C. hominis and C. parvum, which differ in host range, genotype and pathogenicity, are most relevant to humans. C. hominis is restricted to humans, whereas C. parvum also infects other mammals. Here we describe the eight-chromosome ∼9.2-million-base genome of C. hominis. The complement of C. hominis protein-coding genes shows a striking concordance with the requirements imposed by the environmental niches the parasite inhabits. Energy metabolism is largely from glycolysis. Both aerobic and anaerobic metabolisms are available, the former requiring an alternative electron transport system in a simplified mitochondrion. Biosynthesis capabilities are limited, explaining an extensive array of transporters. Evidence of an apicoplast is absent, but genes associated with apical complex organelles are present. C. hominis and C. parvum exhibit very similar gene complements, and phenotypic differences between these parasites must be due to subtle sequence divergence. The genome of Cryptosporidium hominis Ping Xu Giovanni Widmer Yingping Wang Luiz S. Ozaki Joao M. Alves Myrna G. Serrano Daniela Puiu Patricio Manque Donna Akiyoshi Aaron J. Mackey William R. Pearson Paul H. Dear Alan T. Bankier Darrell L. Peterson Mitchell S. Abrahamsen Vivek Kapur Saul Tzipori Gregory A. Buck doi:10.1038/nature02977 Nature 431, 1107 (2004) Nature 431 7012 Letter 1107 1112 http://dx.doi.org/10.1038/nature03043 Hepatocellular carcinoma is generally refractory to clinical treatment. Here, we report that inactivation of the MYC oncogene is sufficient to induce sustained regression of invasive liver cancers. MYC inactivation resulted en masse in tumour cells differentiating into hepatocytes and biliary cells forming bile duct structures, and this was associated with rapid loss of expression of the tumour marker α-fetoprotein, the increase in expression of liver cell markers cytokeratin 8 and carcinoembryonic antigen, and in some cells the liver stem cell marker cytokeratin 19. Using in vivo bioluminescence imaging we found that many of these tumour cells remained dormant as long as MYC remain inactivated; however, MYC reactivation immediately restored their neoplastic features. Using array comparative genomic hybridization we confirmed that these dormant liver cells and the restored tumour retained the identical molecular signature and hence were clonally derived from the tumour cells. Our results show how oncogene inactivation may reverse tumorigenesis in the most clinically difficult cancers. Oncogene inactivation uncovers the pluripotent capacity of tumours to differentiate into normal cellular lineages and tissue structures, while retaining their latent potential to become cancerous, and hence existing in a state of tumour dormancy. MYC inactivation uncovers pluripotent differentiation and tumour dormancy in hepatocellular cancer Catherine M. Shachaf Andrew M. Kopelman Constadina Arvanitis Åsa Karlsson Shelly Beer Stefanie Mandl Michael H. Bachmann Alexander D. Borowsky Boris Ruebner Robert D. Cardiff Qiwei Yang J. Michael Bishop Christopher H. Contag Dean W. Felsher doi:10.1038/nature03043 Nature 431, 1112 (2004) 2004-10-10 Nature 2004-10-10 431 7012 Letter 1112 1117 http://dx.doi.org/10.1038/nature03024 Cyclin-dependent kinases (CDKs) limit the activation of DNA replication origins to once per cell cycle by preventing the assembly of pre-replicative complexes (pre-RCs) during S, G2 and M phases of the cell cycle in the budding yeast Saccharomyces cerevisiae. CDKs inhibit each pre-RC component (ORC, Cdc6, Cdt1/Mcm2-7) by different mechanisms. We show here that the mitotic CDK, Clb2/Cdc28, binds tightly to an amino-terminal domain (NTD) of Cdc6, and that Cdc6 in this complex is unable to assemble pre-RCs. We present evidence indicating that this Clb2-dependent mechanism contributes to preventing re-replication in vivo. CDK interaction with the NTD of Cdc6 is mediated by the cyclin subunit Clb2, and could be reconstituted with recombinant Clb2 protein and synthetic NTD peptides. Tight Clb2 binding occurred only when the NTD was phosphorylated on CDK consensus sites. Human CDKs containing cyclins A, B and E also bound specifically to phospho-NTD peptides. We propose that direct binding of cyclins to phosphopeptide motifs may be a widespread phenomenon contributing to the targeting of CDKs to substrates. Phosphorylation-dependent binding of mitotic cyclins to Cdc6 contributes to DNA replication control Satoru Mimura Takashi Seki Seiji Tanaka John F. X. Diffley doi:10.1038/nature03024 Nature 431, 1118 (2004) 2004-10-20 Nature 2004-10-20 431 7012 Letter 1118 1123 http://dx.doi.org/10.1038/nature03091 Nature423, 762–769 (2003).In this Letter, Fig. 1 is an illustration of the sorting procedure, rather than an original data set, which we did not explicitly describe. Because the x-axis was used for FACS analysis of both corrigendum: Cloning of adiponectin receptors that mediate antidiabetic metabolic effects Toshimasa Yamauchi Junji Kamon Yusuke Ito Atsushi Tsuchida Takehiko Yokomizo Shunbun Kita Takuya Sugiyama Makoto Miyagishi Kazuo Hara Masaki Tsunoda Koji Murakami Toshiaki Ohteki Shoko Uchida Sato Takekawa Hironori Waki Nelson H. Tsuno Yoichi Shibata Yasuo Terauchi Philippe Froguel Kazuyuki Tobe Shigeo Koyasu Kazunari Taira Toshio Kitamura Takao Shimizu Ryozo Nagai Takashi Kadowaki doi:10.1038/nature03091 Nature 431, 1123 (2004) Nature 431 7012 Letter 1123 1123 http://dx.doi.org/10.1038/nj7012-1125a Communication. It's one of those vague yet lofty skills that scientific recruiters say are important, but few define, and fewer still can present concrete examples. In a survey of 77 scientists in academia, biotech and pharma, all emphasized the importance of communication skills and provided Making the match Paul Smaglik doi:10.1038/nj7012-1125a Nature 431, 1125 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Naturejobs 1125 1125 http://dx.doi.org/10.1038/nj7012-1126a Are you on course for the career you want? Don't follow the crowd and lose your direction, warns Eugene Russo. Instead, map out your own postdoc path. Fast Track: charting the course of your postdoc Eugene Russo doi:10.1038/nj7012-1126a Nature 431, 1126 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Naturejobs 1126 1127 http://dx.doi.org/10.1038/nj7012-1128a When I decided to pursue a PhD, I thought the long road to this short acronym would pay off with respect (mainly from people outside academia), more job opportunities and better pay, in academia and industry.But I've now realized there are no guarantees — Graduate Journal: PhD limitations Philipp Angerer doi:10.1038/nj7012-1128a Nature 431, 1128 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Naturejobs 1128 1128 http://dx.doi.org/10.1038/nj7012-1128b Get a foot in the doorThere is no magic trick for landing a good job in science. But if you produce good research or file useful patents, you can take a few steps to plant the seeds of opportunity.Network. Introductions from friends, mentors Recruiters & Industry Grace Wong doi:10.1038/nj7012-1128b Nature 431, 1128 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Naturejobs 1128 1128 http://dx.doi.org/10.1038/nj7012-1128c Julia King, principal of the engineering faculty, Imperial College LondonIt was the champagne lifestyle that first attracted Julia King to a career in science. During the optimistic 1960s, says Imperial's new head of engineering, the newspapers seemed full of pictures of scientists celebrating their Movers doi:10.1038/nj7012-1128c Nature 431, 1128 (2004) 2004-10-27 Nature 2004-10-27 431 7012 Naturejobs 1128 1128