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51.
Don't judge species on their origins 总被引:1,自引:0,他引:1
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Lissauer JJ Fabrycky DC Ford EB Borucki WJ Fressin F Marcy GW Orosz JA Rowe JF Torres G Welsh WF Batalha NM Bryson ST Buchhave LA Caldwell DA Carter JA Charbonneau D Christiansen JL Cochran WD Desert JM Dunham EW Fanelli MN Fortney JJ Gautier TN Geary JC Gilliland RL Haas MR Hall JR Holman MJ Koch DG Latham DW Lopez E McCauliff S Miller N Morehead RC Quintana EV Ragozzine D Sasselov D Short DR Steffen JH 《Nature》2011,470(7332):53-58
When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47?days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation. 相似文献
54.
Extended megadroughts in the southwestern United States during Pleistocene interglacials 总被引:1,自引:0,他引:1
Fawcett PJ Werne JP Anderson RS Heikoop JM Brown ET Berke MA Smith SJ Goff F Donohoo-Hurley L Cisneros-Dozal LM Schouten S Sinninghe Damsté JS Huang Y Toney J Fessenden J WoldeGabriel G Atudorei V Geissman JW Allen CD 《Nature》2011,470(7335):518-521
The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, 'dust-bowl-like' megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C(4) plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ~2?°C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4-6?°C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase. 相似文献
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Mammalian prions cause fatal neurodegenerative conditions including Creutzfeldt-Jakob disease in humans and scrapie and bovine spongiform encephalopathy in animals. Prion infections are typically associated with remarkably prolonged but highly consistent incubation periods followed by a rapid clinical phase. The relationship between prion propagation, generation of neurotoxic species and clinical onset has remained obscure. Prion incubation periods in experimental animals are known to vary inversely with expression level of cellular prion protein. Here we demonstrate that prion propagation in brain proceeds via two distinct phases: a clinically silent exponential phase not rate-limited by prion protein concentration which rapidly reaches a maximal prion titre, followed by a distinct switch to a plateau phase. The latter determines time to clinical onset in a manner inversely proportional to prion protein concentration. These findings demonstrate an uncoupling of infectivity and toxicity. We suggest that prions themselves are not neurotoxic but catalyse the formation of such species from PrP(C). Production of neurotoxic species is triggered when prion propagation saturates, leading to a switch from autocatalytic production of infectivity (phase 1) to a toxic (phase 2) pathway. 相似文献
57.
Programming the magnitude and persistence of antibody responses with innate immunity 总被引:1,自引:0,他引:1
Kasturi SP Skountzou I Albrecht RA Koutsonanos D Hua T Nakaya HI Ravindran R Stewart S Alam M Kwissa M Villinger F Murthy N Steel J Jacob J Hogan RJ García-Sastre A Compans R Pulendran B 《Nature》2011,470(7335):543-547
Many successful vaccines induce persistent antibody responses that can last a lifetime. The mechanisms by which they do so remain unclear, but emerging evidence indicates that they activate dendritic cells via Toll-like receptors (TLRs). For example, the yellow fever vaccine YF-17D, one of the most successful empiric vaccines ever developed, activates dendritic cells via multiple TLRs to stimulate proinflammatory cytokines. Triggering specific combinations of TLRs in dendritic cells can induce synergistic production of cytokines, which results in enhanced T-cell responses, but its impact on antibody responses remain unknown. Learning the critical parameters of innate immunity that program such antibody responses remains a major challenge in vaccinology. Here we demonstrate that immunization of mice with synthetic nanoparticles containing antigens plus ligands that signal through TLR4 and TLR7 induces synergistic increases in antigen-specific, neutralizing antibodies compared to immunization with nanoparticles containing antigens plus a single TLR ligand. Consistent with this there was enhanced persistence of germinal centres and of plasma-cell responses, which persisted in the lymph nodes for >1.5 years. Surprisingly, there was no enhancement of the early short-lived plasma-cell response relative to that observed with single TLR ligands. Molecular profiling of activated B cells, isolated 7 days after immunization, indicated that there was early programming towards B-cell memory. Antibody responses were dependent on direct triggering of both TLRs on B cells and dendritic cells, as well as on T-cell help. Immunization protected completely against lethal avian and swine influenza virus strains in mice, and induced robust immunity against pandemic H1N1 influenza in rhesus macaques. 相似文献
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Sara Ruane Stephen J. Richards John D. McVay Burhan Tjaturadi Keliopas Krey Christopher C. Austin 《Journal of Natural History》2018,52(13-16):917-944
ABSTRACTThe island of New Guinea has been identified as biologically megadiverse but many taxa are still poorly known. This is especially the case for many of the island’s snakes, which by their very nature can be difficult to collect and study. Here we examine the phylogenetic and phylogeographic structure of a poorly studied snake genus, Stegonotus, focusing on the species of New Guinea; until now, Stegonotus has never been examined using modern phylogenetic methods. Using molecular data from 49 individuals representing eight of the ten described species, and including all New Guinea taxa, we estimate a multilocus phylogeny and examine population structure to help identify undescribed taxa. We use morphological data from the corresponding museum vouchered specimens (where available) and also examine additional specimens for taxa not included in the molecular data set to determine morphological differences among putative taxa. We find molecular evidence for four new species of Stegonotus, both morphologically obvious and cryptic, and describe them herein. The recognition of these four species indicates that Stegonotus diversity has been previously underestimated and also suggests that there are likely additional undescribed taxa within the genus. These four taxa increase the number of described species by 40% and further confirm New Guinea as the centre of diversity for the genus.www.zoobank.org/urn:lsid:zoobank.org:pub:9E21390E-3FD4-40EB-9442-31BC92A76B4F 相似文献