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91.
Invasion and the evolution of speed in toads 总被引:1,自引:0,他引:1
Cane toads (Bufo marinus) are large anurans (weighing up to 2 kg) that were introduced to Australia 70 years ago to control insect pests in sugar-cane fields. But the result has been disastrous because the toads are toxic and highly invasive. Here we show that the annual rate of progress of the toad invasion front has increased about fivefold since the toads first arrived; we find that toads with longer legs can not only move faster and are the first to arrive in new areas, but also that those at the front have longer legs than toads in older (long-established) populations. The disaster looks set to turn into an ecological nightmare because of the negative effects invasive species can have on native ecosystems; over many generations, rates of invasion will be accelerated owing to rapid adaptive change in the invader, with continual 'spatial selection' at the expanding front favouring traits that increase the toads' dispersal. 相似文献
92.
ter Steege H Pitman NC Phillips OL Chave J Sabatier D Duque A Molino JF Prévost MF Spichiger R Castellanos H von Hildebrand P Vásquez R 《Nature》2006,443(7110):444-447
The world's greatest terrestrial stores of biodiversity and carbon are found in the forests of northern South America, where large-scale biogeographic patterns and processes have recently begun to be described. Seven of the nine countries with territory in the Amazon basin and the Guiana shield have carried out large-scale forest inventories, but such massive data sets have been little exploited by tropical plant ecologists. Although forest inventories often lack the species-level identifications favoured by tropical plant ecologists, their consistency of measurement and vast spatial coverage make them ideally suited for numerical analyses at large scales, and a valuable resource to describe the still poorly understood spatial variation of biomass, diversity, community composition and forest functioning across the South American tropics. Here we show, by using the seven forest inventories complemented with trait and inventory data collected elsewhere, two dominant gradients in tree composition and function across the Amazon, one paralleling a major gradient in soil fertility and the other paralleling a gradient in dry season length. The data set also indicates that the dominance of Fabaceae in the Guiana shield is not necessarily the result of root adaptations to poor soils (nodulation or ectomycorrhizal associations) but perhaps also the result of their remarkably high seed mass there as a potential adaptation to low rates of disturbance. 相似文献
93.
Rearrangement and transcription of the beta-chain genes of the T-cell antigen receptor in different types of murine lymphocytes 总被引:2,自引:0,他引:2
M Kronenberg J Goverman R Haars M Malissen E Kraig L Phillips T Delovitch N Suciu-Foca L Hood 《Nature》1985,313(6004):647-653
Rearrangements of T-cell receptor beta-chain genes are usually found on both chromosomal homologues, occurring by both deletional and non-deletional mechanisms. Two constant-region (C beta) genes have been identified previously and at least one is transcribed in every helper or cytotoxic T cell tested, but the choice of C beta gene expression is not correlated with the specialized functions of these T lymphocytes. By contrast, four of five suppressor T-cell hybridomas examined have deleted all known joining (J beta) gene segments and C beta genes and therefore may have antigen receptors encoded by different T-cell receptor gene families. 相似文献
94.
The monamycins, a new family of cyclodepsipeptide antibiotics 总被引:1,自引:0,他引:1
K Bevan J S Davies M J Hall C H Hassall R B Morton D A Phillips Y Ogihara W A Thomas 《Experientia》1970,26(2):122-123
95.
P J Artymiuk C C Blake D E Grace S J Oatley D C Phillips M J Sternberg 《Nature》1979,280(5723):563-568
The patterns of atomic displacements in the crystals of hen and human lysozyme derived from independent crystallographic refinement are broadly similar. Analysis of the pattern indicates a close correlation with molecular structure, strongly suggestive of intramolecular motion. The active site of lysozyme is located in a region of high displacement. It is concluded that protein mobility may play a significant part in biological activity and that X-ray crystallography can contribute to its analysis. 相似文献
96.
Experimental annotation of the human genome using microarray technology 总被引:59,自引:0,他引:59
Shoemaker DD Schadt EE Armour CD He YD Garrett-Engele P McDonagh PD Loerch PM Leonardson A Lum PY Cavet G Wu LF Altschuler SJ Edwards S King J Tsang JS Schimmack G Schelter JM Koch J Ziman M Marton MJ Li B Cundiff P Ward T Castle J Krolewski M Meyer MR Mao M Burchard J Kidd MJ Dai H Phillips JW Linsley PS Stoughton R Scherer S Boguski MS 《Nature》2001,409(6822):922-927
97.
Bouquet F Marcenat C Steep E Calemczuk R Kwok WK Welp U Crabtree GW Fisher RA Phillips NE Schilling A 《Nature》2001,411(6836):448-451
A magnetic field penetrates a superconductor through an array of 'vortices', each of which carries one quantum of flux that is surrounded by a circulating supercurrent. In this vortex state, the resistivity is determined by the dynamical properties of the vortex 'matter'. For the high-temperature copper oxide superconductors (see ref.1 for a theoretical review), the vortex phase can be a 'solid', in which the vortices are pinned, but the solid can 'melt' into a 'liquid' phase, in which their mobility gives rise to a finite resistance. (This melting phenomenon is also believed to occur in conventional superconductors, but in an experimentally inaccessible part of the phase diagram.) For the case of YBa2Cu3O7, there are indications of the existence of a critical point, at which the character of the melting changes. But neither the thermodynamic nature of the melting, nor the phase diagram in the vicinity of the critical point, has been well established. Here we report measurements of specific heat and magnetization that determine the phase diagram in this material to 26 T, well above the critical point. Our results reveal the presence of a reversible second-order transition above the critical point. An unusual feature of this transition-namely, that the high-temperature phase is the less symmetric in the sense of the Landau theory-is in accord with theoretical predictions of a transition to a second vortex-liquid phase. 相似文献
98.
Structure of co-crystals of tropomyosin and troponin 总被引:4,自引:0,他引:4
Troponin, a Ca2+-sensitive complex, regulates the motions of tropomyosin on the thin filaments in many muscles. It has three subunits, each with a different architecture and function: TnC binds Ca2+; TnI binds to actin and inhibits contraction; and TnT binds one complex to each tropomyosin molecule. The troponin complex has an elongated shape with TnC and TnI forming a globular 'head' region and TnT a long (approximately 160 A) 'tail'. TnT binds to two widely separated regions of tropomyosin: the head region of the complex is near Cys 190 of tropomyosin and the tail region is near the overlapping joint that links the tropomyosin molecules into filaments. Here we report the X-ray structure determination at 17 A resolution of glutaraldehyde-treated tropomyosin crystals in which native troponin complex or fragments of TnT have been bound. Our results show that the amino-terminal tail end of TnT spans the head-to-tail joint of the tropomyosin filaments, and that the 'head' region of the whole troponin complex binds approximately 200 A away near residues 150-180 of the tropomyosin molecule. 相似文献
99.
Hamuy M Phillips MM Suntzeff NB Maza J González LE Roth M Krisciunas K Morrell N Green EM Persson SE McCarthy PJ 《Nature》2003,424(6949):651-654
Stars that explode as supernovae come in two main classes. A type Ia supernova is recognized by the absence of hydrogen and the presence of elements such as silicon and sulphur in its spectrum; this class of supernova is thought to produce the majority of iron-peak elements in the Universe. They are also used as precise 'standard candles' to measure the distances to galaxies. While there is general agreement that a type Ia supernova is produced by an exploding white dwarf star, no progenitor system has ever been directly observed. Significant effort has gone into searching for circumstellar material to help discriminate between the possible kinds of progenitor systems, but no such material has hitherto been found associated with a type Ia supernova. Here we report the presence of strong hydrogen emission associated with the type Ia supernova SN2002ic, indicating the presence of large amounts of circumstellar material. We infer from this that the progenitor system contained a massive asymptotic-giant-branch star that lost several solar masses of hydrogen-rich gas before the supernova explosion. 相似文献
100.