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81.
Speciation in animals is almost always envisioned as the split of an existing lineage into an ancestral and a derived species. An alternative speciation route is homoploid hybrid speciation in which two ancestral taxa give rise to a third, derived, species by hybridization without a change in chromosome number. Although theoretically possible it has been regarded as rare and hence of little importance in animals. On the basis of molecular and chromosomal evidence, hybridization is the best explanation for the origin of a handful of extant diploid bisexual animal taxa. Here we report the first case in which hybridization between two host-specific animals (tephritid fruitflies) is clearly associated with the shift to a new resource. Such a hybrid host shift presents an ecologically robust scenario for animal hybrid speciation because it offers a potential mechanism for reproductive isolation through differential adaptation to a new ecological niche. The necessary conditions for this mechanism of speciation are common in parasitic animals, which represent much of animal diversity. The frequency of homoploid hybrid speciation in animals may therefore be higher than previously assumed. 相似文献
82.
Birds may hover over or perch on flowers when feeding on nectar, and this assists cross-pollination if they then visit other plants. Here we investigate the curious sterile inflorescence axis of the South African Cape endemic 'rat's tail' plant (Babiana ringens, Iridaceae), whose function--unlike in other bird-pollinated plants--is exclusively to provide a perch for foraging birds. We find that this structure promotes the plant's mating success by causing the malachite sunbird (Nectarinia famosa), its main pollinator, to adopt a position ideal for the cross-pollination of its unusual ground-level flowers. 相似文献
83.
84.
Polymer electrolytes consist of salts dissolved in polymers (for example, polyethylene oxide, PEO), and represent a unique class of solid coordination compounds. They have potential applications in a diverse range of all-solid-state devices, such as rechargeable lithium batteries, flexible electrochromic displays and smart windows. For 30 years, attention was focused on amorphous polymer electrolytes in the belief that crystalline polymer:salt complexes were insulators. This view has been overturned recently by demonstrating ionic conductivity in the crystalline complexes PEO6:LiXF6 (X = P, As, Sb); however, the conductivities were relatively low. Here we demonstrate an increase of 1.5 orders of magnitude in the conductivity of these materials by replacing a small proportion of the XF6- anions in the crystal structure with isovalent N(SO2CF3)2- ions. We suggest that the larger and more irregularly shaped anions disrupt the potential around the Li+ ions, thus enhancing the ionic conductivity in a manner somewhat analogous to the AgBr(1-x)I(x) ionic conductors. The demonstration that doping strategies can enhance the conductivity of crystalline polymer electrolytes represents a significant advance towards the technological exploitation of such materials. 相似文献
85.
Nanoscale hydrodynamics: enhanced flow in carbon nanotubes 总被引:3,自引:0,他引:3
Nanoscale structures that could mimic the selective transport and extraordinarily fast flow possible in biological cellular channels would have a wide range of potential applications. Here we show that liquid flow through a membrane composed of an array of aligned carbon nanotubes is four to five orders of magnitude faster than would be predicted from conventional fluid-flow theory. This high fluid velocity results from an almost frictionless interface at the carbon-nanotube wall. 相似文献
86.
Reich D Patterson N De Jager PL McDonald GJ Waliszewska A Tandon A Lincoln RR DeLoa C Fruhan SA Cabre P Bera O Semana G Kelly MA Francis DA Ardlie K Khan O Cree BA Hauser SL Oksenberg JR Hafler DA 《Nature genetics》2005,37(10):1113-1118
Multiple sclerosis is a common disease with proven heritability, but, despite large-scale attempts, no underlying risk genes have been identified. Traditional linkage scans have so far identified only one risk haplotype for multiple sclerosis (at HLA on chromosome 6), which explains only a fraction of the increased risk to siblings. Association scans such as admixture mapping have much more power, in principle, to find the weak factors that must explain most of the disease risk. We describe here the first high-powered admixture scan, focusing on 605 African American cases and 1,043 African American controls, and report a locus on chromosome 1 that is significantly associated with multiple sclerosis. 相似文献
87.
The structure of a protein depends critically on the complex interactions among its amino acid residues. It has long been hypothesized that interacting residues might tend to coevolve, but it is not known whether such coevolution is a general phenomenon across the proteome. Here, we describe a novel methodology called phylogeny-aided structural analysis, which uncovers robust signals of interacting-residue coevolution in mammalian proteomes. Furthermore, this new method allows the magnitude of coevolution to be quantified. Finally, it facilitates a comprehensive evaluation of various factors that affect interacting-residue coevolution, such as the physicochemical properties of the interactions between residues, solvent accessibility of the residues and their secondary structure context. 相似文献
88.
Zusammenfassung Untersuchungen an Laboratoriums-FledermäusenMyotis lucifugus während aller Phasen der Winterschlaflethargie zeigen, dass Unbeweglichkeit der Tiere entscheidend auf den Verlust an Knochenmineralien wirkt. Die Vermehrung an Osteoklasten sowie die Hyperkalzemie und die Hypophosphatemie bei winterschlafenden Fledermäusen weisen ebenfalls in Richtung der Resorptionsvorgänge im Knochen. 相似文献
89.
90.
Amino-acid composition of soluble and membranous lipoproteins 总被引:3,自引:0,他引:3