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31.
PETER JOHNSTON 《Zoological Journal of the Linnean Society》2011,163(3):959-982
There has been little agreement on the phylogeny of palaeognathous birds, with major differences amongst and between results from morphological and molecular data. Two recently published phylogenies using nuclear and mitochondrial DNA have substantial agreement in overall topology, with the ostrich as sister group of all other extant palaeognaths and a kiwi‐emu‐cassowary clade. Here I report a morphological phylogeny based mainly on new characters from the tongue apparatus and cranial osteology, with a theoretical ancestor as outgroup. A new interpretation of the evolution of the avian palate is included. This phylogeny is very similar to these recent molecular results; this is the first report of such congruence, and offers a credible basis for understanding the evolution of this clade. This phylogeny is fully consistent with a Gondwana vicariance model of evolution. Dates attributed from known geological events place the first extant radiation (ostrich) in the mid‐Cretaceous, and offer a means of calibration of future molecular clock investigations. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 959–983. 相似文献
32.
Uptake of CO2 by aquatic vegetation 总被引:15,自引:10,他引:5
Abstract Photosynthesis by aquatic plants based on the supply of CO2 from air-equilibrated solutions may be limited by the low diffusion coefficient of CO2 in water. For plants in which the transport of CO2 from the bulk medium is by diffusion, and the initial carboxylation uses RUBISCO, CO2 supply can be increased by growth in habitats with fast water flow over the surface (reducing unstirred layer thickness), or with heterotrophically-augmented CO2 levels, including the direct use of sediment CO2. Many aquatic plants using RUBISCO as their initial carboxylase counter the limitations on CO2 supply via the operation of biophysical CO2 concentrating mechanisms which are based on active transport of HCO?3, CO2 or H+ at the plasmalemma, and use bulk-phase HCO?3 or CO2 as the C source. A final group of aquatic plants use biochemical CO2 concentrating mechanisms based on auxiliary carboxylation by PEPc: C4-like and Crassulacean Acid Metabolism–like processes are involved. These various mechanisms for increasing CO2 supply to RUBISCO also help to offset the low specific reaction rate of aquatic plant RUBISCOs at low [CO2] and low [CO2]: [CO2]. In addition to overcoming restrictions on CO2 supply, the various methods of increasing inorganic C availability may also be important in alleviating shortages of nitrogen or photons. 相似文献
33.
34.
Variability of DNA Content in Individual Cells of <Emphasis Type="Italic">Bacillus</Emphasis> 总被引:4,自引:0,他引:4
THE average content of DNA in Bacillus spores is unaffected by the growth medium and is constant for each species1. Within the Bacillus group, however, the average amount of DNA per spore varies from species to species1. A cell of B. cereus contains on average twice as much DNA as the spore and during sporulation this DNA is divided equally between the spore and the sporangium2. Estimates3–5 of genome size vary from 1.3 × 109 to 10 × 109 daltons and the number of genomes per cell from 2 to 44–8. Some of these variations may be associated with differences within the cells rather than differences of methodolqgy; spores within a population vary not only in size and shape, but also in their content of stainable chromatin9. Moreover, in ‘Renografm’ density gradients10, spores band within a range of densities. If spores are taken from a narrow part of this range, regrown and rebanded, the original pattern of dispersal occurs, suggesting that spores in the same population normally show variation in density as well as in size (A. I. Aronson, personal communication). 相似文献
35.
The resistance and capacitance of the membranes of Nitella translucenshave been measured by direct current and alternating currentmethods. Current of the order of 10-7 amp. was injected intothe cell by means of a conventional Ag, AgCl-3N KCl glass microelectrodeinserted into the vacuole of the cell. The change of potentialacross the membrane was recorded by two other internal microelectrodeswhich had been inserted into the cell at known distances fromthe current-injecting electrode. In the direct-current experimentsthe input current was in the form of a square pulse, while sinusoidalcurrents of frequency 25 cycles per second were used in thealternating current experiments. The cell was treated as a shortlength of coaxial cable and from the measurements the followingparameters could be obtained: the space constant (), the membraneresistance (Rm) and the membrane capacitance (Cm). The valuesof Rm ranged from 6.7 to 36 K ohm cm.2 (mean of 21.4 K ohm cm.2)and those of ranged from 1.5 to 5.7 cm. (mean of 2.6 cm.).The capacitance value was about I µF cm.-2 These results are discussed within the framework of our knowledgeof these parameters for other cells, particularly plant cells.The measured electrical resistance is shown to be at least tentimes less than the value estimated from the passive fluxesof the principal ions K, Na, and Cl. It is suggested that thisdiscrepancy, which is usually attributed to non-independentmovement of these ions, could be partially explained on electro-osmoticgrounds. The value of the capacitance is very close to thatwhich is usually obtained for other cell membranes. One exceptionallylow value for Nitella has been quoted in the literature. Thereason for the gross error in this particular measurement isgiven. 相似文献
36.
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38.
Introduction
There is an ever-increasing need for animal models to evaluate efficacy and safety of new therapeutics in the field of rheumatoid arthritis (RA). Particularly for the early preclinical evaluation of human-specific biologicals targeting the progressive phase of the disease, there is a need for relevant animal models. In response to this requirement we set out to develop a model of collagen-induced arthritis (CIA) in a small-sized nonhuman primate species (300 to 400 g at adult age); that is, the common marmoset (Callithrix jacchus). 相似文献39.
Over 3500 patients with recent onset inflammatory polyarthritis (IP) have been recruited by the Norfolk Arthritis Register
(NOAR) since 1990. Longitudinal data from this cohort have been used to examine the prevalence and predictors of remission,
functional disability, radiological outcome, cardiovascular mortality and co-morbidity and the development of non-Hodgkin's
lymphoma. Rheumatoid factor titre, high baseline C-reactive protein and high baseline HAQ score are all predictors of a poor
outcome. There is a strong association between possession of the shared epitope and the development of erosions. Patients
who satisfy the American College of Rheumatology criteria for rheumatoid arthritis (RA) have a worse prognosis than those
who do not. However, it appears that these patients are a poorly defined subset of all those with IP rather than having an
entirely separate disease entity. New statistical techniques offer exciting possibilities for using longitudinal datasets
such as NOAR to explore the long-term effects of treatment in IP and RA. 相似文献
40.
Phylogeny of the Drosophila saltans species group based on combined analysis of nuclear and mitochondrial DNA sequences 总被引:2,自引:0,他引:2
Nucleotide sequences from two nuclear loci, alcohol dehydrogenase and
internal transcribed spacer-1 of the nuclear ribosomal DNA repeats, and two
mitochondrial genes, cytochrome oxidase I and cytochrome oxidase II, were
determined from nine species in the Drosophila saltans species group. The
partition homogeneity test and partitioned Bremer support were used to
measure incongruence between phylogenetic hypotheses generated from
individual partitions. Individual loci were generally congruent with each
other and consistent with the previously proposed morphological hypothesis,
although they differed in level of resolution. Since extreme conflict
between partitions did not exist, the data were combined and analyzed
simultaneously. The total evidence method gave a more resolved and highly
supported phylogeny, as indicated by bootstrap proportions and decay
indices, than did any of the individual analyses. The cordata and elliptica
subgroups, considered to have diverged early in the history of the D.
saltans group, were sister taxa to the remainder of the saltans group. The
sturtevanti subgroup, represented by D. milleri and D. sturtevanti,
occupies an intermediate position in this phylogeny. The saltans and
parasaltans subgroups are sister clades and occupy the most recently
derived portion of the phylogeny. As with previous morphological studies,
phylogenetic relationships within the saltans subgroup were not
satisfactorily resolved by the molecular data.
相似文献