Evaluating the population‐level impact of an invasive species,Ring‐necked Parakeet Psittacula krameri,on native avifauna

The introduction of exotic species to ecosystems can have severe consequences for populations of native organisms, but logistical limitations and shortage of historical data often hinder attempts to quantify the ecological implications of such relationships. The establishment and rapid expansion of Ring‐necked Parakeets Psittacula krameri in England therefore presents a rare opportunity to apply novel analytical methods to existing extensive national bird monitoring data from the UK Breeding Bird Survey for an invasive species. A previous study from Belgium suggests that Ring‐necked Parakeets have the potential to reduce the abundance of Eurasian Nuthatch Sitta europaea through competition for nesting cavities. Our analysis provides no evidence for a significant impact through competition on Nuthatch populations or those of any other cavity‐nesting species within the Parakeet’s current range in the UK. However, we cannot exclude the possibility that competitive exclusion could be occurring at a minority of sites at which availability of nest cavities is limiting. This may yet have significant implications for future conflict if Parakeets continue to increase in numbers and range.     

New morphological evidence supports congruent phylogenies and Gondwana vicariance for palaeognathous birds

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.     

Uptake of CO2 by aquatic vegetation

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.     

Significance of nucleotide sequence alignments: a method for random sequence permutation that preserves dinucleotide and codon usage

The similarity of two nucleotide sequences is often expressed in terms of evolutionary distance, a measure of the amount of change needed to transform one sequence into the other. Given two sequences with a small distance between them, can their similarity be explained by their base composition alone? The nucleotide order of these sequences contributes to their similarity if the distance is much smaller than their average permutation distance, which is obtained by calculating the distances for many random permutations of these sequences. To determine whether their similarity can be explained by their dinucleotide and codon usage, random sequences must be chosen from the set of permuted sequences that preserve dinucleotide and codon usage. The problem of choosing random dinucleotide and codon-preserving permutations can be expressed in the language of graph theory as the problem of generating random Eulerian walks on a directed multigraph. An efficient algorithm for generating such walks is described. This algorithm can be used to choose random sequence permutations that preserve (1) dinucleotide usage, (2) dinucleotide and trinucleotide usage, or (3) dinucleotide and codon usage. For example, the similarity of two 60-nucleotide DNA segments from the human beta-1 interferon gene (nucleotides 196-255 and 499-558) is not just the result of their nonrandom dinucleotide and codon usage.      

Variability of DNA Content in Individual Cells of <Emphasis Type="Italic">Bacillus</Emphasis>

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. Estimates^3–5 of genome size vary from 1.3 × 10⁹ to 10 × 10⁹ daltons and the number of genomes per cell from 2 to 4^4–8. 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).     

The Electrical Resistance and Capacitance of the Membranes of Nitella translucens

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 (R_m) and the membrane capacitance (C_m). The valuesof R_m 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.     

Remarkable leaf anatomical variations in Neurachne and its allies (Poaceae) in relation to G3 and G4 photosynthesis

The leaf blade anatomy of all species of Neurachne, Paraneurachne and Thyridolepis has been examined, with special reference to features reliably indicative of photosynthetic pathway. Neurachne alopecuroidea, N. queenslandica and N. tenuifolia exhibit C₃ anatomy, as do all three Thyridolepis species. Paraneurachne muelleri, N. munroi and N. minor all have C₄ anatomy, of the rare ' Alloteropsis-type'. However, all the species exhibit unusual anatomical features, and N. lanigera cannot be confidently assigned as C₃ or C, on anatomical grounds alone. Taxonomic considerations confirm that the three genera are closely related to one another in the context of the eu-panicoid assemblage as a whole, and that the genus Neurachne itself, although it exhibits variation in photosynthetic pathway, is not amenable to further taxonomic subdivision.