Hierarchical organization of guidance receptors: silencing of netrin attraction by slit through a Robo/DCC receptor complex

Axonal growth cones that cross the nervous system midline change their responsiveness to midline guidance cues: They become repelled by the repellent Slit and simultaneously lose responsiveness to the attractant netrin. These mutually reinforcing changes help to expel growth cones from the midline by making a once-attractive environment appear repulsive. Here, we provide evidence that these two changes are causally linked: In the growth cones of embryonic Xenopus spinal axons, activation of the Slit receptor Roundabout (Robo) silences the attractive effect of netrin-1, but not its growth-stimulatory effect, through direct binding of the cytoplasmic domain of Robo to that of the netrin receptor DCC. Biologically, this hierarchical silencing mechanism helps to prevent a tug-of-war between attractive and repulsive signals in the growth cone that might cause confusion. Molecularly, silencing is enabled by a modular and interlocking design of the cytoplasmic domains of these potentially antagonistic receptors that predetermines the outcome of their simultaneous activation.     

Pemoline levels in brain: enhancement by dimethyl sulfoxide

Pemoline-C(14) dissolved in dimethyl sulfoxide and injected intraperitoneally into rats was found in larger amounts in the brain than was a similar dose given in 0.3 percent tragacanth suspension. This appeared to be related to a partial breakdown of the blood-brain barrier in vivo by the dimethyl sulfoxide.     

A reverse keystone species affects the landscape distribution of woodland avifauna: a case study using the Noisy Miner (<Emphasis Type="Italic">Manorina melanocephala</Emphasis>) and other Australian birds

We explored the effects of a purported ‘reverse keystone species’, the Noisy Miner (Manorina melanocephala) using a long-term, large-scale dataset. Specifically, we identify whether this aggressive bird affects the landscape distribution patterns of other avifauna, by displacing them into, or restricting their distribution to, less productive areas, and in so doing, adheres to ‘isoleg theory’. We sought to determine the effect of abundance of the Noisy Miner on the abundance of other birds (individual species and groups), and determine whether that effect was consistent with varying site productivity, using a negative binomial distribution with a logarithmic link function, and an offset variable to account for variations in search effort. Relationships between abundance of Noisy Miners and habitat variables were examined using a Poisson distribution with a logarithmic link function scaled for extra-variation (quasi-Poisson regression). We demonstrate that when Noisy Miner abundance is low, many small passerine species are more abundant on high productivity sites. However, as Noisy Miner abundance increases, small passerine abundance decreases, with this decrease most apparent on productive sites. The same patterns were not evident for birds considered ‘non-competitors’ of the Noisy Miner. We identify that both site productivity and vegetation structure influence the abundance of the Noisy Miner. We reveal that the species increasingly tolerates ‘less desirable’ habitat attributes with increasing site productivity. The preference of the Noisy Miner for productive areas is likely to have deleterious impacts on the long-term survival and reproductive success of other Australian woodland bird species, many of which have already undergone severe declines.     

Management, breeding, and health records from a captive colony of pekin robins (Leiothrix lutea), 2001 - 2010

Pekin robins (Leiothrix lutea) were once the most widely kept softbills in captivity. As a result of the Convention on the International Trade of Endangered Species of Fauna and Flora (CITES-1997), the worldwide trade of wild-caught pekin robins has been prohibited due to the depletion of native populations of this species. In Brazil, as in other countries, pekin robins imported prior to the enactment of the CITES have disappeared from aviaries because the end of the birds' natural life span has passed, and only very few captive-bred pekin robins now exist. While captive propagation fails to address the primary causes of wild bird population decline, it might help the recovery of populations of this species. This article presents records made over a 10-yr period of a captive colony of pekin robins. Emphasis is placed on the management of the flock, the ailments affecting the birds, and the findings associated with bird losses. The main causes of bird losses included rearing management failures and age-related disorders.     

Spatial sampling design for prediction with estimated parameters

We study spatial sampling design for prediction of stationary isotropic Gaussian processes with estimated parameters of the covariance function. The key issue is how to incorporate the parameter uncertainty into design criteria to correctly represent the uncertainty in prediction. Several possible design criteria are discussed that incorporate the parameter uncertainty. A simulated annealing algorithm is employed to search for the optimal design of small sample size and a two-step algorithm is proposed for moderately large sample sizes. Simulation results are presented for the Matérn class of covariance functions. An example of redesigning the air monitoring network in EPA Region 5 for monitoring sulfur dioxide is given to illustrate the possible differences our proposed design criterion can make in practice.     

Genetische Variabilität

Zusammenfassung Für die Pflanzenzüchtung ist die genetische Variabilität eine entscheidende Voraussetzung. Sie basiert auf Genmutationen, Chromosomenmutationen, Introgressionen, Autopolyploidie, Alloplasmie, transponiblen DNA-Elementen und der Kombination. Diese Variabilitätskomponenten werden charakterisiert. Außerdem wird anhand von Beispielen ihr Einfluß auf die Entwicklung der Kulturpflanzen demonstriert.Um effektiv in der Pflanzenzüchtung arbeiten zu können, bedarf es der Analyse von genetischer Variabilität. Dies geschieht mit Hilfe von Kreuzungsexperimenten und Parameterschätzungen. In zunehmendem Maße werden auch Marker bei der Analyse eingesetzt.Einen wichtigen Faktor zur zielgerichteten Beeinflussung der genetischen Variabilität stellt die Selektion dar. Sie führt zur Einschränkung der Kombination. Die Selektion ist für die Entwicklung von Sorten notwendig. Sie hat aber auch eine Verarmung an genetischer Information zur Folge.Für den weiteren Fortschritt in der Pflanzenzüchtung gilt es, eine genügende genetische Variabilität zu gewährleisten. Dazu bedarf es auch Maßnahmen zu ihrer Erhaltung. Genetische Variabilität muß außerdem verstärkt charakterisiert und analysiert werden.

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Genetic variability

Summary Genetic variability is a decisive prerequisite to plant breeding. It is based on gene mutations, chromosome mutations, introgressions, autopolyploidy, alloplasmy, transposible DNA elements and recombinations. These components of the genetic variability are illustrated and examples are given to demonstrate their contributions to the evolution of crop plants.Effective plant breeding requires the analysis of the genetic variation. It is analysed by hereditary studies and parameter estimations. The utilization of markers is continuously increasing in studies of the genetic variation.Selection is an important factor to a purposive influence on the genetic variability and leads to a restriction of the recombinations. Selection is necessary for the development of varieties but results also in an impoverishment of genetic information.For the continuous progress in plant breeding an adequate genetic variability is to secure. That includes also activities to its conservation. Furthermore the characterization and analysis of the genetic variability has to be intensified.

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Microbial activity and bacterial composition of H2-treated soils with net CO2 fixation

The effects of H₂ gas treatment of an agricultural soil cultivated previously with a mixture of clover (Trifolium pratense) and alfalfa (Medicago sativa) on CO₂ dynamics and microbial activity and composition were analyzed. The H₂ emission rate of 250 nmol H₂ g⁻¹ soil h⁻¹ was similar to the upper limit of estimated H₂ amounts emitted from N₂ fixing nodules into the surrounding soil ([Dong, Z., Layzell, D.B., 2001. H₂ oxidation, O₂ uptake and CO₂ fixation in hydrogen treated soil. Plant and Soil 229, 1-12.]). After 1 week of H₂ supply to soil samples simultaneously with H₂ uptake net CO₂ production declined continuously and this finally led to a net CO₂ fixation rate in the H₂-treated soil of 8 nmol CO₂ g⁻¹ soil h⁻¹. The time course of H₂ uptake and CO₂ fixation in the soils corresponded with an increase in microbial activity and biomass of the H₂-treated soil determined by microcalorimetric measurements, fluorescence in situ hybridization analysis (FISH) and DNA staining (DAPI). Shifts in the bacterial community structure caused by the supply of H₂ were recorded. While the H₂ treatment stimulated β-and γ-subclasses of Proteobacteria, it had no significant effect on α-Proteobacteria. In addition, FISH-detectable bacteria of the Cytophaga-Flavobacterium-Bacteroides phylum increased in numbers.     

PSITTACINE SKULL RADIOGRAPHY

The psittacine skull is a complex anatomic structure, frequently traumatized but difficult to adequately image with standard radiographic procedures. Multiple views including a ventrodorsal, a lateral, and complementary oblique projections are necessary to fully evaluate potential skull fractures in the avian patient. Magnification radiography is a relatively easy procedure that aids the review of small osseous structures. Familiarity with psittacine skull anatomy greatly facilitates radiographic interpretation of cranial trauma.