Weed populations and pathogens

Plant:pathogen systems are complex, highly spatial and fluctuate considerably. The dynamics of their individual populations depends on factors such as their patchiness, shapes and scales of dispersal distributions, genetic polymorphism and their responses to their biotic and abiotic environments. We review knowledge of these population properties in the context of weed management and biological control and discuss their likely influence on the population dynamics of pathogens.     

Electroencephalography and space-occupying lesions in small animals

EEGs have been recorded from 207 dogs and cats with presumed intra-cranial space-occupying lesions; twenty-seven cases were confirmed postmortem. The clinical presenting signs of the series are considered, and the abnormal characters of the EEGs are analysed and discussed. The place of the EEG in differential diagnosis and its possible future value in association with brain surgery are discussed.
Résumé. On a enregistré des électroencéphalogrammes de 207 chiens et chats suspects de lésions intracraniennes expansives; ce diagnostic a pu être confirmé par l'examen nécropsique. On décrit les manifestations cliniques majeures dans cette série et on considère les anomalies de l'E.E.G., dont on analyse les particularités et dont on envisage l'importance diagnostique sous Tangle de la chirurgie du cerveau.
Zusammenfassung. Es wurden EEGs von 207 Katzen und Hunden mit vermuteten raumbean-spruchenden Läsionen im Schädelraum aufgenommen; 27 Fälle da von wurden durch Autopsie bestätigt. Die klinischen Erscheinungsbilder der Serie werden betrachtet und der anomale Gharakter der EEGs wird analysiert und besprochen. Der Platz des EEG in der Differentialdioagnose und sein möglicher künftiger Wert in Zusammenhang mit der Gehirnchirurgie wird besprochen.     

Sensitive and specific detection of Clavibacter xyli subsp. xyli, causal agent of ratoon stunting disease of sugarcane, with a polymerase chain reaction-based assay

A sensitive, specific polymerase chain reaction-based assay was developed for the detection of the causal agent of ratoon stunting disease of sugarcane, Clavibacter xyli subsp. xyli . This assay uses oligonucleotide primers derived from the internal transcribed spacer region between the 16S and 23S rRNA genes of the bacterial rRNA operon. The assay is specific for C. xyli subsp. xyli and does not produce an amplification product from the template of the closely related bacterium C. xyli subsp. cynodontis , nor from other bacterial species. The assay was successfully applied to the detection of C. xyli subsp. xyli in fibrovascular fluid extracted from sugarcane and was sensitive to approximately 22 cells per PCR assay. A multiplex PCR test was also developed which identified and differentiated C. xyli subsp. xyli and C. xyli subsp. cynodontis in a single PCR assay.     

Morphological changes of Trypanosoma vivax in mice

Morphological changes were observed in the blood forms of Trypanosoma vivax strain Y486 in mice on Days 12-13 of infection, following the peak parasitaemia. During this period elongate trypomastigotes, 25-40 micron long, were observed, most showing an anterior movement of the kinetoplast towards the nucleus and some having a blunt posterior end. In a few parasites a complete transformation to the epimastigote form, 40-42 micron long, was observed. Small sphaeromastigotes were also present, especially in the fine capillaries of various organs. Smears and electron microscopy suggested the presence of extra-vascular forms in the spleen.     

When fish shoals meet: outcomes for evolution and fisheries

The mechanisms underlying the social structure of free‐ranging fish shoals have received little attention in comparison to functional studies on shoaling. Recently, however, a number of investigations, both in the marine and in the freshwater environment, have begun to address the underlying mechanisms by concentrating on interactions between free‐ranging shoals. The rates of shoal encounters can influence the opportunities for individual assortment by phenotype and selection of shoal size; act as a constraint on the observed patterns of shoal structure by restricting individual choice behaviour and were found to be high in several small freshwater species (where intershoal distances were small), but lower in marine species where shoals were more dispersed. The duration of encounters may play a role in that it affects both the time available for assessment (of the encountered shoal) as well as that for exchange of individuals. Scarce published information on the outcome of shoal encounters suggests that the outcome of shoal encounters is influenced by shoal composition but not by shoal size. Individual behaviour may have evolved to maintain shoal size when shoals encounter, but when fish populations are depleted by fishing, this trait can exacerbate range and stock collapse. Furthermore, an understanding of the dynamics of shoal encounters has important consequences for the evolution of reciprocal altruism and the transmission of information through social learning within populations. Finally, information on encounter rates between shoals and the number of individuals that are exchanged on such occasions could be important for making predictions about the spread of disease through fish populations.     

Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.