Direct and indirect effects of exotic annual grasses on species composition of a South Australian grassland

Abstract Invasion by Mediterranean annual grasses, such as Avena L. spp. and Bronms L. spp, is one of the major threats to temperate perennial grassland. This study investigated the effects of annual grasses and their litter on the species composition of a grassland near Burra, South Australia. The placement of annual grass litter on soil samples in the glasshouse decreased the establishment or growth of several exotic annual dicots. In the field the addition of annual grass litter slightly decreased the frequency of Danthonia Lam. & DC. tussocks. Furthermore, litter strongly reduced the species richness from 13 species in plots with no litter to nine species in plots with the highest litter level, mainly by decreasing the frequency of common exotic dicots. Native dicot frequency similarly appeared to be decreased by litter addition. In addition to the negative effects of their litter, annual grasses also directly competed with perennial grasses. The magnitude of the competitive effect varied systematically along a slope, suggesting that other factors such as soil properties may control competitive inter actions. The biomass of annual grasses also tended to increase with the addition of their own litter. This combination of positive and negative feedback mechanisms suggests that brief periods favourable for annual grasses, either through management changes or environmental conditions, can lead to persistent changes in the species composition of the system.     

Impact of habitat fragmentation on the genetics of populations in dendritic landscapes

1. The effect of habitat fragmentation on freshwater species has been addressed using brown trout Salmo trutta L. as a model species with a dendritic population structure. 2. Microsatellite loci were employed as molecular markers. Levels of gene flow and population subdivision were determined in more than 1200 brown trout individuals inhabiting four south European rivers with contrasting patterns of fragmentation, defined by the presence of barriers. 3. The genetic units in the four rivers were restricted by artificial barriers, and gene flow among samples within each river was associated with the level of fragmentation of the river. 4. Loss of genetic diversity and dislocation of the dendritic model have been detected in fragmented rivers. These results emphasise the importance of mitigating the impact of dams by constructing passages to restore gene flow along the river, for fish and other migratory species, as well as the need for caution in relation to stocking in isolated areas to avoid problems of inbreeding.     

A revised classification of subtribe Helianthinae (Asteraceae: Heliantheae) II. Derived lineages

Sequence data for internal transcribed spacer (ITS) and partial external transcribed spacer (ETS) regions were combined in a phylogenetic analysis with previously obtained plastid DNA restriction site data to provide a comprehensive molecular phylogenetic hypothesis for derived members of subtribe Helianthinae. Analyses of the two molecular datasets provided conflicting evidence on relationships among some groups, supporting the hypothesis that hybridization has played a significant role in the divergence of the subtribe. A revised generic‐level classification is presented that divides the approximately 350 species of the subtribe among 21 genera. The paraphyletic Viguiera is narrowed to embrace only the type species, V. dentata. Four newly described genera, Dendroviguiera, Gonzalezia, Heiseria and Sidneya, are composed of species formerly included in Viguiera. Aldama is expanded to include 118 species extending from southwestern North America and Mexico to South America. This requires 116 new combinations, including 58 that were recently transferred into Rhysolepis, which is a synonym of Aldama, based on molecular phylogenetic results. One species of Viguiera is transferred to Tithonia, and two combinations in Hymenostephium are validated. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167 , 311–331.     

Landscape-Genetic Analysis of Population Structure in the Texas Gray Fox Oral Rabies Vaccination Zone

ABSTRACT In west-central Texas, USA, abatement efforts for the gray fox (Urocyon cinereoargenteus) rabies epizootic illustrate the difficulties inherent in large-scale management of wildlife disease. The rabies epizootic has been managed through a cooperative oral rabies vaccination program (ORV) since 1996. Millions of edible baits containing a rabies vaccine have been distributed annually in a 16-km to 24-km zone around the perimeter of the epizootic, which encompasses a geographic area >4 × 10⁵ km². The ORV program successfully halted expansion of the epizootic into metropolitan areas but has not achieved the ultimate goal of eradication. Rabies activity in gray fox continues to occur periodically outside the ORV zone, preventing ORV zone contraction and dissipation of the epizootic. We employed a landscape-genetic approach to assess gray fox population structure and dispersal in the affected area, with the aim of assisting rabies management efforts. No unique genetic clusters or population boundaries were detected. Instead, foxes were weakly structured over the entire region in an isolation by distance pattern. Local subpopulations appeared to be genetically non-independent over distances >30 km, implying that long-distance movements or dispersal may have been common in the region. We concluded that gray foxes in west-central Texas have a high potential for long-distance rabies virus trafficking. Thus, a 16-km to 24-km ORV zone may be too narrow to contain the fox rabies epizootic. Continued expansion of the ORV zone, although costly, may be critical to the long-term goal of eliminating the Texas fox rabies virus variant from the United States.     

Cell Surface Saccharides in Three Phytomonas Species Differing in Host Specificity

ABSTRACT. Cell surface carbohydrates of three phytoflagellates, Phytomonas francai. Phytomonas serpens and Phytomonas sp. from different hosts including cassava, coreid insect Phthia picta and the milkweed plant Euphorbia hyssopifolia, respectively, were analysed by agglutination assays employing a battery of highly purified lectins with affinity for receptor molecules containing N-acetylglucosamine (d-GlcNAc), N-acetylgalactosamine (D-GalNAc), galactose, mannose-like (D-Man-like) residues and fucose, and by binding assay using radiolabeled [¹²⁵I]-wheat germ agglutinin (WGA) and fluorescent WGA lectin, as well as glycosidases of known sugar specificity, Escherichia coli K with mannose-affinity fimbrial lectin was also used as an agglutination probe. In general, the presence of D-GlcNAc. D-GalNAc and D-Man-like residues was detected in the phytomonads' plasma membrane. These sugar moieties were confirmed in whole cell hydrolysates as assessed by gas-liquid chromatography (GLC) which in addition, also showed the presence of galactose and xylose. However, marked differences in cell surface carbohydrate structures were observed. Wheat germ agglutinin, which binds to sialic acid and/or d-GlcNAc-containing residues, shows selective agglutinin activities for P. francai and Phytomonas sp., while Bandeiraea simplicifolia II agglutinin (which recognizes d-GlcNAc units) specifically bound to Phytomonas sp. Helix pomatia agglutinin which binds to D-GalNAc-containing residues reacted preferentially with Phytomonas sp. and P. serpens. Con A, which recognizes D-Man-like receptors, agglutinates all the phytomonads; however, the higher interaction was observed with Phytomonas sp. P. francai was selectively agglutinated in the presence of E. coli fimbrial lectin. Fluorescence WGA binding was significantly decreased by N-acetylglucosaminidase activities and the cell agglutination was not altered by neuraminidase treatment, suggesting the presence of an exposed D-GlcNAc moiety on the P. francai and Phytomonas sp. surfaces. Binding studies with [¹²⁵I]-WGA essentially confirmed the fluorescence WGA binding and agglutination assays.     

Neuroendocrine Correlates of Circadian Rhythmicity in Crustaceans

The secretion of neurohormones from the crustacean X-organ –sinus gland system is controlled by environmental influences,light being the most conspicuous. Two sets of photoreceptorsappear to mediate the influence of light on neurosecretion basedon intracellular recordings from X-organ neurons and estimationsof hormone release. Extra-retinal photoreceptors can initiateneurohormonal release from the eyestalk. Neurosecretory activity is also influenced by putative neurotransmitters.GABA is found in high concentrations in the medulla temninalisof the eyestalk and is released by stimulation, in a calcium-dependentmanner. Diurnal variations occur in the amounts of eyestalk neurohormones,either those present in the eyestalk or released by electricalstimulation of the isolated sinus gland. Rhythm phases varyfrom one hormone to another. Neurohormones secreted in the eyestalkare also found in other regions of the central nervous system.Rhythms of neurosecretion are present both in the secretionin the isolated eyestalk and in eyestalkless animals, thus indicatingthat rhythmicity is a distributed property of the neurosecretorysystem.     

Reproductive biology in Acacia caven (Mol.) Mol. (Leguminosae) in the central region of Argentina

Studies on Acacia caven (Mol.) Mol. in central Argentina indicate that the species is polygamous (andromonoecious), some plants having a high proportion of staminate heads. Though pollen/ovule ratios of flowers, inflorescences and plants are at a level common for 'facultative xenogamic' systems, controlled pollination shows a marked xenogamy. The ratio between pollen grains in the polyad and the maximum number of seeds per pod is close to one. Observations support the idea of the inflorescence as a specialized reproductive unit with gynoecia functioning as fixed modules in which all or none of its ovules develop into seeds. Mass flowering prior to the growing season, the absence of other floral resources in the community, the high degree of fruiting limitations and scarce insect visitation suggest that, as in other Acacia , the reproductive system of Acacia caven involves a great sacrifice of floral resources.