Ultrastructural Visualization of Lipids in Trypanosomatids1

An imidazole-buffered osmium tetroxide solution was used to visualize lipids at the ultrastructural level in the following members of the family Trypanosomatidae: Trypanosoma cruzi, T. dionisii, T. vespertilionis, T. rangeli, Crithidia deanei, C. fasciculata, C. oncopelti, and Blastocrithidia culicis. Electron-dense material was seen in various lipid droplets found in all parasites and in the multivesicular structure of members of the sub-genus Schizotrypanum. High contrast of some membranes, mainly those which enclose the mitochondrion, the nucleus, and the endoplasmic reticulum, was observed even in unstained sections. X-ray microanalysis confirmed that the electron density of lipid droplets of B. culicis and membrane-bounded dense granules of C. oncopelti was due to the presence of osmium.     

Entamoeba histolytica: Collagenolytic Activity and Virulence1

Several axenic strains of pathogenic and nonpathogenic Entamoeba histolytica were tested for their capacity to digest native radioactive type I collagen gels and to produce liver abscesses when injected into the liver of newborn hamsters. The results demonstrate that the pathogenic strains of amebas (HM1:IMSS, HM3:IMSS, HM38:IMSS, and HK9) have a collagenolytic activity that closely correlates with their in vivo capacity to produce liver lesions. The nonpathogenic isolate (Laredo) did not show collagenolytic activity and failed to produce lesions in the liver of newborn hamsters. The results also demonstrate that type I collagen obtained from rodents and cats is degraded less by amebic collagenase than is bovine collagen, which is similar to human collagen. These findings suggest that species susceptibility to invasive infection may depend, among other factors, on the characteristics of the extracellular components of host tissues.     

Quantitative trait loci and candidate genes underlying genotype by environment interaction in the response of Arabidopsis thaliana to drought

Drought stress was imposed on two sets of Arabidopsis thaliana genotypes grown in sand under short‐day conditions and analysed for several shoot and root growth traits. The response to drought was assessed for quantitative trait locus (QTL) mapping in a genetically diverse set of Arabidopsis accessions using genome‐wide association (GWA) mapping, and conventional linkage analysis of a recombinant inbred line (RIL) population. Results showed significant genotype by environment interaction (G×E) for all traits in response to different watering regimes. For the RIL population, the observed G×E was reflected in 17 QTL by environment interactions (Q×E), while 17 additional QTLs were mapped not showing Q×E. GWA mapping identified 58 single nucleotide polymorphism (SNPs) associated with loci displaying Q×E and an additional 16 SNPs associated with loci not showing Q×E. Many candidate genes potentially underlying these loci were suggested. The genes for RPS3C and YLS7 were found to contain conserved amino acid differences when comparing Arabidopsis accessions with strongly contrasting drought response phenotypes, further supporting their candidacy. One of these candidate genes co‐located with a QTL mapped in the RIL population.     

Damage caused by mistletoe Misodendrum punctulatum Banks Ex Dc. on architecture and radial growth of Nothofagus pumilio (Poepp. et Endl.) Krasser forests of southern Chile

Parasitic plants rely completely or partially on host plant, namely holoparasitic or hemiparasitic, respectively. The effect of parasitism on host plants is not fully known. Misodendrum punctulatum (Misodendraceae) is the most common hemiparasite species in the southernmost forests of Chile and Argentina, and it has been identified as an important sanitary problem in forestry. In this study we evaluated the M. punctulatum effect on growth rates and architecture of pure Nothofagus pumilio (Nothofagaceae) forests in southern South America (52°10′S; 71°55′W). We established three plots of 30 × 30 m, and 10 cores were extracted from diameter at breast height (d.b.h. = 1.3 m) from living trees in each plot, using increment borers. Tree rings were measured, and anova was used to compare the annual growth rate of both infected and uninfected N. pumilio. The results showed that N. pumilio trees severely infected by M. punctulatum reduce growth rates in contrast with uninfected individuals (P < 0.05). Besides, trees with high‐infection levels evidenced deterioration in its architecture, showing asymmetric and suppressed canopies, according to ad hoc numerical indexes. This study provides a starting point to understand the parasite–host relationship in the Patagonian forests of southern Chile.     

Effects of Inhibitors of Protein Synthesis on Transmembrane Auxin Transport in Cucurbita pepo L. Hypocotyl Segments

Pretreatment of 2?0 mm segments of etiolated zucchini (Cucurbitapepo L.) hypocotyl with cycloheximide (CH) or 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide(MDMP) eliminated the stimulation by N-1-naphthylphthalamicacid (NPA) of net uptake of [1-¹⁴C]indol-3yl-acetic acid ([1-¹⁴C]IAA),but had relatively little effect on the net uptake of IAA inthe absence of NPA. The efflux of [1-¹⁴C]IAA from preloadedsegments was not substantially affected by inhibitor pretreatmentin the absence of NPA, but CH pretreatment significantly inhibitedthe reduction of efflux caused by NPA. Pretreatment with CHor MDMP did not affect net uptake by segments of the pH probe[2-¹⁴C]5,5-dimethyl-oxazolidine-2,4-dione ([2-¹⁴C]DMO), or thenet uptake of [¹⁴C]-labelled 3-O-methylglucose ([¹⁴C]3-0-MeGlu),suggesting that neither inhibitor affected intracellular pHor the general function of proton symporters in the plasma membrane.Both compounds reduced the incorporation of label from [³⁵S]methionineinto trichloroacetic acid (TCA)-insoluble fractions of zucchinitissue, confirming their inhibitory effect on protein synthesis. The steady-state association of [³H]IAA with microsomal vesiclesprepared from zucchini hypocotyl tissue was enhanced by theinclusion of NPA in the uptake medium. The stimulation by NPAof [³H]IAA association with microsomes was substantially reducedwhen the tissue was pretreated with CH. However, CH pretreatmentdid not affect the level of high affinity NPA binding to themembranes indicating that treatments did not result in lossof NPA receptors. It is suggested that the auxin transport site on the effluxcarrier system and the receptor site for NPA may reside on separateproteins linked by a third, rapidly turned-over, transducingprotein. Key words: Auxin carriers, auxin efflux, Cucurbita pepo, phytotropin receptors     

Seasonal changes in a cactus‐hoverfly (Diptera: Syrphidae) network

1. We analysed a cacti‐syrphid community focusing on the exploitation of decaying cacti resources by the flies, i.e. if exploitation exhibited a nested topology as a structural pattern, or whether it was temporally random. If availability of cactus resources was predictable during the rainy season, it would then be exploited by a more structured community, or as resource availability would be unpredictable during the dry season, we should expect it to be exploited by a random community. 2. We registered 12 Copestylum species (9 in dry and 11 in rainy season). Four cactus species were recorded per season, three were shared between seasons. 3. The community of Copestylum larvae in the rainy season was not randomly assembled but highly nested, revealing a highly structured pattern of resource use. It exhibited a random organization for the dry season. The high nestedness value obtained for the rainy season suggests that factors along with competition must play a major role in determining community structure. 4. Succession in the cacti‐syrphid community mediated by microorganisms involved in necrosis is an important factor structuring nested subsets. The studied networks were small, which may limit the power of the analysis, and strong conclusions could also be limited.     

Form and function within a phylogenetic framework: locomotory habits of extant predators and some Miocene Sparassodonta (Metatheria)

In this study, we analysed locomotory habits in extant predators and Sparassodonta species through geometric morphometric techniques and discriminant analyses of the distal humerus in anterior view, proximal ulna in lateral view, and tibia in proximal view. We included a wide sample of extant predators, and considered the phylogenetic and allometric structure in the data sets. We also included some Sparassodonta, a group of carnivorous metatherians that inhabited South America during the Cenozoic, and inferred their locomotory habits. Results suggest the presence of a close relationship between shape and locomotory habits, even after removing the shape component explained by phylogeny in the three postcranial elements. Terrestrial habits were inferred for Arctodictis sinclairi, Borhyaena tuberata, ‘Lycopsis’ longirostrus, and Thylacosmilus atrox. Some degree of cursoriality was highlighted in B. tuberata and T. atrox, and climbing abilities in ‘L.’ longirostrus, and to a lesser degree in B. tuberata. Scansorial habits were inferred for Cladosictis patagonica, Sipalocyon gracilis, Prothylacynus patagonicus, and Pseudonotictis pusillus, and in the case of C. patagonica, some digging ability was also tentatively inferred. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 224–251.     

Neotropical Copestylum (Diptera,Syrphidae) breeding in Agavaceae and Cactaceae including seven new species

We studied 42 species of saprophagous, Neotropical Copestylum (Diptera, Syrphidae) reared from decaying Cactaceae and Agavaceae. Thirty‐three species were reared during fieldwork in Bolivia, Costa Rica, Ecuador, Mexico, Peru, and Trinidad from 1998–2007. Nine species came from museum and private collections. Seven were new species. We describe these new species and the third stage larva and/or puparium and breeding sites of 40 species. Not described are two apparent species related to Copestylum apicale (Loew, 1866) reared from Cactaceae. Resolution of their status was beyond the scope of this paper but reference is made to their distinctive larval morphology. Based on early stage characters all reared species can be placed in ten species groups, all but three of which have been recognized previously on the basis of adult characters. A high level of congruence was found between adult and larval characters in terms of these species groups. Eight of the groups appear to be related closely and may represent a monophyletic lineage within Copestylum that has diversified in xeric habitats. Early stage morphology varied within and amongst groups but two trends in functional morphology are recognizable. One trend is towards feeding in watery decay and the other towards feeding in firmer decay. The latter trend is characterized by species that scoop food and use grinding mills in their head skeletons to break it up. They also have armoured thoraces with varying arrangements of sclerotized spicules or stiffened setae for gripping and protection during tunnelling, a short anal segment, and a short posterior breathing tube for protecting the openings. The former trend is characterized by species with opposite and contrasting features. They filter food and have well‐developed pre‐oral setal filters but they lack grinding mills or only have poorly developed grinding mills. They have reduced thoracic armature, elongate anal segments, and posterior breathing tubes which facilitates simultaneous feeding and respiration. Comparison with 23 Copestylum species reared from bromeliads (Bromeliaceae) suggests a common pattern of diversification in that species groups with the largest body sizes are more specialized.     

Characterization of Acanthamoeba Isolates from Dust of a Public Hospital in Curitiba, Paraná, Brazil

ABSTRACT. Occurrence of Acanthamoeba in the hospital environment may represent a health risk for patients, since these organisms can cause severe opportunistic illness, such as keratitis, and also can harbor pathogenic agents. We analyzed the dust from some environments of a public hospital in Curitiba, Parana State, Brazil. Two distinct populations of Acanthamoeba were isolated in five locations and morphologically classified as group I and group II according to Pussard and Pons. Isolates were identified as Acanthamoeba by PCR using primers to amplify a region of 18S rDNA, which showed variation in the product length among the isolates. A cloned culture of group II showed greater growth at 37 °C and in media with 0.1, 0.5, and 1.0 M mannitol, which are the physiological characteristics of pathogenic Acanthamoeba . Monitoring the presence of Acanthamoeba in hospital units, as well as evaluating the pathogenicity of the isolates, can be an approach to alert the health professionals to improve the disinfection procedures and minimize the risks of treating this problematic disease caused by this protozoan.     

Small‐scale spatial dynamics of vegetation in a grazed Uruguayan grassland

We explored the small‐scale plant species mobility in a subhumid native grassland subjected to grazing by cattle in south‐western Uruguay. We established four permanent plots of 40 × 40 cm, divided in 16 × 16 cells. In each cell, the presence of species was seasonally recorded for 2 years and annually recorded for 4 years. By nesting the cells, we studied the mobility at different scales, from 6.25 cm² to 400 cm². At each scale we measured species richness, cumulative richness and the turnover rates of the dominant species. We found that the cumulative species richness was an increasing power function, with higher accumulation rates with smaller spatial scale. Although species richness showed seasonal fluctuations, the mean species richness was constant during the study period. We detected significant spatio‐temporal variability in mobility patterns among species. Certain species showed a high capacity to colonize new sites, whereas other species rotate among sites that they previously occupied. Grazed communities in Uruguayan Campos are structured as a dense matrix of perennials grasses and forbs, where vegetative propagation is the main form of growth of the species. The small‐scale dynamics and the high variability in the mobility characteristics could be linked with the diversity of growth forms and spatial strategies of the species in this community. We believe that a high degree of small‐scale spatial dynamics contribute to explain the species coexistence and the apparent stability of communities at local scales.