Factors affecting infestation by Triatoma infestans in a rural area of the humid Chaco in Argentina: a multi-model inference approach

Background

Transmission of Trypanosoma cruzi by Triatoma infestans remains a major public health problem in the Gran Chaco ecoregion, where understanding of the determinants of house infestation is limited. We conducted a cross-sectional study to model factors affecting bug presence and abundance at sites within house compounds in a well-defined rural area in the humid Argentine Chaco.

Methodology/Principal Findings

Triatoma infestans bugs were found in 45.9% of 327 inhabited house compounds but only in 7.4% of the 2,584 sites inspected systematically on these compounds, even though the last insecticide spraying campaign was conducted 12 years before. Infested sites were significantly aggregated at distances of 0.8–2.5 km. The most frequently infested ecotopes were domiciles, kitchens, storerooms, chicken coops and nests; corrals were rarely infested. Domiciles with mud walls and roofs of thatch or corrugated tarred cardboard were more often infested (32.2%) than domiciles with brick-and-cement walls and corrugated metal-sheet roofs (15.1%). A multi-model inference approach using Akaike''s information criterion was applied to assess the relative importance of each variable by running all possible (17,406) models resulting from all combinations of variables. Availability of refuges for bugs, construction with tarred cardboard, and host abundance (humans, dogs, cats, and poultry) per site were positively associated with infestation and abundance, whereas reported insecticide use showed a negative association. Ethnic background (Creole or Toba) adjusted for other factors showed little or no association.

Conclusions/Significance

Promotion and effective implementation of housing improvement (including key peridomestic structures) combined with appropriate insecticide use and host management practices are needed to eliminate infestations. Fewer refuges are likely to result in fewer residual foci after insecticide spraying, and will facilitate community-based vector surveillance. A more integrated perspective that considers simultaneously social, economic and biological processes at local and regional scales is needed to attain effective, sustainable vector and disease control.     

The colonization history of Juniperus brevifolia (Cupressaceae) in the Azores Islands

Background

A central aim of island biogeography is to understand the colonization history of insular species using current distributions, fossil records and genetic diversity. Here, we analyze five plastid DNA regions of the endangered Juniperus brevifolia, which is endemic to the Azores archipelago.

Methodology/Principal Findings

The phylogeny of the section Juniperus and the phylogeographic analyses of J. brevifolia based on the coalescence theory of allele (plastid) diversity suggest that: (1) a single introduction event likely occurred from Europe; (2) genetic diversification and inter-island dispersal postdated the emergence of the oldest island (Santa Maria, 8.12 Ma); (3) the genetic differentiation found in populations on the islands with higher age and smaller distance to the continent is significantly higher than that on the younger, more remote ones; (4) the high number of haplotypes observed (16), and the widespread distribution of the most frequent and ancestral ones across the archipelago, are indicating early diversification, demographic expansion, and recurrent dispersal. In contrast, restriction of six of the seven derived haplotypes to single islands is construed as reflecting significant isolation time prior to colonization.

Conclusions/Significance

Our phylogeographic reconstruction points to the sequence of island emergence as the key factor to explain the distribution of plastid DNA variation. The reproductive traits of this juniper species (anemophily, ornithochory, multi-seeded cones), together with its broad ecological range, appear to be largely responsible for recurrent inter-island colonization of ancestral haplotypes. In contrast, certain delay in colonization of new haplotypes may reflect intraspecific habitat competition on islands where this juniper was already present.     

Performance, ruminal changes, behaviour and welfare of growing heifers fed a concentrate diet with or without barley straw

Two experiments were conducted to ascertain the effects of feeding an all-concentrate diet to growing heifers on performance, ruminal fermentation, behaviour and welfare. In experiment 1, eight tethered rumen fistulated Holstein heifers (143 ± 8.7 kg, initial BW) were used to study the effects of treatment on intake, ruminal changes and behaviour. In experiment 2, 48 Friesian female calves (initial BW = 84.5 ± 1.37 kg) were used to study the effects of treatment on performance, behaviour and welfare in feedlot conditions. In both experiments, treatments consisted of concentrate with barley straw (BS) or without barley straw (NBS) and feed was offered at 0830 h on an ad libitum basis. Experiment 1 was performed in four 42-day periods, and sampling was carried out in the last week of each period. Ruminal samples were collected over 3 days at 0, 4, 8 and 12 h post-feeding to measure pH, and volatile fatty acids (VFA) and NH(3)-N concentrations. Maintenance behaviour was video-recorded for 24 h over three consecutive days of each experimental period and feed intake pattern was studied by means of feed bunks mounted on digital platform scales. There were no statistical differences in average daily gain (ADG), concentrate dry matter (DM) intake or CP intake. In contrast, NDF intake and ADF intake were greater in heifers fed BS than NBS. Average ruminal pH was lower, whereas total VFA was greater, in heifers fed NBS diet. There were no differences in NH(3)-N, and in D- and L-lactate concentrations. Time spent in ruminating was shorter, and stereotypies were more frequent in heifers fed diet NBS compared with those fed BS. In experiment 2, nine 28-day periods were established, in which DM intake and ADG were measured, blood and faecal samples were taken for haptoglobin and glucocorticoid metabolites determination, respectively, as welfare indicators, and behaviour was monitored by video recording. Concentrate intake was similar in both treatments, but total feed intake was greater in heifers fed BS diet. As there were no differences in ADG between treatments, gain efficiency was lower in those fed BS than those fed NBS. Blood haptoglobin and faecal glucocorticoids metabolites were not different between treatments. In these competitive conditions, rumination was also reduced and stereotypic behaviour increased by straw exclusion. In conclusion, performance was either not affected or improved by straw exclusion, but animal behaviour was affected, suggesting a negative effect on animal welfare.     

Effects of plant leachates from four boreal understorey species on soil N mineralization, and white spruce (Picea glauca) germination and seedling growth

BACKGROUND AND AIMS: Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and/or (3) delaying seedling growth. METHODS: Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. KEY RESULTS: Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. CONCLUSIONS: These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.     

Site-directed spin labeling studies reveal solution conformational changes in a GAAA tetraloop receptor upon Mg(2+)-dependent docking of a GAAA tetraloop

The Mg(2+)-dependent GAAA tetraloop interaction with its 11 nucleotide receptor is one of the most frequently occurring long-range tertiary interactions in RNAs. To explore conformational changes in the receptor during tetraloop docking, nitroxide spin labels were attached at each of four uridine bases, one at a time, within an RNA molecule containing the receptor sequence. In the presence of Mg2+ and the tetraloop, the electron paramagnetic resonance (EPR) spectrum of one of the labeled bases reflected a large increase in mobility, indicating unstacking of the base upon tetraloop docking. This provides direct evidence that base unstacking is an intrinsic feature of the solution tetraloop-receptor complex formed in the presence of Mg2+. Additional evidence suggests that in solution the bound receptor conformation is similar to that observed in the crystal structure of a group I intron ribozyme domain. In Mg2+ alone, a receptor conformation with an unstacked base was not detectable, suggesting that this conformation is of higher standard state free energy than that of the free receptor. This leads to the conclusion that the extensive RNA-RNA interactions observed in the crystal structure of the tetraloop-receptor complex provide larger interaction energy than the measured apparent affinity between the tetraloop and the free receptor. This is compatible with a high specificity of the tetraloop-receptor interaction.     

Gamma carbonic anhydrases in plant mitochondria

Plant mitochondria contain non-phosphorylating bypasses of the respiratory chain, catalysed by the alternative oxidase (AOX) and alternative NADH dehydrogenases (NDH), as well as uncoupling (UCP) protein. Each of these components either circumvents or short-circuits proton translocation pathways, and each is encoded by a small gene family in Arabidopsis. Whole genome microarray experiments were performed with suspension cell cultures to examine the effects of various 3 h treatments designed to induce abiotic stress. The expression of over 60 genes encoding components of the classical, phosphorylating respiratory chain and tricarboxylic acid cycle remained largely constant when cells were subjected to a broad range of abiotic stresses, but expression of the alternative components responded differentially to the various treatments. In detailed time-course quantitative PCR analysis, specific members of both AOX and NDH gene families displayed coordinated responses to treatments. In particular, the co-expression of AOX1a and NDB2 observed under a number of treatments suggested co-regulation that may be directed by common sequence elements arranged hierarchically in the upstream promoter regions of these genes. A series of treatment sets were identified, representing the response of specific AOX and NDH genes to mitochondrial inhibition, plastid inhibition and abiotic stresses. These treatment sets emphasise the multiplicity of pathways affecting alternative electron transport components in plants.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s11103-005-5514-7     

Characteristics of in vivo murine erythropoietic response to sodium orthovanadate

Current knowledge about the effects of vanadium compounds on erythropoiesis is still reduced and even contradictory. The aim of this work was to evaluate the in vivo effects of a single dose of sodium orthovanadate (OV, 33 mg/kg i.p.) on CF-1 mice in a time course study (0-8 days). Murine erythropoiesis was assessed through a combinatory of experimental approaches. Classical peripheral and bone marrow (BM) hematological parameters were determined. Erythroid maturation in blood stream and hemopoietic tissues (59Fe uptake assays), BM erythroid progenitor frequency (clonogenic assays) and erythroid crucial protein expressions for commitment and survival: GATA-1, erythropoietin receptor (Epo-R) and Bcl-xL (immunoblottings) were evaluated. Neither BM cellularities nor BM viabilities changed noticeably during the study. Peripheral reticulocytes showed a biphasic increment on days 2 and 8 post-OV. hematocrits enhanced transiently between days 2 and 4. 59Fe uptake percentages enhanced in peripheral blood nearly two-fold over control values between 4 and 8 days (p<0.01) without changes in BM and spleen. Additionally, mature erythroid BM compartments: polychromatophilic erythroblasts and orthochromatic normoblasts increased by the eighth day. BFU-E colonies remained near basal values during the whole experience, whilst CFU-E colonies raised 60% over control at 8 days post-OV (p<0.05). GATA-1 and Epo-R were significantly over-expressed from the third until the end of the experimental protocol (p<0.01). Surprisingly, Bcl-xL showed a constitutive expression pattern without changes during the experience. Experimental data let us suggest that OV does not to cause bone marrow cytotoxicity and that it accelerates maturation of BM committed erythroid precursors. Moreover, there are significant correlations among erythroid-related protein expressions: GATA-1 and Epo-R and the frequency of CFU-E. In addition, Bcl-xL expression invariance during the time course study would indicate that the stimulatory effect of OV treatment on erythropoiesis was mainly exerted on the maturation of red cell precursors rather than on the antiapoptosis of erythroid terminal progenitors.