Are ant assemblages of Brazilian veredas characterised by location or habitat type?

Wetland areas in the Brazilian Cerrado, known as “veredas”, represent ecosystems formed on sandy soils with high concentrations of peat, and are responsible for the recharge of aquiferous reservoirs. They are currently under threat by various human activities, most notably the clearing of vegetation for Eucalyptus plantations. Despite their ecological importance and high conservation value, little is known about the actual effects of human disturbance on the animal community. To assess how habitat within different veredas, and plantations surrounding them affect ant assemblages, we selected four independent vereda locations, two being impacted by Eucalyptus monoculture (one younger and one mature plantation) and two controls, where the wetland was surrounded by cerrado vegetation. Ant sampling was conducted in May 2010 (dry season) using three complementary methods, namely baits, pitfall traps, and hand collection, in the wetland and in the surrounding habitats. A total of 7,575 ants were sampled, belonging to seven subfamilies, 32 genera and 124 species.Ant species richness and abundance did not differ between vereda locations, but did between the habitats. When impacted by the monoculture, ant species richness and abundance decreased in wetlands, but were less affected in the cerrado habitat. Ant species composition differed between the three habitats and between vereda locations. Eucalyptus plantations had an ant species composition defined by high dominance of Pheidole sp. and Solenopsis invicta, while natural habitats were defined by Camponotus and Crematogaster species. Atta sexdens was strictly confined to native habitats of non-impacted “veredas”. Eucalyptus monocultures require high quantities of water in the early stages, which may have caused a decrease in groundwater level in the wetland, allowing hypogeic ants such as Labidus praedator to colonise this habitat

Plasmacytoid Dendritic Cells Sequester High Prion Titres at Early Stages of Prion Infection

In most transmissible spongiform encephalopathies prions accumulate in the lymphoreticular system (LRS) long before they are detectable in the central nervous system. While a considerable body of evidence showed that B lymphocytes and follicular dendritic cells play a major role in prion colonization of lymphoid organs, the contribution of various other cell types, including antigen-presenting cells, to the accumulation and the spread of prions in the LRS are not well understood. A comprehensive study to compare prion titers of candidate cell types has not been performed to date, mainly due to limitations in the scope of animal bioassays where prohibitively large numbers of mice would be required to obtain sufficiently accurate data. By taking advantage of quantitative in vitro prion determination and magnetic-activated cell sorting, we studied the kinetics of prion accumulation in various splenic cell types at early stages of prion infection. Robust estimates for infectious titers were obtained by statistical modelling using a generalized linear model. Whilst prions were detectable in B and T lymphocytes and in antigen-presenting cells like dendritic cells and macrophages, highest infectious titers were determined in two cell types that have previously not been associated with prion pathogenesis, plasmacytoid dendritic (pDC) and natural killer (NK) cells. At 30 days after infection, NK cells were more than twice, and pDCs about seven-fold, as infectious as lymphocytes respectively. This result was unexpected since, in accordance to previous reports prion protein, an obligate requirement for prion replication, was undetectable in pDCs. This underscores the importance of prion sequestration and dissemination by antigen-presenting cells which are among the first cells of the immune system to encounter pathogens. We furthermore report the first evidence for a release of prions from lymphocytes and DCs of scrapie-infected mice ex vivo, a process that is associated with a release of exosome-like membrane vesicles

Exotic earthworm effects on hardwood forest floor, nutrient availability and native plants: a mesocosm study

European earthworms are invading previously worm-free hardwood forests across Minnesota and the Great Lakes region. In many of these forests, earthworm invasions have been associated with the loss of a previously thick forest floor. The ability of earthworms to alter and control ecosystem processes has been demonstrated in agricultural systems, but the dynamics and impact of these invasions in native forest ecosystems is largely unknown. The impacts of earthworm invasion are expected to be related to the size and species composition of the earthworm population because different species have different habitat and feeding preferences. We identified four sugar maple dominated forests in north central Minnesota in the Chippewa National Forest with active earthworm invasion. In each site a sample grid of 45 points (30 x 150 m) 10 m apart in three parallel transects with 15 points each was established that spanned a visible leading edge of invasion. Over four years earthworm populations and forest floor thickness were sampled across all transects, thus providing both a space-for-time assessment of decadal scale successional dynamics and a four-year window into shorter time changes. We found a succession of earthworm species across the visible leading edge due to different patterns of colonization by different earthworm species. Marked increases in space and time in earthworm biomass were associated with the development of discrete transition zones where forest floor thickness decreases to zero in as little as 75 m from areas that have forest floor layers up to 10 cm thick with advancement of the visible leading edge of up to 30 m in four years at three of the study sites. The epi-endogeic species Lumbricus rubellus led to the most rapid removal of forest floor material during initial invasion. Epigeic and epi-endogeic species of earthworms may facilitate the establishment of other species of earthworms leading to the establishment of stable populations of endogeic and anecic species, which prevent recovery of the forest floor