Dynamic screening of agricultural contaminants in freshwater ecosystems as part of amphibian biodiversity conservation

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Improving image quality in fast, time-resolved micro-CT by weighted back projection

Time-resolved micro-CT is an increasingly powerful technique for studying dynamic processes in materials and structures. However, it is still difficult to study very fast processes with this technique, since fast scanning is typically associated with high image noise levels. We present weighted back projection, a technique applicable in iterative reconstruction methods using two types of prior knowledge: (1) a virtual starting volume resembling the sample, for example obtained from a scan before the dynamic process was initiated, and (2) knowledge on which regions in the sample are more likely to undergo the dynamic process. Therefore, processes on which this technique is applicable are preferably occurring within a static grid. Weighted back projection has the ability to handle small errors in the prior knowledge, while similar 4D micro-CT techniques require the prior knowledge to be exactly correct. It incorporates the prior knowledge within the reconstruction by using a weight volume, representing for each voxel its probability of undergoing the dynamic process. Qualitative analysis on a sparse subset of projection data from a real micro-CT experiment indicates that this method requires significantly fewer projection angles to converge to a correct volume. This can lead to an improved temporal resolution

Effect of human-induced environmental changes on bird diversity and abundance in natural wetlands of Southwest Ethiopia

The diversity and abundance of wetland birds have been threatened by increasing anthropogenic activities during recent decades. The objective of this study was to determine the effect of human-induced disturbance on bird species richness and abundance of natural wetlands in southwest Ethiopia. Bird surveys were performed at 56 locations during both the wet and dry seasons in 2010 and 2011. Generalized linear modeling (G) was used to correlate species richness with environmental variables. It was found that wetlands with low human disturbance were characterized by a higher richness (n > 10) of wetland dependent specialist birds (depending completely on wetlands for food and nesting) than the highly disturbed wetlands. However, for wetland-associated birds (those able to nest and feed in wetlands as well as in other habitats), there was no significant difference (P = 0.31) in species richness between disturbed and non-disturbed wetlands. The abundance of wetland dependent specialist birds was significantly affected (P < 0.001) by human disturbance, whereas the abundance of wetland associated birds was not (P = 0.39). Fifty-three percent of the variation in species richness of wetland dependent birds was explained by a combination of water depth, sludge depth, conductivity, chlorophyll a, total phosphorus, human disturbance and vegetation cover. It is recommended that anthropogenic activities should be minimized and controlled in and around these wetlands to conserve biodiversity

Towards a food web based control strategy to mitigate an amphibian panzootic in agricultural landscapes

While the emerging amphibian disease chytridiomycosis is causing dramatic and ongoing biodiversity losses worldwide, sustainable strategies to mitigate this global threat to amphibians are currently missing. We here propose a conceptual framework for a novel biological mitigation strategy based on the increasing evidence that naturally occurring micropredators, such as protists, rotifers and crustaceans, are capable of using zoospores of the chytrid pathogens Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) as a food source under controlled laboratory conditions. Pathogen predation may serve as a cost-efficient way to prevent chytridiomycosis outbreaks under natural conditions by reducing zoospore densities and thereby infection loads. This predator-pathogen relationship is not an isolated interaction, but is embedded in the aquatic food web structure that interacts with a wide range of environmental factors. Amphibian breeding ponds are increasingly associated to agricultural landscapes due to ongoing land use occupancy for food production, exposing these water bodies to a variety of environmental stressors such as agrochemical pollution, nutrient enrichment and cattle trampling. Environmental stressors may affect the composition and abundance of aquatic communities, while they can also exert sublethal effects that may reduce the zoospore removal efficiency of micropredators. By carefully controlling environmental stressors, trophic interactions may be steered to optimize chytrid predation with the aim of reducing zoospore densities to such extent that hosts and pathogens can sustainably coexist. We present a scientific outline of this novel concept and provide a framework for ongoing research to develop a complete mitigation strategy against chytridiomycosis based on such food web control

Sediment and nutrient retention capacity of natural riverine wetlands in Southwest Ethiopia

Although wetlands in temperate regions have been studied for their pollutant remediation potential, the sediment and nutrient retention capacity of natural wetlands in tropical environments remains understudied. In this study, a mass balance approach was used to estimate the amount of sediment and nutrients retained at 40 different study sites located in four natural riverine wetlands in Southwest Ethiopia. Awetu and Boye wetlands retained a substantial amount of total suspended solids (TSS) and nutrients whereas Kofe and Kito wetlands had a net release. Overall, the amount of TSS retained by the four wetlands was estimated to be 6266.5 kg/ha/day. On the other hand, the net retention of Total Organic Nitrogen (TON) and Total Phosphorous (TP) was estimated to be 37.6 kg/ha/day and 40.9 kg/ha/day, respectively. A stepwise multiple regression analysis revealed that anthropogenic activities such as farming, grazing, waste dumping and clay mining were the main variables that negatively affected the retention of TSS and nutrients. Farming alone explained 58% of the variation in TSS retention and cattle grazing explained 25% of the variation in TON retention. Therefore, watershed management interventions considering the mitigation of anthropogenic activities could be considered to reduce sediment and nutrient input and release

Camelid reporter gene imaging: a generic method for in vivo cell tracking

BACKGROUND: To combine the sensitivity of bioluminescent imaging (BLI) with the 3D and quantitative properties of pinhole single-photon emission computed tomography (SPECT)/micro-computed tomography (CT) (phSPECT/micro-CT), we generated stable cell lines that express a yellow-fluorescent protein (YFP) and Gaussia luciferase (GLuc) fusion protein (YFP/GLuc). For in vivo phSPECT detection of this YFP/GLuc protein, a nanobody, targeted against yellow and green fluorescent proteins (anti-YFP-Nb), was site specifically labelled with (99m)Tc. METHODS: Human embryonic kidney cells (HEK293T) were cultured and passaged every 3 days. 10E5 cells were transduced with YFP/GLuc-containing vector: both membrane-targeted (MT-YFP/GLuc) and non-targeted (YFP/GLuc) fusion proteins were developed. These vectors were compared against a SKOV-3 cell line stably expressing green fluorescent-firefly luciferase (GFP/Fluc) and HEK293T cells expressing red fluorescent protein in combination with a Gaussia luciferase (Red/GLuc). Transduction efficiencies were scored by fluorescence microscopy, and transduced cells were enriched by fluorescence-activated cell sorting (FACS). GLuc and FLuc functionality was tested in vitro by list-mode BLI. Subsequently, cells were transplanted subcutaneously in athymic (nu/nu) mice (MT-YFP/GLuc: n = 4, YFP/GLuc: n = 6, GFP/FLuc: n = 6, Red/GLuc: n = 4). Labelling efficiency of anti-YFP-Nb was measured using instant thin layer chromatography. One week after transplantation, (99m)Tc-labelled anti-YFP-Nb was injected intravenously and pinhole (ph) SPECT/micro-CT was performed, followed by in vivo BLI. RESULTS: Cells showed high levels of fluorescence after transduction. The cells containing the MT-YFP/GLuc were positive on fluorescence microscopy, with the fluorescent signal confined to the cell membrane. After cell sorting, transduced cells were assayed by BLI and showed a significantly higher light output both in vitro and in vivo compared with non-transduced HEK293T cells. The anti-YFP-Nb labelling efficiency was 98%, and subsequent phSPECT/micro-CT demonstrated visible cell binding and significantly higher transplant-to-muscle ratio for both the MT-YFP/GLuc and YFP/GLuc transplanted cells, compared with the GFP/FLuc and Red/GLuc group. CONCLUSION: This study provides a proof of principle for a nanobody-based cell tracking method, using a YFP/GLuc fusion protein and anti-YFP-Nb in a model of subcutaneously transplanted transduced HEK293T cells