Traditional methods to identify aquatic hyphomycetes rely on the morphology of released conidia, which can lead to misidentifications or underestimates of species richness due to convergent ...morphological evolution and the presence of non-sporulating mycelia. Molecular methods allow fungal identification irrespective of the presence of conidia or their morphology. As a proof-of-concept, we established a quantitative real-time polymerase chain reaction (qPCR) assay to accurately quantify the amount of DNA as a proxy for the biomass of an aquatic hyphomycete species (Alatospora pulchella). Our study showed discrimination even among genetically closely-related species, with a high sensitivity and a reliable quantification down to 9.9 fg DNA (3 PCR forming units; LoD) and 155.0 fg DNA (47 PCR forming units; LoQ), respectively. The assay's specificity was validated for environmental samples that harboured diverse microbial communities and likely contained PCR-inhibiting substances. This makes qPCR a promising tool to gain deeper insights into the ecological roles of aquatic hyphomycetes and other microorganisms.
Background The bacterium Bacillus thuringiensis serovar israelensis (Bti) is commercially produced in various formulations for use as a larvicide worldwide, targeting especially the aquatic larval ...stage of mosquitoes. However, there is a concern that repeated Bti treatments may have both direct and indirect impacts on non-target organisms (NTOs) and the ecosystems they inhabit. This review evaluates the evidence for such impacts. Methods Literature was searched using six bibliographic databases, two search engines, and on specialist web sites. Eligibility screening was performed in two steps on (1) title/abstract, with consistency among reviewers assessed by double-screening 557 articles and (2) full text. Articles included after full text screening were critically appraised independently by two reviewers. Disagreements were reconciled through discussions. Key parameters of included studies are presented in narrative synthesis tables, including risk of bias assessments. Meta-analyses comparing treated with untreated ecosystems and using either the raw mean difference or log response ratio as effect size were performed. Review findings Ninety-five articles covering 282 case studies were included in the review. From these, we identified 119 different response variables, which were divided into nine outcome categories. Most studies investigated NTO abundance or life history (reproduction related outcomes), but diversity and community composition are also well represented as outcome categories. The studies are highly variable in methodology, rigor, and spatio-temporal scale, spanning 1 day to 21 years and from < 1m.sup.2 to > 10,000 m.sup.2. Our metanalyses revealed a consistent negative effect of Bti treatment on abundances of Chironomidae and Crustacea, and also on chironomid emergence, although from a more restricted set of studies and regions. For most remaining response variables, we judged meta-analysis unfeasible, due to low study numbers or insufficient reporting of methods and results. Conclusions There is now a significant body of studies documenting effects of mosquito control using Bti on NTOs or other ecosystem properties, especially associated with negative effects on Chironomidae, as apparent from our meta-analyses. Accordingly, we suggest the potential for negative NTO or other ecosystem effects of Bti treatment should not be discounted a priori. Once a decision to proceed with Bti treatment has been taken, priority should be given to a well-designed program of ongoing monitoring and assessment. The paucity of rigorous studies conducted with low bias risk for most response variables undermines our capacity for evaluating how common many of the effects documented might be. Future research would benefit from a rigorous and well-replicated approach to studying Bti impacts in semi-field mesocosms or in the field, combined with a greater rigor in reporting key methodological details. A greater focus is needed on understanding the environmental factors which regulate the wider effects of mosquito control using Bti on NTOs and ecosystems, to enhance our capacity for predicting where and when Bti is most likely to have additional, negative and indirect ecological impacts. Keywords: Diptera, Biocontrol, Indirect impacts, Non-target organisms, Chironomidae, Whole-ecosystem effects
The breakdown of allochthonous organic matter, is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown ...rate of organic matter, with important consequences for the ecosystem functioning of alpine streams. This study investigated the rate of leaf litter breakdown and how temperature and other factors such as microbial and invertebrate activities influenced this over elevational and temporal gradients. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6 mm), and fine (50 μm) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter, and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations, with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests the potential effects of climate change‐induced temperature increases on ecological processes in such streams.
We aimed at understanding how spatial and temporal water temperatures influenced AOM breakdown in alpine streams. Microbial and macroinvertebrate activities were monitored and showed to be elevated at lower elevations and during warmer periods. Climate change induced warming will therefore potentially change alpine stream ecosystem, standing biomass and promote increased nutrient cycling through AOM breakdown.
Legal frameworks that assess stream ecological integrity rely mostly on structural metrics and implicitly assume that good structure will result in good function. This assumption may, however, be ...challenged. The results of our literature screening show that the structure and function of leaf-associated microbial assemblages can be decoupled, meaning that structure and function are not similarly affected by anthropogenic pressures. This decoupling can be characterized by microbially-mediated leaf litter decomposition remaining stable, increasing, or exhibiting a U-shaped response as structural metrics (e.g., taxonomic diversity) change gradually. When these types of decoupling occur, stream ecological integrity may be misinterpreted when solely based on structural metrics. This misinterpretation may be driven by a structurally-simplified microbial assemblage (e.g., fewer taxa) effectively decomposing leaf litter, which may limit the contribution of structurally-simplified assemblages to further ecosystem level processes (e.g., nutrition of food webs). At the same time, structurally-simplified microbial assemblages may exhibit reduced ecological resilience against pressures. Therefore, we suggest that incorporating both structural and functional metrics will improve stream biomonitoring by increasing our ability to determine the consequences of anthropogenic pressures. Additional use of molecular biological methods and information on microbial traits should improve the assessment of stream ecological integrity.
Biodiversity is under pressure worldwide, with amphibians being particularly threatened. Stressors related to human activity, such as chemicals, are contributing to this decline. It remains, however, ...unclear whether chemicals exhibiting a fungicidal activity could indirectly affect tadpoles that depend on microbially conditioned leaf litter as food source. The indirect effect of fungicides (sum concentration of a fungicide mixture composed of azoxystrobin, carbendazim, cyprodinil, quinoxyfen, and tebuconazole: 100 µg/L) on tadpoles was assessed relative to leaf litter colonized by microbes in absence of fungicides (control) and a worst‐case scenario, that is leached leaf litter without microbial colonization. The quality of leaf litter as food for tadpoles of the European common frog (Rana temporaria) was characterized through neutral lipid fatty acid profiles and microbial sum parameters and verified by sublethal responses in tadpoles (i.e., feeding rate, feces production, growth, and fatty acid composition). Fungicides changed the nutritious quality of leaf litter likely through alterations in leaves’ neutral lipid fatty acid profiles (i.e., changes in some physiologically important highly unsaturated fatty acids reached more than 200%) in combination with a potential adsorption onto leaves during conditioning. These changes were reflected by differences in the development of tadpoles ultimately resulting in an earlier start of metamorphosis. Our data provide a first indication that fungicides potentially affect tadpole development indirectly through bottom‐up effects. This pathway is so far not addressed in fungicide environmental risk assessment and merits further attention.
Tadpoles consuming leaf litter of different quality show changes in their energy reserves, more specifically the composition of fatty acids, and growth dynamics. Low‐quality food ultimately leads to a higher number of individuals entering metamorphosis.
Organic chemicals entering surface waters may interact with aquatic macrophytes, which in turn may reduce potential negative effects on aquatic organisms. The overall objective of the present study ...was to determine the significance of aquatic macrophytes to the retention of organic chemicals in slow‐flowing streams and thus their contribution to the mitigation of the risks that these compounds may pose to aquatic ecosystems. Hence, we conducted a study on the mitigation of the biocides triclosan and triclocarban and the fungicides imazalil, propiconazole and thiabendazole, which were experimentally spiked to five flow‐through stream mesocosms (45 m length, 0.4 m width, 0.26 m water depth, discharge 1 L/s), four of which were planted with the submerged macrophyte Elodea nuttallii (Planch.). Chemical analyses were performed using liquid chromatography‐tandem mass spectrometry following solid‐phase extraction for water samples and accelerated solvent extraction for macrophyte and sediment samples. The peak reductions of biocide and fungicide concentrations from the inlet to the outlet sampling sites were ≥48% in all stream mesocosms, and the peak reductions in the vegetated stream mesocosms were 20 to 25% greater than in the unvegetated mesocosm. On average, 7 ± 3 to 10 ± 3% and 28 ± 8 to 34 ± 14% of the initially applied amount of fungicides and biocides, respectively, were retained by macrophytes. There was a significant correlation between retention by macrophytes and the lipophility of the compounds.
Historically, scientific studies have mainly focused on single anthropogenic stressors and ecosystems compartments (e.g., European Food Safety Authority Panel on Plant Protection Products and Their ...Residues, 2013: ...it is necessary to unite research that addresses the combined impact of stressors or its propagation across ecosystem boundaries. To further this research field on the combined impact of stressors across ecosystem continuums, Bruder et al. provide a novel perspective to include food-web characteristics and biotic interactions in analyses of multiple-stressor effects on ecosystems. While many examples show the consequences of stress-induced alterations in local communities at multiple organizational scales (e.g., effects across trophic levels such as prey-predator interactions), it becomes progressively more important to consider wider spatial and temporal scales and alternative propagation routes through ecosystems, seasons as well as generations (e.g., adaptation and evolution).
Background The bacterium Bacillus thuringiensis serovar israelensis (Bti) is used in many countries as a biological larvicide to control dipteran insects of the suborder Nematocera, especially ...mosquitoes and black flies. Bti is generally accepted to be target-specific and efficient, with low potential for development of resistance among the target species. However, even though Bti may have minimal direct effects on non-target organisms, it might potentially be associated with knock-on effects on food webs and other ecosystem properties, including biodiversity and ecosystem functioning. Evidence from previous research is mixed, with some finding no evidence for indirect effects on biodiversity and ecosystem-level properties, but others indicating that such effects are possible. The fact that many studies have been conducted by organisations coordinating the control programs, and that many of those studies have been published outside peer reviewed scientific journals, highlights the challenges for decision makers and others to assess the results of the existing studies. In this protocol we outline how we aim to systematically and transparently synthesise all available evidence in a forthcoming systematic review. Methods We will use six bibliographic databases/platforms and the online search engines Google and Google Scholar in searches for literature. Searches will also be made on specialist websites. We will screen the search results for eligibility in stage one based on title and abstract, and in stage two based on the full text of the material. At stage one, after testing and clarifying the eligibility criteria, two reviewers will split and single screen the search results. At stage two the articles will be screened independently by two reviewers. We have developed a preliminary critical appraisal tool that will be used as basis for assessing study validity. Each study will be critically appraised independently by two reviewers. Disagreements will be reconciled through discussions seeking to reach consensus. It is unclear whether a quantitative synthesis based on meta-analysis will be feasible. A narrative synthesis will include descriptive statistics outlining the evidence base in terms of bibliographic information and study metadata. A narrative synthesis table in the form of an Excel spreadsheet will be provided. Keywords: Culicidae, Simuliidae, Biodiversity, Food web, Biocontrol, Species interactions, Insecticide, Larvicide, Biopesticide, Indirect impacts
The European Water Framework Directive requires surface water bodies to have a good chemical and ecological status. Although relatively few pesticides are included in the list of priority pollutants, ...they pose, due to their intrinsic biological activity, a significant risk for the integrity of aquatic ecosystems. In this context, the pesticide (up to 128 pesticides including some transformation products) exposure pattern in four agricultural streams and two rivers was determined from 2002 to 2011 under the umbrella of the Swedish national monitoring program employing time-proportional and grab sampling strategies, respectively. After transforming the measured pesticide concentrations into toxic units, the European Uniform Principles for algae (chronic), invertebrates and fish (both acute), which are partly employed as benchmark for pesticide regulation, were only occasionally (<2%) exceeded. Moreover, this evaluation showed no long-term trends over the years. However, recent publications suggested that those thresholds are not protective for ecosystem structure and function, indicating a risk of up to 20% and 35% of the samples from the agricultural streams and the rivers, respectively. Moreover, the monitoring data show a continuous but rather low toxic potential of pesticides for all three trophic levels throughout the year, which suggests pesticides as an evolutionary force in agriculturally impacted aquatic ecosystems. However, the flow-triggered sampling, which was implemented as an additional sampling strategy in one of the agricultural streams starting in 2006, displayed an up to 7-fold underestimation of the maximum concentration in terms of toxic units for daphnids and fish during run-off events. The present study thus underpins that the optimal sampling design for pesticide monitoring strongly depends on its overall purpose. If the long-term exposure pattern is of concern a time-proportional composite sampling strategy is recommended, while for an assessment of peak exposures a flow-event-triggered high-resolution sampling strategy is superior.
•Pesticide concentrations in Swedish streams rarely exceed European Uniform Principles.•A risk for aquatic ecosystem structure and function can nonetheless be anticipated.•Time-proportional weekly samples inform about the long-term average exposure pattern.•Flow proportional event-triggered samples capture peak exposure and duration.
PDF
