Microbial community composition and trophic role along a marked salinity gradient in Laguna Puilar, Salar de Atacama, Chile.

The geological, hydrological and microbiological features of the Salar de Atacama, the most extensive evaporitic sedimentary basin in the Atacama Desert of northern Chile, have been extensively studied. In contrast, relatively little attention has been paid to the composition and roles of microbial communities in hypersaline lakes which are a unique feature in the Salar. In the present study biochemical, chemical and molecular biological tools were used to determine the composition and roles of microbial communities in water, microbial mats and sediments along a marked salinity gradient in Laguna Puilar which is located in the "Los Flamencos" National Reserve. The bacterial communities at the sampling sites were dominated by members of the phyla Bacteroidetes, Chloroflexi, Cyanobacteria and Proteobacteria. Stable isotope and fatty acid analyses revealed marked variability in the composition of microbial mats at different sampling sites both horizontally (at different sites) and vertically (in the different layers). The Laguna Puilar was shown to be a microbially dominated ecosystem in which more than 60% of the fatty acids at particular sites are of bacterial origin. Our pioneering studies also suggest that the energy budgets of avian consumers (three flamingo species) and dominant invertebrates (amphipods and gastropods) use minerals as a source of energy and nutrients. Overall, the results of this study support the view that the Salar de Atacama is a heterogeneous and fragile ecosystem where small changes in environmental conditions may alter the balance of microbial communities with possible consequences at different trophic levels.

Do insect repellents induce drift behaviour in aquatic non-target organisms?

Synthetic insect repellents are compounds applied to surfaces to discourage insects, mainly mosquitoes, from landing on those surfaces. As some of these repellents have repeatedly been detected in surface waters at significant concentrations, they may also exert repellent effects on aquatic non-target organisms. In running water systems, aquatic invertebrates actively enter downstream drift in order to avoid unfavourable environmental conditions. We thus tested the hypothesis that the widely used insect repellents DEET (N,N-Diethyl-m-toluamide), EBAAP (3-[N-butyl-N-acetyl]-aminopropionic acid ethyl ester) and Icaridin (1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropyl ester) induce downstream drift behaviour in the aquatic invertebrates Gammarus pulex (Crustacea, Amphipoda) and Cloeon dipterum (Insecta, Ephemeroptera), using a laboratory-scale drift assay. We found no clear increase in the drift behaviour of both invertebrate species across a concentration gradient of eight orders of magnitude and even beyond maximum environmental concentrations for any of the three repellents. We found no evidence for a direct drift-inducing activity of insect repellents on aquatic non-target organisms.

The smell of good food: volatile infochemicals as resource quality indicators.

Foraging success generally depends on various environmental and physiological factors. Particularly for organisms with limited motility such as gastropods, food searching is a very cost-intensive process. As energy gain through foraging is dependent on both resource quality and quantity, consumers have to be able to differentiate between varying resource items. The effectiveness of food searching could be increased through the perception of diet-derived chemical signals that convey information about a food resource's quality over a certain distance. This strategy would clearly help to optimize movement decisions. In this study, we investigated the foraging behaviour of a freshwater gastropod towards volatile signal substances released from benthic algae grown under high and low nutrient availability, representing high and low food quality, using behavioural assays in the laboratory. Our results demonstrate that volatile organic compounds (VOCs) serve as foraging kairomones for these aquatic, benthic herbivores. Further, we were able to show for the first time that snails are able to differentiate between high- and low-quality food sources, only by the perception of food odours alone (volatile infochemicals). Gas chromatography coupled with mass spectrometry demonstrated quantitative as well as qualitative differences in the chemical composition of the VOCs bouquet, dependent on algal nutrient content. Our results suggest that the recognition of resource quality via the reception of signal substances is likely to be adaptive for consumers with low mobility to maximize ingestion of high-quality resources.