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Geisen S.,Netherlands Institute of Ecology | Rosengarten J.,University of Cologne | Koller R.,Jülich Research Center | Mulder C.,National Institute for Public Health and the Environment RIVM Bilthoven The Netherlands | And 2 more authors.
Environmental Microbiology | Year: 2015

Soils host the most complex communities on Earth, including the most diverse and abundant eukaryotes, i.e. heterotrophic protists. Protists are generally considered as bacterivores, but evidence for negative interactions with nematodes both from laboratory and field studies exist. However, direct impacts of protists on nematodes remain unknown. We isolated the soil-borne testate amoeba Cryptodifflugia operculata and found a highly specialized and effective pack-hunting strategy to prey on bacterivorous nematodes. Enhanced reproduction in presence of prey nematodes suggests a beneficial predatory life history of these omnivorous soil amoebae. Cryptodifflugia operculata appears to selectively impact the nematode community composition as reductions of nematode numbers were species specific. Furthermore, we investigated 12 soil metatranscriptomes from five distinct locations throughout Europe for 18S ribosomal RNA transcripts of C.operculata. The presence of C.operculata transcripts in all samples, representing up to 4% of the active protist community, indicates a potential ecological importance of nematophagy performed by C.operculata in soil food webs. The unique pack-hunting strategy on nematodes that was previously unknown from protists, together with molecular evidence that these pack hunters are likely to be abundant and widespread in soils, imply a considerable importance of the hitherto neglected trophic link 'nematophagous protists' in soil food webs. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

Del Signore A.,Radboud University Nijmegen | Lenders H.J.R.,Radboud University Nijmegen | Hendriks A.J.,Radboud University Nijmegen | Vonk J.A.,University of Amsterdam | And 2 more authors.
River Research and Applications | Year: 2014

We applied species sensitivity distributions (SSDs), commonly used in chemical risk assessment, to quantify the impact of water-flow velocity on the presence of fish species in a river. SSDs for water-flow velocity were derived from observational field data (maximal velocity at which species occur, Vmax) and laboratory measurements (critical swimming velocity, Vcrit). By calculating the potentially affected fraction of the fish species of the river Rhine, effects of water-flow velocity on different life stages and guilds were estimated. Vmax values for adults were significantly higher than those for juveniles and larvae. At water-flow velocity of 60cms-1, half of the adults were affected, while half of the non-adult life stages were affected at velocities of 25 to 29cms-1. There was a positive correlation between body size and fish tolerance to water-flow. As expected, rheophilic species tolerated higher water-flow velocities than eurytopic and limnophilic species. Maximal velocities measured in littoral zones of the Rhine were, on average, 10cms-1, corresponding to an affected fraction of 2%. An increase in water-flow velocity up to 120cms-1 as a result of passing vessels caused an increase in affected species to 75%. For a successful ecological river management, the SSD method can be used to quantify the trait-mediated effects of water-flow alterations on occurring species enabling to compare and rank the effects of chemical and physical stress. © 2014 John Wiley & Sons, Ltd.

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