Warming shifts top-down and bottom-up control of pond food web structure and function.

The effects of global and local environmental changes are transmitted through networks of interacting organisms to shape the structure of communities and the dynamics of ecosystems. We tested the impact of elevated temperature on the top-down and bottom-up forces structuring experimental freshwater pond food webs in western Canada over 16 months. Experimental warming was crossed with treatments manipulating the presence of planktivorous fish and eutrophication through enhanced nutrient supply.

Infrequent marine-freshwater transitions in the microbial world.

Until recently, the evolutionary relationships between marine and freshwater microbes were unclear, but the use of molecular phylogenies is beginning to shed light on this subject. An increasing amount of studies are showing that marine and freshwater microbes (including viruses) are usually not closely related, often grouping into distinct marine and freshwater phylogenetic clusters, similar to what has been reported before for macroorganisms. These studies indicate that marine-freshwater transitions have been infrequent events during the diversification of microbes and that most of these transitions occurred a long time ago in evolutionary terms.

Identification of freshwater Phycodnaviridae and their potential phytoplankton hosts, using DNA pol sequence fragments and a genetic-distance analysis.

Viruses that infect phytoplankton are an important component of aquatic ecosystems, yet in lakes they remain largely unstudied. In order to investigate viruses (Phycodnaviridae) infecting eukaryotic phytoplankton in lakes and to estimate the number of potential host species, samples were collected from four lakes at the Experimental Lakes Area in Ontario, Canada, during the ice-free period (mid-May to mid-October) of 2004. From each lake, Phycodnaviridae DNA polymerase (pol) gene fragments were amplified using algal-virus-specific primers and separated by denaturing gradient gel electrophoresis; 20 bands were extracted from the gels and sequenced.

Isolation independent methods of characterizing phage communities 1: strain typing using fingerprinting methods.

Since most of the phage genomes isolated from natural samples are previously unknown sequences, an isolation-independent approach is necessary to quantify the diversity of natural viral communities. Currently, two different methodological approaches are widely used to obtain genetic fingerprints of natural phage communities. While the separation of different viral genomes with pulsed field gel electrophoresis (PFGE) is based on the size of the genome, denaturing gradient gel electrophoresis (DGGE) uses minor differences in gene base composition to separate fragments of amplified DNA from natural viral communities.

Independent gradients of producer, consumer, and microbial diversity in lake plankton.

Interactions between trophic levels during food web assembly can drive positive correlations in diversity between producers, consumers, and decomposers. However, the contribution of trophic interactions relative to local environmental factors in promoting species diversity is poorly understood, with many studies only considering two trophic levels. Here we examine correlations in diversity among zooplankton, phytoplankton, and bacteria in the pelagic zone of 31 lakes in British Columbia, Canada.