Freshwater Bacterioplankton Metacommunity Structure Along Urbanization Gradients in Belgium

Urbanization is transforming and fragmenting natural environments worldwide, driving changes in biological communities through alterations in local environmental conditions as well as by changing the capacity of species to reach specific habitats. While the majority of earlier studies have been performed on higher plants and animals, it is crucial to increase our insight on microbial responses to urbanization across different spatial scales. Here, using a metacommunity approach, we evaluated the effects of urbanization on bacterioplankton communities in 50 shallow ponds in Belgium (Flanders region), one of the most urbanized areas in Northwest Europe. We estimated the relative importance of local environmental factors (35 abiotic and biotic variables), regional spatial factors and urbanization (built-up area) quantified at two spatial scales (200 m × 200 m and 3 km × 3 km). We show that urbanization at local or regional scales did not lead to strong changes in community composition and taxon diversity of bacterioplankton. Urbanization at regional scale (3 km × 3 km) explained only 2% of community composition variation while at local scale (200 m × 200 m), no effect was detected. Local environmental factors explained 13% (OTUs with relative abundance ≥ 0.1%) to 24% (12 dominant OTUs -≥ 1%) of community variation. Six local environmental variables significantly explained variation in bacterioplankton community composition: pH, alkalinity, conductivity, total phosphorus, abundance of Daphnia and concentration of copper (Cu), of which pH was partly mediated by urbanization. Our results indicate that environmental rather than spatial factors accounted for the variation in bacterioplankton community structure, suggesting that species sorting is the main process explaining bacterioplankton community assembly. Apparently, urbanization does not have a direct and strong effect on bacterioplankton metacommunity structure, probably due to the capacity of these organisms to adapt toward and colonize habitats with different environmental conditions and due to their fast adaptation and metabolic versatility. Thus, bacterioplankton communities inhabiting shallow ponds may be less affected by environmental conditions resulting from urbanization as compared to the impacts previously described for other taxa

Diatom distributions in space and time – a case study from the polar regions

第3回極域科学シンポジウム/第34回極域生物シンポジウム 11月27日（火） 統計数理研究所 ３階セミナー

DNA barcoding for species identification and discovery in diatoms

Les diatomées représentent le plus grand groupe d\u27algues unicellulaires, jouent un rôle fondamental dans la biosphère, et sont importantes en tant qu\u27indicateurs biologiques. L\u27identification sur des bases morphologique exige entre autres un long entraînement, des compétences considérables en microscopie, et l\u27accès à une vaste littérature publiée pour l\u27essentiel sous forme d\u27articles. Durant leur cycle de vie, les cellules de diatomées modifient leur taille et leurs motifs, souvent aussi leur forme, mais le cycle complet n\u27est connu que pour moins de 1 des espèces décrites. De récentes études ont démontré l\u27existence d\u27espèces pseudocryptiques et cryptiques parmi les diatomées, nécessitant des méthodes moléculaires pour leur découverte et reconnaissance. Ces facteurs entre autres soutiennent le développement d\u27un système de taxinomie moléculaire tel que le code barre ADN. Ceci pourrait être un barcoding « puissant », pouvant résoudre presque toutes les espèces, ou « faible », ne pouvant résoudre que des espèces déjà reconnues en microscopie optique. Plusieurs essais d\u27identification de gènes convenables sont achevées et nous évaluons l\u27universalité, la facilité d\u27emploi et le pouvoir discriminatif interspécifique de ces gènes sur les quelques espèces modèles offrant des paires d\u27espèces-s?urs probables. A cet instant, aucun marqueur génétique n\u27est prouvé idéal, mais le LSU rDNA et le rbcL peuvent être acceptables, bien que leurs capacités discriminatoires soient plus faibles que ceux de quelques autres marqueurs. Nous discutons les prochaines étapes pour développer un système complet de code-barres.Également disponible sur Connect.barcodeoflife Diatoms are the largest group of microalgae, play an enormous role in the biosphere, and have major significance as bioindicators. Traditional identification requires inter alia long training, considerable microscopical skill, and use of a vast and scattered literature. During the life cycle, diatom cells change in size and pattern, often also shape, but the full cycle is known in &lt;1 of described species. Recent evidence shows that there are many pseudocryptic and cryptic species of diatoms, requiring molecular methods for discovery and recognition. These and other factors argue that DNA barcoding would be highly beneficial. It could be `strong\u27, resolving nearly all species, or `weak\u27, resolving mostly species already recognized from light microscopy. Attempts have already been made to identify suitable genes and we evaluate these on the basis of universality and practicality, and ability to discriminate between species in the very few `model\u27 systems offering likely examples of sister-species-pairs. No candidate marker is ideal but LSU rDNA and rbcL may be acceptable, though their discriminatory power is lower than that of some other markers. We discuss the next steps in developing a full barcode system.Also available on Connect.barcodeoflife </p

Inoculation history affects community composition in experimental freshwater bacterioplankton communities

Priority effects occur when the arrival order of species or genotypes has a lasting effect on community or population structure. For freshwater bacteria, priority effects have been shown experimentally among individual species, but no experiments have been performed using complex natural communities. We investigated experimentally whether a foreign bacterioplankton community influences the community assembly trajectory when inoculated prior to the local community, whether inoculation time lag affects priority effects, and how the individual OTUs responded to time lag. Two bacterioplankton communities from dissimilar ponds were inoculated into one of the natural media with a time lag of 0, 12, 36 or 60 hours, giving advantage in time to the foreign community. All three time lags resulted in priority effects, as the final community composition of these treatments differed significantly from that of the treatment with no time lag, but compositional shifts were not linear to inoculation time lag. The responses of individual OTUs to time lag were highly diverse and not predictable based on their immigration history or relative abundance in the inocula or control. The observed impact and complexity of priority effects in multi-species systems emphasize the importance of this process in structuring both natural and industrial bacterial communities.status: publishe

Tolerance of resting cells of freshwater and terrestrial benthic diatoms to experimental desiccation and freezing is habitat-dependent

For a wide range of organisms, dormancy is a strategy to overcome adverse conditions in time and space, and one may expect that the stress tolerance of dormant stages is tuned to the habitat in which they occur. We assessed the tolerance of vegetative and resting cells of 17 benthic diatom morphospecies from habitats with contrasting permanency, ranging from moist soils to permanent lakes. Vegetative cells of all morphospecies were highly sensitive to desiccation and, except for strains of some terrestrial taxa, freezing. In contrast, resting cells of several morphospecies tolerated desiccation, especially when preceded by a heat treatment, and resting cells of more strains and morphospecies survived freezing, albeit often with low survival percentages and a large interstrain variation. Strikingly, all strains surviving desiccation and/or freezing belonged to terrestrial morphospecies, i.e. diatoms occurring mainly in wet and moist or temporary dry habitats outside water bodies. These results emphasize the importance of resting cells of terrestrial diatoms for the survival of stress tolerance, especially desiccation, and indicate specific adaptations of terrestrial diatoms to their highly variable habitats

Vijvers in het Dijleland als modelsysteem voor de relatie tussen biodiversiteit en ecosysteem functioneren

status: publishe

An experimental analysis of species sorting and mass effects in freshwater bacterioplankton

© 2014 John Wiley & Sons Ltd. 1. While metacommunities of bacterioplankton are generally considered to be structured primarily by local environmental conditions (through species sorting), additional ecological processes such as dispersal limitation, neutral dynamics or mass effects can influence community structure. Under the mass effects paradigm, continuous or large influxes of organisms, not self-maintaining in the target environment, affect community structure. 2. We used communities of freshwater bacterioplankton to quantify the outcome of mass effects and species sorting in a laboratory experiment in which we exchanged cells between two communities from contrasting ponds (eutrophic and mesotrophic) at a rate of 0.025, 0.25, 2.5 and 12.5% of the cells present per day. 3. When cells were exchanged only once on day 1 of the experiment, the reciprocally exchanged communities in all dispersal treatments remained as divergent, after 20 days, as the unexchanged control communities, reflecting strong species sorting and no strong influences of dispersal limitation and neutral dynamics on the observed bacterioplankton. 4. Under daily cell exchange, however, community similarity between the reciprocally exchanged communities increased significantly with increasing dispersal rate, indicating an increasing influence of mass effects relative to species sorting. The responses differed at the level of community composition and ecosystem processes, and depended on pond identity. At the community level, a daily exchange of 2.5% was necessary to increase community similarity compared with the unexchanged controls, while at the ecosystem process level (Biolog GN2 metabolic profiles), a daily exchange rate of 0.25% was sufficient. 5. Mass effects can evidently overcome species sorting in freshwater bacterioplankton, but only under relatively high dispersal rates that are unlikely to occur in nature among habitats without a direct hydrological connection. Mass effects in the freshwater bacterioplankton acted differently at the community composition and ecosystem process level.status: publishe