Unexpected fish diversity gradients in the Amazon basin.

Using the most comprehensive fish occurrence database, we evaluated the importance of ecological and historical drivers in diversity patterns of subdrainage basins across the Amazon system. Linear models reveal the influence of climatic conditions, habitat size and sub-basin isolation on species diversity. Unexpectedly, the species richness model also highlighted a negative upriver-downriver gradient, contrary to predictions of increasing richness at more downriver locations along fluvial gradients. This reverse gradient may be linked to the history of the Amazon drainage network, which, after isolation as western and eastern basins throughout the Miocene, only began flowing eastward 1-9 million years (Ma) ago. Our results suggest that the main center of fish diversity was located westward, with fish dispersal progressing eastward after the basins were united and the Amazon River assumed its modern course toward the Atlantic. This dispersal process seems not yet achieved, suggesting a recent formation of the current Amazon system.

Bacterial and eukaryotic biodiversity patterns in terrestrial and aquatic habitats in the Sør Rondane Mountains, Dronning Maud Land, East Antarctica.

The bacterial and microeukaryotic biodiversity were studied using pyrosequencing analysis on a 454 GS FLX+ platform of partial SSU rRNA genes in terrestrial and aquatic habitats of the Sør Rondane Mountains, including soils, on mosses, endolithic communities, cryoconite holes and supraglacial and subglacial meltwater lenses. This inventory was complemented with Denaturing Gradient Gel Electrophoresis targeting Chlorophyta and Cyanobacteria. OTUs belonging to the Rotifera, Chlorophyta, Tardigrada, Ciliophora, Cercozoa, Fungi, Bryophyta, Bacillariophyta, Collembola and Nematoda were present with a relative abundance of at least 0.1% in the eukaryotic communities. Cyanobacteria, Proteobacteria, Bacteroidetes, Acidobacteria, FBP and Actinobacteria were the most abundant bacterial phyla. Multivariate analyses of the pyrosequencing data revealed a general lack of differentiation of both eukaryotes and prokaryotes according to habitat type. However, the bacterial community structure in the aquatic habitats was dominated by the filamentous cyanobacteria Leptolyngbya and appeared to be significantly different compared with those in dry soils, on mosses, and in endolithic habitats. A striking feature in all datasets was the detection of a relatively large amount of sequences new to science, which underscores the need for additional biodiversity assessments in Antarctic inland locations.

PESI - a taxonomic backbone for Europe.

BACKGROUND: Reliable taxonomy underpins communication in all of biology, not least nature conservation and sustainable use of ecosystem resources. The flexibility of taxonomic interpretations, however, presents a serious challenge for end-users of taxonomic concepts. Users need standardised and continuously harmonised taxonomic reference systems, as well as high-quality and complete taxonomic data sets, but these are generally lacking for non-specialists. The solution is in dynamic, expertly curated web-based taxonomic tools. The Pan-European Species-directories Infrastructure (PESI) worked to solve this key issue by providing a taxonomic e-infrastructure for Europe. It strengthened the relevant social (expertise) and information (standards, data and technical) capacities of five major community networks on taxonomic indexing in Europe, which is essential for proper biodiversity assessment and monitoring activities. The key objectives of PESI were: 1) standardisation in taxonomic reference systems, 2) enhancement of the quality and completeness of taxonomic data sets and 3) creation of integrated access to taxonomic information. NEW INFORMATION: This paper describes the results of PESI and its future prospects, including the involvement in major European biodiversity informatics initiatives and programs.

Bacterial diversity assessment in Antarctic terrestrial and aquatic microbial mats: a comparison between bidirectional pyrosequencing and cultivation.

The application of high-throughput sequencing of the 16S rRNA gene has increased the size of microbial diversity datasets by several orders of magnitude, providing improved access to the rare biosphere compared with cultivation-based approaches and more established cultivation-independent techniques. By contrast, cultivation-based approaches allow the retrieval of both common and uncommon bacteria that can grow in the conditions used and provide access to strains for biotechnological applications. We performed bidirectional pyrosequencing of the bacterial 16S rRNA gene diversity in two terrestrial and seven aquatic Antarctic microbial mat samples previously studied by heterotrophic cultivation. While, not unexpectedly, 77.5% of genera recovered by pyrosequencing were not among the isolates, 25.6% of the genera picked up by cultivation were not detected by pyrosequencing. To allow comparison between both techniques, we focused on the five phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes and Deinococcus-Thermus) recovered by heterotrophic cultivation. Four of these phyla were among the most abundantly recovered by pyrosequencing. Strikingly, there was relatively little overlap between cultivation and the forward and reverse pyrosequencing-based datasets at the genus (17.1-22.2%) and OTU (3.5-3.6%) level (defined on a 97% similarity cut-off level). Comparison of the V1-V2 and V3-V2 datasets of the 16S rRNA gene revealed remarkable differences in number of OTUs and genera recovered. The forward dataset missed 33% of the genera from the reverse dataset despite comprising 50% more OTUs, while the reverse dataset did not contain 40% of the genera of the forward dataset. Similar observations were evident when comparing the forward and reverse cultivation datasets. Our results indicate that the region under consideration can have a large impact on perceived diversity, and should be considered when comparing different datasets. Finally, a high number of OTUs could not be classified using the RDP reference database, suggesting the presence of a large amount of novel diversity.

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia.

Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial-interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30-45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events.

Historical processes constrain patterns in global diatom diversity.

There is a long-standing belief that microbial organisms have unlimited dispersal capabilities, are therefore ubiquitous, and show weak or absent latitudinal diversity gradients. In contrast, using a global freshwater diatom data set, we show that latitudinal gradients in local and regional genus richness are present and highly asymmetric between both hemispheres. Patterns in regional richness are explained by the degree of isolation of lake districts, while the number of locally coexisting diatom genera is highly constrained by the size of the regional diatom pool, habitat availability, and the connectivity between habitats within lake districts. At regional to global scales, historical factors explain significantly more of the observed geographic patterns in genus richness than do contemporary environmental conditions. Together, these results stress the importance of dispersal and migration in structuring diatom communities at regional to global scales. Our results are consistent with predictions from the theory of island biogeography and metacommunity concepts and likely underlie the strong provinciality and endemism observed in the relatively isolated diatom floras in the Southern Hemisphere.

Bacterial community composition in Lake Tanganyika: vertical and horizontal heterogeneity.

Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.