Genotypic diversity and differentiation among populations of two benthic freshwater diatoms as revealed by microsatellites.

Given their large population sizes and presumed high dispersal capacity, protists are expected to exhibit homogeneous population structure over large spatial scales. On the other hand, the fragmented and short-lived nature of the lentic freshwater habitats that many protists inhabit promotes strong population differentiation. We used microsatellites in two benthic freshwater diatoms, Eunotia bilunaris 'robust' and Sellaphora capitata, sampled from within a pond and connected ponds, through isolated ponds from the same region to western Europe to determine the spatial scale at which differentiation appears.

Sulphur levels in saliva as an estimation of sulphur status in cattle: a validation study.

Effective assessment of sulphur (S) status in cattle is important for optimal health, yet remains difficult. Rumen fluid S concentrations are preferred, but difficult to sample under practical conditions. This study aimed to evaluate salivary S concentration as estimator of S status in cattle.

Lack of phylogeographic structure in the freshwater cyanobacterium Microcystis aeruginosa suggests global dispersal.

Background: Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographic structuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwater cyanobacterium Microcystis aeruginosa.

Limits to gene flow in a cosmopolitan marine planktonic diatom.

The role of geographic isolation in marine microbial speciation is hotly debated because of the high dispersal potential and large population sizes of planktonic microorganisms and the apparent lack of strong dispersal barriers in the open sea. Here, we show that gene flow between distant populations of the globally distributed, bloom-forming diatom species Pseudo-nitzschia pungens (clade I) is limited and follows a strong isolation by distance pattern. Furthermore, phylogenetic analysis implies that under appropriate geographic and environmental circumstances, like the pronounced climatic changes in the Pleistocene, population structuring may lead to speciation and hence may play an important role in diversification of marine planktonic microorganisms.

Strong effects of amoebae grazing on the biomass and genetic structure of a Microcystis bloom (Cyanobacteria).

Despite its importance for bloom toxicity, the factors determining the population structure of cyanobacterial blooms are poorly understood. Here, we report the results of a two-year field survey of the population dynamics of Microcystis blooms in a small hypertrophic urban pond. Microscopic enumeration of Microcystis and its predators and parasites was combined with pigment and microcystin analysis and denaturing gradient gel electrophoresis of the ITS rDNA region to assess population dynamics and structure.

Natural hybrids in the marine diatom Pseudo-nitzschia pungens (Bacillariophyceae): genetic and morphological evidence.

Hybridization between genetically distinguishable taxa provides opportunities for investigating speciation. While hybridization is a common phenomenon in various macro-organisms, natural hybridization among micro-eukaryotes is barely studied. Here we used a nuclear and a chloroplast molecular marker and morphology to demonstrate the presence of natural hybrids between two genetically and morphologically distinct varieties of the marine planktonic diatom Pseudo-nitzschia pungens (vars.