Biogeography of the ubiquitous marine bacterium Alteromonas macleodii determined by multilocus sequence analysis

Twenty‐three isolates of the widely distributed marine bacteria Alteromonas macleodii have been analysed by multilocus sequence analysis combined with phylogenetic and multivariate statistical analyses. The strains originated from the Pacific Ocean, Mediterranean Sea, English Channel, Black Sea and Thailand. Using the nucleotide sequences of nine loci for each of the 23 isolates, a robust identification was achieved of different clades within the single species. Strains generally clustered with the depth in the water column from which the isolate originated. Strains also showed more recombination with isolates from the same vicinity, suggesting that genetic exchange plays a role in diversification of planktonic marine prokaryotes. This study thus shows for the first time for a large set of isolates of a species of planktonic marine prokaryotes that multilocus sequence analysis overcomes the problems associated with the analysis of individual marker genes or presence of extensive recombination events. It can thus achieve intraspecific identification to the level of genotypes and, by comparison with relevant environmental data, ecotypes.     

Macroinvertebrate communities of mediterranean ponds (North Iberian Plateau): importance of natural and human-induced variability

1. The effects of natural and human‐induced variability on the composition of macroinvertebrate communities of 28 ponds located in the North Iberian Plateau (Spain) were studied to determine the best predictors of community structure. 2. Constrained ordination was used to identify the main factors explaining the among‐pond variance in abundance (as catch per unit effort) of total macroinvertebrate and Chironomidae assemblages and trophic structure (functional feeding groups). 3. Variance partitioning showed that human disturbance (represented by a pond condition index, total phosphorus concentration and pesticides) was the best predictor of macroinvertebrate community structure, whereas factors, such as habitat and biotic variables were of secondary importance. Factors controlling the chironomid community were broadly similar to those acting on the whole community of macroinvertebrates. In contrast, trophic structure was mainly determined by habitat and biotic variables. 4. Our results show that macroinvertebrates may be used as effective indicators of the ecological status of Mediterranean ponds. The Chironomidae deserve special attention because they were the dominant group in the study ponds and the strongest explanatory variable for their distribution was degradation.     

Flow and Oxygen Transfer Characteristics of an Intravenous Membrane Oxygenator: A Computational Study

Spectral element computational simulations of the conservation of mass, momentum and species equations are performed to investigate the flow and oxygen transfer characteristics of an Intravenous Membrane Oxygenator (IMO). The simulations consider a three-dimensional IMO computational model consisting of equally-spaced fibers, an elastic balloon with non-permeable walls positioned longitudinally within the vena cava, and a Newtonian and time-dependent incompressible flow. Flow characteristics and oxygen transfer parameters are determined for operating conditions of a stationary and a pulsating balloon. For the stationary balloon configuration the flow is two-dimensional, parallel, laminar and without secondary flows for the Reynolds number range of 5.7-455.2. Evaluations of the oxygen transfer characteristics for the stationary balloon indicate that the main transport mechanisms are diffusion and convection in the crosswise and streamwise directions, respectively. Additionally, evaluations of oxygen transfer rates and Sherwood numbers in this Reynolds number range indicate that the oxygen transfer rate reaches an asymptotic limit at relatively moderate Reynolds numbers. For the pulsating balloon, flow characteristic results demonstrate the existence of a strong secondary flow around the fiber, and between the balloon and the fiber. This secondary flow induces oscillatory crosswise and streamwise velocities and a seemingly random spanwise flow which enhances the flow mixing as well as the transport of oxygen from the fiber surface to the bulk flow.     

Molecular evidence for allopolyploid speciation and a single origin of the western Mediterranean orchid Dactylorhiza insularis (Orchidaceae)

The hybrid origin of the western Mediterranean orchid Dactylorhiza insularis was demonstrated by genetic markers. Allozyme data showed that throughout its range D. insularis has an allotriploid constitution and reproduces apomictically. The parental species of D. insularis were identified as D. romana andD. sambucina; they contributed 2 alleles and 1 allele, respectively, at the allozyme loci studied. The maternal species of D. insularis was D. romana , as inferred from cpDNA ( trn L(UAA) intron). High genetic similarities were found when comparing present populations of D. romana and D. sambucina with their respective genomes 'frozen' in D. insularis. Dactylorhiza insularis showed fixed (or nearly fixed) heterozygosity at 11 out of the 19 loci studied, and poor genetic variation: eight multilocus genotypes were detected at allozyme level. No multilocus genotype differs from the most similar one by more than one allele substitution. All D. insularis individuals showed the same cpDNA haplotype (I) , regardless of their geographic origin and multilocus genotype. The I haplotype is similar, but not identical to that found in D. romana (R). No recurrent formation of D. insularis was observed in hybrid zones between D. romana and D. sambucina , where diploid sexual hybrids (F_1; F_n, backcrosses) were detected. Available data agree with a single origin for D. insularis , which possibly occurred in the present postglacial, when D. romana and D. sambucina , expanding from their glacial refugia, came into contact. The genetic homogeneity found between D. romana and D. markusii , both from their locus classicus , indicates that the latter is a junior synonym of D. romana; on the other hand, D. romana and D. sambucina are well differentiated species ( D_Nei = 0.59).     

Chemical Signaling in Ciliates

ABSTRACT. For long, our knowledge of the biology of ciliate pheromones has long relied solely upon the study of the two structurally unrelated "gamones" identified in culture filtrates of a Blepharisma species. However, the characterization of a number of polypeptide pheromones secreted by Euplotes raikovi and E. octocarinatus has now established that structural relationships of homology usually link these molecules, which is consistent with the genetic basis of the mating type systems evolved by these species. In this context, our growing appreciation of the conserved and variable elements of the pheromone architecture should foster progress in the understanding of pheromone-receptor interactions and thus, provide important clues into pheromone mechanisms of action.     

Phylogeny and biogeography of Yellow-headed and Blue-fronted Parrots (Amazona ochrocephala and Amazona aestiva) with special reference to the South American taxa

The Yellow-headed Parrot ( Amazona ochrocephala ) has a broad Neotropical distribution, ranging from Mexico to the Amazon Basin, and a history of complex taxonomy and controversial species limits. Recent molecular analyses have started to clarify the taxonomic arrangement of the complex, but have not included a representative geographical sampling from South America. These studies have shown that the Yellow-headed complex can be divided into three main lineages, and seems to be paraphyletic, due to the inclusion of the Blue-fronted Parrot ( Amazona aestiva ) that occurs in central South America. Here we present a phylogenetic analysis based on mitochondrial DNA sequences of 45 representatives of the Yellow-headed complex from South and Central America, plus 13 Blue-fronted individuals from different localities in South America. Our analyses recover the three primary lineages found previously in the Yellow-headed complex, show that there is genetic structure in the South American lineage, which can be divided into two well-supported, closely related clades, and demonstrate that Blue-fronted samples are distributed in both clades. Differentiation of South American Blue-fronted and Yellow-headed Parrot populations does not correspond to the plumage differences used to distinguish the Blue-fronted Parrot from the Yellow-headed Parrot, nor to plumage differences used to distinguish among South American Yellow-headed subspecies. This suggests that traditional taxonomy based on plumage characters needs revision, and that this may be an interesting example of ongoing divergence-with-gene-flow related to the forest/open area ecotone in southern Amazonia.