3,134 publications from this institution
Using in silico amplified fragment length polymorphism (AFLP) fingerprints, we explore the relationship between sequence similarity and phylogeny accuracy to test when, in terms of genetic divergence, the quality of AFLP data becomes too low to be informative for a reliable phylogenetic reconstruction. We generated DNA sequences with known phylogenies using balanced and unbalanced trees with recent, uniform and ancient radiations, and average branch lengths (from the most internal node to the tip) ranging from 0.02 to 0.4 substitutions per site. The resulting sequences were used to emulate the AFLP procedure. Trees were estimated by maximum parsimony (MP), neighbor-joining (NJ), and minimum evolution (ME) methods from both DNA sequences and virtual AFLP fingerprints. The estimated trees were compared with the reference trees using a score that measures overall differences in both topology and relative branch length. As expected, the accuracy of AFLP-based phylogenies decreased dramatically in the more divergent data sets. Above a divergence of approximately 0.05, AFLP-based phylogenies were largely inaccurate irrespective of the distinct topology, radiation model, or phylogenetic method used. This value represents an upper bound of expected tree accuracy for data sets with a simple divergence history; AFLP data sets with a similar divergence but with unbalanced topologies and short ancestral branches produced much less accurate trees. The lack of homology of AFLP bands quickly increases with divergence and reaches its maximum value (100%) at a divergence of only 0.4. Low guanine-cytosine (GC) contents increase the number of nonhomologous bands in AFLP data sets and lead to less reliable trees. However, the effect of the lack of band homology on tree accuracy is surprisingly small relative to the negative impact due to the low information content of AFLP characters. Tree-building methods based on genetic distance displayed similar trends and outperformed parsimony at low but not at high divergences. However, the impact of using alternative phylogenetic methods on tree accuracy was generally small relative to the uncertainty arising from factors such as divergence, nonhomology of bands, or the low information content of AFLP characters. Nevertheless, our data suggest that under certain circumstances, AFLPs may be suitable to reconstruct deeper phylogenies than usually accepted.
Cadmium was determined in biological materials by electrothermal atomic absorption spectrometry after ultrasound-assisted treatment of slurried samples prepared in the autosampler cups with an acidic diluent. Parameters influencing Cd extraction into the liquid phase of the slurry, such as ultrasound amplitude, sonication time, particle size, acid concentration and sample mass used for preparing the slurry, were investigated. Quantitative recoveries of Cd from mussel tissue were obtained using a 20% amplitude, a 1 min sonication time and 3% nitric acid, demonstrating that the resulting supernatant in the autosampler cup can be used for sampling. Particle size had no effect on Cd extraction from mussel tissue in the range <50 and >200 μm, the recovery being quantitative. Extraction of Cd from several CRMs, such as BCR CRM 60 (Lagarosiphon major) Aquatic Plant, BCR CRM 278 Mussel Tissue, NRCC DORM-2 Dogfish Muscle and NRCC DOLT-2 Dogfish Liver, was also successful under the conditions mentioned above along with the original particle size distribution provided for these materials. Non-quantitative extraction was obtained with materials that have a typical inorganic matrix, such as BCR CRM 145R Sewage Sludge and BCR CRM 320 River Sediment. Homogeneity testing was carried out by comparison of between- and within-batch precision as well as homogeneity factors. The LOD for Cd in the solid biological samples was 0.019 μg g –1 when a 10 mg sample mass was slurried in a volume of 1.5 ml. In all cases, an acceptable homogeneity was observed even when using a sample mass of 10 mg for slurry preparation. In addition, the proposed approach for analyte extraction should provide further advantages in comparison with conventional slurry sampling, such as an improved precision, since the representative sub-sample is the whole mass taken for slurry preparation, lower background signals and a decreased build-up of carbonaceous residues inside the graphite tube.
Long-term stability and high scalability are significant issues in plasmonic optical fiber sensors. This work presents a highly scalable and low-cost all-chemical approach for production of gold-coated silver thin-films, ensuring high performance and chemical stability.
Adsorption of dissolved organic matter (DOM) to two species of marine phytoplankton (Isochrysis galbana and Thalassiosira weissflogii) was evaluated and quantified, and effects of DOM on the growth rate and Pb bioavailability were tested for I. galbana and compared with T. weissflogii. Isochrysis galbana growth rate was stimulated by different types of DOM. Humic acids (HA) had the highest stimulatory effect on cell growth followed by Suwannee river dissolved organic matter (SRDOM) and fulvic acids (FA). DOM also enhanced Pb adsorption and internalization by I. galbana, and the magnitude of these effects followed the same order: HA > SRDOM—FA, which was also the same order observed for the magnitude of DOM adsorption to surfaces. It is hypothesized that DOM adsorption on membrane surfaces may be a necessary step to cause both the increase in growth rate and the increase in Pb internalization by the algae, effects not observed in the case of the diatom T. weissflogii, an organism with an outer silica wall, thought to be the primary site of DOM adsorption. The different degree of effects caused by the different types of DOM may be explained according to their physicochemical properties.
Recombination is a key evolutionary process that shapes the architecture of genomes and the genetic structure of populations. Although many statistical methods are available for the detection of recombination from DNA sequences, their absolute and relative performance is still unknown. Here we evaluated the performance of 14 different recombination detection algorithms. We used the coalescent with recombination to simulate DNA sequences with different levels of recombination, genetic diversity, and rate variation among sites. Recombination detection methods were applied to these data sets, and whether they detected or not recombination was recorded. Different recombination methods showed distinct performance depending on the amount of recombination, genetic diversity, and rate variation among sites. The model of nucleotide substitution under which the data were generated did not seem to have a significant effect. Most methods increase power with more sequence divergence. In general, recombination detection methods seem to capture the presence of recombination, but they are not very powerful. Methods that use substitution patterns or incompatibility among sites were more powerful than methods based on phylogenetic incongruence. Most methods do not seem to infer more false positives than expected by chance. Especially depending on the amount of diversity in the data, different methods could be used to attain maximum power while minimizing false positives. Results shown here will provide some guidance in the selection of the most appropriate method/s for the analysis of the particular data at hand.
Calvo, C; Hermida, R C; Ayala, D E; Lopez, J E; Dominguez, M J; Covelo, M; Mojon, A; Fernandez, J R Author Information