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At least 433 records · Page 24Linked to original sources
PubMed2000

Human urine certified reference material for arsenic speciation.

BACKGROUND: Chemical speciation analysis is essential for the biological monitoring of inorganic arsenic exposure using urine as indicator medium. There is increasing demand for a certified reference material (CRM) of urine matrix for arsenic speciation. METHODS: Urine (10 L) was collected from non-occupationally exposed Japanese males. We prepared 954 bottles of urine, each containing approximately 10 mL, after filtering and blending the urine stock. The urine in each bottle was freeze-dried. Between-bottle homogeneity was confirmed by measuring the concentrations of selected minor and trace elements in the material and subsequent statistical analysis. Certification was based on a collaborative analysis involving 15 laboratories. RESULTS: Certified values were determined for arsenobetaine (0.069+/-0.012 mg As/L), dimethylarsinic acid (0.036+/-0.009 mg As/L), and total arsenic (0.134+/-0.011 mg/L) as well as for total selenium (0.059+/-0.005 mg/L) and zinc (0.62+/-0.05 mg/L), based on the analytical values from the collaborating laboratories. Reference values are given for copper (0.010 mg/L) and lead (0.0011 mg/L), based on definitive analysis at the National Institute for Environmental Studies (NIES). CONCLUSIONS: The present CRM, NIES CRM No. 18 Human Urine, is the first human urine CRM for arsenic speciation and will be of value for analytical quality assurance of the biological monitoring of arsenic exposure.

Arsenicals↗
PubMed2000

Arsenic speciation based on ion exchange high-performance liquid chromatography hyphenated with hydride generation atomic fluorescence and on-line UV photo oxidation.

An on-line method capable of the separation of arsenic species was developed for the speciation of arsenite As(III), arsenate As(V), monomethylarsenic (MMA) and dimethylarsenic acid (DMA) in biological samples. The method is based on the combination of high-performance liquid chromatograph (HPLC) for separation, UV photo oxidation for sample digestion and hydride generation atomic fluorescence spectrometry (HGAFS) for sensitive detection. The best separation results were obtained with an anion-exchange AS11 column protected by an AG11 guard column, and gradient elution with NaH2PO4 and water as mobile phase. The on-line UV photo oxidation with 1.5% K2S2O8 in 0.2 mol L(-1) NaOH in an 8 m PTFE coil for 40 s ensures the digestion of organoarsenic compounds. Detection limits for the four species were in the range of 0.11-0.15 ng (20 microL injected). Procedures were validated by analysis of the certified reference materials GBW09103 freeze-dried human urine and the results were in good agreement with the certified values of total arsenic concentration. The method has been successfully applied to speciation studies of blood arsenic species with no need of sample pretreatment. Speciation of arsenic in blood samples collected from two patients after the ingestion of realgar-containing drug reveals slight increase of arsenite and DMA, resulting from the digestion of realgar.

Arsenates↗
PubMed1998

[Application of capillary electrophoresis in speciation analysis].

Each species has different chemical and biological behaviors. Toxicity is often dependent on it. So element speciation is important in a variety of environmental, biological, geological, and medical applications. Recently, capillary electrophoresis(CE) has been applied to speciation analysis owing to its high efficiency and short analysis time. This paper reviews the applications of CE-UV and CE-ICP-MS in speciation analysis and discusses some related problems.

Arsenic↗
PubMed2001

Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish.

Mechanisms of speciation in cichlid fish were investigated by analyzing population genetic models of sexual selection on sex-determining genes associated with color polymorphisms. The models are based on a combination of laboratory experiments and field observations on the ecology, male and female mating behavior, and inheritance of sex-determination and color polymorphisms. The models explain why sex-reversal genes that change males into females tend to be X-linked and associated with novel colors, using the hypothesis of restricted recombination on the sex chromosomes, as suggested by previous theory on the evolution of recombination. The models reveal multiple pathways for rapid sympatric speciation through the origin of novel color morphs with strong assortative mating that incorporate both sex-reversal and suppressor genes. Despite the lack of geographic isolation or ecological differentiation, the new species coexists with the ancestral species either temporarily or indefinitely. These results may help to explain different patterns and rates of speciation among groups of cichlids, in particular the explosive diversification of rock-dwelling haplochromine cichlids.

Animals↗
PubMed2002

[Uptake and distribution of Cu, Zn, Pb and Cd in maize related to metals speciation change in rhizosphere].

The behavior of heavy metals in terrestrial system and the mechanism of VAM plant in toleranting excessive heavy metals in soil were examined with VAM maize(Zea mays L.). After seven-week cultivation in sewage-sludging soil, the biomass of VAM (Glomus mosseae) maize was found 1.5 times higher than non-mycorrhizal one. Compared with non-mycorrhizal maize, the accumulation of Cu, Zn and Pb by mycorrhizal maize was reduced by 10%, 18% and 29%, respectively, but the accumulation of Cd was the same. The distribution and speciation change of Cu, Zn, Pb and Cd in rhizosphere of VAM and non-mycorrhizal maize were analyzed by using the technique of sequential extraction. Except a significant increase in exchangeable Cu in rhizosphere of VAM maize, the increased amount of test metals bound to organic matter, carbonates, iron and manganese oxides were significantly higher than those in rhizosphere of non-mycorrhizal maize, indicating that the speciation of metals in rhizosphere of mycorrhizal maize growing in contaminated soil tended to be relatively stable. Meanwhile, the influence of metal speciation in rhizosphere on its bioavailability as well as the mechanism of mycorrhizal plant in toleranting excess metals were also discussed.

Cadmium↗
PubMed2002

Herbivorous insects: model systems for the comparative study of speciation ecology.

Does ecological divergence drive species-level evolutionary diversification? How so and to what degree? These questions were central to the thinking of the evolutionary synthesis. Only recently, however, has the ecology of speciation become an important focus of empirical study. Here, we argue that ecologically specialized, phylogenetically diverse, and experimentally tractable herbivorous insect taxa offer great opportunities to study the myriad mechanisms by which ecology may cause reproductive isolation and promote speciation. We call for the development and integrated experimental study of a taxonomic diversity of herbivore model systems and discuss the availability and recent evaluation of suitable taxa. Most importantly, we describe a general comparative framework that can be used to rigorously test a variety of hypotheses about the relative contributions and the macroevolutionary generality of particular mechanisms. Finally, we illustrate important issues for the experimental analysis of speciation ecology by demonstrating the consequences of specialized host associations for ecological divergence and premating isolation in Neochlamisus bebbianae leaf beetles.

Animals↗
PubMed2002

Sexual isolation and speciation in bacteria.

Like organisms from all other walks of life, bacteria are capable of sexual recombination. However, unlike most plants and animals, bacteria recombine only rarely, and when they do they are extremely promiscuous in their choice of sexual partners. There may be no absolute constraints on the evolutionary distances that can be traversed through recombination in the bacterial world, but interspecies recombination is reduced by a variety of factors, including ecological isolation, behavioral isolation, obstacles to DNA entry, restriction endonuclease activity, resistance to integration of divergent DNA sequences, reversal of recombination by mismatch repair, and functional incompatibility of recombined segments. Typically, individual bacterial species are genetically variable for most of these factors. Therefore, natural selection can modulate levels of sexual isolation, to increase the transfer of genes useful to the recipient while minimizing the transfer of harmful genes. Interspecies recombination is optimized when recombination involves short segments that are just long enough to transfer an adaptation, without co-transferring potentially harmful DNA flanking the adaptation. Natural selection has apparently acted to reduce sexual isolation between bacterial species. Evolution of sexual isolation is not a milestone toward speciation in bacteria, since bacterial recombination is too rare to oppose adaptive divergence between incipient species. Ironically, recombination between incipient bacterial species may actually foster the speciation process, by prohibiting one incipient species from out-competing the other to extinction. Interspecific recombination may also foster speciation by introducing novel gene loci from divergent species, allowing invasion of new niches.

Bacteria↗
PubMed2002

[The application of inductively coupled plasma atomic emission spectrometry/mass spectrometry in the trace elements and speciation analysis of traditional Chinese Medicine].

A review on the content and speciation analysis of trace element in traditional chinese medicine (TCM) by ICP-AES/MS was presented. The study is mainly focused on the following subjects: sample digestion techniques; determination and speciation analysis of trace elements. The development trend of this area in the near future is briefly introduced. 58 references are cited. The results show that the microwave digestion techniques is a idea pretreatment method of sample for tradition chinese medicine; ICP-AES/MS and all kinds of hyphenated techniques for atomic optical/mass spectrometry/chromatography are very useful for the determination and speciation analysis of trace elements in TCM.

Drug Contamination↗
PubMedDate not supplied

Plasma spectrometry for elemental speciation and characterization in beverages.

A review is presented on recent applications of plasma spectrometric techniques for speciation analysis in beverages. The 3 most common ways of characterizing beverages in addition to elemental speciation are also discussed: total element analysis, isotope ratio, and statistical characterization. To date, most of the elemental characterization in beverages with plasma techniques has been performed in the statistical evaluation of wines and in teas. However, despite the increasing interest in elemental speciation, most of the plasma-based techniques in beverage studies are used for total metal detection and the full capabilities of inductively coupled plasma techniques have yet to be realized.

Beer↗
PubMed2005

Genealogical footprints of speciation processes in wild tomatoes: demography and evidence for historical gene flow.

Multilocus studies assessing patterns of nucleotide polymorphism within and among closely related species provide access to genealogical information bearing on demographic and geographic aspects of their speciation history. However, the technical difficulties in obtaining sufficient sequence data have severely limited this approach thus far, especially in outbred plant taxa. We employ the analytical framework of divergence population genetics in testing the isolation model of speciation in three self-incompatible species of wild tomatoes (clade Lycopersicon), in particular the assumption of divergence without gene flow. Based on DNA sequence data for 13 nuclear loci, average levels of silent polymorphism vary more than three-fold among species. We estimate a large effective population size for the ancestral species, quite similar to that of the highly polymorphic L. peruvianum. The other two species, however, exhibit concordant signatures of population-size reduction. These demographic inferences are biologically plausible and consistent with results obtained from standard neutrality tests. While the isolation model cannot be rejected by goodness-of-fit criteria, patterns of intragenic linkage disequilibrium in L. peruvianum are indicative of historical introgression at least in some regions of the genome. Considered jointly with the geographic pattern of postzygotic reproductive isolation, our results suggest that speciation occurred under residual gene flow, implying natural selection as one of the evolutionary forces driving the diversification of tomato lineages.

Base Sequence↗
PubMed2006

The value of metals bioavailability and speciation information for ecological risk assessment in arid soils.

When evaluating the risk chemicals may pose to mammals and birds in ecological risk assessments (ERAs), it is common practice to conservatively assume that all (100%) of a chemical in an environmental medium is bioavailable to receptors. This assumption often leads to overestimating ecological risk and may ultimately result in costly and unnecessary risk management actions. While effects of bioavailability and speciation of metals such as arsenic (As) and lead (Pb) have been considered in human health risk assessment, these effects are rarely taken into consideration when assessing risks to mammals and birds. An ERA was conducted at the former Col-Tex refinery site in Colorado City, Texas, USA, to characterize risks to select wildlife species from exposure to chromium (Cr) and Pb found in soils. The focus on these metals was based on results of a screening-level ERA that found that Cr and Pb were posing ecological risks at the site. Soils were analyzed for total Cr and Pb, trivalent Cr (CrIII), hexavalent Cr (CrVI), organic Pb, and the bioavailability and speciation of Pb. Results for Pb and Cr indicated that >94% of the Cr was present as the less toxic and immobile Cr(III) and that >99% of the Pb in soils was present as inorganic Pb. Lead bioaccessibility measured by in vitro testing ranged from 8% to 77.8%, depending on location of individual soil samples. Results demonstrated that Pb and Cr bioavailability and speciation information can raise soil cleanup concentrations while being protective of ecological receptors. The costs of performing the ERA were de minimus compared to the reduction in remediation costs at the site. The refined hazard estimates allowed informed decision making in the management and segregation of soils, allowing for effective risk management at the site.

Animals↗
PubMed2024

Extreme elevational migration spurred cryptic speciation in giant hummingbirds.

The ecoevolutionary drivers of species niche expansion or contraction are critical for biodiversity but challenging to infer. Niche expansion may be promoted by local adaptation or constrained by physiological performance trade-offs. For birds, evolutionary shifts in migratory behavior permit the broadening of the climatic niche by expansion into varied, seasonal environments. Broader niches can be short-lived if diversifying selection and geography promote speciation and niche subdivision across climatic gradients. To illuminate niche breadth dynamics, we can ask how "outlier" species defy constraints. Of the 363 hummingbird species, the giant hummingbird (Patagona gigas) has the broadest climatic niche by a large margin. To test the roles of migratory behavior, performance trade-offs, and genetic structure in maintaining its exceptional niche breadth, we studied its movements, respiratory traits, and population genomics. Satellite and light-level geolocator tracks revealed an >8,300-km loop migration over the Central Andean Plateau. This migration included a 3-wk, ~4,100-m ascent punctuated by upward bursts and pauses, resembling the acclimatization routines of human mountain climbers, and accompanied by surging blood-hemoglobin concentrations. Extreme migration was accompanied by deep genomic divergence from high-elevation resident populations, with decisive postzygotic barriers to gene flow. The two forms occur side-by-side but differ almost imperceptibly in size, plumage, and respiratory traits. The high-elevation resident taxon is the world's largest hummingbird, a previously undiscovered species that we describe and name here. The giant hummingbirds demonstrate evolutionary limits on niche breadth: when the ancestral niche expanded due to evolution (or loss) of an extreme migratory behavior, speciation followed.

Animals↗
PubMed2006

Sympatric speciation: why the controversy?

Two recent studies provide convincing evidence that speciation without geographic isolation--sympatric speciation--has occurred within isolated island habitats, but we remain ignorant of how frequent the process really is.

Animals↗
PubMed2026

Differentiated extraction strategies for selenium speciation in hyperaccumulator and non-hyperaccumulator plants via orthogonal LC-AFS.

The growing demand for selenium (Se)-enriched products highlights the need for accurate and accessible Se speciation analysis. In this study, a cost-effective orthogonal liquid chromatography-atomic fluorescence spectrometry (LC-AFS) method was developed for the determination of seven Se species (SeO3 2-, SeO4 2-, SeLan, SeMet, SeCys2, MeSeCys, and γ-GluMeSeCys), providing an alternative to ICP-MS-based approaches. Differences in Se accumulation mechanisms between hyperaccumulator Cardamine hupingshanensis and non-hyperaccumulator wheat significantly affected extraction efficiency. The sequential aqueous-enzymatic extraction increased SeLan recovery in C. hupingshanensis from 5.06 to 143.74 μg Se g-1, a 28.41-fold increase, while anaerobic extraction enhanced SeMet recovery in wheat from 98.73 to 112.17 μg Se g-1. Consequently, matrix-specific strategies improved Se recoveries from 20.82% to 80.65% in C. hupingshanensis and from 34.11% to 90.02% in wheat. These findings highlight the importance of matrix-specific extraction for accurate Se speciation analysis.

Cardamine hupingshanensis↗
PubMed2024

The centromere landscapes of four karyotypically diverse Papaver species provide insights into chromosome evolution and speciation.

Understanding the roles played by centromeres in chromosome evolution and speciation is complicated by the fact that centromeres comprise large arrays of tandemly repeated satellite DNA, which hinders high-quality assembly. Here, we used long-read sequencing to generate nearly complete genome assemblies for four karyotypically diverse Papaver species, P. setigerum (2n = 44), P. somniferum (2n = 22), P. rhoeas (2n = 14), and P. bracteatum (2n = 14), collectively representing 45 gapless centromeres. We identified four centromere satellite (cenSat) families and experimentally validated two representatives. For the two allopolyploid genomes (P. somniferum and P. setigerum), we characterized the subgenomic distribution of each satellite and identified a "homogenizing" phase of centromere evolution in the aftermath of hybridization. An interspecies comparison of the peri-centromeric regions further revealed extensive centromere-mediated chromosome rearrangements. Taking these results together, we propose a model for studying cenSat competition after hybridization and shed further light on the complex role of the centromere in speciation.

Centromere↗
PubMed2005

Rapid radiation and cryptic speciation in mediterranean triplefin blennies (Pisces: Tripterygiidae) combining multiple genes.

The genus Tripterygion is the unique genus of the family Tripterygiidae in the Mediterranean Sea and in the northeastern Atlantic coast. Three species and four subspecies had been described: Tripterygion tripteronotus and Tripterygion melanurus (T. m. melanurus and T. m. minor) are endemic of the Mediterranean, and T. delaisi (T. d. delaisi and T. d. xanthosoma) is found in both areas. We used five different genes (12S, 16S, tRNA-val, COI, and 18S) to elucidate their taxonomy status and their phylogenetic relationships. We employed different phylogenetic reconstructions that yielded different tree topologies. This discrepancy may be caused by the speciation process making difficult the reconstruction of a highly supported tree. All pair comparisons between these three species showed the same genetic divergence indicating that the speciation process could have been resolved by a rapid radiation event after the Messinian Salinity Crisis (5.2Mya) leading to a trichotomy. Our molecular data revealed two clearly supported clades within T. tripteronotus, whose divergence largely exceeded that found between other fish species, consequently these two groups should be considered two cryptic species diverging 2.75-3.32Mya along the Pliocene glaciations. On the contrary, none of the genes studied supported the existence of two subspecies of T. melanurus. Finally, the two subspecies of T. delaisi were validated and probably originated during the Quaternary climatic fluctuations (1.10-1.23Mya), however their distribution ranges should be redefined.

Animals↗
PubMed2006

Speciation by hybridization in Heliconius butterflies.

Speciation is generally regarded to result from the splitting of a single lineage. An alternative is hybrid speciation, considered to be extremely rare, in which two distinct lineages contribute genes to a daughter species. Here we show that a hybrid trait in an animal species can directly cause reproductive isolation. The butterfly species Heliconius heurippa is known to have an intermediate morphology and a hybrid genome, and we have recreated its intermediate wing colour and pattern through laboratory crosses between H. melpomene, H. cydno and their F1 hybrids. We then used mate preference experiments to show that the phenotype of H. heurippa reproductively isolates it from both parental species. There is strong assortative mating between all three species, and in H. heurippa the wing pattern and colour elements derived from H. melpomene and H. cydno are both critical for mate recognition by males.

Animals↗
PubMed2006

Genetic evidence for complex speciation of humans and chimpanzees.

The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here we develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human-chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. Our analysis also shows that human-chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently.

Animals↗