Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “speciation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed2004

Speciation genes.

Until recently, the genes that cause reproductive isolation remained black boxes. Consequently, evolutionary biologists were unable to answer several questions about the identities and characteristics of "speciation genes". Over the past few years, however, evolutionary geneticists have finally succeeded in isolating several such genes, providing our first glimpse at factors that are thought to be representative of those underlying the origin of species. Evolutionary analysis of these genes suggests that speciation results from positive Darwinian selection within species. Molecular evolutionary study of the genes causing reproductive isolation may represent an important new phase in the study of speciation.

Animals↗
PubMed2005

Chromium speciation in environmental samples by solid phase extraction on Chromosorb 108.

In the present work, a solid phase extraction system has been proposed for speciation of Cr(III) and Cr(VI) in the real samples. The procedure based on the adsorption of chromium(III) as dithizonate chelate on the Chromosorb 108 resin. After reduction of Cr(VI) by concentrated H2SO4 and ethanol, the system was applied to the total chromium. Cr(VI) was calculated as the difference between the total Cr content and the Cr(III) content. The influences of the analytical parameters including pH of the aqueous solution, amounts of dithizone, eluent type, sample volume and flow rates of the sample and eluent solution were investigated. No considerable interferences have been observed from other investigated anions and cations on the chromium speciation. The adsorption capacity of sorbent was 4.50 mg/g Cr(III). The detection limit of Cr(III) is 0.75 microg/L. The proposed method was applied to the speciation of chromium in environmental samples including natural waters and total chromium preconcentration in microwave digested Turkish tobacco, coffee and soil samples with satisfactory results. In order to verify the accuracy of the method, two certified reference materials (NIST SRM 1573a Tomato Leaves and RTC-CRM 025-050 Metals on Soil) were analyzed and the results obtained were in good agreement with the certified values. The relative errors and relative standard deviations were below 5% and 9%, respectively.

Adsorption↗
PubMed2004

A model approach for evaluating effects of remedial actions on mercury speciation and transport in a lake system.

This paper provides a model approach for understanding mercury cycling in aquatic systems. The information gained is then used for evaluating three remedial actions, namely, natural attenuation, dredging and capping. Onondaga Lake, NY was used as a model aquatic system. Mercury transport and speciation in both the water column and the benthic sediment were simulated by using a Water Quality Analysis Simulation Program. Model predictions for the water column generally agreed with the measured values reported in literature for Onondaga Lake. Sensitivity analyses of the model were conducted for determining the impact of transport mechanisms and speciation mechanisms. Advection, sorption and settling were important mechanisms of Hg transport in the water column. In the benthic sediment, settling of Hg from the water column was the most important input source of Hg. Reduction, methylation and demethylation were important mechanisms of Hg speciation in both the water column and the benthic sediment. Assuming that Hg loading is steady, natural attenuation showed no positive impact for remediation of Hg-contaminated aquatic systems as compared with dredging and capping.

Fresh Water↗
PubMed2005

Effects of pH and phosphate on metal distribution with emphasis on As speciation and mobilization in soils from a lead smelting site.

Arsenic in soils from the Asarco lead smelter in East Helena, Montana was characterized by X-ray absorption spectroscopy (XAS). Arsenic oxidation state and geochemical speciation were analyzed as a function of depth (two sampling sites) and surface distribution. These results were compared with intensive desorption/dissolution experiments performed in a pH stat reactor for samples from the site with the highest degree of As heterogeneity. The objectives of the study were to investigate the solid-phase geochemical As speciation, assess the speciation of As in solutions equilibrated with the solids under controlled pH (pH=4 or 6) and Eh (using hydrogen or air) environments, observe the effects of phosphate on the release of As into solution, and examine the effects of phosphate on metal mobility in the systems. Arsenic was predominantly found in the As(V) valence state, though there was evidence that As(III) and As(0) were present also. The dominant geochemical phase was scorodite (FeAsO4.2H2O). The pH was controlled in the pH stat experiments by the addition of equinormal solutions of monoprotic (HNO3), diprotic (H2SO4), or triprotic (H3PO4) acids. For many of the divalent metal cations, solution concentrations greatly decreased in the presence of phosphate. Solutions were also analyzed for anions. Evidence exists for sulfate release into solution. More As was released into solution at lower pH. A slight increase in solution arsenate occurs with the addition of phosphate, but the risk posed from the increased desorption/dissolution of As must be weighed against the decrease in solution concentrations of many metals especially Pb. If tailings from this site underwent acidification (e.g., acid mine drainage), in situ sequestration of metals by phosphate could be combined with placement of subsurface permeable reactive barriers for capture of As to reduce the risk associated with arsenic and trace metal mobilization. Results from this study could be used in risk management plans for sites similar to the Pb smelter site examined here.

Arsenicals↗
PubMed2005

Arsenic speciation and mobilization in CCA-contaminated soils: influence of organic matter content.

A laboratory incubation experiment was conducted to investigate the influence of organic matter content on arsenic speciation and mobilization in chromated copper arsenate (CCA)-contaminated soils. The study was performed with four synthetic CCA-contaminated soils, with a range of organic matter content (mixture of peat moss and poultry manure) varying between 0.5% and 15% (w/w), under unsaturated and aerobic conditions for 40 days. Changes in water-soluble arsenic speciation (As(V), As(III), MMAA, DMAA) were monitored over time in soil extracts by HPLC-ICP-MS and in the soil solid phase (As(III), As(V)) by a solvent extraction method. Irrespective of organic matter content, As(V) was the predominant soil bound and aqueous phase arsenic species. However, over 40 days, a high soil organic matter content (7.5% and 15%) was able to entail formation of soil bound As(III). Moreover, total water-soluble arsenic was positively correlated with dissolved organic carbon (r(2)=0.88). However, the organic matter content did not influence arsenic speciation in the soluble fraction; neither As(V) reduction nor arsenic biomethylation occurred within 40 days. An increase in dissolved organic carbon content promoted both As(V) and As(III) solubilization in soils. Also, over time, organic matter contents of 7.5% and 15% entailed the persistence of soluble As(V), likely due to the high content of dissolved organic compounds which prevented its sorption onto soil. Based on this data, the environmental risk of aerobic CCA-contaminated soils rich in organic matter may be due to an enhanced availability of soluble As(V) over time, rather than to the formation of the more toxic and more mobile As(III).

Arsenates↗
PubMed2006

Speciation of iodine in solid environmental samples by iodine K-edge XANES: application to soils and ferromanganese oxides.

A method was developed for speciation of iodine in solid materials using X-ray absorption near-edge structure (XANES). This method was used to identify the iodine species (mainly inorganic iodine) in environmental samples. It was shown that the XANES spectra of iodide and iodate sorbed within solid materials can be simulated by the linear combination of the spectra of iodide and iodate ions in water. The distribution coefficient (Kd) between soil and water was obtained independently for iodide and iodate, based on iodine speciation both in the solid phase, by XANES, and in the aqueous phase, by HPLC-ICP-MS. It was found that the Kd of iodate is larger than that of iodide by a factor of more than six, showing the more soluble nature of iodide. It was suggested that iodate can form in soil even when iodide is injected into the soil-water system under conditions within the iodide-stable field of the Eh-pH diagram of iodine. This is caused by the much higher affinity of iodate for solid surfaces than iodide. In soil samples under various water saturation conditions, or various Eh conditions, the iodide fraction in water increases with decreasing Eh, which results in an increase in the dissolved total iodine fraction in soil water. The speciation method using XANES was also applied to iodine in a natural soil sample and marine ferromanganese oxides. It is suggested that iodine K-edge XANES is a promising tool for determining the iodide/iodate ratio in natural solid samples, which contributes to better understanding of the behavior of iodine at the Earth's surface.

Journal Article↗
PubMed2004

Arsenic speciation in human urine: are we all the same?

We studied the arsenic speciation in human urine samples by using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). We investigated the arsenic speciation in the urine collected from nine volunteers during a 3-day period after a meal of blue mussels, Mytilus edulis. We also studied the effect of cooking on the arsenic speciation. Arsenobetaine and dimethylarsinic acid (DMAA) were the major arsenic metabolites found in the urine samples. Significant amounts of unknown metabolites were also detected. The excretion patterns of arsenic from individuals were generally similar except for two subjects. One of whom excreted high amounts of arsenobetaine even though no arsenic-rich food was eaten for 3 days before the experiment. The results reveal that we need a better understanding of the metabolism of arsenic compounds by human.

Animals↗
PubMed2004

Speciation in the apple maggot fly: a blend of vintages?

The importance of speciation without the complete geographical separation of diverging populations (sympatric speciation) has become increasingly accepted. One of the textbook examples of recent speciation in sympatry is the apple maggot fly Rhagoletis pomonella, in which genetically differentiated host races feed on either hawthorn or apple. Three recent articles by Feder and collaborators show that the history of these host races is more complicated than was previously realized. Genes that differentiate races of flies that feed on either apple or hawthorn are located in chromosomal rearrangements. This variation forms a latitudinal cline that must have been established long before apples were available as hosts. Furthermore, there is also new evidence for the very recent evolution of a derived preference for volatile chemicals that are typical of apple fruits among apple-feeding flies. These results show that adaptation to apple populations has involved both the sorting of ancestral adaptive variation and the selection of novel mutations.

Journal Article↗
PubMed2004

Glacial cycles and the tempo of avian speciation.

How old are most species of North American birds? A longstanding debate centers on whether Pleistocene events caused substantial avian diversification. Two new syntheses of speciation times by Johnson and Cicero, and Weir and Schluter provide compelling evidence of recent Pleistocene speciation, whereas diversification rate analyses by Zink et al. suggest that most speciation events occurred earlier. Although these results are seemingly contradictory, when considered together they provide a robust and complementary perspective on the tempo of avian diversification in North America.

Journal Article↗
PubMed2004

Field and laboratory arsenic speciation methods and their application to natural-water analysis.

The toxic and carcinogenic properties of inorganic and organic arsenic species make their determination in natural water vitally important. Determination of individual inorganic and organic arsenic species is critical because the toxicology, mobility, and adsorptivity vary substantially. Several methods for the speciation of arsenic in groundwater, surface-water, and acid mine drainage sample matrices using field and laboratory techniques are presented. The methods provide quantitative determination of arsenite [As(III)], arsenate [As(V)], monomethylarsonate (MMA), dimethylarsinate (DMA), and roxarsone in 2-8 min at detection limits of less than 1 microg arsenic per liter (microg As L(-1)). All the methods use anion exchange chromatography to separate the arsenic species and inductively coupled plasma-mass spectrometry as an arsenic-specific detector. Different methods were needed because some sample matrices did not have all arsenic species present or were incompatible with particular high-performance liquid chromatography (HPLC) mobile phases. The bias and variability of the methods were evaluated using total arsenic, As(III), As(V), DMA, and MMA results from more than 100 surface-water, groundwater, and acid mine drainage samples, and reference materials. Concentrations in test samples were as much as 13,000 microg As L(-1) for As(III) and 3700 microg As L(-1) for As(V). Methylated arsenic species were less than 100 microg As L(-1) and were found only in certain surface-water samples, and roxarsone was not detected in any of the water samples tested. The distribution of inorganic arsenic species in the test samples ranged from 0% to 90% As(III). Laboratory-speciation method variability for As(III), As(V), MMA, and DMA in reagent water at 0.5 microg As L(-1) was 8-13% (n=7). Field-speciation method variability for As(III) and As(V) at 1 microg As L(-1) in reagent water was 3-4% (n=3).

Arsenic↗
PubMed2004

Effects of pH and competing anions on the speciation of arsenic in fixed ionic strength solutions by solid phase extraction cartridges.

Anion exchange resins (AERs) separate As(V) and As(III) in solution by retaining As(V) and allowing As(III) to pass through. Anion exchange resins offer several advantages including cost, portability, and ease of use. The use of AERs for the instantaneous speciation of As minimizes the effects of preservatives on As species analysis. The aims of this study were to: (1) Examine the effects of pH and competing anions on the efficacy of solid phase extraction cartridges (SPECs) for speciation of As in a 0.01 molL(-1) NaNO(3) background electrolyte. (2) Identify optimal conditions (e.g. flow rates) for As speciation. (3) Calculate method detection limits (MDLs) from spiked background electrolyte and percent recoveries of As species from spiked extracts of mine wastes. The most effective SPEC retained As(V) through a range of environmentally relevant pH values (4-8). The mass loading capacity for As(V) was reduced in the background electrolyte (0.006 mg) compared with As(V) in deionized H(2)O (0.75 mg). Some retention (10-20%) of As(III) occurred on pre-wetted cartridges. Approximately 98% of spiked As(III) passed through dry cartridges. The recommended flow rate (0.5 mL min(-1)) was increased to 5 mL min(-1) without significant effect on As(V) retention. The presence of anions decreased the retention of As(V) with sulfate and phosphate having the greatest impact. MDLs were 0.004 mg L(-1) for both inorganic species. Spike recoveries in 0.01 M NaNO(3) mine waste extracts averaged 94% for As(III) and 107% for As(V).

Anion Exchange Resins↗
PubMed2005

Effect of citric acid on aluminum hydrolytic speciation.

The mechanisms of the influence of organics on Al transformation were not fully understood. This study investigated the effect of citric acid on Al speciation in partially neutralized aluminum solution. The partially neutralized solution was prepared with 20 mmol L(-1) AlCl3 without citrate (citrate/Al molar ratio of 0, control) or with citrate (citrate to Al molar ratios between 0.1 and 3.0) at pH between 3.0 and 7.0. The nature of aluminum hydrolytic products as influenced by citrate complexation was investigated by turbidity measurement, ferron kinetic color development, peak line width in 27Al nuclear magnetic resonance (NMR) deconvolution demodule quantitative methods, and the MinteqA2 chemical speciation program. Sulfate precipitates from Al solution as influenced by citrate were examined by X-ray diffraction (XRD) analysis and atomic force microscopy (AFM). The turbidity of the Al solution increased with increasing pH values. Increases in citrate/Al molar ratio from 0 to 0.1 decreased dramatically the turbidity due to citrate complexation. The 27Al NMR peak at 6 ppm of the Al solution at a citrate/Al molar ratio of 0.5 shifted to 8 and 10 ppm in the solutions at citrate/Al molar ratio of 1.0 and 3.0, respectively. Comparison of 27Al NMR data and the data obtained from the MinteqA2 chemical speciation program, indicate that the Al-citrate complexes as revealed by 27Al NMR data are largely Al(citrate), AlH(citrate)+, and Al(citrate)(2)3- complexes (99-112%) in the pH range of 4.5-6.5. The non-detected Al fractions by the MinteqA2 program account for 82-99% of the non-detected Al fractions by NMR quantitation in the same pH range. The AFM of sulfate precipitates from solutions with low citrate/Al molar ratios (i.e., 0.01, pH 4.5, aged 40 days) shows that Al13 sulfate precipitates were ellipse-shaped. These ellipse-shaped precipitates were aggregated when solution pH increased from 4.5 to 7.0 (aged 40 days), indicating the fast hydrolytic rate of Al at high pH. The sulfate precipitates from solution with a high citrate/Al molar ratio (i.e., 0.05, pH 4.5, aged 40 days) also shows aggregate of particles, and XRD non-crystallized precipitates the hampering effect of citrate on Al precipitates.

Aluminum↗
PubMed2006

Speciation of phosphorus fractionation in river sediments by explanatory data analysis.

This article investigates the controls on sediment phosphorus (P) speciation dynamics as a function of its fractionation into chemically defined operational pools along a river continuum. A total of 27 variables were analyzed in bed sediment samples collected for one year from six sampling points, along a 75km river continuum (Louros River, NW Greece). Multivariate explanatory analysis of the complex experimental data matrix was performed in order to unravel the spatial pattern of P speciation. Non-parametric examinations were also applied in order to elucidate the temporal variations encountered in the speciation of P. The results suggest that inorganic P species control P bioavailability in space and time. Organic P was found to be very reactive among the various fractions thus changing its bioavailability but exhibited no temporal variation. The utility of the proposed approach in the differentiation of natural and anthropogenic P inputs and their classification to point and non-point sources is demonstrated presenting a significant improvement compared to mere fractionation analysis.

Biological Availability↗
PubMed2007

Dissolved iron and its speciation in a shallow eutrophic lake and its inflowing rivers.

It has been suggested that iron is a limiting factor on bloom-forming cyanobacteria in lake water. Although the availability of iron for phytoplankton depends significantly on its speciation, little is known about iron speciation in natural lake water. We investigated the horizontal distribution and temporal variation of dissolved iron and its chemical speciation in Lake Kasumigaura and its two inflowing rivers. Concentrations of dissolved iron and its organic ligands, determined by cathodic stripping voltammetry, clearly decreased as lake water flowed from the river entry points toward the center of the lake, indicating their riverine origin. The fraction of iron occurring in organic complexes tended to increase with the water flow. These results suggest that most of the dissolved iron in river water forms unstable soluble species, such as inorganic iron; thus, these unstable iron species may be scavenged in the mouths of rivers, and stable organic complexes of iron may flow to the center of the lake. Furthermore, most of the dissolved iron (88.2-99.9%) was present as organic complexes, and the inorganic iron level in Lake Kasumigaura (pFe' value=7.8-13.6) was similar to that observed in the open ocean. This result suggests that iron is an important factor determining the structure of the phytoplankton community in Lake Kasumigaura.

Cyanobacteria↗
PubMed2004

Tempo of speciation in a butterfly genus from the Southeast Asian tropics, inferred from mitochondrial and nuclear DNA sequence data.

Molecular systematics is frequently beset with phylogenetic results that are not fully resolved. Researchers either state that the absence of resolution is due to character conflict, explosive speciation, or some combination of the two, but seldom do they carefully examine their data to distinguish between these causes. In this study, we exhaustively analyze a set of nuclear and mitochondrial nucleotide data for the Asian tropical butterfly genus Arhopala so as to highlight the causes of polytomies in the phylogenetic trees, and, as a result, to infer important biological events in the history of this genus. We began by using non-parametric statistical methods to determine whether the ambiguously resolved regions in these trees represent hard or soft polytomies. In addition we determined how this correlated to number of inferred changes on branches, using parametric maximum likelihood estimations. Based on congruent patterns in both mitochondrial and nuclear DNA sequences, we concluded that at two stages in the history of Arhopala there have been accelerated instances of speciation. One event, at the base of the phylogeny, generated many of the groups and subgroups currently recognized in this genus, while a later event generated another major clade consisting of both Oriental and Papuan species groups. Based on comparisons of closely related taxa, the ratio of instantaneous rate of evolution between mitochondrial and nuclear DNA evolution is established at approximately 3:1. The earliest radiation is dated between 7 and 11 Ma by a molecular clock analysis, setting the events generating much of the diversity of Arhopala at well before the Pleistocene. Periodical flooding of the Sunda plateau during interglacial periods was, therefore, not responsible for generating the major divisions in the genus Arhopala. Instead, we hypothesize that large-scale climatic changes taking place in the Miocene have induced the early acceleration in speciation.

Animals↗
PubMed1998

Correlation of parasite speciation and specificity with host evolutionary relationships.

Protopolystoma (Monogenea, Polystomatidae) is strictly specific to the anuran amphibian genus Xenopus. The host group is characterised by a polyploid series in which chromosome numbers reflect diploid, tetraploid, octoploid and dodecaploid constitutions; the series is considered to have evolved through interspecies hybridisation and genome duplication. This study correlates information on host evolutionary relationships with patterns of parasite speciation and host specificity. Protopolystoma is restricted to one subgenus (Xenopus) with multiples of 36 chromosomes, and is absent from the subgenus Silurana (with multiples of 20 chromosomes). Molecular, biochemical and karyotype evidence distinguishes three subgroups within Xenopus. Representative species from each subgroup, Xenopus muelleri, Xenopus fraseri and Xenopus laevis, have been examined for polystomatid infection. Two species of Protopolystoma occur in each of these host species. In X. muelleri, the two Protopolystoma species reflect parasite co-speciation corresponding with the divergence of two sibling host species. Xenopus fraseri and X. laevis (both with 2n = 36 chromosomes) are implicated in the hybrid origin of two octoploid species, Xenopus wittei and Xenopus vestitus (both 2n = 72). The relationships of the Protopolystoma species in these Xenopus taxa reflect this presumed ancestry. Xenopus wittei carries two species of Protopolystoma, one shared with X. fraseri and the other shared with X. laevis. Xenopus vestitus carries a single species of Protopolystoma which is shared with X. laevis but there is no "heirloom" which reflects its hybrid origin involving X. fraseri. In addition to these shared parasite species which may reflect shared host genes, X. fraseri and X. laevis each carry separate species-specific Protopolystoma which do not occur in other Xenopus species even where there is evidence of common genetic information (as in the allopolyploid wittei and vestitus). This case study may be interpreted as indicating a powerful influence of host genetic factors on susceptibility to infection, host-specificity, and parasite speciation.

Animals↗
PubMed2001

Sample treatment in chromatography-based speciation of organometallic pollutants.

Speciation analysis is nowadays performed routinely in many laboratories to control the quality of the environment, food and health. Chemical speciation analyses generally include the study of different oxidation state of elements or individual organometallic compounds. The determination of the different chemical forms of elements is still an analytical challenge, since they are often unstable and concentrations in different matrices of interest are in the microg l(-1) or even in the ng l(-1) range (e.g., estuarine waters) or ng g(-1) in sediments and biological tissues. For this reason, sensitive and selective analytical atomic techniques are being used as available detectors for speciation, generally coupled with chromatography for the time-resolved introduction of analytes into the atomic spectrometer. The complexity of these instrumental couplings has a straightforward consequence on the duration of the analysis, but sample preparation to separate and transfer the chemical species present in the sample into a solution to be accepted readily by a chromatographic column is the more critical step of total analysis, and demands considerable operator skills and time cost. Traditionally, liquid-liquid extraction has been employed for sample treatment with serious disadvantages, such as consumption, disposal and long-term exposure to organic solvent. In addition, they are usually cumbersome and time-consuming. Therefore, the introduction of new reagents such as sodium tetraethylborate for the simultaneous derivatization of several elements has been proposed. Other possibilities are based in the implementation of techniques for efficient and accelerated isolation of species from the sample matrix. This is the case for microwave-assisted extraction, solid-phase extraction and microextraction, supercritical fluid extraction or pressurized liquid extraction, which offer new possibilities in species treatment, and the advantages of a drastic reduction of the extraction time and the embodiment into on-line flow analysis systems. This new generation of treatment techniques constitutes a good choice as fast extraction methods for feasible species-selective analysis of organometallic compounds under the picogram level, that can be used for national regulatory agencies, governmental and industrial quality control laboratories, and consequently, for manufacturers of analytical instrumentation.

Chromatography↗
PubMed2002

Capillary electrophoresis-inductively coupled plasma-mass spectrometry: an attractive complementary technique for elemental speciation analysis.

Some basic and practical aspects of interfacing capillary electrophoresis to inductively coupled plasma-mass spectrometry (CE-ICP-MS) are reviewed in this article with emphasis on the use of this hyphenated technique for elemental speciation analysis. The principles behind the techniques of both CE and ICP-MS are introduced. The interfacing of CE to ICP-MS is discussed including several devices and nebulizers reported in literature. A brief account of their advantages and limitations is given. The various CE-ICP-MS applications for elemental speciation analysis are also reviewed. Some issues concerning the future of CE-ICP-MS for the elemental speciation analyses are discussed.

Electrophoresis, Capillary↗