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 181 records · Page 10Linked to original sources
PubMed2003

Internal redistribution of radiolabelled silver among tissues of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation.

Influence of water Ag(I) speciation on pharmacokinetics of Ag(I) during a post-exposure period was investigated in rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla). The rainbow trout is sensitive to waterborne ionic Ag(+) whereas the eel is tolerant. The fish were acclimated to either of two chloride concentrations, 10 or 1200 microM, in synthetic soft water and then exposed to a sublethal 24-h pulse of 1.3 microgl(-1) of 110mAg(I) added as 110mAgNO(3) in these waters. The protocol provided exposures to mainly the free ion Ag(+) (low chloride water) or mainly AgCl(aq) (high chloride water). Contents and concentrations of 110mAg(I) in tissues and body fluids were then monitored over a 67-day post-exposure period in Ag(I)-free water of the same chloride levels. Changing the speciation of Ag(I) in the water had no effect on the whole body load of 110mAg(I), but did result in differences in internal distribution. In trout, changing water Ag(I) speciation significantly altered elimination or accumulation of Ag(I) in several body compartments. Notably, trout exposed to AgCl(aq) eliminated 110mAg(I) from the kidney more quickly than trout exposed to Ag(I) primarily as Ag(+). This elimination was matched by higher concentrations of 110mAg in liver of trout exposed to Ag(I) primarily as AgCl(aq). In eel, shifting speciation from Ag(+) to AgCl(aq) hastened elimination of 110mAg(I) from mid and posterior intestine and increased 110mAg(I) retention in kidney. While there was no difference between the two fish species in whole body 110mAg(I) load, most internal body compartments of trout had higher 110mAg(I) concentrations than those in eel early in the experiment. Because tissue-specific elimination times were longer in eel than in trout, these differences were generally cancelled by the end of the 67-day depuration period. The only exception was the liver, which in trout continued to accumulate 110mAg(I) throughout the experiment but in eel remained unchanged. The combined effect of 110mAg(I) movements in the two species was that trout retained all their accumulated 110mAg(I) through the 67-day period, whereas the body burden of 110mAg(I) in eel was reduced to half initial values by day 67.

Adaptation, Physiological↗
PubMed2001

Parallel speciation: a key to sympatric divergence.

Until recently, our view of speciation was that reproductive isolation evolves during long periods of allopatry through the accumulation of genetic differences that result in genetic incompatibility. This view now contrasts with new findings that characters affecting reproductive isolation can diverge rapidly in sympatry as a result of natural selection. Recent studies combining research on phylogeny and ecology of natural populations cast new light on patterns, timescales and mechanisms, and emphasize the role of ecological factors in speciation. Studies of parallel speciation provide a strong case for sympatric speciation and for natural selection generating reproductive barriers.

Journal Article↗
PubMed2001

Speciation in the fossil record.

It is easy to claim that the fossil record says nothing about speciation because the biological species concept (which relies on interbreeding) cannot be applied to it and genetic studies cannot be carried out on it. However, fossilized organisms are often preserved in sufficient abundance for populations of intergrading morphs to be recognized, which, by analogy with modern populations, are probably biological species. Moreover, the fossil record is our only reliable documentation of the sequence of past events over long time intervals: the processes of speciation are generally too slow to be observed directly, and permanent reproductive isolation can only be verified with hindsight. Recent work has shown that some parts of the fossil record are astonishingly complete and well documented, and patterns of lineage splitting can be examined in detail. Marine plankton appear to show gradual speciation, with subsequent morphological differentiation of lineages taking up to 500000 years to occur. Marine invertebrates and vertebrates more commonly show punctuated patterns, with periods of rapid speciation followed by long-term stasis of species lineages.

Journal Article↗
PubMed2001

Theory and speciation.

The study of speciation has become one of the most active areas of evolutionary biology, and substantial progress has been made in documenting and understanding phenomena ranging from sympatric speciation and reinforcement to the evolutionary genetics of postzygotic isolation. This progress has been driven largely by empirical results, and most useful theoretical work has concentrated on making sense of empirical patterns. Given the complexity of speciation, mathematical theory is subordinate to verbal theory and generalizations about data. Nevertheless, mathematical theory can provide a useful classification of verbal theories; can help determine the biological plausibility of verbal theories; can determine whether alternative mechanisms of speciation are consistent with empirical patterns; and can occasionally provide predictions that go beyond empirical generalizations. We discuss recent examples of progress in each of these areas.

Journal Article↗
PubMed2000

Chromium occurrence in the environment and methods of its speciation.

This article includes a survey of chromium (Cr) occurrence in different environmental compartments, its pathways in the environment and the cross-sectional presentation of Cr speciation methods against the background of Cr chemistry. The aim of the article is to demonstrate that knowledge of interconversion processes between different Cr forms is necessary to understand its behaviour and role in the environment, in addition to enabling reliable Cr speciation analysis to be performed. The current methods of Cr speciation are presented, characterized and their usefulness discussed. These must rely on superior separation and detection capabilities since Cr in environmental compartments is mostly at trace or ultra-trace level. The need for using unique techniques of sampling, storage, handling and separation for Cr speciation is documented.

Journal Article↗
PubMed2000

Speciation of inorganic lead and ionic alkyllead compounds by GC/MS in prescreened rainwaters

A simple and novel screening method for lead compounds in environmental waters is proposed. The analytes, in an acetic medium, are sorbed on a C60 fullerene column as diethyldithiocarbamate complexes and subsequently eluted with isobutyl methyl ketone (IBMK), the lead being determined by flame atomic absorption spectrometry. The screening method acts as filter and indicates whether the target analytes are present above or below the detection limit of the method (0.5 ng/mL), giving no false positives. Positive samples were speciated by GC/MS, using a flow system similar to that of the screening method. Lead(II) and ionic di- and trialkyllead are derivatized with a Grignard reagent. Both methods use similar chemical and flow variables except for the eluent, IBMK in the screening method and n-hexane in the speciation method. The GC/MS speciation method is very sensitive; it exhibits a linear range of 0.02-5 ng/mL, and detection limits of 1-4 ng/L are achieved. Also, its repeatibility, as RSD, is less than 6%. The method was applied to the speciation of Pb2+ and di- and trialkyllead in positive prescreened rainwater samples from three different urban areas.

Journal Article↗
PubMed2004

Coupling speciation and isotope dilution techniques to study arsenic mobilization in the environment.

We have developed an approach to isolate mechanisms controlling mobility and speciation of As in soil-water systems. The approach uses a combination of isotopic exchange and chromatographic/mass spectrometric As speciation techniques. We used this approach to identify mechanisms responsible for changes in the concentration of soluble As in two contaminated soils (Eaglehawk and Tavistock) subjected to different redox conditions and microbial activity. A high proportion of the total As in both soils was present in a nonlabile form. Incubation of the soils under anaerobic conditions led to changes in the concentration of soluble As in each soil but did not change the As speciation or the proportion of total As in labile forms in the soils. Hence, a decrease in soluble As in the Eaglehawk soil was the result of an Eh-induced pH decrease, enhancing the solid-phase sorption of As(V). An increase in soluble As in the Tavistock soil was due to an Eh-induced pH increase, decreasing solid-phase sorption of As(V). Incubation of the soils under aerobic conditions with microbial activity stimulated by addition of glucose resulted in no change in the solution concentration or speciation of As in the Eaglehawk soil, but led to a large increase in the concentration of soluble As in the Tavistock soil. This increase was due to conversion of exchangeable forms of As(V) into less strongly sorbed As(III) species. Incubation under anaerobic conditions in the presence of glucose resulted in a large increase in the concentration of soluble As in both soils; however, different mechanisms were found to be responsible for the increase in each soil. In the Eaglehawk soil higher concentrations of As were again due to conversion of exchangeable forms of As(V) into less strongly sorbed As(III) species. In contrast in the Tavistock soil, the increased As in solution was the result of release of As(V) from the large reservoir of nonlabile soil As.

Arsenic↗
PubMed2005

Effect of chemical speciation on toxicity of mercury to Escherichia coli biofilms and planktonic cells.

While it is known that microbial uptake of mercury (Hg) by planktonic cultures is influenced by the extracellular speciation of mercury in aquatic systems, Hg uptake in biofilm cultures is understudied. We compared the importance of Hg(II) speciation in toxicity to both planktonic and biofilm cultures of the Gram-negative bacterium Escherichia coli 055. Variable chloride chemistry experiments were carried out to modify mercury speciation. Biofilms were observed to be more resistant to Hg than planktonic cells. In both planktonic and biofilm cultures, the toxicity of Hg increased and then decreased along the chloride gradient. The percent reduction in cell viability was linearly related to the concentration of HgCl2(0) when Hg-chloro complexes dominated the speciation, consistent with a passive diffusion model. However, toxicity to both planktonic cells and biofilms at low salinities could not be explained by passive diffusion alone, which suggests that microbial uptake of Hg in both planktonic cells and biofilms may occur by both passive diffusion of neutral species and facilitated uptake. The relationship between toxicity and chloride concentration was similar in the presence and absence of a biofilm, indicating that the presence of the biofilm does not drastically change the relative availability of the dominant mercury species.

Biofilms↗
PubMed2005

Dynamic speciation analysis and bioavailability of metals in aquatic systems.

Dynamic metal speciation analysis in aquatic ecosystems is emerging as a powerful basis for development of predictions of bioavailability and reliable risk assessment strategies. A given speciation sensor is characterized by an effective time scale or kinetic window that defines the measurable metal species via their labilities. Here we review the current state of the art for the theory and application of dynamic speciation sensors. We show that a common dynamic interpretation framework, based on rigorous flux expressions incorporating the relevant diffusion and reaction steps, is applicable for a suite of sensors that span a range of time scales. Interpolation from a kinetic spectrum of speciation data is proposed as a practical strategy for addressing questions of bioavailability. Case studies illustrate the practical significance of knowledge on the dynamic features of metal complex species in relation to biouptake, and highlight the limitations of equilibrium-based models.

Bacteria↗
PubMed2004

Influence of uranium speciation on normal rat kidney (NRK-52E) proximal cell cytotoxicity.

Uranium is a naturally occurring heavy metal. Its extensive use in the nuclear cycle and for military applications has focused attention on its potential health effects. Acute exposures to uranium are toxic to the kidneys where they mainly cause damage to proximal tubular epithelium. The purpose of this study was to investigate the biological consequences of acute in vitro uranyl exposure and the influence of uranyl speciation on its cytotoxicity. NRK-52E cells, representative of rat kidney proximal epithelium, were exposed to uranyl-carbonate and -citrate complexes, which are the major complexes transiting through renal tubules after acute in vivo contamination. Before NRK-52E cell exposure, these complexes were diluted in classical or modified cell culture media, which can possibly modify uranyl speciation. In these conditions, uranium cytotoxicity appears after 16 h of exposure. The CI50 cytotoxicity index, the uranium concentration leading to 50% dead cells after 24 h of exposure, is 500 microM (+/-100 microM) and strongly depends on uranyl counterion and cell culture medium composition. Computer modeling of uranyl speciation is reported, enabling one to draw a parallel between uranyl speciation and its cytotoxicity.

Animals↗
PubMed2005

The chemical speciation of uranium in water does not influence its absorption from the gastrointestinal tract of rats.

Studies of the chemical speciation of uranium in water can enhance the knowledge of the mechanisms of its absorption from the gastrointestinal tract and its storage in the body. They can also help to improve the dosimetric models recommended by the International Commission on Radiological Protection (ICRP). The aim of this work was to assess the influence of uranium speciation on its absorption from the gastrointestinal tract by using both computer speciation modeling and direct measurement of the fractional absorption in vivo in rats after ingestion of five different samples of contaminated water. Preliminary ex vivo studies with human saliva and gastric juice showed that 90% of uranium was recovered with the natural components of the fluid studied. The computer studies of uranium speciation among the electrolytes of these fluids showed that under the set conditions, the chemical species changed in a broadly similar manner under the influence of fluid composition and pH. In vivo studies in rats validated these observations by indicating an average fractional absorption of about 0.4% for each of five different water samples. It is concluded that the chemical form of uranium in the water ingested did not influence its absorption into the body.

Animals↗
PubMed1980

Physicochemical speciation of lead in drinking water.

Recent studies have highlighted the importance of drinking water as a route of human exposure to lead. Whilst there are ample data on lead concentrations in drinking water, little is known of its physical and chemical forms (physicochemical speciation). Such information is important as the speciation of ingested lead influences the efficiency of absorption from the gastrointestinal tract. Knowledge of speciation should also provide a fuller understanding of the factors controlling the solubility of lead in potable waters and hence assist in devising the most cost-effective means of plumbosolvency control. We have determined experimentally the speciation of lead in three different tapwaters and report here diverse forms of dissolved and particle-associated lead, dependent primarily on the chemical matrix of the raw water.

Cations↗
PubMed2005

Reinforcement drives rapid allopatric speciation.

Allopatric speciation results from geographic isolation between populations. In the absence of gene flow, reproductive isolation arises gradually and incidentally as a result of mutation, genetic drift and the indirect effects of natural selection driving local adaptation. In contrast, speciation by reinforcement is driven directly by natural selection against maladaptive hybridization. This gives individuals that choose the traits of their own lineage greater fitness, potentially leading to rapid speciation between the lineages. Reinforcing natural selection on a population of one of the lineages in a mosaic contact zone could also result in divergence of the population from the allopatric range of its own lineage outside the zone. Here we test this with molecular data, experimental crosses, field measurements and mate choice experiments in a mosaic contact zone between two lineages of a rainforest frog. We show that reinforcing natural selection has resulted in significant premating isolation of a population in the contact zone not only from the other lineage but also, incidentally, from the closely related main range of its own lineage. Thus we show the potential for reinforcement to drive rapid allopatric speciation.

Animals↗
PubMed1999

Sexual imprinting, learning and speciation

Learned mate preferences may play an important role in speciation. Sexual imprinting is a process whereby mate preferences are affected by learning at a very young age, usually using a parent as the model. We suggest that while the origins of learning appear to lie in the advantages of individual recognition, sexual imprinting results from selection for recognition of conspecifics. This is because efficient early learning about one's own species is favoured in the presence of heterospecifics. If different species are hybridizing, both sexual imprinting and learning to avoid heterospecifics during adulthood promote assortative mating and hence speciation. As a result of sexual imprinting, speciation may also be completed in allopatry when divergence between populations is sufficient to prevent interbreeding when the populations reunite, even in the absence of genetic evolution of mate preference. The role of behaviour and learning in completing the speciation process is relatively overlooked. In particular the evolution of sexual imprinting as a result of selection against hybridization warrants more study.

Journal Article↗
PubMed1992

NSPEC: a chemical speciation program for personal computers.

The details of a computer program, NSPEC, which simulates chemical speciation in aqueous systems, are presented. NSPEC has been designed explicitly for the IBM PC family of computers and is a departure from normal speciation programs in that it is controlled through interaction with a series of menus. The program is more user-friendly than other comparable speciation programs, can write the results files in formats suitable for importing into other programs, and, in many instances gives results faster than speciation programs running on microcomputers.

Algorithms↗
PubMed2001

Potential for the speciation of Zn using fast protein liquid chromatography (FPLC) and convective interaction media (CIM) fast monolithic chromatography with FAAS and electrospray (ES)-MS-MS detection.

Analytical procedures were developed for the speciation of Zn using fast protein liquid chromatography (FPLC), flame atomic absorption spectrometry (FAAS) and convective interaction media (CIM) fast monolithic chromatography with FAAS and electrospray (ES)-MS-MS detection. The investigation was performed on synthetic solutions (2 microg cm-3 Zn) of hydrated Zn2+ species and Zn complexes with citrate, oxalate and EDTA (ligand-to-Zn molar ratio 100:1) over a pH range from 5.4 to 7.4. It was found that Zn interacts with various buffers and the careful adjustment of the pH with diluted solutions of KOH is, therefore, required. FPLC separations were carried out on a Mono Q HR 5/5 strong anion-exchange column, applying an aqueous 1 mol dm(-3) NH4NO3 linear gradient elution over 15 min, at a flow rate of 1.0 cm3 min(-1). The separated Zn species were determined in 1.0 cm3 eluate fractions "off line" by FAAS. Speciation of Zn was also performed on a weak anion-exchange CIM DEAE fast monolithic disc by applying an aqueous 0.4 mol dm(-3) NH4NO3 linear gradient elution over 7.5 min, at a flow rate of 2.0 cm3 min(-1) and determination of the separated Zn species in 1.0 cm3 eluate fractions "off line" by FAAS. Zn-binding ligands in separated fractions were also characterized by electrospray (ES)-MS-MS analysis. The CIM DEAE disc was found to be more efficient in the separation of negatively charged Zn complexes than the Mono Q FPLC column. On the CIM DEAE disc Zn-citrate was separated from both Zn-oxalate and from Zn-EDTA. All these species were also separated from hydrated Zn2+, which was eluted with the solvent front. This method has an advantage over commonly used analytical techniques for the speciation of Zn which are only able to distinguish between labile and strong Zn complexes. Good repeatability of the measurements (RSD 2-4%), tested for six parallel determinations (2 microg cm(-3) Zn) of Zn-EDTA, Zn-citrate and Zn-oxalate was found at a pH of 6.4 on a CIM DAEA disc. The limit of detection (3s) for the separated Zn species was 10 ng cm(-3). The proposed analytical procedure was applied to the speciation of Zn in aqueous soil extracts and industrial waste water from a lead and zinc mining area.

Journal Article↗
PubMed2001

Speciation of aluminium(III) in natural waters using differential pulse voltammetry with a pyrocatechol violet-modified electrode.

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm(-3) NaOAc-HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm(-3) NH3.H2O-NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII-natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll's 8-hydroxyquinoline extraction-ion exchange method.

Aluminum↗
PubMed2002

Heavy metal speciation in the composting process.

Composting is one of the more efficient and environment friendly methods of solid waste disposal and has many advantages when compared with landfill disposal on which the UK and Ireland are currently heavily dependent. Composting is a very complicated process involving intensive microbial activity and the detailed mechanisms of the process have yet to be fully understood. Metal speciation information can provide an insight into the metal-microbial interaction and would help in the evaluation of the quality of compost. This would facilitate the exploitation of composts in remediation of heavy metal contaminated land. In this work a systematic approach to metal speciation in compost has been taken by applying the three-step method for operationally defined metal speciation of soils and sediments, developed by the European Commission's Standards, Measurement and Testing Programme to monitor the change in metal speciation with time (up to 106 days) for four different waste composting processes. The results have shown that in general metals become less available for the first extraction step as the composting process proceeds. This implies that composting tends to redistribute the metals from more labile forms to more fixed forms which may explain why the application of composts could be useful for with heavy metal contaminated land. There are exceptions to this trend and in some cases, certain metals appear to behave differently depending on the source of the compost.

Bacteria↗