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At least 793 records · Page 44Linked to original sources
PubMed2002

Sexual signaling and speciation, a microevolutionary perspective.

Despite the growing evidence that sexual selection can drive speciation, the evolution of sexual signals in natural populations is far from being well-understood. Sexual signals evolve in response to a variety of factors. Some of the most important selective factors are conspecifics, transmission efficiency in a particular environment, detection by predators, and phylogenetic constraints. These factors have been addressed quite successfully in studies of single types of signals in both vertebrates and invertebrates. However, it is less clear how multimodal signals evolve because the factors listed above will act on every component of the signaling system, and the relative weights of each type of signal must be taken into account. Species of Drosophila are excellent for such analyses because they are amenable to both phenotypic experimentation and genetic manipulation. This paper presents an approach that involves two analyses: studies of which signals are sexually selected within a species, and parallel studies of the signals that are involved in behavioral isolation between closely related species. If the same signal characteristics are involved in both processes, they would provide support for the hypothesis that sexual selection can drive speciation. This approach is illustrated with studies of Hawaiian Drosophila and a review of signals that could be sexually selected in Drosophila melanogaster.

Animals↗
PubMed2002

Divergence and reproductive isolation in the early stages of speciation.

To understand speciation we need to identify the factors causing divergence between natural populations. The traditional approach to gaining such insights has been to focus on a particular theory and ask whether observed patterns of reproductive isolation between populations or species are consistent with the hypothesis in question. However, such studies are few and they do not allow us to compare between hypotheses, so often we cannot determine the relative contribution to divergence of different potential factors. Here, I describe a study of patterns of phenotypic divergence and premating and postmating isolation between populations of the grasshopper Chorthippus parallelus. Information on the phylogeographic relationships of the populations means that a priori predictions from existing hypotheses for the evolution of reproductive isolation can be compared with observations. I assess the relative contributions to premating isolation, postmating isolation and phenotypic divergence of long periods of allopatry, adaptation to different environments and processes associated with colonisation (such as population bottlenecks). Likelihood analysis reveals that long periods of allopatry in glacial refugia are associated with postmating reproductive isolation, but not premating isolation, which is more strongly associated with colonisation. Neither premating nor postmating isolation is higher between populations differing in potential environmental selection pressures. There are only weak correlations between patterns of genetic divergence and phenotypic divergence and no correlation between premating and postmating isolation. This suggests that the potential of a taxon to exercise mate choice may affect the types of factor that promote speciation in that group. I discuss the advantages and disadvantages of the general approach of simultaneously testing competing hypotheses for the evolution of reproductive isolation.

Acoustic Stimulation↗
PubMed2003

[Primary speciation analysis of iron in edible flowers].

In this paper seven primary speciations of iron in three edible flowers, i.e. chrysanthemum, cottonrose hibiscus and honeysucker have been studied by atomic absorption spectrometry. Speciation parameters of iron such as extractive rate, residue rate, immerse-residue ratio in the samples were calculated. It was found that the first extractive rates of Fe were higher than the second ones in all three edible flowers, and the immerse-residue ratios of Fe were similar to the extractive rates. But the extraction of iron in all three edible flowers were no more than fifty percent. It is showed that the iron isn't easy to extract by water in the three edible flowers. The recovery was in the range of 96.5%-103.2% and RSD was in the range of 1.2%-3.1%. The results were satisfactory.

Chrysanthemum↗
PubMed2002

[Speciation of 9 trace elements in a traditional Chinese medicine long dan cao by flow injection-inductively coupled plasma mass spectrometry with a focused microwave assisted extraction system].

A method based on focused microwave extraction for leaching 9 trace elements in traditional Chinese medicine Long Dan Cao was introduced. An online C18 enrichment-separation system and an HP4500 ICP mass spectrometer with a flow injection system was established for the separation and determination of inorganic speciation and organic speciation of the selected elements. Orthogonal design was applied for the optimization of microwave leaching conditions. The results showed that the temperature was the major factor for the leaching recoveries.

Calcium↗
PubMed2001

[Speciation of metals and metalloids in biomolecules by hyphenated techniques].

This paper introduces briefly the analytical methods recently published in the literature on the speciation of arsenic, selenium and cadmium in biological samples using hyphenated techniques, HPLC-ICP-MS, HPLC-ES-MS/MS, and CE-ES-MS/MS. The coupling SEC-ICP-MS is the most popular technique for the first screening of unknown sample in view of the presence of macro molecular species of element. But due to its insufficient resolution, complementary chromatographic separations have to be carried out in order to guarantee the purity of the signal. CZE-ICP-MS is a powerful tool in trace metal speciation. In case standards and reference materials are not available, ES-MS/MS is the best technique in the characterization of metal complexes. During analysis care should be taken to avoid contamination of the sample and break-up of the original metal-protein bond during the separation process. Due to lack of standards and reference materials, the application of hyphenated technique has been looking for new species rather than determining a known compound. The difficult problems are whether a signal produced by a detector belongs to a particular compound and the identification of this compound.

Arsenic↗
PubMed2003

[Digital signal acquisition and processing software for atomic fluorescence spectrometry and its application to elemental speciation].

A program was developed to collect and process digital signal by using Visual C++ for atomic fluorescence spectrometry (AFS). The software solves the data acquisition problem of coupling AFS with HPLC and other successive separation techniques. This program employs three signal processing techniques, i.e. Savitzky-Golay smoothing, Fourier filter and wavelet denoising, to smooth and filter the noisy data. The processes and comparisons of these techniques have been discussed. The program was successfully applied to the preliminary study of Cd speciation by using cation exchange HPLC coupled to AFS, and will provide a new possibility for extending the application of atomic fluorescence spectrometry to the field of elemental speciation analysis.

Cadmium↗
PubMed2003

Removal and speciation of heavy metals along the treatment path of wastewater in subsurface-flow constructed wetlands.

This study was conducted to: (1) evaluate the performance of constructed wetlands in removing Zn, Pb and Cd, respectively, and Zn, Pb, Cd and Cu in combination and (2) investigate the speciation patterns of the dissolved metals differentiated according to their detectability by anodic stripping voltammetry (ASV) and their lability towards Chelex resin along the treatment path of metal-containing wastewater in horizontal subsurface-flow constructed wetlands. Four laboratory scale wetland units planted with cattails (Typha latifolia) were operated outdoors for six months. Three of the units were, respectively, fed with primary-treated domestic wastewater spiked with Zn(II), Pb(II) and Cd(II) whilst the fourth was spiked with a combination of Zn(II), Pb(II), Cd(II) and Cu(II). The results demonstrate that a metal removal efficiency of over 99% was achievable for wetland units treating the metals singly or in combination provided the sorption capacity of the media was not exceeded. When treating the metals in combination, an antagonistic effect, more significantly for Pb and Cd, on the sorptive metal uptake by media was observed. Based on the metal speciation patterns, the wetland system seemed to be capable of maintaining the ASV-labile metal species at relatively low level (< 10%) before media exhaustion.

Biodegradation, Environmental↗
PubMed1992

The effect of seafood consumption on the assessment of occupational exposure to arsenic by urinary arsenic speciation measurements.

The determination of arsenite, arsenate, dimethylarsenic acid (DMA) and monomethylarsonic acid (MMA) in urine has been used for assessing occupational exposure to inorganic arsenic because these species were thought to be unaffected by dietary arsenic. However, this investigation reports how the consumption of certain types of seafood can lead to an increase in the amount of DMA excreted and hence an elevation in the urinary arsenic speciation total. Urine samples collected from volunteers between 4-20 hours after the ingestion of moderate-sized portions of mackerel, herring, crab or tuna, showed mean increases in the arsenic speciation totals of between 1.8 and 6.9 times compared with the levels in samples collected before the seafood was consumed. These findings have important implications in devising a biological monitoring strategy for workers exposed to inorganic arsenic.

Animals↗
PubMedDate not supplied

Fractionation and redox speciation of antimony in agricultural soils by hydride generation--atomic fluorescence spectrometry and stability of Sb(III) and Sb(V) during extraction with different extractant solutions.

This stability of Sb(III) and Sb(V) species was studied during single extraction from soils by water. EDTA, diluted H2SO4 and H3PO4, and oxalic acid/oxalate solutions, with and without ascorbic acid, were used as stabilizing reagent of both Sb species. Antimony redox speciation in soil extracts was performed by selective hydride generation-atomic fluorescence spectrometry. Simulated extraction procedures (without soil) showed that, except in oxalate medium, Sb(III) was oxidized to Sb(V), and this reaction was avoided with ascorbic acid. Recovery studies from a spiked agricultural soil showed that no oxidation but sorption of Sb(III) occurred during the extraction process in water and H2SO4 medium, and quantitative oxidation in EDTA and oxalate medium. With ascorbic acid, this oxidation was totally avoided in EDTA and partially avoided in oxalate solution. A new sequential extraction procedure was proposed and applied to the fractionation and redox speciation of antimony in agricultural soils, using EDTA + ascorbic acid, pH 7 (available under complexing and moderately reducible conditions); oxalic acid/oxalate + ascorbic acid (extractable in reducible conditions) and HNO3 + HCl + HF (residual fraction). The proposed extraction scheme can provide information about the availability and mobility of antimony redox species in agricultural soils.

Agriculture↗
PubMedDate not supplied

Speciation and bioavailability of selenium in yeast-based intervention agents used in cancer chemoprevention studies.

This study investigated the speciation and bioavailability of selenium in yeast-based intervention agents from multiple manufacturers from several time points. Sources of selenized yeast included Nutrition 21 (San Diego, CA), which supplied the Nutritional Prevention of Cancer (NPC) Trial from 1981-1996; Cypress Systems (Fresno, CA; 1997-1999); and Pharma Nord (Vejle, Denmark; 1999-2000), which supplied the Prevention of Cancer by Intervention by Selenium (PRECISE) Trial pilot studies. The low-molecular-selenium species were liberated from the samples by proteolytic hydrolysis followed by separation by ion exchange liquid chromatography and detection by inductively coupled plasma-mass spectrometry. The results for the NPC tablets showed that selenomethionine, together with 3 unidentified selenium compounds, were predominant in the sample hydrolysates. The relative amounts of the 4 selenium species varied (p < 0.05) among several of the 7 tablet batches used during the course of the NPC Trial. In comparison, 5 batches of more recently produced selenized yeasts, which were used as a source of selenium in the PRECISE and other trials, contained less of the unknown compounds and more selenomethionine at 54-60% of the total selenium in the yeasts. One batch of yeast, however (from 1985), which originated from the same producer as the yeast used in the NPC tablets, contained only 27% of selenium in the sample as selenomethionine. Human subjects receiving 200 microg selenium/day in the UK PRECISE Pilot Trial showed a higher concentration (p < 0.01) and higher increase from baseline in plasma selenium than did the same dosage used in the NPC Trial. Differences in intake, speciation, or bioavailability of selenium from the yeast-based supplements in the population groups studied may explain this. Furthermore, the selenium concentration in whole blood from the Danish PRECISE Pilot Trial was higher (p < 0.001) than that obtained with synthetic L-selenomethionine in a comparable group of Danes, both groups having been treated with 300 microg selenium/day.

Anticarcinogenic Agents↗
PubMedDate not supplied

Total arsenic determination and speciation in infant food products by ion chromatography-inductively coupled plasma-mass spectrometry.

Health risk associated with dietary arsenic intake may be different for infants and adults. Seafood is the main contributor to arsenic intake for adults while terrestrial-based food is the primary source for infants. Processed infant food products such as rice-based cereals, mixed rice/formula cereals, milk-based infant formula, applesauce and puree of peaches, pears, carrots, sweet potatoes, green beans, and squash were evaluated for total and speciated arsenic content. Arsenic concentrations found in rice-based cereals (63-320 ng/g dry weight) were similar to those reported for raw rice. Results for the analysis of powdered infant formula by inductively coupled plasma-mass spectrometry (ICP-MS) indicated a narrow and low arsenic concentration range (12 to 17 ng/g). Arsenic content in puree infant food products, including rice cereals, fruits, and vegetables, varies from <1 to 24 ng/g wet weight. Sample treatment with trifluoroacetic acid at 100 degrees C were an efficient and mild method for extraction of arsenic species present in different food matrixes as compared to alternative methods that included sonication and accelerated solvent extraction. Extraction recoveries from 94 to 128% were obtained when the summation of species was compared to total arsenic. The ion chromatography (IC)-ICP-MS method selected for arsenic speciation allowed for the quantitative determination of inorganic arsenic [As(III) + As(V)], dimethylarsinic acid (DMA), and methylarsonic acid (MMA). Inorganic arsenic and DMA are the main species found in rice-based and mixed rice/formula cereals, although traces of MMA were also detected. Inorganic arsenic was present in freeze-dried sweet potatoes, carrots, green beans, and peaches. MMA and DMA were not detected in these samples. Arsenic species in squash, pears, and applesauce were not detected above the method detection limit [5 ng/g dry weight for As(III), MMA, and DMA and 10 ng/g dry weight for As(V)].

Arsenic↗
PubMed2004

[Speciation and distribution characters of rare earth elements in the Baotou Section of the Yellow River].

As a whole of water column, suspended matter and surface sediment in the mainstream and the branch taking up industry wastewater, speciation and distribution characters of rare earth elements (REEs) were investigated systemically in the Baotou section of the Yellow River. This study shows that rare earth elements in the mainstream of the Baotou section of the Yellow River mainly exist in suspended particles, and the dissolved contents are in extremely minute quantities. REEs mainly exist in dissolved particles in the branch taking up industry wastewater, and suspended sigma REE and dissolved sigma REE are obviously higher than those in the mainstream. The change of sigma REE of dissolved particles in water phase along the Baotou section of the Yellow River is very similar to that of sigma REE of suspended particles, and consistent along the main river, it is that sigma REE increase appreciably from the control profile to the keystone discharged section, come to a head in the D site and reduce in the E site. This distribution pattern indicates pile industry wastewater of Baotou to rare earth elements in the mainstream of the Yellow River, particularly LREE. The REE distribution in the mainstream of the Baotou section of the Yellow River is the same, with LREE enrichment and Eu depletion. But LREE origin of D site is different from the other sites by excursion of LREE distribution curve and other geochemical parameters, they are origin of industry wastewater piled, otherwise the other four sites are origin of loess altiplano. And HREE are origin of loess altiplano in all the sites. The speciation characteristics of REE in the sediments and suspended matter are quite similar with the amount in as follows: residual >> bound to carbonates, bound to Fe-Mn oxides > bound to organic matter >> exchangeable. REEs exchangeable in surface sediment and suspended matter in the branch taking up industry wastewater are higher than those in the mainstream, it confirms that REEs in the mainstream mainly exist in suspended particles, and mainly exist in dissolved particles in the branch.

Geologic Sediments↗
PubMedDate not supplied

PARSAFE: computer program for safety assessment and optimization of parenteral nutrition formulations based on chemical speciation analysis.

Instability arising from the formation of precipitates and lipid emulsion aggregates is common in parenteral nutrition formulations due to the concentration- and pH-dependent incompatibility of some of the vital ingredients. Previously, the boundaries between stability and instability could only be established through the use of laborious and expensive empirical methods. The predictive technique with the concept of chemical speciation (based on the analysis of many competitive thermodynamic equilibriums) has been adapted for use with parenteral fluids so that these detrimental events may now be avoided. A comprehensive computer program, PARSAFE ((C) 1991. Sponsors interested in this program should contact D.R.W.) has been developed for this purpose. PARSAFE encompasses chemical-speciation techniques and contains a large data base of commonly used intravenous fluid constituents together with the appropriate thermodynamic equilibrium constants describing their interactions so that stability prediction may be readily achieved in hospital pharmacy laboratories. We review the relevant physical chemistry required for the successful implementation of PARSAFE and outline the audit trails involved in the development of the predictive model.

Algorithms↗
PubMed2004

Dynamic of lead speciation in sewage sludge composting.

A large-scale sewage sludge composting experiment was conducted to develop an understanding of changes that occur to Pb chemical speciation, distribution and bio-availability during the course of composting. The four-stage Tessier sequential extraction method was employed to investigate the dynamics of heavy metal Pb speciation (exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and sulphides, residual) during the course of sewage sludge composting. The concentrations of the total Pb and the five Pb fractions concentrations were increased during the whole stage of compost. However, the percentages of Pb distribution with respect to total Pb were changed in the following manner: exchangeable, bound to Fe-Mn oxides and bound to carbonates Pb with respect to total Pb were increased, while the percentages of bound to organic matter and sulphides, and residual Pb with respect to total Pb were decreased during composting. The data showed that the quantity of Pb in the less toxic portion, such as consisting of organic matter and sulphides bound and residual Pb, was increased, and that the contamination and bio-availability of heavy metal Pb in sewage sludge was reduced during the composting process.

Biological Availability↗
PubMed2004

[Speciation of aluminum in natural waters by fluorimetry].

Fluorimetric method has been proposed for the speciation of Al in natural waters, based on the different competitive complexation behavior of analytical reagent and natural organic matter to Al. With eriochrome blue black R (EBBR) or morin, the monomeric inorganic Al (Al(i)) was determined, while with 8-hydroxylquinoline, the total monomeric Al (Al(a)) was obtained. The analytical results of Al speciation in natural water are close to those by Driscoll's method. The method is simple and reliable. Fractionation of Al was realized by selecting appropriate reagents under the pH of natural water determined. The merits of this novel strategy are that the disturbance to original equilibrium of Al species is minimized and the results conform to the actual situation of natural waters.

Aluminum↗
PubMed2005

The role of deleterious mutations in allopatric speciation.

Allopatric speciation is often assumed to occur as a consequence of adaptive divergence between two isolated populations. However, there are some scenarios in which reproductive isolation can be favored due to accumulated unconditionally deleterious mutations. If deleterious mutations have synergistic epistatic effects, it is shown here that the average fitness of recombinants between two parental lines with a given number of fixed mutations is lower than that of the parents in both the F1 and F2 generations. If individual mutations are only slightly deleterious, then they will tend to fixation at a high enough rate to cause lower hybrid fitness. If the fitness effects of mutation give rise to antagonistic epistasis, the hybrids tend to have a higher average fitness than the parental lines, suggesting a possible scenario for the origin of hybrid vigor. The other model of deleterious mutations investigated is the accumulation of knockout mutants in a duplicated gene family. While neutral in the parental lines, upon contact the F1 and later generations have a significant probability of carrying double knockouts. Under this scenario, selection may also favor reproductive isolation between the two lines. Even when the selection coefficients generated are too low to drive speciation, epistatic interactions between deleterious mutations offer a possible explanation for both outbreeding depression and hybrid vigor.

Biological Evolution↗
PubMed2005

[Effects of aluminum speciation on wheat root growth and its enzyme activity].

Aluminum speciation is recognized to associate with environmental pH. In this paper, the effects of aluminum speciation (A1a, A1b) on the growth, protein content, acid phosphatase (AP) activity of wheat root were studied by changing the pH of aluminum solutions. Two concentrations of total aluminum, 25 micromol x L(-1) (T1) and 75 micromol x L(-1) (T2), were set up in the test solutions, and four levels of pH, 4.0, 4.5, 5.0 and 5.5, were regulated for each solution. The results indicated that the growth of wheat root in T1 and T2 was strongly inhibited by low doses of Ala and Alb, while the changing trend of protein content and AP activity varied when exposed to different composition of active A1. When the A1a concentration was above 90% of the active Al concentration, the protein content was reduced while the AP activity was enhanced by Al at pH 4.0, but it was reverse at pH 5.0 when the concentration of Ala and Alb was below 10 micromol x L(-1), respectively.

Acid Phosphatase↗
PubMedDate not supplied

[Problems of studying the genetic background of speciation as examplified by Drosophila virilis group].

Possible ways of studying the genetic bases of speciation have been shown on the example of published data and authors' results. The data were used, which were obtained on different Drosophila species. Possible application of mapping by localization of the gene of quantitative traits and genetic transformation for solution of the problems of speciation is discussed.

Animals↗