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PubMed1986

Speciation by monobrachial centric fusions.

Fixation of centric fusions in natural populations often encounters minimal meiotic problems due to the ability of trivalents to segregate normally; therefore, little sterility barrier is achieved between a founder population and the parental stock. However, a strong sterility barrier can develop between different founder populations fixed for centric fusions that are monobrachially homologous in the resulting biarmed chromosomes (one arm is homologous but the other is nonhomologous). Hybridization through secondary contact then results in complex multivalents, which encounter problems in segregation and produce unbalanced gametes. Speciation mediated by centric fusions is a peripatric speciation model that does not postulate populational phenomena atypical of those characteristic of most mammals. The model appears applicable to a diversity of mammalian taxa such as bats of the Rhogeessa tumida-parvula complex, shrews of the Sorex araneus complex, and rodents of the Mus musculus and Rattus rattus complexes.

Journal Article↗
PubMed1986

Neuroanatomy influences speciation rates among anurans.

Evolutionary divergence among animal courtship signals is an important component of the speciation process. In anurans, the preferential response of females to the mating call of conspecific males often maintains reproductive isolation among populations. Much of the information in the call is initially processed in the inner ear, and there is considerable variation in the structure of this organ among lineages of frogs. This variation is responsible for differences in the frequency range to which frog species are sensitive and thus influences the frequency range over which mating calls can effectively diverge. Data suggest that this influence of neuroanatomy on mating call divergence is partly responsible for the different rates of speciation among lineages of frogs.

Journal Article↗
PubMed1986

Alternative adaptations, speciation, and phylogeny (A Review).

Alternative adaptations-different adaptive phenotypes maintained in the same life stage and the same population but not necessarily simultaneously expressed in the same individual-represent contrasting character sets produced by the same genome, in effect allowing a single species to occupy more than one sympatric niche. Such alternatives are particularly likely to give rise to novel adaptations because of selection for extreme dissimilarity between them and because established traits buffer populations against extinction while independently expressed alternatives evolve in new directions. Particular alternatives can be suddenly fixed in populations with little or no genetic change, leading to a period of rapid evolution (especially, of morphology) exaggerating the characteristics of the newly fixed form. This burst of change would facilitate rapid speciation and could produce "punctuated" patterns of evolution. Evidence from a wide variety of organisms shows that alternative phenotypes are exceedingly common in nature and that they are probably important in speciation and macroevolution. Although many of these ideas and observations have been noted piecemeal by previous authors, bringing them together demonstrates the probable importance of alternative adaptations in the origin of major evolutionary novelties and calls for a revision of current and traditional ideas about the role of behavior and ontogeny in the genesis of organic diversity.

Journal Article↗
PubMed1987

Geographic dialects in blind mole rats: role of vocal communication in active speciation.

We compared and contrasted the physical structure of male "courtship" calls of 59 subterranean mole rats belonging to the Spalax ehrenbergi superspecies in Israel, comprising 11 populations of four chromosomal species (2N = 52, 54, 58, and 60). We also conducted behavioral auditory discrimination tests of 144 females of the four species in the laboratory. The results indicate that each chromosomal species has a vocal dialect significantly different from all others, although the call of 2N = 60, the last derivative of speciation, is not yet fully differentiated. Females of 2N = 52, 54, and 58 preferred their homospecific mates' calls, whereas females of 2N = 60 did not. We conclude that call differentiation builds up gradually and provides an efficient ethological reproductive premating isolation mechanism between the emerging species in the active speciation of mole rats in Israel.

Animals↗
PubMed1999

Mutation, recombination, and incipient speciation of bacteria in the laboratory.

Mutations in the DNA mismatch repair system increase mutation and recombination. They may thereby promote the genetic divergence that underlies speciation, after which the reacquisition of a functional repair system may sustain that divergence by creating a barrier to recombination. We tested several lines of Escherichia coli, derived from a common ancestor and evolved for 20,000 generations, for their recombination ability. Some lines, but not others, had become mismatch repair-defective mutators during experimental evolution, providing different opportunities for DNA sequence divergence. We knocked out the repair system in lines that had retained this function, and we restored function to those lines that had become defective. We then estimated recombination rates in various crosses between these repair-deficient and -proficient strains. The effect of the mismatch repair system on recombination was greatest in those lines that had evolved nonfunctional repair, indicating they had undergone more sequence divergence and, consequently, were more sensitive to the recombination-inhibiting effect of a functional repair system. These results demonstrate the establishment of an incipient genetic barrier between formerly identical lines, and they support a model in which the mismatch repair system can influence speciation dynamics through its simultaneous effects on mutation and recombination.

Biological Evolution↗
PubMed1989

Speciation of arsenic in ambient aerosols collected in Los Angeles.

First-time measurements of the potentially toxic inorganic species of arsenic (arsenite and arsenate) have been obtained in fine (less than 2.5 microns AD) and coarse (greater than 2.5 microns AD) atmospheric particles in the Los Angeles area. A recently developed method that includes procedures for sample collection, preparation, and analysis was used in this study. Size-fractionated aerosol samples were collected with a high-volume dichotomous virtual impactor that employed polytetrafluoroethylene filters. Results were obtained for the recovery of arsenic standards added to unexposed and collected filters. Data from this study, indicated that the recently developed speciation method can be used to determine concentrations of As(III) and As(V) in atmospheric particulate matter samples. Size-fractionated aerosol samples were collected in the city of Industry during January and February 1987. In most samples, As(III) and As(V) were above the detection limit (approximately 1 ng m-3 of either species) in both aerosol size fractions. A greater portion (about 75 percent) of the two species were observed in the fine particles. The As(III)/As(V) ratio for both particle sizes was close to 1 (i.e., an equal mixture of both species). Comparison of total suspended particulate arsenic measured by the speciation method to that measured by a routine California Air Resources Board-approved procedure showed good agreement (r = 0.94), indicating both methods were approximately equivalent for the collection and analysis of aerosol arsenic.

Aerosols↗
PubMed2002

Mercury speciation in sediments of a tropical coastal environment.

The speciation of mercury in tropical coastal areas, although scarcely studied, has presented an odd behaviour when compared with the results obtained in temperate environments. In this work, we measured the concentrations of mercury species (mercuric mercury, methyl-mercury and dimethyl-mercury) in the sediments of Sepetiba Bay (Brazil) and compared these with geochemical parameters. Twenty-eight sediment samples were extracted in an open microwave system and mercury speciation was carried out by ethylation, cryogenic focusing, gas chromatography and quartz furnace atomic absorption spectrometry. Fraction < 63 microm, organic carbon and total sulphur contents and redox potential were measured in order to outline the geochemical characteristics of the sediments. While mercuric mercury presented concentrations ranging between 22.65 and 134.61 ng g(-1), methyl-mercury concentrations ranged between < 2.0 and 4.4 ng g(-1). Only a few dimethyl-mercury concentrations were relatively high (up to 14.6 ng g(-1)). The results of mercuric mercury presented an unexpected positive correlation with sulphur contents showing that mercury is forming stable sulphide complexes, even under very reducing conditions. This would render mercury available for t he formation of methyl- or dimethyl-mercury that would be both fixed in the sediments and volatilised.

Brazil↗
PubMed2000

Comparison and evaluation of chemically speciated mobile source PM2.5 particulate matter profiles.

Mobile sources are significant contributors to ambient PM2.5, accounting for 50% or more of the total observed levels in some locations. One of the important methods for resolving the mobile source contribution is through chemical mass balance (CMB) receptor modeling. CMB requires chemically speciated source profiles with known uncertainty to ensure accurate source contribution estimates. Mobile source PM profiles are available from various sources and are generally in the form of weight fraction by chemical species. The weight fraction format is commonly used, since it is required for input into the CMB receptor model. This paper examines the similarities and differences in mobile source PM2.5 profiles that contain data for elements, ions, elemental carbon (EC) and organic carbon (OC), and in some cases speciated organics (e.g., polycyclic aromatic hydrocarbons [PAHs]), drawn from four different sources. Notable characteristics of the mass fraction data include variability (relative contributions of elements and ions) among supposedly similar sources and a wide range of average EC:OC ratios (0.60 +/- 0.53 to 1.42 +/- 2.99) for light-duty gasoline vehicles (LDGVs), indicating significant EC emissions from LDGVs in some cases. For diesel vehicles, average EC:OC ratios range from 1.09 +/- 2.66 to 3.54 +/- 3.07. That different populations of the same class of emitters can show considerable variability suggests caution should be exercised when selecting and using profiles in source apportionment studies.

Air Pollution↗
PubMed2001

A study of gas-phase mercury speciation using detailed chemical kinetics.

Mercury speciation in combustion-generated flue gas was modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for the chlorination and oxidation of key flue-gas components, including elemental mercury (Hg0). Results indicated that the performance of the model is very sensitive to temperature. Starting with pure HCl, for lower reactor temperatures (less than approximately 630 degrees C), the model produced only trace amounts of atomic and molecular chlorine (Cl and Cl2), leading to a drastic underprediction of Hg chlorination compared with experimental data. For higher reactor temperatures, model predictions were in good accord with experimental data. For conditions that produce an excess of Cl and Cl2 relative to Hg, chlorination of Hg is determined by the competing influences of the initiation step, Hg + Cl = HgCl, and the Cl recombination reaction, 2Cl = Cl2. If the Cl recombination reaction is faster, Hg chlorination will eventually be dictated by the slower pathway Hg + Cl2 = HgCl2.

Air Pollution↗
PubMed2002

Effect of NOx control processes on mercury speciation in utility flue gas.

The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NOx control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NOx control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH3, has been evaluated. The influence of NH3 on fly ash Hg reactions also is being investigated.

Air Pollutants↗
PubMed2006

Seaweeds along KwaZulu-Natal Coast of South Africa--4: Elemental uptake by edible seaweed Caulerpa racemosa (sea grapes) and the arsenic speciation.

The elemental uptake by edible seaweed Caulerpa racemosa (Sea grapes), a marine macroalgae (chlorophyta, green alga) grown richly along KwaZulu-Natal coastline. The total concentrations of seven elements, namely Mn, Fe, As, B, Ti, Zn and Hg in Caulerpa racemosa were monitored for a one-year cycle (June 2002 to May 2003) at four selected sampling sites spread over 150 km wide from North to South. The C. racemosa possess high arsenic, boron and titanium accumulating ability, but low iron uptake. A typical C. racemosa sample at Treasure Beach in the vicinity of Durban Metropolis in autumn contained Mn (5.2+/-ppm), Fe (0.21+/-0.01 ppm), As (8.5+/-0. ppm), B (1090+/-ppb), Ti (159+/-ppb), Zn (3.8+/-0.1 ppb), and Hg (189+/-ppb). The general trend found at all sites was high elemental concentrations in winter and a decrease in concentrations from winter to spring and summer. C. racemosa recorded highest mercury levels (>205 ppb) during the summer season at the Zinkwasi site. The arsenic speciation in four abundant seaweeds from the beaches of Indian Ocean in the KwaZulu-Natal coast is investigated. The speciation of arsenic in two rhodophyta seaweeds, Plocamium corallorhiza and Gelidium abbottiorum, and two chlorophyta seaweeds, Ulva lactuca and Caulerpa racemosa at four sampling sites during the summer of 2003, is elucidated. Caulerpa racemosa had highest total arsenic (in ppb) reaching (8850+/-200) at Zinkwasi, and the concentrations of the other arsenic species analysed are As (III) (194+/-10), As(V) (568+/-27), methylarsonic acid (494+/-22) and dimethylarsinic acid (373+/-12). In an indirect estimation, C. racemosa had 81+/-2% aresenosugars.

Arsenic↗
PubMedDate not supplied

Speciation analysis and the occurrence of aluminum turbidity.

Determinations of particulate Al (pAl), leachable particulate Al (lpAl), and soluble Al (sAl) along the treatment sequence were used to investigate the occurrence of turbidity at drinking-water plants using aluminum coagulation. The behavior of Al species during filtration was normal when sAl remained at a constant level, while pAl was completely eliminated. When sAl was constant while pAl was not completely eliminated, the presence of residual pAl could be attri buted to problems of filtration effectiveness. When sAl decreased during filtration, the residual pAl could also originate from transformations such as precipitation occurring in the filtration media. When sAl increased, the residual pAl could also originate from precipitate detachments. Increases in sAl during filtration or the presence of partially leachable pAl were associated with deteriorations in residual pAl along filtration runs. The presence of nonleachable pAl denoted the existence of different aluminum forms. This was a supplementary indicator of treatment problems and affected the relationship with turbidity. In addition to demonstrating the occurrence of aluminum turbidity, speciation analysis offered a characterization of turbidity and its origin. By contributing to the evidence as well as the understanding of treatment problems, these speciation methodologies can be useful to minimize aluminum turbidity.

Aluminum↗
PubMed2002

Distribution and speciation of heavy metals in surface sediments from Guanting Reservoir, Beijing.

Surface sediments in Guanting reservoir of Beijing were studied to evaluate the heavy metal pollution. The concentrations of heavy metals lie in the sequence: Zn > Pb > Cr > Cu > Ni > Co > Mo > Cd. Significant relationship (p<0.01) between the elements Cr, Ni, Co, Cu and Ni indicates that they derived from a common geological origin. While the elements Zn, Pb and Cd correlate each other. Speciation analysis showed that most of the elements were found in the residual fraction. Enrichment of the elements Zn, Pb and Cd were found in the entrance of the rivers to the reservoir and the sampling site close to the dam. The sediment size-dependent distribution and their speciation distribution in these two sites are also distinctly different from other sediment sites. All these may indicate potential pollution of elements Zn, Pb and Cd in Guanting reservoir.

China↗
PubMed1982

Speciation of the "viridans" streptococci.

A simple scheme for the speciation of clinical isolates of "viridans" streptococci based on nine physiological characteristics is presented. Use of this scheme will enable successful speciation of most "viridans" strep isolates in any laboratory and allow for the accumulation of data necessary for the definition of clinical syndromes or unique clinical problems associated with particular species.

Culture Media↗
PubMed1999

Arsenic speciation in humans and food products: a review.

Although acute intoxication has become rare, arsenic (As) is still a dangerous pollution agent for industrial workers and people living in the vicinity of emission sources. In humans, only inorganic As is toxic; organic forms present in large amounts in the environment are nontoxic. It is therefore important to be able to differentiate one group from the other using appropriate speciation methods. The authors review the present knowledge of the distribution of As in humans and food products. The three steps of the speciation methods (sample preparation, species separation, and detection) are described. For liquid samples, a clean-up step (C18 cartridge extraction, dilution, or freezing) is necessary to eliminate proteins and salts from the matrix. For solid organic samples, the first step consists of the digestion of tissues followed by solvent extraction sometimes coupled with a C18 extraction. The separation of As species is accomplished by different high-performance liquid chromatography (HPLC) methods (ion-exchange, ion-pairing, and micellar liquid chromatography). The detection methods are compatible with HPLC and are able to detect As species in the microgram-per-liter range. Inductively coupled plasma (ICP) atomic emission spectrometry is more frequently used, but suffers from interference by organic solvents in the mobile phases. Atomic absorption spectrometry methods give sensitivities of the same order. ICP-mass spectrometry has the advantage of specificity and can be 100- to 1000-fold more sensitive than previous methods.

Arsenic↗
PubMedDate not supplied

Speciation of sulfur-containing compounds in diesel by comprehensive two-dimensional gas chromatography.

Sulfur-containing compounds in diesel have been speciated by comprehensive two-dimensional gas chromatography (GCxGC) with a sulfur chemiluminescence detector (SCD). The advantages of GCxGC technique are higher resolution and greater sensitivity. GCxGC-SCD can achieve the class separation of sulfur-containing compounds with an appropriate separation column combination. The major classes of sulfur-containing compounds in diesel are benzothiophenes and dibenzothiophenes. Relative concentration of each class as well as each carbon number family can be quantitated by the summation of the integrated areas corresponding to the individual group(s) in the GCxGC space. In practical applications, GCxGC-SCD can be used to characterize different diesels and to reflect desulfurization process efficiency. In this study, GCxGC-SCD has demonstrated its value in speciation of sulfur-containing compounds classes, which is difficult to accomplish by any other single technique.

Journal Article↗
PubMed1995

Molecular evolution of the duplicated Amy locus in the Drosophila melanogaster species subgroup: concerted evolution only in the coding region and an excess of nonsynonymous substitutions in speciation.

From the analysis of restriction maps of the Amy region in eight sibling species belonging to the Drosophila melanogaster species subgroup, we herein show that the patterns of duplication of the Amy gene are almost the same in all species. This indicates that duplication occurred before speciation within this species subgroup. From the nucleotide sequence data, we show a strong within-species similarity between the duplicated loci in the Amy coding region. This is in contrast to a strong similarity in the 5' and 3' flanking regions within each locus (proximal or distal) throughout the species subgroup. This means that concerted evolution occurred only in the Amy coding region and that differentiated evolution between the duplication occurred in the flanking regions. Moreover, when comparing the species, we also found a significant excess of nonsynonymous substitutions. In particular, all the fixed substitutions specific to D. erecta were found to be nonsynonymous. We thus conclude that adaptive protein evolution occurred in the lineage of D. erecta that is a "specialist" species for host plants and probably also occurs in the process of speciation in general.

Amino Acid Sequence↗
PubMed1996

The speciation history of Drosophila pseudoobscura and close relatives: inferences from DNA sequence variation at the period locus.

Thirty-five period locus sequences from Drosophila pseudoobscura and its siblings species, D. p. bogotana, D. persimilis, and D. miranda, were studied. A large amount of variation was found within D. pseudoobscura and D. persimilis, consistent with histories of large effective population sizes. D. p. bogotana, however, has a severe reduction in diversity. Combined analysis of per with two other loci, in both D. p. bogotana and D. pseudoobscura, strongly suggest this reduction is due to recent directional selection at or near per within D. p. bogotana. Since D. p. bogotana is highly variable and shares variation with D. pseudoobscura at other loci, the low level of variation at per within D. p. bogotana can not be explained by a small effective population size or by speciation via founder event. Both D. pseudoobscura and D. persimilis have considerable intraspecific gene flow. A large portion of one D. persimilis sequence appears to have arisen via introgression from D. pseudoobscura. The time of this event appears to be well after the initial separation of these two species. The estimated times since speciation are one mya for D. pseudoobscura and D. persimilis and 2 mya since the formation of D. miranda.

Amino Acid Sequence↗