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At least 865 records · Page 48Linked to original sources
PubMed2006

Use of electrospray ionization mass spectrometry for the study of Ln(III) complexation and extraction speciation with calixarene-CMPO in the fuel partitioning concept.

The calixarene-bearing CMPO groups belong to a family of extracting agents recently developed for nuclear reprocessing. These molecules exhibit specific properties to separate actinides(III) from lanthanides(III) in nitric acid solution. Speciation of two distinct calixarene-CMPO (carbamoyl phosphine oxide), substituted either in the wide rim or in the narrow rim with lanthanides (La, Eu, Yb), was undertaken. The complexation behaviour in single phase or in liquid-liquid extraction was examined with two different electrospray spectrometer source geometries. The stoichiometries of the different complexes were reported and the selectivity of these calixarenes towards lanthanides was determined. The results obtained were concordant for the two spectrometers and confirm that electrospray mass spectrometry is a useful tool to study non-covalently bonded complexes.

Journal Article↗
PubMed1996

Inhibition of hydroperoxide-induced DNA single-strand breakage by 1, 10-phenanthroline in HL-60 cells: implications for iron speciation.

The speciation of intracellular iron which reacts with hydroperoxides to cause DNA damage was investigated in HL-60 cells using 1,10-phenanthroline (OP) to compete with ligands for iron. HL-60 cells were treated with various concentrations of OP for 30 min at 37 degrees C followed by 30 min treatment with H2O2 or t-butylhydroperoxide (tert-BuOOH) at 4 degrees C. Single-strand breaks (SSBs) were measured by alkaline elution. OP (5 microM) completely inhibited production of SSBs by tert-BuOOH. This contrasts with results for H2O2, for which it was not possible to inhibit all SSBs even at OP concentrations up to 60 microM. Induction of SSBs by tert-BuOOH decreased according to a SSB:OP ratio of 1:3.28 +/- 0.23 (+/-1 SE). This is consistent with inhibition achieved by occupation of all coordination sites on iron by OP, such as by formation of Fe(OP)3. In contrast, after subtraction of the noninhibitable fraction, SSBs induced by H2O2 decreased according to a 1:1.53 +/- 0.26 ratio. This suggests that inhibition of H2O2-induced SSBs is partially or wholly achieved by formation of different structures than Fe(OP)3. Tert-BuOOH did not cause SSBs in nuclei isolated from HL-60 cells. However, H2O2 induced SSBs which were inhibited 45 +/- 8% (+/- 1 SD) by dimethyl sulfoxide. Analysis of the concentration dependence of inhibition by dimethyl sulfoxide indicated that the H2O2-reactive iron in nuclei possessed an average distance of 4.8 nm from DNA. This compares with a previously obtained distance in whole cells of 6.9 nm, for which 5 microM OP pretreatments decreased to 4.8 nm. These data indicate that tert-BuOOH generates DNA-damaging radicals through reaction with a subset of the different cell iron species which react with H2O2.

Cell Nucleus↗
PubMed2002

Copper speciation in the gill microenvironment of carp (Cyprinus carpio) at various levels of pH.

The fish gill microenvironment of Cyprinus carpio under stress of copper exposure was investigated. pH and other parameters including free copper activity, alkalinity, and inorganic and organic carbons in the surrounding water (inspired water) and in the gill microenvironment (expired water) were measured or calculated at various levels of pH and varying total copper concentrations. The chemical equilibrium calculation (from MINEQA2) and complexation modeling (mucus-copper) were coupled to calculate both species distribution. The results indicate that the pH in the fish gill microenvironment was different from that in the surrounding water with a balance point around 6.9. The secretion of both CO(2) and mucus was affected in both linear and nonlinear ways when the fish were exposed to elevated concentrations of copper. The complexation capacity of the gill mucus was characterized by a conditional stability constant (logk(Cu-mucus)) of 5.37 along with a complexation equivalent concentration (L(Cu-mucus)) of 0.96 mmol Cu/mg C. For both the fish microenvironment and the surrounding water, the dominant copper species shifted from Cu(2+) to CuCO(3)(0) and to Cu(OH)(2)(0) when the pH of the surrounding water changed from 6.12 to 8.11. The change in copper speciation in the gill microenvironment is smaller than that in the surrounding water due to the pH buffering capacity of the fish gills.

Animals↗
PubMed1999

Epigenetic inheritance, genetic assimilation and speciation.

Epigenetic inheritance systems enable the environmentally induced phenotypes to be transmitted between generations. Jablonka and Lamb (1991, 1995) proposed that these systems have a substantial role during speciation. They argued that divergence of isolated populations may be first triggered by the accumulation of (heritable) phenotypic differences that are later followed and strengthened by genetic changes. The plausibility of this idea is examined in this paper. At first, we discuss the "exploratory" behaviour of an epigenetic inheritance system on a one peak adaptive landscape. If a quantitative trait is far from the optimum, then it is advantageous to induce heritable phenotypic variation. Conversely, if the genotypes get closer to the peak, it is more favorable to canalize the phenotypic expression of the character. This process would lead to genetic assimilation. Next we show that the divergence of heritable epigenetic marks acts to reduce or to eliminate the genetic barrier between two adaptive peaks. Therefore, an epigenetic inheritance system can increase the probability of transition from one adaptive state to another. Peak shift might be initiated by (i) slight changes in the inducing environment or by (ii) genetic drift of the genes controlling epigenetic variability. Remarkably, drift-induced transition is facilitated even if phenotypic variation is not heritable. A corollary of our thesis is that evolution can proceed through suboptimal phenotypic states, without passing through a deep adaptive valley of the genotype. We also consider the consequences of this finding on the dynamics and mode of reproductive isolation.

Animals↗
PubMed2000

Competitive speciation in quantitative genetic models.

We study sympatric speciation due to competition in an environment with a broad distribution of resources. We assume that the trait under selection is a quantitative trait, and that mating is assortative with respect to this trait. Our model alternates selection according to Lotka-Volterra-type competition equations, with reproduction using the ideas of quantitative genetics. The recurrence relations defined by these equations are studied numerically and analytically. We find that when a population enters a new environment, with a broad distribution of unexploited food sources, the population distribution broadens under a variety of conditions, with peaks at the edge of the distribution indicating the formation of subpopulations. After a long enough time period, the population can split into several subpopulations with little gene flow between them.

Animals↗
PubMed2000

Rapid speciation via parallel, directional selection on regulatory genetic pathways.

Regulatory genetic pathways are ubiquitous in organisms and play a central role in the realization of the phenotype during development. We explored the proposition that these pathways can provide a plausible source of the epistatic variation that has been implicated in the evolution of postzygotic reproductive isolation. We modeled gene regulation as a matching function between the product of one locus and the promoter site of the next locus in the pathway, with binding strength determining the amount of product. When the phenotype is subject to parallel selection in a pair of independent populations, we find that the fitnesses of F(1)and F(2)hybrids often drop to very low values as the populations respond in genetically different and incompatible ways. The simulations support the predictions of the analytical models. Hybrid fitness reduction occurs more often as the number of loci in the pathway increases, and as the binding site interactions become more complex. Less hybrid fitness reduction is seen when the populations start with imperfect binding in the pathway. In contrast, when we constructed the phenotype without gene regulation using multiplicative rules, isomorphic to the additive phenotype commonly assumed in evolutionary models, we found no appreciable F(1)fitness reduction and only slight F(2)fitness reduction. The interaction of genetic drift and mutation, even at very high rates, did not reduce hybrid fitness at all on the time-scales we considered. Clearly, the evolution of regulatory genetic pathways can play an important role in speciation, but much more empirical information is needed on the effect of allelic variability in regulatory site interactions before this role is fully understood.

Animals↗
PubMed1998

Rapid speciation, morphological evolution, and adaptation to extreme environments in South African sand lizards (Meroles) as revealed by mitochondrial gene sequences.

Data derived from the morphology of the seven species of South African sand lizards, Meroles (Reptilia, Lacertidae), and their outgroups produce a robust estimate of phylogeny when a maximum parsimony approach is applied. The estimate is fully resolved with little character conflict and internal branches are relatively long. This analysis indicates that Meroles is a true clade that includes the aberrant lacertid long separated as Aporosaura anchietae. The tree is pectinate, its successive external branches representing species with increasing adaptation to desert conditions, especially aeolian sand habitats. This pattern, and the robustness of the tree, support a model of invasion of severe habitats in which successive rounds of speciation, displacement, and adaptation result in spread into extreme ecological situations. To test the robust morphological phylogeny and, indirectly, the model as well, DNA from mitochondrial 12S and 16S ribosomal genes was sequenced and analyzed by both maximum parsimony and maximum likelihood approaches. Trees produced were largely congruent with that derived from morphology, although different from ones resulting from protein electrophoresis. However, in contrast to the internal branches of the morphological tree, those of the DNA maximum likelihood tree are quite short. The DNA data provide some corroboration for the relationships within Meroles based on morphology and consequently for the model as well. The disparity in internal branch lengths between the maximum parsimony morphological and maximum likelihood DNA trees may well indicate that the multiple adaptations to desert conditions arising on the main lineage of Meroles evolved quite rapidly. In this study DNA thus not only corroborates the phylogeny but also provides evidence about another aspect of evolutionary history.

Adaptation, Physiological↗
PubMed2001

Patterns of speciation inferred from mitochondrial DNA in North American Chthamalus (Cirripedia: Balanomorpha: Chthamaloidea).

Chthamalus is a cosmopolitan genus of high intertidal barnacles that are difficult to distinguish morphologically. This study focuses on a single subgeneric group of Chthamalus that is found on the coasts of North and Central America to determine the age and pattern of speciation among these species. Two comparisons of genetic divergence are made across the Panamanian Isthmus, allowing estimates of the substitution rate to be made for two mitochondrial genes coding for COI and 16S rRNA in these barnacles. These data suggest that the little morphological diversification that there has been in Chthamalus occurred early in the history of the genus, and subsequent radiations were probably induced by transient periods of population separation during late Miocene to Recent climatic changes.

Animals↗
PubMed2002

Gene transfer in bacteria: speciation without species?

Although Bacteria and Archaea reproduce by binary fission, exchange of genes among lineages has shaped the diversity of their populations and the diversification of their lineages. Gene exchange can occur by two distinct routes, each differentially impacting the recipient genome. First, homologous recombination mediates the exchange of DNA between closely related individuals (those whose sequences are sufficient similarly to allow efficient integration). As a result, homologous recombination mediates the dispersal of advantageous alleles that may rise to high frequency among genetically related individuals via periodic selection events. Second, lateral gene transfer can introduce novel DNA into a genome from completely unrelated lineages via illegitimate recombination. Gene exchange by this route serves to distribute genes throughout distantly related clades and therefore may confer complex abilities--not otherwise found among closely related lineages--onto the recipient organisms. These two mechanisms of gene exchange play complementary roles in the diversification of microbial populations into independent, ecologically distinct lineages. Although the delineation of microbial "species" then becomes difficult--if not impossible--to achieve, a cogent process of speciation can be predicted.

Bacteria↗
PubMed1994

Andean tapaculos of the genus Scytalopus (Aves, Rhinocryptidae): a study of speciation using DNA sequence data.

Tapaculos of the genus Scytalopus are secretive birds which tunnel like mice through dense understory of humid forest in the Andes, Central America, and south-eastern Brazil. Their agoraphobic habits make Scytalopus species highly sensitive to habitat discontinuities, so they are well suited for analyzing diversification patterns in montane forest biota. This study uses DNA sequence data to test hypotheses about past speciation events. The DNA data support that allopatric and parapatric populations with different songs represent different species. The high degree of phylogenetic resolution obtained by DNA-data permits a better description of geographical patterns of endemism. The data suggests that the commonly observed biogeographic pattern, where related species have long linear distributions along the Andes in different altitudinal zones, arose by divergence in disjunct isolates rather than by parapatric divergence. The approach seems well suited for identifying areas that have a special role for the diversification process. The paper finally discusses how detailed phylogenetic studies can be used to test interpretations of biogeographic patterns of high relevance for pinpointing top priority areas for conservation.

Animals↗
PubMed1992

Molecular phylogeny of some polychaete annelids: an initial approach to the Atlantic-Mediterranean speciation problem.

The polychaete Eupolymnia nebulosa (family Terebellidae) displays two alternative modes of reproduction. In the Mediterranean, larvae are brooded in a mucous mass while in the Atlantic and English Channel, larvae follow a plank-tonic development. This paper attempts to discern whether this difference is expressed at the population, infraspecies, or species level. Specimens of E. nebulosa and representatives of a number of control species were sampled from Atlantic/English Channel and Mediterranean locations. Genetic sequencing of the Large-subunit ribosomal RNA 5' end of six representative species allowed one to infer the relative position of E. nebulosa within the Terebellidae and the position of the latter within the animal kingdom. The relative genetic distances calculated between the different species were also used to approach the speciation problem raised by the differences between the Mediterranean and Atlantic/English Channel population of E. nebulosa. The genetic distance between Mediterranean and Atlantic populations of both E. nebulosa and Lanice conchilega are of the same order, suggesting that differences between the populations of E. nebulosa are infraspecific.

Animals↗
PubMed1994

Exchanges of short polymorphic DNA segments predating speciation in feline major histocompatibility complex class I genes.

Sequence comparisons of 14 distinct MHC class I cDNA clones isolated from species representing the three major taxonomic lineages of Felidae (domestic cat lineage, ocelot lineage, and pantherine lineage) revealed that feline MHC class I alleles have highly mosaic structures with short polymorphic sequence motifs that are rearranged between alleles of individual MHC loci, between MHC class I genes within cat species, and between homologous MHC loci in different species. The pattern of sequence variation in felids supports the role of the following factors in production and maintenance of MHC variation: (1) gradual spontaneous mutation; (2) selective pressure to conserve certain residues but also to vary in hypervariable regions, notably residues that functionally participate in antigen recognition and presentation; and (3) recombination-mediated gene exchange between alleles and between related genes. The overall amount of genetic variation observed among MHC class I genes in the Felidae family is no greater than the amount of variation within any outbred cat species (i.e., domestic cat, ocelot). The occurrence of equivalent levels of polymorphism plus the simultaneous persistence of the same sequence motifs in divergent feline species suggest that most MHC class I nucleotide site polymorphism predated species divergences. Ancient polymorphisms have been transmitted through the speciation events and modern feline MHC class I alleles were derived by recombinational exchange of polymorphic sequence motifs. Moreover, some of these sequence motifs were found in other mammalian MHC class I genes, such as classical human HLA-B5, nonclassical human HLA-E class I genes, and bovine class I genes. These results raise the prospect of an ancient origin for some motifs, although the possibility of convergence in parallel mammalian radiations cannot be excluded.

Amino Acid Sequence↗
PubMed1982

Genome evolution in pocket gophers (genus Thomomys). I. Heterochromatin variation and speciation potential.

A basic dichotomy exists in the amount and chromosomal position of constitutive heterochromatin (C-bands) in species of pocket gophers, genus Thomomys. Members of the "talpoides-group" of species (e.g., T. talpoides and T. monticola) have C-bands restricted to the centromeric regions. These taxa are characterized by Robertsonian patterns of karyotypic evolution. In contrast, species within the "bottae-group" are characterized by extensive amounts of heterochromatin, placed as whole-arm and apparent whole-chromosome (T. bottae) or as large interstitial blocks (T. umbrinus). These species are characterized by extensive non-Robertsonian variation in karyotype, variation which may be expressed from local population polymorphism to between population or species polytypy. Within T. bottae, the number of whole-arm heterochromatic autosomes is inversely proportional to the number of uniarmed chromosomes in the complement, which ranges from 0 to 36 across the species populations. In all-biarmed karyotypic populations, upward to 60 percent of the linear length of the genome is composed of heterochromatin. Populations with extensive heterochromatin variation and those with similar amounts meet and hybridize freely in nature. The implications of these date for current ideas on the function of heterochromatin, particularly as related to speciation models, are discussed.

Animals↗
PubMed1983

Enumeration and speciation of group D streptococci from above and below a sewer outfall, their susceptibilities to six antibiotics and a comparison with clinical isolates.

Isolates of group D streptococci from above and below a sewer outfall and a series of clinical isolates have been speciated to sub-species level. From below the sewer outfall, Streptococcus faecalis var. faecalis predominates whereas above the outfall, S. faecium var. casseliflavus predominates. S. faecalis var. faecalis, S. faecalis var. liquefaciens and S. faecalis var. zymogenes were the predominant sub-species in the clinical isolates where S. faecium var. casseliflavus was virtually absent. S. faecalis var. liquefaciens and S. faecalis var. zymogenes were uncommon in the environmental isolates. S. faecium and S. durans were more abundant in the environmental than in the clinical isolates. The use of group D streptococci as indicators of faecal pollution would seem more suited to higher, rather than lower, levels of pollution. A statistically significant increase in resistance to antibiotics (ampicillin, penicillin, streptomycin, gentamicin, erythromycin and tetracycline) was seen in isolates from below the outfall compared with those from above and a further significant increase was seen in the clinical isolates compared with the former. Resistance to tetracycline was most common and ampicillin was the only antibiotic tested to which no resistance was detected. Multiple antibiotic resistance was rare in the environmental isolates. Even in moderately polluted water, there is not a large pool of antibiotic resistance.

Ampicillin↗
PubMed1994

Speciation and paraphyly in western Mediterranean hares (Lepus castroviejoi, L. europaeus, L. granatensis, and L. capensis) revealed by mitochondrial DNA phylogeny.

Mitochondrial DNA (mtDNA) variation among specimens of the northwestern African hare (Lepus capensis schlumbergeri) and three European hares sampled in Spain (L. castroviejoi and L. granatensis, which are endemic to the Iberian Peninsula, and L. europaeus) was analyzed using seven restriction endonucleases. Fourteen haplotypes were found among the 34 animals examined. Restriction site maps were constructed and the phylogeny of the haplotypes was inferred. mtDNA of L. capensis was the most divergent, which is consistent with its allopatric African distribution and with an African origin of European hares. We estimated that mtDNA in hares diverges at a rate of 1.5-1.8% per MY assuming that the European and African populations separated 5-6 MYBP. Maximum intraspecies nucleotides divergences were 1.3% in L. capensis, 2.7% in L. castroviejoi, and 2.3% in L. granatensis but 13.0% in L. europaeus. The latter species contained two main mtDNA lineages, one on the branch leading to L. castroviejoi and the other on that leading to L. granatensis. The separation of these two lineages from the L. castroviejoi or L. granatensis lineages appears to be much older than the first paleontological record of L. europaeus in the Iberian peninsula. This suggests that the apparent polyphyly of L. europaeus is due not to secondary introgression, but to the retention of ancestral polymorphism in L. europaeus. The results suggest that L. europaeus either has evolved as a very large population for a long time or has been fractionated. Such a pattern of persistence of very divergent lineages has also been reported in other species of highly mobile terrestrial mammals. As far as mtDNA is concerned. L. europaeus appears to be the common phylogenetic trunk which has diversified during dispersion over the European continent and from which L. castroviejoi and L. granatensis speciated separately in southwest Europe.

Animals↗
PubMed1982

A review of the taxonomy and speciation of the genus Echinococcus Rudolphi 1801.

The taxonomy of Echinococcus is reviewed and consideration given to speciation within the genus. The morphological and other biological characteristics of all species and subspecies so far described are given, and evidence for the existence of other intraspecific variants is presented. A total of 16 species have been described but only four have well-defined characteristics and are generally accepted as being taxonomically valid; E. granulosus, E. multilocularis, E. oligarthrus and E. vogeli. The taxonomic status of intraspecific variants is uncertain. Some authorities consider that the majority of described subspecies are invalid taxonomically. However, concern is expressed that previous taxonomic considerations of Echinococcus have not taken into account the nature of its reproductive mechanism which, like that of most cestodes, defies the application of traditional taxonomic concepts and definitions derived from dioecious cross-fertilising organisms. At the present time intraspecific variants of Echinococcus are referred to as strains. The existence of such strains, particularly of E. granulosus, in different parts of the world is firmly established. Their importance in the epidemiology of hydatidosis has high-lighted the needed to establish criteria for their differentiation and characterisation. The limitations of morphology as a sole differential criterion are emphasised. Attention is given to recent studies on strain variation which have demonstrated the value of applying several different criteria in which the developmental, physiological and biochemical characteristics of different strains are compared in conjunction with morphological investigations.

Animals↗
PubMed1989

Speciation of arsenic in Dutch total diets: methodology and results.

In the last decade 311 duplicate portions of the 24-h diet of Dutch citizens were collected and lyophilized. All samples were assayed for total arsenic and, in addition, the 20 samples which ranked highest in total arsenic were selected for arsenic speciation i.e., the separate determination of organic-bound arsenic and inorganic arsenic. For the determination of total arsenic, the test portion is wet-digested and the digest reduced with KI/SnCl2/Zn to give AsH3 which is measured by molecular absorption spectrometry. Inorganic arsenic is also measured as AsH3 after acid extraction of the test portion and subsequent NaBH4 reduction of the extract. The residue of the acid extraction and the NaBH4-reduced extract are combined, wet-digested and the digest reduced with NaBH4 to give AsH3 originating from organic-bound arsenic. Samples spiked at different levels with inorganic and organic-bound arsenic were analysed and gave recoveries for inorganic arsenic of 94% to 122% (n = 6) and for organic-bound arsenic of 87% to 104% (n = 6). On average, the inorganic fraction is 30% of the total arsenic intake; range 3% to 50% (n = 14). The inorganic arsenic fraction decreases with increasing level of total arsenic intake. The highest oral inorganic arsenic intake was 60 micrograms; the tolerable daily intake (TDI) for a 60-kg individual is 120 micrograms inorganic arsenic. Organic and inorganic arsenic measured were summed and compared with the results of the total arsenic determination; differences were less than 15%. (Since inorganic arsenic is a contaminant and not an additive, the abbreviation TDI is preferred here over ADI (acceptable daily intake) which is retained for additives.)

Arsenic↗
PubMed1978

Satellite DNAs in eukaryotes: a non-adaptive mechanism of speciation which originated with sexual reproduction?

Satellite DNAs may have originated during evolution at the same time as sexual reproduction in order to suppress crossingover between the 2 heterogametic sex chromosomes, and may have acquired a function of sterility barriers in hybrid species during evolution. This origin of satellite DNAs appears to be reflected in different stages of speciation: partial and total heterogametic sex hybrid sterility and full hybrid sterility might correspond to subspecies, semispecies and full species.

Animals↗