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PubMed2005

Mobility and speciation of Cd, Cu, and Zn in two acidic soils affected by simulated acid rain.

Through a batch experiment, the mobility and speciation of heavy metals (Cd, Cu, Zn) in two acidic forest soils from Hunan Province were studied. The results showed that the release and potential active speciation of Cd, Cu, and Zn in the tested contaminated red soil (CRS) and yellow red soil (CYRS) increased significantly with pH decreasing and ion concentrations increasing of simulated acid rain, and these effects were mainly decided by the pH value of simulated acid rain. Cd had the highest potential risk on the environment compared with Cu and Zn. Cd existed mainly in exchangeable form in residual CRS and CYRS, Cu in organically bound and Mn-oxide occluded forms, and Zn in mineral forms due to the high background values.

Acid Rain↗

PubMed2005

The effect of Wolbachia versus genetic incompatibilities on reinforcement and speciation.

Wolbachia is a widespread group of intracellular bacteria commonly found in arthropods. In many insect species, Wolbachia induce a cytoplasmic mating incompatibility (CI). If different Wolbachia infections occur in the same host species, bidirectional CI is often induced. Bidirectional CI acts as a postzygotic isolation mechanism if parapatric host populations are infected with different Wolbachia strains. Therefore, it has been suggested that Wolbachia could promote speciation in their hosts. In this article we investigate theoretically whether Wolbachia-induced bidirectional CI selects for premating isolation and therefore reinforces genetic divergence between parapatric host populations. To achieve this we combined models for Wolbachia dynamics with a well-studied reinforcement model. This new model allows us to compare the effect of bidirectional CI on the evolution of female mating preferences with a situation in which postzygotic isolation is caused by nuclear genetic incompatibilities (NI). We distinguish between nuclear incompatibilities caused by two loci with epistatic interactions, and a single locus with incompatibility among heterozygotes in the diploid phase. Our main findings are: (1) bidirectional CI and single locus NI select for premating isolation with a higher speed and for a wider parameter range than epistatic NI; (2) under certain parameter values, runaway sexual selection leads to the increase of an introduced female preference allele and fixation of its preferred male trait allele in both populations, whereas under others it leads to divergence in the two populations in preference and trait alleles; and (3) bidirectional CI and single locus NI can stably persist up to migration rates that are two times higher than seen for epistatic NI. The latter finding is important because the speed with which mutants at the preference locus spread increases exponentially with the migration rate. In summary, our results show that bidirectional CI selects for rapid premating isolation and so generally support the view that Wolbachia can promote speciation in their hosts.

Animals↗

PubMed2005

Changes of Cu, Zn, and Cd speciation in sewage sludge during connposting.

The potential toxicity risks from heavy metals depend on their chemical speciation. The four stages of the Tessier sequential extraction method were employed to investigate changes in heavy metal speciation (Cu, Zn, and Cd) of sewage sludge during forced aeration composting, and then to identify whether the composting process would reduce or enhance their toxicities. Throughout the composting process, the exchangeable, carbonate-bound, Fe-Mn oxide-bound, and organic matter-bound fractions of Cu were converted to the residual Cu fraction. The organic matter-bound Cu fraction greatly contributed to this transformation. Residual Zn fraction was transformed to the Fe-Mn oxide-bound and organic matter-bound fractions after composting. The residual Zn fraction was a major contributor to the organic matter-bound Zn fraction. The availability of Cu and Zn was reduced by composting such that the risk of heavy metal toxicity decreased with prolonged treatment times. Additionally, attention should be paid to the increased availability of Cd in sewage sludge after composting treatment.

Hydrogen-Ion Concentration↗

PubMedDate not supplied

[Geographical variation in the species Montivagum dihumerale and speciation in chigger mites (Acari: Trombiculidae)].

Intraspecific morphological variation of the chigger mite species Montivagum dihumerale (Traub et Nadchatram, 1967) is studied. Eco-geographic rules of the variation are revealed. General size of mites is found to be increased along with the rise of the high-mountain character of the landscape in the collection localities. The numbers of idiosomal setae are varied independently from the size parameters and geographically close populations are proved to be the most similar by these characters. At the same time, numbers of the setae of different types play the leading role in the discrimination of closely related Montivagum species, while the eco-geographical rules have not been found in this genus at the level of interspecific differences. As a result, the hypothesis is set up, that a significant degree of isolation of local populations separated from each other by high mountain ranges of the Central Asia is the main factor of speciation in the genus Montivagum. Regional character of this speciation mode is confirmed by the comparison with other chigger mites taxa.

Animals↗

PubMed2006

[New approaches to selenium speciation].

A review of the recent developments in selenium speciation analysis was presented, focusing on the techniques of separation, interface, elemental specific detection and identification of selenium species; the methods of sample storage and pretreatment storage for selenium speciation were also introduced.

Chromatography, Gas↗

PubMed1990

The Spalacidae: evolutionary history, speciation and population biology.

The evolutionary history of Spalacidae is reviewed taxonomically, paleontologically and neontologically. We focused selectively on taxonomy, biogeography, paleontology and evolutionary origins, chromosomal evolution, population biology and the species concept in Spalacidae. We concluded that the taxonomy of Spalacidae needs a modern revision based on chromosome and molecular-genetic data, beside that of morphology, physiology and behavior. The subterranean Spalacidae originated probably from a muroid-cricetoid stock in Asia Minor or vicinity, in Upper Oligocene times and adaptively radiated underground in the Balkans, steppic Russia and Middle East, extending into North Africa. The major important evolutionary feature in peripatric or allopatric speciation and adaptive radiation was karyotypic evolution, primarily through Robertsonian changes. More than 30 karyotypes (2n = 38-62; NF = 72-124) earlier represented by 8 classical species, occur primarily allopatrically or parapatrically, with only marginal sympatry, across the Eastern Mediterranean range of the family. Most karyotypes represent biospecies adapted at multiple organizational levels to their different ecologies. A short overview is presented on population biology and life history parameters of the Spalacidae which result in K-selected, "equilibrium species". Speciation in action and adaptive radiation embracing molecular and organismal adptations to the subterranean unique ecotope and to four different climatic regimes, have been multidisciplinarily studied in the Israeli Spalax ehrenbergi superspecies.

Animals↗

PubMed1983

A methodology for speciation of methyltins in mammalian tissues.

Exposure to methyltin compounds results in morphologically detectable damage to several mammalian organ systems. Although reliable dose-response relationships have been described, a fast method for quantitating levels of various methyltin species in target organs has been unavailable. It has been possible to measure organotins as total tin using atomic absorption spectrometry, but speciation of methyltins has proved difficult. We present a rapid method for quantitative analysis and speciation of methyltins, direct from mammalian tissues. Methyltin compounds (monomethyltin trichloride, dimethyltin dichloride, trimethyltin chloride, and tetramethyltin) are purged from freshly homogenized mouse kidney and brain tissues using NaBH4. The volatile organotin hydrides produced are cryogenically trapped on the head of a gas chromatographic column (at -40 degrees C) and eluted using a linear temperature program (15 degrees C/min to 190 degrees C). The compounds are detected using selected ion monitoring in a Hewlett Packard 5985-B mass spectrometer. Quantitation is achieved by integration of the areas of the chromatographic peaks. Linear response is obtained over the range of 1 ng to 30 micrograms for each compound. Recoveries of methyltins spiked into tissues are greater than 85%.

Animals↗

PubMed1980

Intergeneric hybridization and speciation between two leptosporangiate ferns.

The oosphere of Pteridium aquilinum is surrounded by a 'special membrane' which does not appear to resist the fertile spermatozoon of Gymnogramme calomelanos var. chrysophylla and monospermy results. Our hybridization findings also indicate that the membrane maintains speciation. The spermatozoon of Gymnogramme is strongly attracted but some injury is sustained during its passage through the mucilage of the archegonium neck. Nevertheless, rupture of the membrane, herein designated the cortical complex of speciation (CCS), is followed by expulsion of the oosphere-cytoplasm for which an osmotic mechanism is proposed.

Crosses, Genetic↗

PubMed1994

Protein speciation and potential effects on membrane transport and immobilization illustrated by alpha-chymotrypsin.

Protein speciation via physiochemical and biochemical processes presents both challenges and opportunities for membrane applications and research. Different types of speciation and its potential effects are illustrated with the well-known enzyme, alpha-chymotrypsin. This enzyme is capable of self-association and undergoing post-translational modifications. Self-association is shown to alter transport fluxes and also be manipulable. The post-translational modifications generate catalytically-active species that are difficult to detect and different in stability. The presence of different species can conceivably impact on the fabrication, performance, and analysis of immobilized enzyme systems.

Biological Transport↗

PubMed1993

Effects of iron loading on uptake, speciation, and chelation of iron in cultured myocardial cells.

Accumulation of Fe in the myocardium in circumstances of transferrin saturation is associated with heart failure in Fe-loaded patients. To characterize the underlying causes of this phenomenon, we measured the flux as well as the speciation of Fe in normal and Fe-loaded cultures of rat myocardiocytes. Fe loading with low-molecular-weight Fe (ferric ammonium citrate) promoted a dose- and time-dependent increase in the rate of uptake of non-transferrin-bound Fe (NTBI) that was positively correlated (R = 0.9, p < 0.005) with cellular iron content. At concentrations sufficient to produce this up-regulation, membrane integrity was unaffected but the rate of spontaneous beating of the cells was decreased by 60%. The enhanced rate of NTBI uptake in Fe-loaded cells reverted to control rates after treatment with therapeutic concentrations of Fe chelators deferoxamine, 1,2-dimethyl-3-hydroxypyrid-4-one and 1,2-diethyl-3-hydroxypyrid-4-one under conditions where approximately 80% of the cellular Fe was removed by chelation. Fe loading of cultured myocytes also induced shifts in Fe speciation. Thus the ratio of Fe bound in hemosiderin-like precipitates to ferritin-bound Fe increased twofold, from a range of 0.84 to 1.44 in control cells to 1.96 to 3.3 in iron-loaded cells. This increased ratio was similar to that measured in the heart and liver of a thalassemic patient who underwent a double transplant for the failure of both organs, even though the Fe content of the heart (mean, 5.8 mg Fe/gm dry weight) was much less than that of the liver (28.1 mg/gm dry weight). These results suggest that increased rates of uptake of NTBI may exacerbate iron loading of the heart and contribute to iron-mediated cardiotoxicity, whereas the clinical benefits of chelation therapy may be enhanced by the down-regulation of NTBI uptake.

Animals↗

PubMedDate not supplied

Involvement of analytical chemistry in chemical speciation of metals in clinical samples.

The different chemical species of the trace elements in a living system are determinants for their physiological behaviour. Their study is necessary to improve the understanding of trace element kinetics and metabolism. In a complex matrix, such as biological fluids and tissues, some trace elements will occur as free or mononuclear ions; other as low molecular weight complexes, as reversible or irreversible macromolecular complexes. Speciation investigations entail the separation of the compounds, followed by the measurement of the trace element in the different fractions. Frame-work-procedures are outlined and attention is drawn on the many difficulties that can be encountered. These include the complexity of the matrix, insufficient specificity of the separation of biocompounds, fortuitous contaminations with trace elements, and cutting the original metal-protein binding. State of the art description is given for the speciation studies of AI, As, Cd, Cr, Co, Cu, Hg, Ni, Pb, Pt, Se, Sn, and Zn.

Aluminum↗

PubMed1997

Biochemical speciation of enterococci causing human infections.

As Enterococci are now coming up as important nosocomial pathogens, their speciation and antibiotic sensitivity testing is important. 120 isolates of Enterococci from various clinical samples were physiologically and biologically characterised. Speciation on the basis of recommended methods revealed 114(95%) as E. faecalis and 6(5%) as E. faecium. Antibiogram of the 120 isolates showed that 100(83.3%) were sensitive to Ampicillin. Combination of Penicillin and Gentamicin was more effective. E. faecium was more drug resistant.

Ampicillin↗

PubMed2025

Genomic analyses of three Acanthus L. species provide insight into polyploidization-driven speciation and evolution.

Allopolyploidy fundamentally influences plant evolution, yet the genomic dynamics of allotetraploidization remain incompletely understood. We investigated Acanthus tetraploideus (2n = 4x = 96), an ecologically significant allotetraploid true mangrove from Indo-West Pacific intertidal zones. Our prior integrative investigations indicate that A. tetraploideus originated through hybridization of the diploid species A. ilicifolius and A. ebracteatus with subsequent chromosome doubling. Here, we present complete chromosome-scale genome assemblies for all three species, representing the first genomic resources for true mangrove polyploid research. Our analysis reveals that the three species have experienced at least four rounds of polyploidization events, with the most recent, approximately 53 mya, possibly an Acanthus-specific event. The allotetraploid A. tetraploideus, which emerged between 1.5 and 2.2 mya, has A. ebracteatus as its maternal progenitor and A. ilicifolius as its paternal one. Through a comprehensive genomic comparison and analysis of homoeologous gene expression, we propose a gradual evolutionary trajectory for allotetraploidy in A. tetraploideus. Despite the allotetraploidization event dating back to around 2 mya, A. tetraploideus retains a high degree of colinearity with its ancestral genomes, with the majority (76.2%) of duplicated genes retained and no significant sub-genome bias in gene expression. Furthermore, we have identified positive selection in specific genes that may facilitate the adaptation of Acanthus mangrove species to their intertidal habitats. These findings establish A. tetraploideus as a model for studying allopolyploid evolution while providing new insights into mangrove speciation processes.

Genome, Plant↗

PubMed2006

Quantitative genetics of speciation: additive and non-additive genetic differentiation between Drosophila madeirensis and Drosophila subobscura.

The role of dominance and epistasis in population divergence has been an issue of much debate ever since the neoDarwinian synthesis. One of the best ways to dissect the several genetic components affecting the genetic architecture of populations is line cross analysis. Here we present a study comparing generation means of several life history-traits in two closely related Drosophila species: Drosophila subobscura, D. madeirensis as well as their F1 and F2 hybrids. This study aims to determine the relative contributions of additive and non-additive genetic parameters to the differentiation of life-history traits between these two species. The results indicate that both negative dominance and epistatic effects are very important in the differentiation of most traits. We end with considerations about the relevance of these findings for the understanding of the role of non-additive effects in speciation.

Animals↗

PubMed2006

Conservation: losing biodiversity by reverse speciation.

A large fraction of the world's species diversity is of recent evolutionary origin, and has evolved as a by-product of divergent adaptation in heterogeneous environments. Recent research provides a dire warning that homogenizing environments may cause the rapid loss of such species through a reversal of the speciation process.

Animals↗

PubMed2006

Multiple rounds of speciation associated with reciprocal gene loss in polyploid yeasts.

A whole-genome duplication occurred in a shared ancestor of the yeast species Saccharomyces cerevisiae, Saccharomyces castellii and Candida glabrata. Here we trace the subsequent losses of duplicated genes, and show that the pattern of loss differs among the three species at 20% of all loci. For example, several transcription factor genes, including STE12, TEC1, TUP1 and MCM1, are single-copy in S. cerevisiae but are retained in duplicate in S. castellii and C. glabrata. At many loci, different species have lost different members of a duplicated gene pair, so that 4-7% of single-copy genes compared between any two species are not orthologues. This pattern of gene loss provides strong evidence for speciation through a version of the Bateson-Dobzhansky-Muller mechanism, in which the loss of alternative copies of duplicated genes leads to reproductive isolation. We show that the lineages leading to the three species diverged shortly after the whole-genome duplication, during a period of precipitous gene loss. The set of loci at which single-copy paralogues are retained is biased towards genes involved in ribosome biogenesis and genes that evolve slowly, consistent with the hypothesis that reciprocal gene loss is more likely to occur between duplicated genes that are functionally indistinguishable. We propose a simple, unified model in which a single mechanism--passive gene loss-enabled whole--genome duplication and led to the rapid emergence of new yeast species.

Alleles↗

PubMed2006

Speciation genetics: evolving approaches.

Much progress has been made in the past two decades in understanding Darwin's mystery of the origins of species. Applying genomic techniques to the analysis of laboratory crosses and natural populations has helped to determine the genetic basis of barriers to gene flow which create new species. Although new methodologies have not changed the prevailing hypotheses about how species form, they have accelerated the pace of data collection. By facilitating the compilation of case studies, advances in genetic techniques will help to provide answers to the next generation of questions concerning the relative frequency and importance of different processes that cause speciation.

Animals↗

PubMed2006

Incipient speciation through niche expansion: an example from the Arctic charr in a subarctic lake.

Two reproductive isolated morphs of Arctic charr (Salvelinus alpinus), termed profundal and littoral charr according to their different spawning habitats, co-occur in the postglacial lake Fjellfrøsvatn in North Norway. All profundal charr live in deep water their entire life and have a maximum size of 14cm, while the littoral charr grow to 40cm. Some small and young littoral charr move to the profundal zone in an ontogenetic habitat shift in the ice-free season and the rest of the population remains in epilimnic waters. The two morphs had different diet niches in the profundal zone: the profundal charr ate typical soft-bottom prey (chironomid larvae, pea mussels and benthic copepods), while the young littoral charr mainly consumed crustacean zooplankton. In four other lakes without a profundal morph (i.e. monomorphic populations), young charr also performed ontogenetic habitat shifts to the profundal zone and fed on zooplankton. The profundal morph of Fjellfrøsvatn therefore utilize a food resource niche that neither the littoral morph nor comparable monomorphic populations exploit. This suggests that intraspecific resource competition has driven incipient ecological speciation of the profundal charr of Fjellfrøsvatn. The exploitation of the soft-bottom resources by the profundal charr supports earlier experimental findings that the profundal morph is genetically different in trophic behaviour and morphology. The sympatric ecological divergence within the profundal habitat is possible because unexploited food resources (soft-bottom profundal prey) are available. Apparently, this represents a case of incipient segregation by expansion to new resource types (niche invasion), and not by subdivision of one broad ancestral niche.

Aging↗