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Divergent
Terms modified by Divergent Selected AbstractsDivergent and Linear Solid-Phase Synthesis of PNA Containing Thiazole Orange as Artificial BaseEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2005Dilip V. Jarikote Abstract Fluorescent nucleobase surrogates provide nucleic acids with interesting properties. We have recently introduced thiazole orange as base surrogate into PNA and found that the so-called FIT (Forced Intercalation of Thiazole orange) PNA probes signal hybridization by enhancements of fluorescence. Common approaches of modifying nucleobases or introducing nucleobase surrogates draw upon the usage of monomer building blocks that have been synthesized in solution phase. The need to prefabricate a base-modified building block can hold up progress if several base modifications or base surrogates are to be evaluated. Herein, a method for divergent solid-phase synthesis is presented that serves the purpose to facilitate the screening for base surrogates that fluoresce upon hybridization. An Fmoc/Aloc-protected submonomer allowed the application of commonly used Fmoc-based solid-phase synthesis protocols while removal of the fully orthogonal Aloc group enabled the on-resin introduction of base surrogates after the linear chain assembly had been completed. The divergent solid-phase synthesis strategy is automatable, gives overall yields matching those of linear solid-phase synthesis and, most importantly, provides rapid access to any kind of base-modified PNA. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Are German, Japanese and Anglo-Saxon Strategic Decision Styles Still Divergent in the Context of Globalization?*JOURNAL OF MANAGEMENT STUDIES, Issue 6 2005Chris Carr abstract Issues of globalization and divergence in terms of national systems and cultures are equally contentious, yet equally important, in the context of increasing cross-continental co-operation. This article investigates comparative strategic decision styles in Britain, the USA, Germany and Japan. An industry at an advanced stage in terms of globalization, vehicle components manufacture, was selected in order to explore the extent of convergence and whether this has changed. Between 1989 and 1998, field case studies were made of 100 strategic investment decisions (SIDs) by manufacturers in these four countries. Longitudinal judgements were supplemented by earlier comparative strategy field research carried out in 60 suppliers between 1980 and 1983, and two longitudinal case studies, one from the UK and one from Japan, interviewed throughout both these periods and again in 2002. Two competing hypotheses, derived from rich research literatures, are investigated. The first (H1) suggests that national institutional and cultural factors exert profound differences, and should therefore be afforded more significance as globalization proceeds further. The second (H2) is apparently contradictory and emphasizes that institutions and organizations are likely to respond to convergence pressures, spurred by global capital markets and competition on the one hand, and a diffusion of ,professional management' practices on the other. Japanese firms generally, and German family firms in particular, were still found to exhibit deep-rooted differences from the Anglo-Saxon model, which appears to confirm H1. However study of German public companies reveals that their strategic approaches are far less divergent from what is now an increasingly consistent Anglo-Saxon model than they were a decade ago, which appears to confirm the competing hypothesis H2. [source] Techne versus Technoscience: Divergent (and Ambiguous) Notions of Food "Quality" in the French Debate over GM CropsAMERICAN ANTHROPOLOGIST, Issue 4 2007CHAIA HELLER In the French debate over genetically modified organisms (GMOs), actors present divergent definitions of food quality located between poles of technoscience and techne. Although scientists often define food quality in terms of technoscience, assessing food safety, small farmers often appeal to technes of production, positing GMOs as a rupture with artisanal culture. Whereas small farmers (from the union the Confédération Paysanne [CP]) deploy notions of "techne" to promote their anti-GMO campaign, they often define quality in an ambiguous way, vacillating between ideas of agricultural method (technique) or production scale. Despite this ambiguity, the CP successfully designates GMOs as la malbouffe, or "bad" food, establishing themselves as protectors of artisanal technés such as Roquefort. Finally, unlike many cultures that cast GMOs as "unnatural," the CP tends to frame GMOs as "uncultural." In the French debate, the CP posits culture against a "culturelessness" associated with technoscience and industry-driven foods such as GMOs and McDonald's. [source] Reliability and validity of the sexual pressure scale,RESEARCH IN NURSING & HEALTH, Issue 4 2006Rachel Jones Abstract The purpose of this study was to develop the Sexual Pressure Scale (SPS) as a valid and reliable measure of gender stereotypical expectations to engage in sexual behavior. Data were collected using audio computer-assisted self-interview in 306 urban women, aged 18 to 29. Exploratory principal components analysis with varimax rotation yielded 19 items consisting of five factors: Condom Fear, Sexual Coercion, Women's Sex Role, Men Expect Sex, and Show Trust, accounting for 62% of the variance. Divergent and convergent validity were supported, respectively, by negative relationships of SPS factors with dyadic trust and positive relationships with sexual victimization and sexual risk behavior. Alpha reliability was .81; factor reliabilities ranged from .63 to .82. A valid assessment of sexual pressure can suggest the extent to which stereotypical gender expectations structure women's freedom to explore partner and condom use choices. © 2006 Wiley Periodicals, Inc. Res Nurs Health 29: 281,293, 2006. [source] ChemInform Abstract: Divergent and Regioselective Synthesis of 1,2,4- and 1,2,5-Trisubstituted Imidazoles.CHEMINFORM, Issue 2 2009Bruno Delest Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Schizophrenia; from structure to function with special focus on the mediodorsal thalamic prefrontal loopACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2009B. Pakkenberg Objective:, To describe structural and biochemical evidence from postmortem brains that implicates the reciprocal connections between the mediodorsal thalamic nucleus and the prefrontal cortex in cognitive symptoms of schizophrenia. Method:, The estimation of the regional volumes and cell numbers was obtained using stereological methods. The biochemical analyses of molecular expression in postmortem brain involve quantitative measurement of transcripts and proteins by in-situ (RNA) or Western blot/autoradiography in brains from patients with schizophrenia and comparison subjects. Results:, Stereological studies in postmortem brain from patients with schizophrenia have reported divergent and often opposing findings in the total number of neurons and volume of the mediodorsal (MD) thalamic nucleus, and to a lesser degree in its reciprocally associated areas of the prefrontal cortex. Similarly, quantitative molecular postmortem studies have found large inter-subject and between-study variance at both the transcript and protein levels for receptors and their interacting molecules of several neurotransmitter systems in these interconnected anatomical regions. Combined, large variation in stereological and molecular studies indicates a complex and heterogeneous involvement of the MD thalamic-prefrontal loop in schizophrenia. Conclusion:, Based on a considerable heterogeneity in patients suffering from schizophrenia, large variation in postmortem studies, including stereological and molecular postmortem studies of the MD thalamus and frontal cortex, might be expected and may in fact partly help to explain the variable endophenotypic traits associated with this severe psychiatric illness. [source] All- trans retinoic acid-induced ectopic limb and caudal structures: Murine strain sensitivities and pathogenesisDEVELOPMENTAL DYNAMICS, Issue 6 2008Xiaoyan Liao Abstract Treatment of pregnant mice at the egg cylinder stage with retinoic acid (RA) has caused ectopic hindlimbs in the offspring. Proposed causes of ectopic hindlimbs include homeotic transformation or multiple axis formation. Two mouse strains were determined to be divergent in susceptibility to this malformation (C57BL/6N, highly sensitive; SWV/Fnn, less sensitive). Ectopic limbs were hindlimbs (expressing Pitx1 and Tbx4 but not Tbx5), yet they also expressed the predominantly forelimb Hoxb8. Ectopic body axis formation was indicated by gene expression for ectopic primitive streaks, notochords, and nodes, as well as inhibition of anterior visceral endoderm and mesodermal migration. The earlier in development that embryos were examined, the higher the rate of ectopic hindlimb development and axis formation. Ectopic axis formation and cell migration inhibition had the same strain susceptibility as the dysmorphogenesis. We propose that all extra hindlimbs were derived from ectopic axis formation, perturbation of which is genetic background dependent. Developmental Dynamics 237:1553,1564, 2008. © 2008 Wiley-Liss, Inc. [source] Comparative phylogeography of salmonid fishes (Salmonidae) reveals late to post-Pleistocene exchange between three now-disjunct river basins in SiberiaDIVERSITY AND DISTRIBUTIONS, Issue 4 2003E. Froufe Abstract. We use a comparative phylogeographical framework to evaluate the hypothesis of hydrological exchange during the Pleistocene among the now disjunct Lena, Amur, and Enisei basins in Siberia, and to provide evidence on the causal mechanism of their present day faunal dissimilarities. Approximately 600 bases of the mitochondrial control region were sequenced in five distinct lineages among three genera of salmonid fishes, Hucho, Brachymystax and Thymallus. All three basins were fixed for divergent (2,5.4%) lineages of Thymallus whereas a single shared haplotype was present in all three basins for Hucho taimen (Pallas, 1773) and one shared haplotype between the Lena and Amur basins out of a total of five for blunt-snouted and one out of five for sharp-snouted Brachymystax lenok (Pallas, 1773). For both blunt- and sharp-snouted lenok the haplotypes found within each basin did not form clades, so no relationship between genotypes and geographical occurrence was found. Our data support relatively recent hydrological mixing of the major river drainage systems in eastern and far-eastern Siberia, congruent with the hypothesis of large-scale palaeo-hydrological exchange stemming from glacial advance, retreat and melting during Pleistocene climate fluctuations. Furthermore, these results in conjunction with a comparison of overall faunal composition suggest that environmental differences rather than historical contingency may be responsible for the faunal dissimilarities of the Amur, Lena, and Enisei river basins. [source] A low-dimensional physically based model of hydrologic control of shallow landsliding on complex hillslopesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008Ali Talebi Abstract Hillslopes have complex three-dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and soil depth. To investigate the stability of complex hillslopes (with different slope curvatures and plan shapes), we combine the hillslope-storage Boussinesq (HSB) model with the infinite slope stability method. The HSB model is based on the continuity and Darcy equations expressed in terms of storage along the hillslope. Solutions of the HSB equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. The presented model is composed of three parts: a topography model conceptualizing three-dimensional soil mantled landscapes, a dynamic hydrology model for shallow subsurface flow and water table depth (HSB model) and an infinite slope stability method based on the Mohr,Coulomb failure law. The resulting hillslope-storage Boussinesq stability model (HSB-SM) is able to simulate rain-induced shallow landsliding on hillslopes with non-constant bedrock slope and non-parallel plan shape. We apply the model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). In the presented model, the unsaturated storage has been calculated based on the unit head gradient assumption. To relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case, we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method. The results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability. Therefore, it can be concluded that the presented dynamic slope stability model (HSB-SM) can be used safely for slope stability analysis on complex hillslopes. Our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others, whilst divergent convex hillslopes remain stable (even after intense rainfall). In addition, the relation between subsurface flow and hillslope stability has been investigated. Our analyses show that the minimum safety factor (FS) occurs when the rate of subsurface flow is a maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Copyright © 2008 John Wiley & Sons, Ltd. [source] The relative importance of latitude matching and propagule pressure in the colonization success of an invasive forbECOGRAPHY, Issue 6 2006John L. Maron Factors that influence the early stages of invasion can be critical to invasion success, yet are seldom studied. In particular, broad pre-adaptation to recipient climate may importantly influence early colonization success, yet few studies have explicitly examined this. I performed an experiment to determine how similarity between seed source and transplant site latitude, as a general indicator of pre-adaptation to climate, interacts with propagule pressure (100, 200 and 400 seeds/pot) to influence early colonization success of the widespread North American weed, St. John's wort Hypericum perforatum. Seeds originating from seven native European source populations were sown in pots buried in the ground in a field in western Montana. Seed source populations were either similar or divergent in latitude to the recipient transplant site. Across seed density treatments, the match between seed source and recipient latitude did not affect the proportion of pots colonized or the number of individual colonists per pot. In contrast, propagule pressure had a significant and positive effect on colonization. These results suggest that propagules from many climatically divergent source populations can be viable invaders. [source] Is the matrix a sea?ECOLOGICAL ENTOMOLOGY, Issue 1 2005Habitat specificity in a naturally fragmented landscape Abstract., 1. Metapopulation and island biogeography theory assume that landscapes consist of habitat patches set in a matrix of non-habitat. If only a small proportion of species conform to the patch,matrix assumptions then metapopulation theory may only describe special cases rather than being of more general ecological importance. 2. As an initial step towards understanding the prevalence of metapopulation dynamics in a naturally fragmented landscape, the distribution of beetle species in three replicates of three habitat types was examined, including rainforest and eucalypt forest (the habitat patches), and buttongrass sedgeland (the matrix), in south-west Tasmania, Australia. 3. Ordination methods indicated that the buttongrass fauna was extremely divergent from the fauna of forested habitats. Permutation tests showed that the abundance of 13 of 17 commonly captured species varied significantly among habitats, with eight species confined to eucalypts or rainforest, and three species found only in buttongrass. Approximately 60% of species were confined to forested habitat implying that metapopulation theory has the potential to be very important in the forest,buttongrass landscape. 4. Although floristically the rainforest and eucalypts were extremely distinct, the beetle faunas from eucalypts and rainforests overlapped substantially. Therefore rainforest patches connected by eucalypt forest represent continuous habitat for most species. 5. Other studies report a wide range of values for the proportion of patch-specific species in fragmented landscapes. Understanding the environmental or historical conditions under which a high proportion of species become patch specialists would help to identify where spatial dynamic theory may be especially applicable, and where habitat loss and fragmentation poses the greatest threat to biodiversity. [source] Predators temper the relative importance of stochastic processes in the assembly of prey metacommunitiesECOLOGY LETTERS, Issue 11 2009Jonathan M. Chase Abstract Communities assemble through a combination of stochastic processes, which can make environmentally similar communities divergent (high ,-diversity), and deterministic processes, which can make environmentally similar communities convergent (low ,-diversity). Top predators can influence both stochasticity (e.g. colonization and extinction events) and determinism (e.g. size of the realized species pool), in community assembly, and thus their net effect is unknown. We investigated how predatory fish influenced the scaling of prey diversity in ponds at local and regional spatial scales. While fish reduced both local and regional richness, their effects were markedly more intense at the regional scale. Underlying this result was that the presence of fish made localities within metacommunities more similar in their community composition (lower ,-diversity), suggesting that fish enhance the deterministic, relative to the stochastic, components of community assembly. Thus, the presence of predators can alter fundamental mechanisms of community assembly and the scaling of diversity within metacommunities. [source] Molecular phylogeny and phylogeography of flightless beetles Parechthistatus gibber and Hayashiechthistatus inexpectus (Coleoptera: Cerambycidae) inferred from mitochondrial COI gene sequencesENTOMOLOGICAL SCIENCE, Issue 2 2008Hiroshi NAKAMINE Abstract To elucidate the speciation patterns of two endemic flightless cerambycid beetles, Parechthistatus gibber and Hayashiechthistatus inexpectus, molecular phylogenetic analysis was carried out. A 1144 bp region of the cytochrome oxidase subunit I gene was sequenced for individuals from 51 local populations of these species. There were nine haplotype lineages of P. gibber, and H. inexpectus was included within a P. gibber lineage. These lineages were highly divergent and occurred in different regions. Based on previously published molecular change rates for the COI gene (1.5,2.3% per million years), the time of divergence of P. gibber COI haplotypes was inferred to be 3.0,4.6 million years ago, in the Pliocene. [source] Effect of PCR amplicon size on assessments of clone library microbial diversity and community structureENVIRONMENTAL MICROBIOLOGY, Issue 5 2009Julie A. Huber Summary PCR-based surveys of microbial communities commonly use regions of the small-subunit ribosomal RNA (SSU rRNA) gene to determine taxonomic membership and estimate total diversity. Here we show that the length of the target amplicon has a significant effect on assessments of microbial richness and community membership. Using operational taxonomic unit (OTU)- and taxonomy-based tools, we compared the V6 hypervariable region of the bacterial SSU rRNA gene of three amplicon libraries of c. 100, 400 and 1000 base pairs (bp) from each of two hydrothermal vent fluid samples. We found that the smallest amplicon libraries contained more unique sequences, higher diversity estimates and a different community structure than the other two libraries from each sample. We hypothesize that a combination of polymerase dissociation, cloning bias and mispriming due to secondary structure accounts for the differences. While this relationship is not linear, it is clear that the smallest amplicon libraries contained more different types of sequences, and accordingly, more diverse members of the community. Because divergent and lower abundant taxa can be more readily detected with smaller amplicons, they may provide better assessments of total community diversity and taxonomic membership than longer amplicons in molecular studies of microbial communities. [source] Actinorhodopsins: proteorhodopsin-like gene sequences found predominantly in non-marine environmentsENVIRONMENTAL MICROBIOLOGY, Issue 4 2008Adrian K. Sharma Summary Proteorhodopsins are light-energy-harvesting transmembrane proteins encoded by genes recently discovered in the surface waters of the world's oceans. Metagenomic data from the Global Ocean Sampling expedition (GOS) recovered 2674 proteorhodopsin-related sequences from 51 aquatic samples. Four of these samples were from non-marine environments, specifically, Lake Gatun within the Panama Canal, Delaware Bay and Chesapeake Bay and the Punta Cormorant Lagoon in Ecuador. Rhodopsins related to but phylogenetically distinct from most sequences designated proteorhodopsins were present at all four of these non-marine sites and comprised three different clades that were almost completely absent from marine samples. Phylogenomic analyses of genes adjacent to those encoding these novel rhodopsins suggest affiliation to the Actinobacteria, and hence we propose to name these divergent, non-marine rhodopsins ,actinorhodopsins'. Actinorhodopsins conserve the acidic amino acid residues critical for proton pumping and their genes lack genomic association with those encoding photo-sensory transducer proteins, thus supporting a putative ion pumping function. The ratio of recA and radA to rhodopsin genes in the different environment types sampled within the GOS indicates that rhodopsins of one type or another are abundant in microbial communities in freshwater, estuarine and lagoon ecosystems, supporting an important role for these photosystems in all aquatic environments influenced by sunlight. [source] The structure of a local population of phytopathogenic Pseudomonas brassicacearum from agricultural soil indicates development under purifying selection pressureENVIRONMENTAL MICROBIOLOGY, Issue 3 2001Johannes Sikorski Among the isolates of a bacterial community from a soil sample taken from an agricultural plot in northern Germany, a population consisting of 119 strains was obtained that was identified by 16S rDNA sequencing and genomic fingerprinting as belonging to the recently described species Pseudomonas brassicacearum. Analysis of the population structure by allozyme electrophoresis (11 loci) and random amplified polymorphic DNA,polymerase chain reaction (RAPD,PCR; four primers) showed higher resolution with the latter method. Both methods indicated the presence of three lineages, one of which dominated strongly. Stochastic tests derived from the neutral theory of evolution (including Slatkin's exact test, Watterson's homozygosity test and the Tajima test) indicated that the population had developed under strong purifying selection pressure. The presence of strains clearly divergent from the majority of the population can be explained by in situ evolution or by influx of strains as a result of migration or both. Phytopathogenicity of a P. brassicacearum strain determined with tomato plants reached the level obtained with the type strain of the known pathogen Pseudomonas corrugata. The results show that a selective sweep was identified in a local population. Previously, a local selective sweep had not been seen in several populations of different bacterial species from a variety of environmental habitats. [source] Past success and convergent thinking in groups: The role of group-focused attributionsEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 4 2004Jack A. Goncalo Past success often causes groups to think narrowly around strategies that have worked in the past, even when environmental change has rendered these strategies ineffective. From a psychological perspective, this research seems to indicate that past success may give rise to convergent thinking in groups. Why might successful groups be prone to convergent thinking? I argue that the relationship between past success and convergent thinking may depend on the attributions that groups generate to explain their shared success. In this paper, I focus on two distinct attributions at the group level: Individual-focused attributions that reflect the idiosyncratic characteristics of individual group members and group-focused attributions that reflect the emergent properties of the group as a whole. I found that group-focused attributions for past success cause groups to generate fewer ideas that are, on average, more convergent. In contrast, individual-focused attributions cause groups to generate more ideas that are on average more divergent. These findings suggest that the experience of success may actually stimulate divergent thinking depending on how a group chooses to explain it. Copyright © 2004 John Wiley & Sons, Ltd. [source] COMPARATIVE GENOMIC AND POPULATION GENETIC ANALYSES INDICATE HIGHLY POROUS GENOMES AND HIGH LEVELS OF GENE FLOW BETWEEN DIVERGENT HELIANTHUS SPECIESEVOLUTION, Issue 8 2009Nolan C. Kane While speciation can be found in the presence of gene flow, it is not clear what impact this gene flow has on genome- and range-wide patterns of differentiation. Here we examine gene flow across the entire range of the common sunflower, H. annuus, its historically allopatric sister species H. argophyllus and a more distantly related, sympatric relative H. petiolaris. Analysis of genotypes at 26 microsatellite loci in 1015 individuals from across the range of the three species showed substantial introgression between geographically proximal populations of H. annuus and H. petiolaris, limited introgression between H. annuus and H. argophyllus, and essentially no gene flow between the allopatric pair, H. argophyllus and H. petiolaris. Analysis of sequence divergence levels among the three species in 1420 orthologs identified from EST databases identified a subset of loci showing extremely low divergence between H. annuus and H. petiolaris and extremely high divergence between the sister species H. annuus and H. argophyllus, consistent with introgression between H. annuus and H. petiolaris at these loci. Thus, at many loci, the allopatric sister species are more genetically divergent than the more distantly related sympatric species, which have exchanged genes across much of the genome while remaining morphologically and ecologically distinct. [source] RIVER CAPTURE, RANGE EXPANSION, AND CLADOGENESIS: THE GENETIC SIGNATURE OF FRESHWATER VICARIANCEEVOLUTION, Issue 5 2006C. P. Burridge Abstract River capture is potentially a key geomorphological driver of range expansion and cladogenesis in freshwater-limited taxa. While previous studies of freshwater fish, in particular, have indicated strong relationships between historical river connections and phylogeographic pattern, their analyses have been restricted to single taxa and geological hypotheses were typically constructed a posteriori. Here we assess the broader significance of river capture among taxa by testing multiple species for the genetic signature of a recent river capture event in New Zealand. During the Quaternary an upper tributary of the Clarence River system was diverted into the headwaters of the Wairau River catchment. Mitochondrial DNA (control region and cytochrome b) sequencing of two native galaxiid fishes (Galaxias vulgaris and Galaxias divergens) supports headwater exchange: populations from the Clarence and Wairau Rivers are closely related sister-groups, whereas samples from the geographically intermediate Awatere River are genetically divergent. The upland bully Gobiomorphus breviceps (Eleotridae), in contrast, lacks a genetic signature of the capture event. We hypothesize that there is an increased likelihood of observing genetic signatures from river capture events when they facilitate range expansion, as is inferred for the two galaxiid taxa studied here. When river capture merely translocates genetic lineages among established populations, by contrast, we suggest that the genetic signature of capture is less likely to be retained, as might be inferred for G. breviceps. Rates of molecular evolution calibrated against this recent event were elevated relative to traditional estimates, consistent with the contribution of polymorphisms to branch lengths at shallow phylogenetic levels prior to fixation by purifying selection and drift. [source] REPRODUCTIVE ISOLATION CAUSED BY NATURAL SELECTION AGAINST IMMIGRANTS FROM DIVERGENT HABITATSEVOLUTION, Issue 4 2005Patrik Nosil Abstract The classification of reproductive isolating barriers laid out by Dobzhansky and Mayr has motivated and structured decades of research on speciation. We argue, however, that this classification is incomplete and that the unique contributions of a major source of reproductive isolation have often been overlooked. Here, we describe reproductive barriers that derive from the reduced survival of immigrants upon reaching foreign habitats that are ecologically divergent from their native habitat. This selection against immigrants reduces encounters and thus mating opportunities between individuals from divergently adapted populations. It also reduces the likelihood that successfully mated immigrant females will survive long enough to produce their hybrid offspring. Thus, natural selection against immigrants results in distinctive elements of premating and postmating reproductive isolation that we hereby dub "immigrant inviability". We quantify the contributions of immigrant inviability to total reproductive isolation by examining study systems where multiple components of reproductive isolation have been measured and demonstrate that these contributions are frequently greater than those of traditionally recognized reproductive barriers. The relevance of immigrant inviability is further illustrated by a consideration of population-genetic theory, a review of selection against immigrant alleles in hybrid zone studies, and an examination of its participation in feedback loops that influence the evolution of additional reproductive barriers. Because some degree of immigrant inviability will commonly exist between populations that exhibit adaptive ecological divergence, we emphasize that these barriers play critical roles in ecological modes of speciation. We hope that the formal recognition of immigrant inviability and our demonstration of its evolutionary importance will stimulate more explicit empirical studies of its contributions to speciation. [source] POSTMATING SEXUAL SELECTION: ALLOPATRIC EVOLUTION OF SPERM COMPETITION MECHANISMS AND GENITAL MORPHOLOGY IN CALOPTERYGID DAMSELFLIES (INSECTA: ODONATA)EVOLUTION, Issue 2 2004A. Cordero Rivera Abstract Postmating sexual selection theory predicts that in allopatry reproductive traits diverge rapidly and that the resulting differentiation in these traits may lead to restrictions to gene flow between populations and, eventually, reproductive isolation. In this paper we explore the potential for this premise in a group of damselflies of the family Calopterygidae, in which postmating sexual mechanisms are especially well understood. Particularly, we tested if in allopatric populations the sperm competition mechanisms and genitalic traits involved in these mechanisms have indeed diverged as sexual selection theory predicts. We did so in two different steps. First, we compared the sperm competition mechanisms of two allopatric populations of Calopteryx haemorrhoidalis (one Italian population studied here and one Spanish population previously studied). Our results indicate that in both populations males are able to displace spermathecal sperm, but the mechanism used for sperm removal between both populations is strikingly different. In the Spanish population males seem to empty the spermathecae by stimulating females, whereas in the Italian population males physically remove sperm from the spermathecae. Both populations also exhibit differences in genital morphometry that explain the use of different mechanisms: the male lateral processes are narrower than the spermathecal ducts in the Italian population, which is the reverse in the Spanish population. The estimated degree of phenotypic differentiation between these populations based on the genitalic traits involved in sperm removal was much greater than the differentiation based on a set of other seven morphological variables, suggesting that strong directional postmating sexual selection is indeed the main evolutionary force behind the reproductive differentiation between the studied populations. In a second step, we examined if a similar pattern in genital morphometry emerge in allopatric populations of this and other three species of the same family (Calopteryx splendens, C. virgo and Hetaerina cruentata). Our results suggest that there is geographic variation in the sperm competition mechanisms in all four studied species. Furthermore, genitalic morphology was significantly divergent between populations within species even when different populations were using the same copulatory mechanism. These results can be explained by probable local coadaptation processes that have given rise to an ability or inability to reach and displace spermathecal sperm in different populations. This set of results provides the first direct evidence of intraspecific evolution of genitalic traits shaped by postmating sexual selection. [source] Novel ,-carboxyglutamic acid-containing peptides from the venom of Conus textileFEBS JOURNAL, Issue 12 2006Eva Czerwiec The cone snail is the only invertebrate system in which the vitamin K-dependent carboxylase (or ,-carboxylase) and its product ,-carboxyglutamic acid (Gla) have been identified. It remains the sole source of structural information of invertebrate ,-carboxylase substrates. Four novel Gla-containing peptides were purified from the venom of Conus textile and characterized using biochemical methods and mass spectrometry. The peptides Gla(1),TxVI, Gla(2),TxVI/A, Gla(2),TxVI/B and Gla(3),TxVI each have six Cys residues and belong to the O -superfamily of conotoxins. All four conopeptides contain 4- trans -hydroxyproline and the unusual amino acid 6- l -bromotryptophan. Gla(2),TxVI/A and Gla(2),TxVI/B are isoforms with an amidated C-terminus that differ at positions +1 and +13. Three isoforms of Gla(3),TxVI were observed that differ at position +7: Gla(3),TxVI, Glu7,Gla(3),TxVI and Asp7-Gla(3),TxVI. The cDNAs encoding the precursors of the four peptides were cloned. The predicted signal sequences (amino acids ,46 to ,27) were nearly identical and highly hydrophobic. The predicted propeptide region (,20 to ,1) that contains the ,-carboxylation recognition site (,-CRS) is very similar in Gla(2),TxVI/A, Gla(2),TxVI/B and Gla(3),TxVI, but is more divergent for Gla(1),TxVI. Kinetic studies utilizing the Conus,-carboxylase and synthetic peptide substrates localized the ,-CRS of Gla(1),TxVI to the region ,14 to ,1 of the polypeptide precursor: the Km was reduced from 1.8 mm for Gla (1),TxVI lacking a propeptide to 24 µm when a 14-residue propeptide was attached to the substrate. Similarly, addition of an 18-residue propeptide to Gla(2),TxVI/B reduced the Km value tenfold. [source] Nucleocytoplasmic protein traffic and its significance to cell functionGENES TO CELLS, Issue 10 2000Yoshihiro Yoneda In eukaryotic cells, cell functions are maintained in an orderly manner through the continuous traffic of various proteins between the cell nucleus and the cytoplasm. The nuclear import and export of proteins occurs through nuclear pore complexes and typically requires specific signals: the nuclear localization signal and nuclear export signal, respectively. The transport pathways have been found to be highly divergent, but are known to be largely mediated by importin ,-like transport receptor family molecules. These receptor molecules bind to and carry their cargoes directly or via adapter molecules. A small GTPase Ran ensures the directionality of nuclear transport by regulating the interaction between the receptors and their cargoes through its GTP/GDP cycle. Moreover, it has been recently elucidated how the transport system is involved in various functions of cell physiology, such as cell cycle control. [source] Longitudinal evaluation reveals a complex spectrum of virological profiles in hepatitis B virus/hepatitis C virus,coinfected patients,,HEPATOLOGY, Issue 1 2006Giovanni Raimondo Hepatitis B virus (HBV) and hepatitis C virus (HCV) coinfection is often associated with severe forms of liver disease. However, comprehensive studies are lacking, and scant information is available regarding the virological behavior over time in coinfected patients. This study enrolled 133 untreated HBV/HCV-positive patients (male/female = 102/31; median age 51 years [range: 22-83 years]) who were longitudinally followed up for 1 year with bimonthly evaluation of HBV/HCV viremia levels and liver biochemistry. Thirty of these patients had triple infection with hepatitis Delta virus (HDV), while 103 patients were HDV-negative. In the HDV-negative group, active infection with both HBV and HCV was revealed in 24 cases, inactive infection by both viruses was seen in 15 cases, active HBV/inactive HCV was seen in 15 cases, and inactive HBV/active HCV was seen in 49 cases. However, 32 subjects (31%) presented dynamic virological profiles characterized by fluctuation of HBV and/or HCV viremia levels that at different time points were over or under the cutoff limits. Consequently, a correct diagnosis could be performed in these subjects only by serially repeating the virological tests 1 year apart. Similarly, 15 of the 30 HDV-positive subjects showed active HBV and/or HCV infection, with fluctuating virological patterns in 8 cases. In conclusion, this study showed that the virological patterns in HBV/HCV coinfection are widely divergent and have dynamic profiles. A careful longitudinal evaluation of the viremia levels of both viruses is essential for making a correct diagnosis and tailoring the appropriate therapeutic schedule in coinfected patients. (HEPATOLOGY 2005.) [source] A mouse model for cystic biliary dysgenesis in autosomal recessive polycystic kidney disease (ARPKD),HEPATOLOGY, Issue 5 2005Markus Moser Autosomal recessive polycystic kidney disease (ARPKD) is an important cause of liver- and renal-related morbidity and mortality in childhood. Recently, PKHD1, the gene encoding the transmembrane protein polyductin, was shown to be mutated in ARPKD patients. We here describe the first mouse strain, generated by targeted mutation of Pkhd1. Due to exon skipping, Pkhd1ex40 mice express a modified Pkhd1 transcript and develop severe malformations of intrahepatic bile ducts. Cholangiocytes maintain a proliferative phenotype and continuously synthesize TGF-,1. Subsequently, mesenchymal cells within the hepatic portal tracts continue to synthesize collagen, resulting in progressive portal fibrosis and portal hypertension. Fibrosis did not involve the hepatic lobules, and we did not observe any pathological changes in morphology or function of hepatocytes. Surprisingly and in contrast to human ARPKD individuals, Pkhd1ex40 mice develop morphologically and functionally normal kidneys. In conclusion,our data indicate that subsequent to formation of the embryonic ductal plate, dysgenesis of terminally differentiated bile ducts occurs in response to the Pkhd1ex40 mutation. The role of polyductin in liver and kidney may be functionally divergent, because protein domains essential for bile duct development do not affect nephrogenesis in our mouse model. Supplementary material for this article can be found on the HEPATOLOGYwebsite (http://www.interscience.wiley.com/jpages/0270-9139/suppmat/index.html). (HEPATOLOGY 2005.) [source] Geomorphic controls and transition zones in the lower Sabine RiverHYDROLOGICAL PROCESSES, Issue 14 2008Jonathan D. Phillips Abstract Instream flow science and management requires identification of characteristic hydrological, ecological, and geomorphological attributes of stream reaches. This study approaches this problem by identifying geomorphic transition zones along the lower Sabine River, Texas and Louisiana. Boundaries were delineated along the lower Sabine River valley based on surficial geology, valley width, valley confinement, network characteristics (divergent versus convergent), sinuousity, slope, paleomeanders, and point bars. The coincidence of multiple boundaries reveals five key transition zones separating six reaches of distinct hydrological and geomorphological characteristics. Geologic controls and gross valley morphology play a major role as geomorphic controls, as does an upstream-to-downstream gradient in the importance of pulsed dam releases, and a down-to-upstream gradient in coastal backwater effects. Geomorphic history, both in the sense of the legacy of Quaternary sea level changes, and the effects of specific events such as avulsions and captures, are also critical. The transition zones delineate reaches with distinct hydrological characteristics in terms of the relative importance of dam releases and coastal backwater effects, single versus multi-channel flow patterns, frequency of overbank flow, and channel-floodplain connectivity. The transitional areas also represent sensitive zones which can be expected to be bellwethers in terms of responses to future environmental changes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Regulatory T cells and intestinal homeostasisIMMUNOLOGICAL REVIEWS, Issue 1 2005Janine L. Coombes Summary:, Murine models of inflammatory bowel disease (IBD) are useful tools for the study of the pathogenesis and regulation of intestinal inflammation. Colitis can be induced in immune-deficient mice following transfer of populations of T cells or following infection with Helicobacter hepaticus and other intestinal pathogens. In these situations, colitis occurs as a result of the absence of a specialized population of regulatory cells, as transfer of CD4+CD25+ T cells prevents disease. Importantly, from a clinical perspective, CD4+CD25+ T cells can also reverse an established colitis. CD4+CD25+ T cells proliferate both in the secondary lymphoid organs and at the site of inflammation, suggesting that regulation occurs both locally and systemically. CD4+CD25+ T cells are not only capable of regulating other T cells but are also capable of suppressing components of the innate immune system. Control of colitis is dependent on the presence of the immunosuppressive cytokines interleukin-10 and transforming growth factor-,, although their roles are divergent and complex. Regulatory T cells represent one of the host's mechanisms to prevent immune pathology during chronic immune stimulation. Enhancement of regulatory T-cell activity may be useful to control autoreactive T-cell responses and inhibit harmful inflammatory diseases such as asthma and IBD. [source] Do functional subsets of leukocytes arise by divergent or linear differentiation?IMMUNOLOGY, Issue 4 2002Alistair Noble Summary The T helper type 1 (Th1)/Th2 paradigm has been extended to a wide variety of leukocyte lineages since its inception, including innate immune cells such as dendritic cells and natural killer (NK) cells. Recently, studies of human NK cells have led to the proposition of a new model of linear differentiation in which cell phenotype is controlled by regulation of proliferation versus differentiation, rather than by divergent differentiation programmes. It was suggested that this model might also apply to T cells. Here we discuss the relevance of each model to different leukocyte lineages and argue that the linear differentiation model does not apply to ,, T cells. [source] Accuracy of reported weight and menstrual status in teenage girls with eating disordersINTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 4 2005Ingemar Swenne MD Abstract Objective The current study investigated the accuracy of reported current and historical weights and of menstrual status in teenage girls with eating disorders. Method Reported current weight in one interview was compared with measured weight at another occasion. Reported historical weights were compared with documented weights from growth charts of the school health services. Reports of menstrual status from two different interviews were compared. Results The overall correlation between reported and measured/documented weight was high. Current weight was reported with high accuracy in all diagnostic groups and without tendencies to underreport. Patients with bulimia nervosa, but not those with anorexia nervosa, underreported their historical top weight. The most common reason for large discrepancies between reported and documented historical weights was that the two weights compared referred to different time points. The reports on menstrual status were divergent for 13% of the patients, most notably 4 of 15 patients on oral contraceptives had been categorized as having menstruations in one of the interviews. Conclusion Reported weight history and menstrual status are of high accuracy in teenage girls with eating disorders. © 2005 by Wiley Periodicals, Inc. [source] Cloning and sequencing of Indian water buffalo interleukin-18 cDNAINTERNATIONAL JOURNAL OF IMMUNOGENETICS, Issue 2 2005P. Chaudhury Summary Full-length cDNA (582 bp) of the interleukin-18 (IL-18) gene of the Indian water buffalo (Bubalus bubalis) was amplified by reverse transcriptase,polymerase chain reaction (RT-PCR) and sequenced. The deduced amino acid sequence has 99% and 95% similarity with the IL-18 sequences of cattle and sheep, respectively. There are two amino acid substitutions at positions 132 and 182 in buffalo IL-18 compared with that of cattle. Phylogenetic analysis showed that the IL-18 sequence of fish forms a different lineage and is most divergent from that of cattle, buffalo, sheep, pig, dog, horse, human, monkey, mouse, rat and chicken. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||