Home About us Contact
|
Home About us Contact | ||
|
|
||
Structuring
Kinds of Structuring Terms modified by Structuring Selected AbstractsPast Times: Temporal Structuring of History and MemoryETHOS, Issue 2 2006Kevin Birth In On Collective Memory, Maurice Halbwachs asks, "Why does society establish landmarks in time that are placed close together,and usually in a very irregular manner, since for certain periods they are almost entirely lacking,whereas around such salient events sometimes many other equally salient events seem to gather, just as street signs and other signposts multiply as a tourist attraction approaches?" (1992:175). The recognition of the "irregular manner" of history and memory only emerges in contrast to a concept of the regularity of time implied by objectifying chronologies. Furthermore, such irregularity suggests that concepts of time other than chronology are crucial for understanding representations of the past, and experiences of the past in the present. This article draws on nondirected interviews conducted in rural Trinidad in which subjects discussed significant events in their lives. In examining this material, I address Halbwachs's question by emphasizing nonchronological, cultural models of time that organize autobiographical narratives. These cultural models position autobiographical narratives in space and connect them to events of historical significance. [time, memory, intersubjectivity, labor, Trinidad] [source] Direct Laser Interference Structuring as a Tool to Gradually Tune the Wetting Response of Titanium and Polyimide SurfacesADVANCED ENGINEERING MATERIALS, Issue 10 2009Michael Hans Direct laser interference structuring has been used for topographical surface design on titanium and polyimide. The wetting response of processed materials showed a roughness-dependant increase in contact angle starting at initially hydrophilic conditions. [source] Silica-Based, Organically Modified Host Material for Waveguide Structuring by Two-Photon-Induced PhotopolymerizationADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Stefan Krivec Abstract The three-dimensional fabrication of optical waveguides has gained increasing interest in recent years to establish interconnections between electrical components on a very small scale where copper circuits encounter severe limitations. In this work the application of optically clear, organically modified porous silica monoliths and thin films as a host material for polymeric waveguides to be inscribed into the solid host structure by two-photon-induced photopolymerization is investigated. Porosity is generated using a lyotropic liquid crystalline surfactant/solvent system as a template for the solid silica material obtained by a sol,gel transition of a liquid precursor. In order to reduce the brittleness of the purely inorganic material, organic,inorganic co-precursor molecules that contain poly(ethylene glycol) chains are synthesized and added to the mixture, which successfully suppresses macroscopic cracking and leads to flexible thin films. The structure of the thus-obtained porous organic,inorganic hybrid material is investigated by atomic force microscopy. It is shown that the modified material is suitable for infiltration with photocurable monomers and functional polymeric waveguides can be inscribed by selective two-photon-induced photopolymerization. [source] Nanoscale Structuring and InvestigationIMAGING & MICROSCOPY (ELECTRONIC), Issue 4 2006Crossbeam Tool with Ultra High Resolution FIB Technology Recent developments in nano- and semiconductor technology have substantially increased the demand for accurate and efficient site specific cross-sectioning of specimens and preparation of TEM samples. Moreover, nano-research is facing new challenges for manipulation, observation, and modification of devices on a submicron scale. [source] Earnings Management through Transaction Structuring: Contingent Convertible Debt and Diluted Earnings per ShareJOURNAL OF ACCOUNTING RESEARCH, Issue 2 2005CAROL MARQUARDT ABSTRACT In this article we examine whether firms structure their convertible bond transactions to manage diluted earnings per share (EPS). We find that the likelihood of firms issuing contingent convertible bonds (COCOs), which are often excluded from diluted EPS calculations under Statement of Financial Accounting Standard (SFAS) 128, is significantly associated with the reduction that would occur in diluted EPS if the bonds were traditionally structured. We also document that firms' use of EPS-based compensation contracts significantly affects the likelihood of COCO issuance and find weak evidence that reputation costs, measured using earnings restatement data, play a role in the structuring decision. These results are robust to controlling for alternative motivations for issuing COCOs, including tax and dilution arguments. In addition, an examination of announcement returns reveals that investors view the net benefits and costs of COCOs as offsetting one another. Our results contribute to the literature on earnings management, diluted EPS, financial reporting costs, and financial innovation. [source] Structuring of genetic diversity in Albizia gummifera C.A.Sm. among some East African and Madagascan populationsAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Judith Ssali Nantongo No abstract is available for this article. [source] Formation of Nanostructures in Multi Component Systems Based on Organic Polymer and Coordination Metal CompoundMACROMOLECULAR SYMPOSIA, Issue 1 2006Nataly Kozak Abstract Structuring of polyurethane (PU) networks is analyzed under influence of transition metal coordination compounds: mono-ionic ,-diketonates and polyheteronuclear metal-organic complexes. Formed in situ nanostructures both organic and inorganic were found in organic polymer modified with coordination metal compound. Influence of coordination junction point spatial symmetry and content of metal ion in modifier on structure and dielectric characteristics of modified PUs is analyzed using X-ray, EPR, SEM and transmission optical microscopy, DRS and DSC methods. [source] Genetic structure among closely spaced leks in a peripheral population of lesser prairie-chickensMOLECULAR ECOLOGY, Issue 2 2004Juan L. Bouzat Abstract We evaluated the genetic structure of birds from four closely spaced leks in a peripheral population of lesser prairie-chickens (Tympanuchus pallidicinctus). Analyses of molecular variance revealed significant genetic structuring among birds from different leks for six microsatellite loci (FST = 0.036; P = 0.002), but we found no genetic differentiation at the mtDNA control region. Significant deviations from Hardy,Weinberg revealed an excess of homozygote genotypes within each of the leks studied (FIS = 0.190,0.307), indicative of increased inbreeding. Estimates of relatedness using microsatellite data suggest that the genetic structuring among lesser prairie-chicken leks occurs in part because of a lek mating system in which males at some leks are related. Structuring may also be caused by stochastic effects associated with a historical decline in population size leading to small, semi-isolated leks and high site fidelity by reproductive males. Results from this study suggest that microspatial genetic structuring may occur in lek-mating bird species with low levels of dispersal. [source] A Strategic Planning Process for a Small Nonprofit Organization: A Hospice ExampleNONPROFIT MANAGEMENT & LEADERSHIP, Issue 2 2000Cynthia Massie Mara Strategic planning is an essential part of management. However, planning processes can consume great amounts of time and resources that small, nonprofit organizations may lack. Moreover, the process that is used can be tedious and may result in plans that are discarded before or during their implementation. In this article, a strategic planning process is presented that incorporates a Policy Delphi group technique and Situation Structuring, a computer program that assists participants in structuring or defining the problems to be addressed in the plan. The organization to which the process is applied is a small, nonprofit hospice. Both the planning process and an evaluation of the implementation of the resultant strategic plan are examined. [source] Wealth Effects of Diversification and Financial Deal Structuring: Evidence from REIT Property Portfolio AcquisitionsREAL ESTATE ECONOMICS, Issue 3 2003Robert D. Campbell This study examines the strategic characteristics and shareholder wealth effects of a popular vehicle for Real Estate Investment Trust growth in the 1990s: the acquisition of a portfolio of properties from a single seller. We examine a sample of 209 REIT portfolio acquisitions during 1995-2001. We observe a wide variety of financing strategies and find an array of different categories of sellers. Contrary to results reported in real estate transactions of this sort in the past, we find that announcement-period shareholder returns are significantly positive in the aggregate. We present evidence that excess returns to acquirers result from (1) wealth benefits received when companies reconfirm their geographical focus in the acquisition, (2) positive information conveyed by the use of project-specific private debt and (3) a positive signal sent to the market when transactions are financed by stock privately placed with financial institutions. [source] Lack of Genetic Structuring among Tropical Brazilian Wood Stork Populations and Low Genetic Differentiation from North American PopulationsBIOTROPICA, Issue 2 2004Cristiano Dosualdo Rocha ABSTRACT The Wood Stork (Mycteria americana) is a wading bird inhabiting subtropical and tropical regions of the American continent. This species is considered endangered in the United States. We compared variability and genetic structuring of nine Brazilian Pantanal subpopulations with an North American population using eight allozyme loci data (MPI, ICD, NSP, EST-D, LDH, PGM, 6PGD, and PEP-A) and four microsatellite loci data (WS1, WS2, WS4, and WS6). Average expected heterozygosity of Pantanal population was similar (0.198 ± 0.065) to that expected for the North American population (0.231 ± 0.066). No significant genetic differentiation was found among Pantanal subpopulations (Fst= 0.012) and low differentiation was detected between Pantanal and North American populations (Fst= 0.023). Lack of differentiation among Pantanal subpopulations may have been due to high gene flow level among birds of neighbor breeding colonies and low natal philopatry. We propose that low differentiation between North and South American populations has arisen either because these populations occupied neighboring regions during late glaciation or because there is a continuous gene flow between them, via Central American or northern South American populations. RESUMO O Cabeça-seca (Mycteria americana) é uma ave aquática habitante das regiões tropicais e subtropicais do continente americano. Essa espécie está ameaçada de extinção nos Estados Unidos. Nós comparamos a variabilidade e a estruturação genética de nove subpopulações brasileiras do Pantanal com as da população norte americana, baseando-se em dados de oito locos alozímicos (MPI, ICD, NSP, EST-D, LDH, PGM, 6PGD, e PEP-A) e em dados de quatro locos de microssatélites (WS1, WS2, WS4, e WS6). A heterozigosidade média esperada para a população do Pantanal (0.198 ± 0.065) foi semelhante á esperada para a população norte americana (0.231 ± 0.066). Não foi encontrada diferenciação genética significativa entre as subpopulaçóes do Pantanal (Fst= 0.012) e baixa diferenciação genética foi detectada entre as populações do Pantanal e a norte americana (.Fst= 0.023). A não diferenciação entre subpopulações do Pantanal pode ser resultante de um alto nível do fluxo génico entre aves de colónias reprodutivas vizinhas e da baixa filopatria natal. Nós propomos que a baixa diferenciação entre as populações norte e sul americanas seja decorrente da ocupaçaTo de regiões vizinhas por essas populações durante a última glaciação ou devido á existéncia de fluxo contínue entre elas, via populações da América Central ou do norte da América do Sul. [source] Risky Business: Economic Uncertainty, Market Reforms and Female Livelihoods in Northeast GhanaDEVELOPMENT AND CHANGE, Issue 5 2000Brenda Chalfin This article examines the implications of economic uncertainty for rural markets and the livelihoods of female traders. It does so through a case study of a community in northern Ghana caught in the throes of a structural adjustment-driven privatization initiative. In order to fully comprehend the nature of the economic uncertainties in which rural economic actors are enmeshed and the manner in which they resist, engage or engender these conditions, two theoretical lenses are interposed. One, focusing on structural dissolution and an overall process of rural, and especially female, disempowerment, is drawn from recent approaches to African political economy. The other, gleaned from the field of economic anthropology, attends to the agency and knowledge of rural entrepreneurs in the face of unstable and imperfect market conditions. By bringing together these different analytic traditions, the critical significance of uncertainty within the complex process of rural economic transformation and reproduction becomes evident. Rather than functioning as a diagnostic of economic crisis and insecurity, uncertainty can be a strategic resource integral to the constitution of markets, livelihoods and economic coalitions. Such a perspective, privileging the institutional potentials of local social practice, makes apparent the forceful role played by female traders in the structuring of rural marketing systems even in the face of externally-induced and sometimes dramatic shifts in material conditions. [source] A prime inference on genetic diversity (RAPDs) in the marine fish Atherinella brasiliensis (Teleostei, Atherinopsidae) from Southern BrazilACTA ZOOLOGICA, Issue 2 2010Maria Cristina Da Silva Cortinhas Abstract Da Silva Cortinhas, M. C., Glienke, C., Prioli, A. J., Noleto, R. B., Matoso, D. A. and Cestari, M. M. 2010. A prime inference on genetic diversity (RAPDs) in the marine fish Atherinella brasiliensis (Teleostei, Atherinopsidae) from Southern Brazil. ,Acta Zoologica (Stockholm) 91: 242,248 As a result of the importance of Atherinella brasiliensis in estuarine environments, random amplified polymorphic DNA (RAPD) markers were used to verify the genetic diversity in A. brasiliensis from two different places in Paranaguá Bay (Paraná State) and one from the Conceição Lagoon (Santa Catarina State). Cytogenetic data have shown a high karyotypic diversity in some populations, although in others this peculiarity demonstrates rearrangements such as heterochromatinization. In the present study, a low level of genetic structuring between the samples from Conceição Lagoon compared with the others was observed through principal coordinate analysis (PCO), analysis of molecular variance and Mantel test according to 79 RAPD markers. As this specie does not perform horizontal migration and the individuals of Conceição Lagoon are isolated, three hypotheses are proposed to explain the results: (i) similar environments may show homogeneous populations not depending on the geographical distance, (ii) because vicariant events that formed the bays occurred in a recent period, the fragmentation effects over the structuring of the genetic diversity may still be low and not totally detectable by the RAPD technique and (iii) the isolation time or the number of generations may not be enough to promote a possible differentiation and genetic structuring between the specimens of these three places. The specimens of these places present a low level of differentiation and genetic structuring so we can consider them as a unique homogeneous population. [source] Invasive species of Heracleum in Europe: an insight into genetic relationships and invasion historyDIVERSITY AND DISTRIBUTIONS, Issue 1 2007árka Jahodová ABSTRACT Several species of the genus Heracleum (Umbelliferae) were introduced into Europe from south-west Asia in the 19th century and are now widespread in many countries. At least three invasive taxa with unresolved relationships to one another are thought to occur in Europe: Heracleum mantegazzianum Sommier & Levier, H. sosnowskyi Manden, and H. persicum Desf. ex Fischer. They are tall plants forming extensive stands with a high cover. To elucidate genetic relationships between the species, and gain insight into their invasion history, samples were collected from native ranges in Asia and invaded ranges of the three species in Europe and analysed using amplified fragment length polymorphism. Five other Heracleum species were also studied and in total, 189 samples from 72 populations were analysed. The results confirmed that there are three distinct tall Heracleum species invading in Europe. Within each of the three species, plants collected in the invaded range are genetically close to those from their native ranges. A close genetic relationship between the three invasive Heracleum species in Europe was also found. A high overall genetic variability detected in the invaded range suggests that the majority of invading populations were not affected by a genetic bottleneck and that rapid evolution, drift, or hybridization played a role in genetic structuring of invading populations. For H. mantegazzianum, genetic distance of populations in the native range significantly decreased with geographical distance, but not in the invaded range. It is likely that the current pattern of genetic diversity in Europe resulted from multiple introductions of all three species. [source] Opposite shell-coiling morphs of the tropical land snail Amphidromus martensi show no spatial-scale effectsECOGRAPHY, Issue 4 2006Paul G. Craze Much can be learned about evolution from the identification of those factors maintaining polymorphisms in natural populations. One polymorphism that is only partially understood occurs in land snail species where individuals may coil clockwise or anti-clockwise. Theory shows that polymorphism in coiling direction should not persist yet species in several unrelated groups of land snails occur in stably polymorphic populations. A solution to this paradox may advance our understanding of evolution in general. Here, we examine two possible explanations: firstly, negative frequency-dependent selection due to predation; secondly, random fixation of alternative coiling morphs in tree-sized demes, giving the impression of wider polymorphism. We test these hypotheses by investigating morph-clustering of empty shells at two spatial scales in Amphidromus martensi populations in northern Borneo: the spatial structure of snail populations is relatively easy to estimate and this information may support one or other of the hypotheses under test. For the smaller scale we make novel use of a statistic previously used in botanical studies (the K-function statistic), which allows clustering of more than one morph to be simultaneously investigated at a range of scales and which we have corrected for anisotropy. We believe this method could be of more general use to ecologists. The results show that consistent clustering or separation of morphs cannot be clearly detected at any spatial scale and that predation is not frequency-dependent. Alternative explanations that do not require strong spatial structuring of the population may be needed, for instance ones involving a mechanism of selection actively maintaining the polymorphism. [source] Comparison of Different Strategies on DNA Chip Fabrication and DNA-Sensing: Optical and Electrochemical ApproachesELECTROANALYSIS, Issue 22 2005Sabine Szunerits Abstract New strategies for the construction of DNA chips and the detection of DNA hybridization will be discussed in this review. The focus will be on the use of polypyrrole as a linker between a substrate and oligonucleotide probes. The modification step is based on the electrochemical copolymerization of pyrrole and oligonucleotides bearing a pyrrole group on its 5, end. This strategy was employed for the immobilization of oligonucleotides on millimeter-sized electrodes, microelectrode arrays, as well as for the local structuring of homogeneous gold surfaces. Our approaches for the localized patterning of gold surfaces will be also discussed. Localized immobilization was achieved by using an electrospotting technique, where a micropipette served as an electrochemical cell where spot sizes with 800,,m diameters were fabricated. The use of a microcell using a Teflon covered metal needle with a cavity of 100,,m resulted in immobilized probe spots of 300,,m. Scanning electrochemical microscopy (SECM) was also used, and surface modifications of 100,,m were obtained depending on the experimental conditions. Different detection methods were employed for the reading of the hybridization event: fluorescence imaging, surface plasmon resonance imaging (SPRI), photocurrent measurements, and voltamperometric measurements using intercalators. Their advantages concerning the various immobilization strategies will also be discussed. [source] Effects of environmental pollution on microsatellite DNA diversity in wood mouse (Apodemus sylvaticus) populationsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2005Veerle Berckmoes Abstract Ten microsatellite DNA loci were surveyed to investigate the effects of heavy metal pollution on the genetic diversity and population genetic structure of seven wood mouse (Apodemus sylvaticus) populations along a heavy metal pollution gradient away from a nonferrous smelter in the south of Antwerp (Flanders, Belgium). Analysis of soil heavy metal concentrations showed that soil Ag, As, Cd, Cu, and Pb decreased with increasing distance from the smelter. Genetic analyses revealed high levels of genetic variation in all populations, but populations from the most polluted sites in the gradient did not differ from those of less-polluted sites in terms of mean observed and expected heterozygosity level and mean allelic richness. No correlation was found between measures of genetic diversity and the degree of heavy metal pollution. However, an analysis of molecular variance and a neighbor-joining tree suggested a contamination-related pattern of genetic structuring between the most polluted and less polluted sites. Pairwise FST values indicated that populations were significantly genetically differentiated, and assignment tests and direct estimates of recent migration rates suggested restricted gene flow among populations. Additionally, genetic differentiation increased significantly with geographical distance, which is consistent with an isolation-by-distance model. We conclude that, at least for our microsatellite DNA markers, genetic diversity in the studied wood mouse populations is not affected greatly by the heavy metal pollution. [source] Structured Looseness: Everyday Social Order at an Israeli KindergartenETHOS, Issue 3 2006Deborah Golden In this article, I address notions of social order as these are conveyed to young children in an early education setting. On the basis of an ethnographic account of an Israeli kindergarten, I describe the routine structuring of everyday life at the kindergarten, as well as the ways in which this routine structuring was consistently undermined, primarily by the teacher herself. Specifically, the study shows how the relatively enfeebled routine structuring of daily life facilitated the emergence of alternative models of social order, namely, collective order and personal order embodied by the teacher. The interplay of structure and looseness discerned at the kindergarten is addressed in terms of the institutional distinctiveness of early education settings, as well as with reference to the Israeli sociocultural context. It is suggested that the study of the organization of daily life in early education settings may enrich our understanding of socialization into enduring perceptions of social order and of the sources of its legitimacy. [education, classroom ethnography, children, Israel, kindergarten] [source] Phase Reversion-Induced Nanograined/Ultrafine-Grained Structures in Austenitic Stainless Steel and their Significance in Modulating Cellular Response: Biochemical and Morphological Study with Fibroblasts,ADVANCED ENGINEERING MATERIALS, Issue 12 2009R. Devesh Kumar Misra Materials science, engineering, and biological sciences have been combined to improve the tissue compatibility of medical devices. In this regard, nano/ultrafine structuring of austenitic stainless steel obtained using an innovative approach of "phase-reversion" has been evaluated for modulation of cellular activity. The biochemical and morphology study with fibroblasts point toward the improvement of tissue compatibility on comparison with coarse-grained structures, strengthening the foundation of nanostructured materials for bio-medical applications. [source] Direct Laser Interference Structuring as a Tool to Gradually Tune the Wetting Response of Titanium and Polyimide SurfacesADVANCED ENGINEERING MATERIALS, Issue 10 2009Michael Hans Direct laser interference structuring has been used for topographical surface design on titanium and polyimide. The wetting response of processed materials showed a roughness-dependant increase in contact angle starting at initially hydrophilic conditions. [source] ESTIMATING A GEOGRAPHICALLY EXPLICIT MODEL OF POPULATION DIVERGENCEEVOLUTION, Issue 3 2007L. Lacey Knowles Patterns of genetic variation can provide valuable insights for deciphering the relative roles of different evolutionary processes in species differentiation. However, population-genetic models for studying divergence in geographically structured species are generally lacking. Since these are the biogeographic settings where genetic drift is expected to predominate, not only are population-genetic tests of hypotheses in geographically structured species constrained, but generalizations about the evolutionary processes that promote species divergence may also be potentially biased. Here we estimate a population-divergence model in montane grasshoppers from the sky islands of the Rocky Mountains. Because this region was directly impacted by Pleistocene glaciation, both the displacement into glacial refugia and recolonization of montane habitats may contribute to differentiation. Building on the tradition of using information from the genealogical relationships of alleles to infer the geography of divergence, here the additional consideration of the process of gene-lineage sorting is used to obtain a quantitative estimate of population relationships and historical associations (i.e., a population tree) from the gene trees of five anonymous nuclear loci and one mitochondrial locus in the broadly distributed species Melanoplus oregonensis. Three different approaches are used to estimate a model of population divergence; this comparison allows us to evaluate specific methodological assumptions that influence the estimated history of divergence. A model of population divergence was identified that significantly fits the data better compared to the other approaches, based on per-site likelihood scores of the multiple loci, and that provides clues about how divergence proceeded in M. oregonensis during the dynamic Pleistocene. Unlike the approaches that either considered only the most recent coalescence (i.e., information from a single individual per population) or did not consider the pattern of coalescence in the gene genealogies, the population-divergence model that best fits the data was estimated by considering the pattern of gene lineage coalescence across multiple individuals, as well as loci. These results indicate that sampling of multiple individuals per population is critical to obtaining an accurate estimate of the history of divergence so that the signal of common ancestry can be separated from the confounding influence of gene flow,even though estimates suggest that gene flow is not a predominant factor structuring patterns of genetic variation across these sky island populations. They also suggest that the gene genealogies contain information about population relationships, despite the lack of complete sorting of gene lineages. What emerges from the analyses is a model of population divergence that incorporates both contemporary distributions and historical associations, and shows a latitudinal and regional structuring of populations reminiscent of population displacements into multiple glacial refugia. Because the population-divergence model itself is built upon the specific events shaping the history of M. oregonensis, it provides a framework for estimating additional population-genetic parameters relevant to understanding the processes governing differentiation in geographically structured species and avoids the problems of relying on overly simplified and inaccurate divergence models. The utility of these approaches, as well as the caveats and future improvements, for estimating population relationships and historical associations relevant to genetic analyses of geographically structured species are discussed. [source] ISOLATION BY DISTANCE IN EQUILIBRIUM AND NONEQUILIBRIUM POPULATIONS OF FOUR TALITRID SPECIES IN THE MEDITERRANEAN SEAEVOLUTION, Issue 5 2000Elvira De Matthaeis Abstract Allozymic variation at 21,23 loci was studied in 28 populations of Talitrus saltator, 23 populations of Orchestia montagui, 13 populations of O. stephenseni, and five populations of Platorchestia platensis from the Mediterranean Basin. Different levels of gene flow (Nm,) were detected within each species at the scale of the whole Mediterranean: O. montagui and P. platensis had low population structure, with levels of Nm, 1, whereas the T. saltator and O. stephenseni populations have values of Nm, < 1. The relationship between Nm, and geographic distance was analyzed to test for the presence of an isolation by distance pattern in the spatial genetic variation within each species. A model of isolation by distance is useful to describe the pattern of genetic structuring of study species at the scale of the whole Mediterranean: geographic distance explained from 28% to 70% of the variation in gene flow. In the Aegean area all species showed an island model of genetic structuring regardless of the levels of gene flow. [source] FREQUENCY AND SPATIAL PATTERNING OF CLONAL REPRODUCTION IN LOUISIANA IRIS HYBRID POPULATIONSEVOLUTION, Issue 1 2000John M. Burke Abstract., The plant genera in which natural hybridization is most prevalent tend to be outcrossing perennials with some mechanism for clonal (i.e., asexual) reproduction. Although clonal reproduction in fertile, sexually reproducing hybrid populations could have important evolutionary consequences, little attention has been paid to quantifying this parameter in such populations. In the present study, we examined the frequency and spatial patterning of clonal reproduction in two Louisiana iris hybrid populations. Allozyme analysis of both populations revealed relatively high levels of genotypic diversity. However, a considerable amount of clonality was apparent. Nearly half of all genets (47%) in one population and more than half (61%) in the other had multiple ramets. Furthermore, both populations exhibited relatively high levels of genetic structuring, a pattern that resulted from the aggregation of clonal ramets. The occurrence of clonal reproduction in hybrid populations could not only facilitate introgression through an increase in the number of flowering ramets per genet and/or the survivorship of early generation hybrids, but might also influence the mating system of such populations. Any potential increase in the selfing rate due to cross-pollination among ramets of the same genet may, in turn, increase the likelihood of homoploid hybrid speciation. [source] The crystal structure of pyruvate decarboxylase from Kluyveromyces lactisFEBS JOURNAL, Issue 18 2006Implications for the substrate activation mechanism of this enzyme The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis has been determined to 2.26 Å resolution. Like other yeast enzymes, Kluyveromyces lactis pyruvate decarboxylase is subject to allosteric substrate activation. Binding of substrate at a regulatory site induces catalytic activity. This process is accompanied by conformational changes and subunit rearrangements. In the nonactivated form of the corresponding enzyme from Saccharomyces cerevisiae, all active sites are solvent accessible due to the high flexibility of loop regions 106,113 and 292,301. The binding of the activator pyruvamide arrests these loops. Consequently, two of four active sites become closed. In Kluyveromyces lactis pyruvate decarboxylase, this half-side closed tetramer is present even without any activator. However, one of the loops (residues 105,113), which are flexible in nonactivated Saccharomyces cerevisiae pyruvate decarboxylase, remains flexible. Even though the tetramer assemblies of both enzyme species are different in the absence of activating agents, their substrate activation kinetics are similar. This implies an equilibrium between the open and the half-side closed state of yeast pyruvate decarboxylase tetramers. The completely open enzyme state is favoured for Saccharomyces cerevisiae pyruvate decarboxylase, whereas the half-side closed form is predominant for Kluyveromyces lactis pyruvate decarboxylase. Consequently, the structuring of the flexible loop region 105,113 seems to be the crucial step during the substrate activation process of Kluyveromyces lactis pyruvate decarboxylase. [source] Paradigm shifts in marine fisheries genetics: ugly hypotheses slain by beautiful factsFISH AND FISHERIES, Issue 4 2008Lorenz Hauser Abstract By providing new approaches to the investigation of demographic and evolutionary dynamics of wild populations, molecular genetics has led to fundamental changes in our understanding of marine ecology. In particular, genetic approaches have revolutionized our understanding in three areas: (i) most importantly, they have contributed to the discovery of extensive genetic population structure in many marine species, overturning the notion of large, essentially homogenous marine populations limiting local adaptation and speciation. (ii) Concomitant differences in ecologically important traits now indicate extensive adaptive differentiation and biocomplexity, potentially increasing the resilience to exploitation and disturbance. Evidence for rapid adaptive change in many populations underlies recent concerns about fisheries-induced evolution affecting life-history traits. (iii) A compilation of recent published research shows estimated effective population sizes that are 2,6 orders of magnitude smaller than census sizes, suggesting more complex recruitment dynamics in marine species than previously assumed. Studies on Atlantic cod are used to illustrate these paradigm shifts. In our synthesis, we emphasize the implications of these discoveries for marine ecology and evolution as well as the management and conservation of exploited marine fish populations. An important implication of genetic structuring and the potential for adaptive divergence is that locally adapted populations are unlikely to be replaced through immigration, with potentially detrimental consequences for the resilience to environmental change , a key consideration for sustainable fisheries management. [source] Age-related movement patterns and population structuring in southern garfish, Hyporhamphus melanochir, inferred from otolith chemistryFISHERIES MANAGEMENT & ECOLOGY, Issue 4 2009M. A. STEER Abstract, The southern garfish, Hyporhamphus melanochir (Val.), is an important inshore fishery species in South Australia. Over the past few years there have been concerns with this fishery, which is now considered to be over-exploited. Currently, the fishery is assumed to consist of two separate stocks, but there is no understanding of movement patterns both within and between these two stocks to justify this assumption. Otolith chemistry was used to infer age-related patterns of movement, delineate potential sub-populations and determine the extent of mixing within South Australian coastal waters. Results indicated that the population structuring of garfish is more complex than previously assumed and it seems that stocks can be discriminated at a much finer spatial scale. Garfish collected from sites separated by <60 km displayed significantly different chemical signatures (relative concentrations of 7Li, 24Mg, 55Mn, 88Sr and 138Ba) in their otoliths, especially during their second year of growth, indicating that they had inhabited different water bodies. From a broader perspective, South Australian garfish can be partitioned into six regional components with various levels of inter-mixing. From these results, it was suggested that assessment and management of the fishery may have to be restructured to align with the smaller spatial units. [source] Seasonal variation in rod recapture rates indicates differential exploitation of Atlantic salmon, Salmo salar, stock componentsFISHERIES MANAGEMENT & ECOLOGY, Issue 3 2007J. L. THORLEY Abstract, Differential exploitation of the various components of a fish stock can adversely affect the diversity, abundance and long-term survival of the entire stock. Many anadromous salmonid stocks exhibit a seasonal structuring of their run-timing that allows fisheries managers to map monthly rod catches onto stock components. To estimate the rod exploitation levels of the various run-timing groups, fishing guides on the River Spey, Scotland, floy-tagged 786 rod-caught and released Atlantic salmon, Salmo salar L., between 2000 and 2002 and recorded recaptures. Whereas 25% of the fish tagged early in March were recaptured, only 2% of those tagged early in June were caught a second time. Exploitation is biased towards the early-running stock components which current assessments show to be least abundant. Management of Atlantic salmon based on an average exploitation rate is inappropriate. [source] Linking spatial pattern of bottom fish assemblages with water masses in the North SeaFISHERIES OCEANOGRAPHY, Issue 1 2009SIEGFRIED EHRICH Abstract Understanding the links between large scale spatial structuring of fish assemblages and shaping factors is essential to develop comprehensive ecosystem-based fisheries management. In this study, we investigated spatial patterns of bottom fish assemblages in the North Sea in relation to prevailing water masses in the region. We based our analysis on catch data from the German Small-Scale Bottom Trawl Survey conducted between 1987 and 2005 and used both ordination techniques and Mantel tests. Spatial variability of bottom fish assemblages was larger than inter-annual variability. Five significantly different bottom fish assemblages were associated with the following prevailing hydrographical regimes: i) the English Channel, ii) Continental Coastal, iii) central North Sea, iv) northern North Sea, and v) northern Atlantic water masses. Associations were generated by gradients in relative proportions of abundant species such as grey gurnard (Eutrigla gurnardus), dab (Limanda limanda), whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus) and Norway pout (Trisopterus esmarki). Taking into account large scale spatial structuring of catch data Mantel tests confirmed significant correlation between the fish assemblages and hydrographical variables. In summary, our results strongly support the hypotheses that hydrographical features such as water masses, fronts, and residual currents could shape bottom fish associations in the North Sea. Spatial demarcations of bottom fish assemblages indicated by this study can be used to support ecosystem-based fisheries management strategies. [source] Highly Extensible Bio-Nanocomposite Films with Direction-Dependent PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Akhilesh K. Gaharwar Abstract The structure and mechanical properties of bio-nanocomposite films made from poly(ethylene oxide) (PEO) that is physically cross-linked with silicate nanoparticles, Laponite, are investigated. Direction-dependent mechanical properties of the films are presented, and the effect of shear orientation during sample preparation on tensile strength and elongation is assessed. Repeated mechanical deformation results in highly extensible materials with preferred orientation and structuring at the nano- and micrometer scales. Additionally, in vitro biocompatibility data are reported, and NIH 3T3 fibroblasts are observed to readily adhere and proliferate on silicate cross-linked PEO while maintaining high cell viability. [source] Linking herbivore-induced defences to population dynamicsFRESHWATER BIOLOGY, Issue 3 2006IRENE VAN DER STAP Summary 1.,Theoretical studies have shown that inducible defences have the potential to affect population stability and persistence in bi- and tritrophic food chains. Experimental studies on such effects of prey defence strategies on the dynamics of predator,prey systems are still rare. We performed replicated population dynamics experiments using the herbivorous rotifer Brachionus calyciflorus and four strains of closely related algae that show different defence responses to this herbivore. 2.,We observed herbivore populations to fluctuate at a higher frequency when feeding on small undefended algae. During these fluctuations minimum rotifer densities remained sufficiently high to ensure population persistence in all the replicates. The initial growth of rotifer populations in this treatment coincided with a sharp drop in algal density. Such a suppression of algae by herbivores was not observed in the other treatments, where algae were larger due to induced or permanent defences. In these treatments we observed rotifer population densities to first rise and then decline. The herbivore went extinct in all replicates with large permanently defended algae. The frequency of herbivore extinctions was intermediate when algae had inducible defences. 3.,A variety of alternative mechanisms could explain differential herbivore persistence in the different defence treatments. Our analysis showed the density and fraction of highly edible algal particles to better explain herbivore persistence and extinctions than total algal density, the fraction of highly inedible food particles or the accumulation of herbivore waste products or autotoxins. 4.,We argue that the rotifers require a minimum fraction and density of edible food particles for maintenance and reproduction. We conjecture that induced defences in algae may thus favour larger zooplankton species such as Daphnia spp. that are less sensitive to shifts in their food size spectrum, relative to smaller zooplankton species, such as rotifers and in this way contributes to the structuring of planktonic communities. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||