Nest structure and occurrence of three species of Azteca (Hymenoptera, Formicidae) in Cecropia pachystachya (Urticaceae) in non-floodable and floodable pantanal areas

Thirty Cecropia pachystachya trees were examined in non-floodable and floodable areas to investigate the association between C. pachystachya and Azteca ants in the Pantanal of Mato Grosso do Sul, Brazil. The species Azteca ovaticeps, Azteca isthmica, and Azteca alfari were found nesting inside domatia of C. pachystachya. A. ovaticeps was the most frequent species in the trees in the floodable area, while A. isthmica and A. alfari, in the non-floodable area. A. ovaticeps and A. isthmica maintained more entrance/exit holes in comparison to A. alfari. All Azteca species maintained entrance/exit holes in the closest domatia to the apical area of the branch, due to proximity to Müllerian and pearl bodies, suggesting that these species of Azteca were influenced by their environment during evolution and became specialized. All internodal septa of each examined branch were perforated by ants, indicating the branches were inhabited by a single colony.

A two-mean reverting-factor model of the term structure of interest rates

This paper presents a two--factor model of the term structure ofinterest rates. We assume that default free discount bond prices aredetermined by the time to maturity and two factors, the long--term interestrate and the spread (difference between the long--term rate and theshort--term (instantaneous) riskless rate). Assuming that both factorsfollow a joint Ornstein--Uhlenbeck process, a general bond pricing equationis derived. We obtain a closed--form expression for bond prices andexamine its implications for the term structure of interest rates. We alsoderive a closed--form solution for interest rate derivatives prices. Thisexpression is applied to price European options on discount bonds andmore complex types of options. Finally, empirical evidence of the model'sperformance is presented.

An experimental study of discharge partitioning and flow structure at symmetrical bifurcations

Recent research has examined the factors controlling the geometrical configuration of bifurcations, determined the range of stability conditions for a number of bifurcation types and assessed the impact of perturbations on bifurcation evolution. However, the flow division process and the parameters that influence flow and sediment partitioning are still poorly characterized. To identify and isolate these parameters, three-dimensional velocities were measured at 11 cross-sections in a fixed-walled experimental bifurcation. Water surface gradients were controlled, and systematically varied, using a weir in each distributary. As may be expected, the steepest distributary conveyed the most discharge ( was dominant) while the mildest distributary conveyed the least discharge ( was subordinate). A zone of water surface super-elevation was co-located with the bifurcation in symmetric cases or displaced into the subordinate branch in asymmetric cases. Downstream of a relatively acute-angled bifurcation, primary velocity cores were near to the water surface and against the inner banks, with near-bed zones of lower primary velocity at the outer banks. Downstream of an obtuse-angled bifurcation, velocity cores were initially at the outer banks, with near-bed zones of lower velocities at the inner banks, but patterns soon reverted to match the acute-angled case. A single secondary flow cell was generated in each distributary, with water flowing inwards at the water surface and outwards at the bed. Circulation was relatively enhanced within the subordinate branch, which may help explain why subordinate distributaries remain open, may play a role in determining the size of commonly-observed topographic features, and may thus exert some control on the stability of asymmetric bifurcations. Further, because larger values of circulation result from larger gradient disadvantages, the length of confluence-diffluence units in braided rivers or between diffluences within delta distributary networks may vary depending upon flow structures inherited from upstream and whether, and how, they are fed by dominant or subordinate distributaries. Copyright (C) 2011 John Wiley & Sons, Ltd.

Comparative phylogeography of mutualists and the effect of the host on the genetic structure of its partners.

Whether or not species participating in specialized and obligate interactions display similar and simultaneous demographic variations at the intraspecific level remains an open question in phylogeography. In the present study, we used the mutualistic nursery pollination occurring between the European globeflower Trollius europaeus and its specialized pollinators in the genus Chiastocheta as a case study. Explicitly, we investigated if the phylogeographies of the pollinating flies are significantly different from the expectation under a scenario of plant-insect congruence. Based on a large-scale sampling, we first used mitochondrial data to infer the phylogeographical histories of each fly species. Then, we defined phylogeographical scenarios of congruence with the plant history, and used maximum likelihood and Bayesian approaches to test for plant-insect phylogeographical congruence for the three Chiastocheta species. We show that the phylogeographical histories of the three fly species differ. Only Chiastocheta lophota and Chiastocheta dentifera display strong spatial genetic structures, which do not appear to be statistically different from those expected under scenarios of phylogeographical congruence with the plant. The results of the present study indicate that the fly species responded in independent and different ways to shared evolutionary forces, displaying varying levels of congruence with the plant genetic structure

Market structure and hospital efficiency: Evaluating potential effects of deregulation in a national health service

In this article we examine the potential effect of market structureon hospital technical efficiency as a measure of performance controlled byownership and regulation. This study is relevant to provide an evaluationof the potential effects of recommended and initiated deregulation policiesin order to promote market reforms in the context of a European NationalHealth Service. Our goal was reached through three main empirical stages.Firstly, using patient origin data from hospitals in the region of Cataloniain 1990, we estimated geographic hospital markets through the Elzinga--Hogartyapproach, based on patient flows. Then we measured the market level ofconcentration using the Herfindahl--Hirschman index. Secondly, technicaland scale efficiency scores for each hospital was obtained specifying aData Envelopment Analysis. According to the data nearly two--thirds of thehospitals operate under the production frontier with an average efficiencyscore of 0.841. Finally, the determinants of the efficiency scores wereinvestigated using a censored regression model. Special attention waspaid to test the hypothesis that there is an efficiency improvement in morecompetitive markets. The results suggest that the number of competitors inthe market contributes positively to technical efficiency and there is someevidence that the differences in efficiency scores are attributed toseveral environmental factors such as ownership, market structure andregulation effects.

Mycorrhizal ecology and evolution: the past, the present, and the future.

1406 I. 1407 II. 1408 III. 1410 IV. 1411 V. 1413 VI. 1416 VII. 1418 1418 References 1419 SUMMARY: Almost all land plants form symbiotic associations with mycorrhizal fungi. These below-ground fungi play a key role in terrestrial ecosystems as they regulate nutrient and carbon cycles, and influence soil structure and ecosystem multifunctionality. Up to 80% of plant N and P is provided by mycorrhizal fungi and many plant species depend on these symbionts for growth and survival. Estimates suggest that there are c. 50 000 fungal species that form mycorrhizal associations with c. 250 000 plant species. The development of high-throughput molecular tools has helped us to better understand the biology, evolution, and biodiversity of mycorrhizal associations. Nuclear genome assemblies and gene annotations of 33 mycorrhizal fungal species are now available providing fascinating opportunities to deepen our understanding of the mycorrhizal lifestyle, the metabolic capabilities of these plant symbionts, the molecular dialogue between symbionts, and evolutionary adaptations across a range of mycorrhizal associations. Large-scale molecular surveys have provided novel insights into the diversity, spatial and temporal dynamics of mycorrhizal fungal communities. At the ecological level, network theory makes it possible to analyze interactions between plant-fungal partners as complex underground multi-species networks. Our analysis suggests that nestedness, modularity and specificity of mycorrhizal networks vary and depend on mycorrhizal type. Mechanistic models explaining partner choice, resource exchange, and coevolution in mycorrhizal associations have been developed and are being tested. This review ends with major frontiers for further research.

Leaf-litter amount as a factor in the structure of a ponerine ants community (Hymenoptera, Formicidae, Ponerinae) in an eastern Amazonian rainforest, Brazil

Leaf-litter amount as a factor in the structure of a ponerine ants community (Hymenoptera, Formicidae, Ponerinae) in an eastern Amazonian rainforest, Brazil. Leaf-litter may be an important factor in structuring ponerine ant communities (Hymenoptera, Formicidae, Ponerinae) in tropical rainforests. We specifically examined how leaf-litter affects the structure of a ponerine ant community in primary Amazonian rainforest sites at the Ferreira Penna Scientific Station, Pará, Brazil. A total of 53 species belonging to eight genera of three ponerine tribes were collected with mini-Winkler extractors. The amount of leaf-litter positively affected the abundance and richness of the ponerine ant community, and also influenced species composition. Nearby samples often had low species similarity, especially when adjacent samples differed in the amount of leaf-litter. Leaf-litter availability in Amazonian primary forests is a key factor for distribution of ground-dwelling ponerine species, even at small scales.

Employee referrals and the inter-industry wage structure

This paper investigates the role of employee referrals in the labor market.Using an original data set, I find that industries that pay wage premia andhave characteristics associated with high-wage sectors rely mainly on employeereferrals to fill jobs. Moreover, unemployment rates are higher in industries which use employee referrals more extensively. This paper develops an equilibrium matching model which can explain these empirical regularities. Inthis model, the matching process sorts heterogeneous firms and workers into two distinct groups: referrals match "good" jobs to "good" workers, while formalmethods (e.g., newspaper ads and employment agencies) match less-attractive jobs to disadvantaged workers. Thus, well-connected workers who learn quickly aboutjob opportunities use referrals to jump job queues, while those who are less well placed in the labor market search for jobs through formal methods. The split of firms and workers between referrals and formal search is, however, not necessarily efficient. Congestion externalities in referral search imply that unemployment would be closer to the optimal rate if firms and workers 'at themargin' searched formally.

Ownership structure, customer satisfaction and brand equity

This paper studies the interaction between ownership structure, taken as a proxy for shareholders commitment, and customer satisfaction - the main driver of consumer loyalty - and their impact on a firm s brand equity. The results show that customer satisfaction has a positive direct effect on brand equity but an indirect negative one because of reductions in ownership concentration. This latter effect emerges when managers are mainly customer-oriented. Such result gives out a warning signal that highlights the perverse effect of implementing policies, focused excessively on satisfying customers at the expense of shareholders, on a firm s brand equity. The empirical analysis uses an incomplete panel data comprising 69 firms from 11 nations, for the period 2002-2005.

Neurobiologia, coscienza e neuroetica. Ricerche filosofiche in margine al dialogo tra G.P. CHANGEUX e P. RICOEUR

Le neuroscienze occupano oggi un ruolo essenziale nel dibattito scientifico e filosofico, nonché in quello delle scienze umane. Esse costituiscono la sfida più seria al sapere fin qui elaborato intorno ai fondamenti dell'esperienza di coscienza, poiché si propongono come capaci di rispondere alla domanda di origine e funzionamento della coscienza. Le neuroscienze cognitive stanno, oggi, rivoluzionando la nostra concezione della mente e delle sue funzioni. Ci forniscono nuovi dati sulla natura delle sensazioni, della memoria, della percezione e dei processi di astrazione. L'epistemologia è rientrata così pienamente nell'ambito di una disciplina sperimentale, come diversi filosofi (da Hume a Quine) hanno auspicato. È, alla fine, evoluta nell'esperienza odierna della cosiddetta "epistemologia sperimentale", luogo che coniuga il rigore sperimentale della scienza con la profondità e la sofisticazione argomentativa della tradizione filosofica. Come arriviamo a conoscere? Quali vincoli poniamo a quello che deve essere conosciuto? Perché seguiamo certe vie invece di altre? Come arriviamo a formulare giudizi e a prendere decisioni? Che valore ha la conoscenza già acquisita nell'elaborazione di nuove esperienze? In particolare, che peso hanno le aspettative e i ricordi in questo processo? Qual è il rapporto fra esperienza, conoscenza e memoria? Come si fissano e come si richiamano i ricordi? Qual è il rapporto fra coscienza e memoria? Sono alcune delle domande che l'autore si pone in questa ottica e alle quali cerca di rispondere, a partire dall'analisi e valutazione del dialogo-dibattito fra J.-P. Changeux e P. Ricoeur, per apprenderne il linguaggio, capire i problemi sollevati, adattarsi alla complessità della materia. Nel contesto della filosofia della mente, la "lettura" della discussione ripercorre i relativi percorsi attraverso l'analisi delle loro opere, da un lato quelle dello scienziato (sulla struttura e dinamica del cervello, la teoria dell'epigenesi e stabilizzazione selettiva, le speculazioni sull'uomo neuronale e i rilievi antropologici, le teorie della conoscenza e della coscienza, oltre che sulla conoscenza matematica, gli argomenti di estetica ed etica); dall'altro lato quelle del filosofo (dal Cogito riflessivo alla scoperta dell'ermeneutica, dalle eterogenee riflessioni sul Conflitto delle interpretazioni alla grande teoria sulla creatività del linguaggio, le conclusioni teoriche sull'ermeneutica del sé e l'ontologia dell'agire). Il punto di arrivo è la determinazione delle relative posizioni: quella di Changeux tra i neuroscienziati che si occupano di questioni filosofiche, epistemologiche ed etiche, e quella di Ricoeur tra i filosofi che si occupano di neuroscienze. La conclusione della tesi si svolge in un approfondimento teoretico che dalla nozione di "traccia" porta all'esperienza della "memoria", al fine di intrecciare i fili della discussione ripercorsa ed offrire una sponda non forzata al dibattito più ampio. Il tema della memoria è privilegiato per ragioni intrinseche, poiché si tratta di uno dei temi precipui delle neuroscienze, della filosofia della mente e della fenomenologia. A un primo livello viene instaurato su questo punto un confronto epistemologico tra la proposta della neurofenomenologia (Varala, ad esempio) e la posizione tenuta in particolare da Ricoeur rispetto ad essa e al suo "progetto unificante", posizione defilata e, per certi aspetti, criticamente dubbiosa sul fatto che si possa davvero giungere a un "terzo discorso". Si riferisce poi del largo interesse e dei risultati più significativi della riflessione fenomenologica antica e moderna sulla memoria. A un secondo livello vengono illustrati i programmi di ricerca recenti della neurofenomenologia su questo argomento all'interno delle scienze cognitive e si dà conto dei risultati più significativi. Ad un terzo e conclusivo livello, si approfondisce il significato teologico della memoria. Les neurosciences ont aujourd'hui un rôle essentiel dans le débat scientifique et philosophique, ainsi que dans celui des sciences humaines. Elles constituent le défi le plus sérieux aux savoir qu'on a construit jusqu'ici sur les fondements de l'expérience de conscience, attendu qu'elles-mêmes se considèrent capables de répondre à la demande sur l'origine e le fonctionnement de la conscience. Les neurosciences cognitives sont aujourd'hui en train de révolutionner notre conception de l'esprit et des ses fonctions. Elles nous offrent des nouvelles données au sujet de la nature de nos sensations, mémoire, perception et procédés d'abstraction. Aussi l'épistémologie est rentrée pleinement dans le domaine d'une discipline expérimentale, comme plusieurs philosophes (de Hume à Quine) l'ont souhaité. Elle s'est enfin adressée, dans l'expérience actuelle, vers la soi-disant "épistémologie expérimentale", lieu qui met en accord la rigueur expérimentale de la science avec la profondeur et la sophistiquée finesse argumentative de la tradition philosophique. Comment en arrivons-nous à connaître? Quels liens mettons-nous à ce qu'on doit être connu? Pourquoi suivons-nous certaines vois au lieu d'autres? Comment en arrivons-nous à formuler des opinions et à prendre des décisions? Quelle valeur a la connaissance qu'on a déjà acquise par l'élaboration des nouvelles expériences? En particulier, quelle est l'importance des attentes et des souvenirs dans cette évolution? Quel est le rapport entre expérience, connaissance e mémoire? Comment fixons et rappelons-nous nos souvenirs? Quel est le rapport entre conscience et mémoire? Ces sont quelques-unes des questions que l'auteur se pose dans cette perspective et aux quelles essaie de répondre a partir de l'analyse et l'évaluation du dialogue-débat entre fra J.-P. Changeux et P. Ricoeur, pour en apprendre le langage, comprendre les problèmes soulevés, s'adapter à la complexité du sujet. Dans le contexte de la philosophie du cerveau, la "lecture" du dialogue reparcourt les parcours des deux interlocuteurs par l'analyse de leur ouvrages, d'une part celles du savant (sur la structure et la dynamique du cerveau, la théorie de l'épigenèse et stabilisation sélective; les spéculations sur l'homme neuronal et les commentaires anthropologiques; les théories de la connaissance et de la conscience, de même que sur la connaissance de la mathématique, les sujets d'esthétique et étique; d'autre part celles du philosophe (du Cogito réflexif à la découverte de l'herméneutique, de les hétérogènes réflexions sur le Conflit des interprétations à la grande théorie sur la créativité du langage, les conclusions théoriques sur l'herméneutique du soi et l'ontologie de l'agir). L'issue est la determination des relatives positions: celle de Changeux parmi les neuro-scientifiques qui s'occupent de questions philosophiques, épistémologiques et éthiques, et celle de Ricoeur parmi les philosophes qui s'occupent de neurosciences. La conclusion de la thèse se développe dans un approfondissement théorétique que de la notion de "trace" à l'expérience de la "mémoire", à l'effet de nouer les fils de la discussion passée en revue et d'assurer un appui pas forcé au débat plus vaste. Le thème de la mémoire a été choisi pour des raisons intrinsèques, puisqu'il est un des thèmes principaux des neurosciences, de la philosophie de l'esprit et de la phénoménologie. Sur un premier plan épistémologique il est établi une comparaison entre la proposition de la neurophénoménologie (Varala, par exemple) et la position soutenue en particulier par Ricoeur au sujet de ce courant phénoménologique et de son "projet unifiant", position défilée et, à certains égards, critiquement hésitante sur le fait qu'on puisse vraiment en venir à un "troisième discours". On rend compte du grand intérêt et des résultats les plus significatifs de la réflexion phénoménologique ancienne et moderne sur la mémoire. Sur un second plan neurophénoménologique on illustre des plans de recherche récents sur cet argument au-dedans des sciences cognitives et on rend compte des résultats les plus distinctives. Sur un troisième et conclusif plan on approfondit le sens théologique de la mémoire.

Genetic structure of populations of Pissodes castaneus (De Geer) (Coleoptera, Curculionidae) using amplified fragment length polymorphism

Genetic structure of populations of Pissodes castaneus (De Geer) (Coleoptera, Curculionidae) using amplified fragment length polymorphism. The objective of this study was to determine the genetic structure of populations of Pissodes castaneus from different areas and on different species of Pinus using the PCR-AFLP technique. Twenty samples were analyzed, representing 19 populations from Brazil and one from Florence, Italy, which is the region of origin of P. castaneus. The four combinations of primers generated a total of 367 fragments of DNA, and 100% of polymorphic loci, indicating high degree of molecular polymorphism. The dendrogram did not reveal trends for grouping the populations in relation to origin. The low genetic similarity (0.11 between the most distant groups) and genetic distances of 0.13 and 0.44 for 10 out of the 20 samples may indicate several founding events or multiple introductions of heterogeneous strains into Brazil. The allelic fixation index (Fst) was 0.3851, considered high, and the number of migrants (Nm) was 0.3991, indicating low gene flow among populations. The highest genetic distances were between the population from Irani, SC and Cambará do Sul, RS and Bituruna, PR, indicating an independent founding event or a particular allelic fixation in the former location. The high genetic diversity among populations points out that the populations are genetically heterogeneous with a diverse gene pool in the surveyed areas, what makes them to respond differently to control measures.

Electron microscopy of RecA-DNA complexes: Two different states, their functional significance and relation to the solved crystal structure

Seven different electron microscopy techniques habe been employed to study the RecA protein of E. coli. This review provides a summary of the conclusions that have been drawn from these studies, and attempts to relate these observations to models for the role of RecA protein in homologous recombination.

Testing the response of macroinvertebrate functional structure and biodiversity to flooding and confinement

The aim of the present study was to investigate the relative importance of flooding- and confinement-related environmentalfeatures in explaining macroinvertebrate trait structure and diversity in a pool of wetlands located in a Mediterranean riverfloodplain. To test hypothesized trait-environment relationships, we employed a recently implemented statistical procedure, thefourth-corner method. We found that flooding-related variables, mainly pH and turbidity, were related to traits that confer an abilityof the organism to resist flooding (e.g., small body-shape, protection of eggs) or recuperate faster after flooding (e.g., short life-span, asexual reproduction). In contrast, confinement-related variables, mainly temperature and organic matter, enhanced traits that allow organisms to interact and compete with other organisms (e.g., large size, sexual reproduction) and to efficiently use habitat and resources (e.g., diverse locomotion and feeding strategies). These results are in agreement with predictions made under the River Habitat Templet for lotic ecosystems, and demonstrate the ability of the fourth-corner method to test hypothesis that posit traitenvironment relationships. Trait diversity was slightly higher in flooded than in confined sites, whereas trait richness was not significantly different. This suggests that although trait structure may change in response to the main environmental factors, as evidenced by the fourth-corner method, the number of life-history strategies needed to persist in the face of such constraints remains more or less constant; only their relative dominance differs