Various Hypotheses (various + hypothesis)

Distribution by Scientific Domains
Distribution within Life Sciences


Selected Abstracts


Growth and movement patterns of early juvenile European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay based on otolith microstructure and chemistry

FISHERIES OCEANOGRAPHY, Issue 3 2010
NAROA ALDANONDO
Abstract Various hypotheses have been put forward to explain the mechanisms in the Bay of Biscay that result in a good recruitment of European anchovy. Anchovy larvae from the spawning area in the Gironde River plume are advected towards off-shelf waters, where juveniles are commonly observed. Otolith microstructural and chemical analysis were combined to assess the importance of this off-shelf transport and to determine the relative contribution of these areas for anchovy survival. Chemical analysis of otoliths showed that anchovy juveniles in the Bay of Biscay can be divided into two groups: a group that drifts towards off-shelf waters early in their life and returns later, and a group that remains in the low salinity waters of the coastal area. The first group presents significantly faster growth rates (0.88 mm day,1) than those remaining in the coastal waters (0.32 mm day,1). This may be due to off-shelf waters being warmer in spring/summer, and to the fact that the lower food concentration is compensated for by higher prey visibility. Furthermore, the group of juveniles that drifted off the spawning area and had faster growth rates represents 99% of the juvenile population. These findings support the hypothesis that anchovy in the Bay of Biscay may use off-shelf waters as a spatio-temporal loophole, suggesting that transport off the shelf may be favourable for recruitment. [source]


Fragrances, male display and mating behaviour of Euglossa hemichlora: a flight cage experiment

PHYSIOLOGICAL ENTOMOLOGY, Issue 4 2003
Thomas Eltz
Abstract., Male euglossine bees (Apidae: Euglossini) collect volatile substances (fragrances) from floral and nonfloral sources and store them in hair-filled cavities in their hind tibiae. Over time, males accumulate large quantities of complex and species-specific blends of fragrances. Various hypotheses have been put forward to explain this behaviour, including the idea that fragrance stores reflect the genetic quality of individual males and have evolved through sexual selection and female choice. Clear support of this hypothesis is lacking, largely because male,female interactions are both rare and difficult to observe in nature. Here, we report a flight cage experiment performed in Panama that permitted mating between virgin females (raised from brood cells) and males captured in the forest at fragrance baits. In the cage, eight individually marked males defended small territories around vertical perch sites and showed a characteristic display, which included a previously unreported ,leg-crossing' movement, possibly related to fragrance release. A total of six copulations and three copulatory attempts by Euglossa hemichlora were observed and partly recorded on video. The copulations, all of which were initiated by the female landing on a male perch, were short (4,10 s) and showed no signs of the transfer of chemical substances from male to female. In some cases, the male hovered directly over the female before descending to mount her, possibly facilitating fragrance evaluation by the female. After the experiment, the contents of the males' hind legs were analysed by gas chromatography-mass spectroscopy, which detected complex mixtures of terpenoids and aromatics (totalling 70 different compounds) dominated by hexahydrofarnesyl acetone, farnesene epoxide, ocimene and p -dimethoxy benzene. Individual total amounts of fragrances were neither related to display activity or perch occupancy by given males, nor to the frequency of matings achieved. Display activity was the only positive correlate of mating frequency. Generally, individuals had uniformly large amounts of stored fragrances in comparison to a previous study of three other species of Panamanian Euglossa. [source]


The relationship between socio-sexual behavior and salivary cortisol in bonobos: tests of the tension regulation hypothesis

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2009
Gottfried Hohmann
Abstract Bonobos are known for their pacifistic behavior and their large repertoire of behaviors that are thought to serve conflict resolution. One is an unusual form of ventro-ventral mounting that facilitates genital contacts (GC). Various hypotheses have been proposed to explain its function. In this study we tested predictions of the tension regulation hypothesis using salivary cortisol as a marker for social stress. The results indicate a temporal relationship between GC and cortisol levels. Compared with baseline data and matched samples of unrestricted food access, rates of GC increased when access to food sources was restricted. Cortisol levels were highest when access to food was constrained. However, because the behavioral and hormonal responses occurred when viewing the stimulus at a distance and preceded the physical presence of the stimulus, we conclude that the anticipation of a competitive situation was sufficient to induce social stress. Contrary to our prediction, targets of aggression did not have higher rates of GC nor did they solicit GC more often than others. Furthermore, higher GC rates did not correlate with a more pronounced decrease in cortisol levels. Not all results obtained in this study supported the predictions concerning the regulatory function of GC on social tension and further research is needed to explore this question. However, the results indicate that the anticipation of competition may be sufficient to induce a costly physiological response, and that high levels of resource competition may have lasting effects on physical stress and stress management. Am. J. Primatol. 71:223,232, 2009. © 2008 Wiley-Liss, Inc. [source]


How to evaluate metacognitive functioning in psychotherapy?

CLINICAL PSYCHOLOGY AND PSYCHOTHERAPY (AN INTERNATIONAL JOURNAL OF THEORY & PRACTICE), Issue 4 2003
The metacognition assessment scale, its applications
In this article the authors present a method and a scale for the evaluation of the metacognitive profiles of psychotherapy patients. There will be a description of the metacognitive function and of the alterations that occur to it during treatment. Various hypotheses will then be considered: (1) that the metacognitive function has a modular structure; (2) that for each type of psychopathological condition there is a different metacognitive deficit profile; (3) that to be successful psychotherapy needs to involve an improvement in any deficient metacognitive sub-function. There will then be a presentation of the Metacognition Assessment Scale (MAS) for the assessment of metacognitive deficits during psychotherapy. We shall then describe the first results we have on the application of the scale. Finally there will be an analysis of two patients suffering from Personality Disorders and a demonstration of what metacognitive deficit profile each one has and how it is modified over the course of psychotherapy treatment. The article ends with a discussion of the hypotheses made at the start in the light of the results that have emerged.,Copyright © 2003 John Wiley & Sons, Ltd. [source]


Brochosome influence on parasitisation efficiency of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) egg masses by Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae)

ECOLOGICAL ENTOMOLOGY, Issue 5 2005
Hans-Paul Velema
Abstract., 1.,Many cicadellid females in the tribe Proconiini (Hemiptera: Cicadellidae) cover their egg masses with specialised, usually rod-shaped, brochosomes as the eggs are being laid. The brochosomes are produced in Golgi complexes in the Malpighian tubules of Cicadellidae. In contrast to the gravid females, adult males, pre-reproductive adult females, and nymphal males and females produce specialised, usually spherically shaped brochosomes. Brochosomes are also used to cover the external surfaces of nymphs and newly moulted adult males and females. 2.,The function of the brochosome covering the egg masses is unknown but various hypotheses have been suggested, including protecting the eggs against pathogens, predators, and parasitoids. Based on preliminary observations of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) parasitising the eggs of the cicadellid, Homalodisca coagulata (Say), it is speculated here that brochosomes covering an egg mass hinder parasitisation of eggs by G. ashmeadi. This hypothesis was tested by observing G. ashmeadi females foraging on leaves with H. coagulata egg masses heavily covered with rod-shaped brochosomes vs. those lacking brochosomes. 3.,Cox's proportional hazards model was used to evaluate the probability, per unit time, that a female G. ashmeadi displayed the sequence of behaviours that ended in successful oviposition as influenced by five variables: (a) presence or absence of brochosomes on an egg mass, (b) the leaf surface, upper or lower, being searched by the parasitoid (the egg masses are laid in the parenchyma on the lower leaf surface), (c) the parasitoid's previous ovipositional experience, (d) egg mass size, and (e) the parasitoid's age. 4.,Brochosomes significantly decreased oviposition efficacy of G. ashmeadi females. Scanning electron microscopy showed that females exposed to brochosome-covered egg masses had brochosomes adhering to their tarsi, legs, antennae, and eyes, all of which prompted extensive bouts of grooming. [source]


Estimating the number of alcohol-attributable deaths: methodological issues and illustration with French data for 2006

ADDICTION, Issue 6 2010
Grégoire Rey
ABSTRACT Aims Computing the number of alcohol-attributable deaths requires a series of hypotheses. Using French data for 2006, the potential biases are reviewed and the sensitivity of estimates to various hypotheses evaluated. Methods Self-reported alcohol consumption data were derived from large population-based surveys. The risks of occurrence of diseases associated with alcohol consumption and relative risks for all-cause mortality were obtained through literature searches. All-cause and cause-specific population alcohol-attributable fractions (PAAFs) were calculated. In order to account for potential under-reporting, the impact of adjustment on sales data was tested. The 2006 mortality data were restricted to people aged between 15 and 75 years. Results When alcohol consumption distribution was adjusted for sales data, the estimated number of alcohol-attributable deaths, the sum of the cause-specific estimates, was 20 255. Without adjustment, the estimate fell to 7158. Using an all-cause mortality approach, the adjusted number of alcohol-attributable deaths was 15 950, while the non-adjusted estimate was a negative number. Other methodological issues, such as computation based on risk estimates for all causes for ,all countries' or only ,European countries', also influenced the results, but to a lesser extent. Discussion The estimates of the number of alcohol-attributable deaths varied greatly, depending upon the hypothesis used. The most realistic and evidence-based estimate seems to be obtained by adjusting the consumption data for national alcohol sales, and by summing the cause-specific estimates. However, interpretation of the estimates must be cautious in view of their potentially large imprecision. [source]


Analysis of Simulated Martian Regolith Using an Array of Ion Selective Electrodes

ELECTROANALYSIS, Issue 15-16 2005
Stefan
Abstract A prototype miniature array of polymer membrane and solid state ion selective electrodes was developed for the purpose of performing an in-situ analysis of the soluble ionic species in Martian regolith (soil). The array contains a total of 27 electrodes for K+, Na+, Ca2+, Mg2+, NH, Ba2+, NO, Cl,, and Li+, each in triplicate. Barium electrodes were used to indirectly monitor sulfate through precipitation by the addition of barium chloride while the lithium electrodes served as a reference for the array by having a constant lithium concentration as a background for all solutions. The array was tested with several types of simulants, soils, and sawdust from a Mars meteorite, all with varying salt content, meant to approximate the various hypotheses regarding the ionic composition of the Martian soil. The activities of anions and cations determined with the array were compared to ion chromatography data. [source]


Measuring sexual size dimorphism in birds

IBIS, Issue 3 2003
Julian G. Greenwood
Numerous studies have examined sexual size dimorphism in birds and speculated upon the reasons for its existence. Whilst most studies have focused on individual species or groups of related species, a few have attempted to disentangle the various hypotheses that have been put forward to explain its occurrence. Typical of the latter studies is that by Jehl and Murray (1986), in which they argued that sexual size dimorphism was primarily the result of sexual selection (see also Bennett & Owens 2002). Although some studies have looked at patterns in sexual size dimorphism without calculating a figure to represent the difference (e.g. Amadon 1959), most have examined measurements of birds and used these to calculate such a figure. Traditionally in such studies, measurements used have included wing-length, culmen-length, tarsus-length and mass, although McGillivray (1989) took the sum of 18 skeletal measurements and used their male and female means to determine sexual size dimorphism. Wing-length has commonly been used to determine sexual size dimorphism, although lack of repeatability of measurements may render it less useful than skeletal measurements like tarsus-length as in studies of Dunlin Calidris alpina (Blomqvist et al. 1997) and Savannah Sparrows Passerculus sandwichensis (Rising & Somers 1989); however, Gosler et al. (1998) found wing-length measurements to be more repeatable than other metrics in a group of 27 passerines. [source]


An assessment of ,international best practice' in visitor attraction management: does Scotland really lag behind?

INTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 1 2007
Brian Garrod
Abstract This paper compares and contrasts selected management practices among visitor attractions in Scotland, Australia, Canada and New Zealand. The catalyst for the study was the growing perception that management practices among visitor attractions in Scotland are becoming increasingly outdated and that the sector needs to learn from ,international best practice' in this respect. A postal questionnaire was sent to all paid-admission visitor attractions in the four countries. In total, 1022 visitor attractions replied, representing an overall response rate of 41%. Chi-square analysis was then used to test various hypotheses relating to the uptake of these management practices. A key conclusion is that although management practices do vary significantly among the four countries, Scotland does not necessarily lag behind. Indeed, Scottish visitor attractions seem to lead the way in many respects. Meanwhile, the study finds no strong evidence to suggest that visitor attractions in the other three countries have indeed identified and are following a common ,international best practice'. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Computation and analysis of multiple structural change models

JOURNAL OF APPLIED ECONOMETRICS, Issue 1 2003
Jushan Bai
In a recent paper, Bai and Perron (1998) considered theoretical issues related to the limiting distribution of estimators and test statistics in the linear model with multiple structural changes. In this companion paper, we consider practical issues for the empirical applications of the procedures. We first address the problem of estimation of the break dates and present an efficient algorithm to obtain global minimizers of the sum of squared residuals. This algorithm is based on the principle of dynamic programming and requires at most least-squares operations of order O(T2) for any number of breaks. Our method can be applied to both pure and partial structural change models. Second, we consider the problem of forming confidence intervals for the break dates under various hypotheses about the structure of the data and the errors across segments. Third, we address the issue of testing for structural changes under very general conditions on the data and the errors. Fourth, we address the issue of estimating the number of breaks. Finally, a few empirical applications are presented to illustrate the usefulness of the procedures. All methods discussed are implemented in a GAUSS program. Copyright © 2002 John Wiley & Sons, Ltd. [source]


On the Determinants and Dynamics of Trade Credit Use: Empirical Evidence from Business Start-ups

JOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 1-2 2006
Nancy Huyghebaert
Abstract: Business start-ups provide an excellent opportunity for testing various hypotheses on why firms use trade credit. At the time of start-up, failure risk and financial constraints are typically large. Also, start-ups have no established relationships with banks and suppliers. The literature has related all these features to trade credit use. Moreover, as firms grow older, these characteristics become less pronounced, allowing us to test the dynamics of trade credit use. We find that start-ups use more trade credit when financial constraints are large, when suppliers have a financing advantage over banks in financing high-risk firms, when entrepreneurs value private benefits of control and when transaction costs are important. Furthermore, the dynamic implications of these theories are supported. [source]


The burgeoning field of statistical phylogeography

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004
L. L. Knowles
Abstract In the newly emerging field of statistical phylogeography, consideration of the stochastic nature of genetic processes and explicit reference to theoretical expectations under various models has dramatically transformed how historical processes are studied. Rather than being restricted to ad hoc explanations for observed patterns of genetic variation, assessments about the underlying evolutionary processes are now based on statistical tests of various hypotheses, as well as estimates of the parameters specified by the models. A wide range of demographical and biogeographical processes can be accommodated by these new analytical approaches, providing biologically more realistic models. Because of these advances, statistical phylogeography can provide unprecedented insights about a species' history, including decisive information about the factors that shape patterns of genetic variation, species distributions, and speciation. However, to improve our understanding of such processes, a critical examination and appreciation of the inherent difficulties of historical inference and challenges specific to testing phylogeographical hypotheses are essential. As the field of statistical phylogeography continues to take shape many difficulties have been resolved. Nonetheless, careful attention to the complexities of testing historical hypotheses and further theoretical developments are essential to improving the accuracy of our conclusions about a species' history. [source]


A review of acoustic playback techniques for studying avian vocal duets

JOURNAL OF FIELD ORNITHOLOGY, Issue 2 2010
Sarah B. Douglas
ABSTRACT Playback experiments involve the broadcast of natural or synthetic sound stimuli and provide a powerful tool for studying acoustic communication in birds. Playback is a valuable technique for exploring vocal duetting behavior because it allows investigators to test predictions of the various hypotheses for duet function. Here, we adopt a methodological perspective by considering various challenges specific to studying duetting behavior, and highlighting the utility of different playback designs for testing duet function. Single-speaker playback experiments allow investigators to determine how duetting birds react to different stimuli, but do not simulate duets in a spatially realistic manner. Multi-speaker playback experiments are superior to single-speaker designs because duet stimuli are broadcast with spatial realism and unique and additional predictions can be generated for testing duet function. In particular, multi-speaker playback allows investigators to evaluate how birds respond to male versus female duet contributions separately, based on reactions to the different loudspeakers. Interactive playback allows investigators to ask questions about the time- and pattern-specific singing behavior of birds, and to understand how singing strategies correspond to physical behavior during vocal interactions. Although logistically challenging, interactive playback provides a powerful tool for examining specific elements of duets (such as the degree of coordination) and may permit greater insight into their functions from an operational perspective. Interactive playback designs where the investigator simulates half of a duet may be used to describe and investigate the function of pair-specific and population-wide duet codes. Regardless of experimental design, all playback experiments should be based on a sound understanding of the natural duetting behavior of the species of interest, and should aim to produce realistic and carefully controlled duet simulations. Future studies that couple playback techniques with other experimental procedures, such as Acoustic Location System recordings for monitoring the position of birds in dense vegetation or multimodal techniques that combine acoustic with visual stimuli, are expected to provide an even better understanding of these highly complex vocal displays. RESUMEN Los experimentos de reproducción de sonidos grabados involucran el uso de sonido natural o sintético y proveen una herramienta poderosa para el estudio de la comunicación acústica de las aves. La reproducción de sonidos grabados es una técnica valiosa para explorar las duetas vocales porque permite probar las predicciones de varios hipótesis sobre la función de duetas. Aquí, adoptamos una perspectiva metodológica, considerando los varios retos específicos al estudio del comportamiento de duetas y resaltando la utilidad de diferentes diseños de reproducción de sonidos grabados para probar la función de las duetas. Experimentos de reproducción de sonidos grabados hechas con un parlante permiten una determinación de como las aves que realizan duetas reaccionan a diferentes estímulos, pero no simulan las duetas de una manera espacialmente realística. Experimentos de reproducción de sonidos grabados hechas con múltiples parlantes son superiores a diseños con un solo parlante porque transmiten el sonido de una manera espacialmente realística y generan predicciones únicas y adicionales para probar la función de la dueta. En particular, la reproducción de sonidos grabados con múltiples parlantes permite una evaluación de cómo las aves responden a las contribuciones del macho y de la hembra separadamente, basado en sus reacciones a los diferentes parlantes. La reproducción de sonidos grabados interactiva permite hacer preguntas temporalmente especificas y en relación a patrones especificas sobre el comportamiento de canto. También permite entender como las estrategias de canto corresponden al comportamiento físico durante las interacciones vocales. Aunque es un reto logístico, la reproducción de sonidos grabados interactiva provee una herramienta poderosa para examinar elementos específicos de las duetas (como el grado de coordinación) y podría permitir un mayor conocimiento sobre sus funciones de una perspectiva operacional. Los diseños de la reproducción de sonidos grabados interactivas, en la cual el investigador simula la mitad de una dueta, podrían ser usadas para describir e investigar la función de los códigos de dueta específicos a una pareja y a una población. Sin importar el tipo de diseño experimental, todos los experimentos de reproducción de sonidos grabados deberían ser basadas en una buena comprensión del comportamiento natural de las duetas en la especie de interés, y deberían tener la meta de producir simulaciones de duetas realísticas y cuidadosamente controladas. Se espera que los estudios futuros cuales combinan técnicas de la reproducción de sonidos grabados con otros procedimientos experimentales, como grabaciones del Sistema de Ubicación Acústica para monitorear la posición de aves en vegetación densa, o técnicas multimodales que combinan estímulos acústicos con estímulos visuales, provean un mejor entendimiento de estos despliegues vocales altamente complejos. [source]


Absence of leukocyte microchimerism in oral lichen planus (OLP): an in situ hybridisation study

JOURNAL OF ORAL PATHOLOGY & MEDICINE, Issue 7 2001
T. Lombardi
Abstract: Oral lichen planus (OLP) is a relatively common chronic inflammatory disease. The majority of patients are between 30 and 50 years of age with a higher incidence in females. The aetiology is unknown and various hypotheses on the pathogenic mechanisms, including autoimmunity, have been proposed over the years. In the present study, we investigated whether leukocyte microchimerism, a biological situation implicated in the aetiology of some autoimmune diseases, might play a role in the pathogenesis of OLP. We used in situ hybridisation to identify Y chromosome DNA in a series of formalin-fixed paraffin-embedded oral mucosa biopsies of women with established clinical and histological disease who had given birth to a male child. The positive control, two mucosal specimens from a man with OLP, showed over 90% of keratinocytes and cells within the inflammatory infiltrate, a positive nuclear signal. The negative control, biopsies from three women having carried only female foetuses and one nulliparous woman, all with OLP, did not show any nuclear signal. In the fifteen selected cases of OLP biopsies from women who had only male offspring, nucleated cells containing the Y chromosome were not detected within the chronic inflammatory infiltrate. These results suggest that unlike some other immunologically mediated diseases, leukocyte microchimerism does not seems to be involved in the pathogenesis of OLP. [source]


An empirical investigation of interviewer-related factors that discourage the use of high structure interviews

JOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 1 2004
Filip Lievens
High structure interviews appear to be less frequently used in personnel management practice than might be expected given their good reliability and validity. Although several authors have speculated on the factors of resistance to high structure interviews, empirical research is very scarce. Two studies are conducted among experienced human resources representatives who frequently conduct employment interviews. The first study provides a fine-grained description of the degree of structure used in interviews, showing that in most interviews constraints are placed only on the topical areas to be covered and that scoring is done only on multiple criteria. The second study tests various hypotheses regarding interviewer-related factors, which may lead to lower levels of structure in interviews. Results show that when interviewers are concerned about establishing an informal contact with interviewees, want to have discretion over interview questions, and want to develop interviews efficiently, they are less inclined to use higher levels of structure in interviews. Conversely, people who participated in interviewing workshops and Conventional types report using significantly higher levels of structure. Implications for improving interviewer motivation to use higher levels of structure in interviews are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Latitudinal gradient of taxonomic richness: combined outcome of temperature and geographic mid-domains effects?

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 3 2005
A. Brayard
Abstract For several decades, the origin and ecological consequences of large-scale continental and marine Latitudinal Gradients of Taxonomic Richness (LGTR) have been intensively debated. Among the various hypotheses, it has been proposed that a LGTR is the by-product of a geographic mid-domain effect, i.e. the result of a random distribution of ranges of taxa between physical hard boundaries such as the continent/ocean interface. In order to more realistically evaluate the role of the mid-domain effect on the origin and evolution of the LGTR of marine planktonic organisms, we present a 2D model based on a cellular-automaton approach in which sea surface temperatures (SST) and currents are forced in the biogeographic dispersal of a randomly generated clade (a 2D ,geophyletic' model). Sensitivity experiments allow to evaluate the effects of currents, SST and the geographical origin of a clade on the formation and shape of a LGTR for planktonic organisms when coupled with a geographic mid-domain effect. Results are discussed in the light of the empirical LGTR of extant planktonic Foraminifera in the Atlantic Ocean. Independently of any other biotic or abiotic parameter, inclusive of the surface currents and origination/extinction absolute and relative rates, our simulations show that the coupling of the mid-domain effect with two critical parameters, namely the shape and intensity of the SST gradient and the geographic origin of a clade, produces realistic patterns of diversity when compared with the observed LGTR of extant atlantic planktonic foraminifera. The results illustrate a non-linear relation between a unimodal latitudinal SST gradient and a resulting bimodal LGTR characterized by a drop in species richness near the equator. This relation indicates that the SST gradient exerts a mid-domain effect on the LGTR. The latitudinal positions of the modal values of the LGTR are also found to be influenced by the geographic origin of the simulated clade. Résumé Depuis plusieurs décennies, l'origine et l'interprétation écologique des Gradients Latitudinaux de Richesse Taxonomique (LGTR) marins ou continentaux, ont été intensivement débattues. Parmi de nombreuses hypothèses, il a été proposé qu'un LGTR puisse être le sous-produit d'un effet de milieu de domaine géographique, i.e. le résultat d'une distribution aléatoire des répartitions des taxa entre deux limites physiques telles que l'interface continent/océan. Afin d'évaluer plus efficacement le rôle de cet effet sur l'origine et l'évolution des LGTR des organismes planctoniques marins, nous proposons un modèle 2D basé sur une approche de type automate cellulaire dans laquelle les températures des eaux de surface (SST) et les courants régulent la dispersion biogéographique d'une phylogénie générée aléatoirement (un modèle «géophylétique»). Ce modèle permet d'évaluer les effets des courants, des SST et de la dépendance thermique des espèces sur la mise en place et la forme d'un LGTR impliquant des organismes planctoniques. Il permet aussi de discuter des influences respectives de ces paramètres quand ils sont superposés à l'effet de milieu de domaine géographique. Les résultats sont discutés à partir du LGTR empirique des foraminifères planctoniques atlantiques actuels. Indépendamment de tout autre paramètre biotique ou abiotique, y compris les courants ainsi que les taux relatifs et absolus d'apparition et d'extinction, les simulations font apparaître que le couplage de l'effet de milieu de domaine à deux contraintes principales, la forme et l'intensité du gradient de SST ainsi que la localisation géographique de l'origine du clade, produit des représentations réalistes de la diversité comparées au LGTR observé pour les foraminifères planctoniques actuels de l'océan atlantique. Nos résultats indiquent une relation non-linéaire entre la structure globale d'un gradient unimodal de SST et le LGTR bimodal correspondant, montrant une baisse de richesse spécifique au niveau de l'équateur. Cette relation suggère que le gradient de SST exerce un effet de milieu de domaine thermique sur le LGTR. Les positions latitudinales des modes du LGTR sont aussi influencées par le lieu d'origine du clade simulé. [source]


Phylogeny, phylogeography, and geographic variation of Sylvisorex howelli (Soricidae), an endemic shrew of the Eastern Arc Mountains, Tanzania

JOURNAL OF ZOOLOGY, Issue 4 2005
William T. Stanley
Abstract The Eastern Arc Mountains of eastern Africa are notable for the high levels of endemism exhibited by various forest-dwelling organisms of this ancient montane archipelago. There has been virtually no assessment of the variation among populations of small mammal species living on these unique mountains, but recent faunal surveys have produced sufficient material to initiate such studies. Cranial morphometric and DNA sequence data were examined from six populations of Sylvisorex howelli Jenkins, 1984, an endemic shrew found in several different massifs of the Eastern Arc Mountains, to assess variation across the archipelago in the context of various hypotheses of historical biogeography. Twenty-two cranial measurements were analysed using principal components analysis. Age classes (based on tooth wear) and sex had little effect on the variation exhibited by the variables studied. Overall, specimens of S. howelli from the East Usambara Mountains are smaller than specimens from other known populations. The mitochondrial ND2 and 12S rRNA genes from representatives of each montane population of S. howelli in addition to several crocidurine taxa from eastern Africa and three soricine outgroup species were sequenced to assess phylogenetic relationships among these taxa. Neither maximum likelihood, maximum parsimony, nor Bayesian analyses support monophyly of the genus Sylvisorex, but S. howelli populations were consistently recovered as a well-supported clade. Over 40 individuals of S. howelli from six disjunct montane ranges, comprising the entire known distribution of the species, were sequenced for 504 base pairs of ND2 to investigate phylogeographic patterns. Phylogenetic analysis recovered six reciprocally monophyletic haplotype clades grouped by locality. Branch lengths are consistent with relatively long periods of isolation among populations from the Uluguru, Ukaguru, Nguru, Nguu, East Usambara and West Usambara Mountains, with low levels of diversity observed within each population. These results are interpreted within the historical context of the Eastern Arc Mountains. [source]


Disentangling the proximate factors of deforestation: The case of the Monarch butterfly Biosphere Reserve in Mexico

LAND DEGRADATION AND DEVELOPMENT, Issue 1 2009
J. Honey-Rosés
Abstract Understanding the causes of environmental degradation can lead to more effective forest management. Often, the discussion about the causes of deforestation confuses issues across spatial and temporal scales. Such is the case in the Monarch Butterfly Biosphere Reserve (MBBR) in Mexico where various hypotheses compete to explain the deforestation observed there. This paper analyzes these hypotheses using the analytical approaches developed by the literature on environmental degradation and biodiversity loss. This paper first distinguishes between proximate factors and underlying socioeconomic forces. It then reviews recent deforestation studies to evaluate the relative impact of each proximate factor observed in the MBBR. Illegal logging stands out as the factor with the most empirical support. In contrast, agricultural clearing, while frequently cited as major driver of forest loss, has much less empirical backing. These conclusions update the deforestation diagnosis for this protected area and suggest that more attention should be directed at understanding the illicit timber trade. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Mustelid scent-marking in managed ecosystems: implications for population management

MAMMAL REVIEW, Issue 3-4 2000
Michael R. Hutchings
ABSTRACT Scent-marking is the primary form of communication for mustelids and is important in understanding their sociobiology. In addition, mustelids interact with managed ecosystems or may themselves be managed. However, little is known about the scent-marking behaviour of most mustelids or the impact of management on this behaviour. Mustelids have a number of different scent mark types that can be used for several possible functions, creating a flexible system of varied scent-marking strategies both across and within species. We review the types of scent marks used by European mustelids in relation to their social systems and consider the various hypotheses proposed for their function. Scent-marking behaviour is not fixed for each species, but varies with habitat and population density. We use Badgers (Meles meles) as an example of mustelids acting as reservoirs of disease and Otters (Lutra lutra) as an example of a key conservation species, to demonstrate the applied importance of understanding natural patterns of mustelid scent-marking strategies and the impact of habitat and population management on them. [source]


On the Coates,Sinnott Conjecture

MATHEMATISCHE NACHRICHTEN, Issue 10 2009
Cristian D. Popescu
Abstract In [5], Coates and Sinnott formulated a far reaching conjecture linking the values ,F/k,S(1 , n) for even integers n , 2 of an S -imprimitive, Galois-equivariant L -function ,F/k,S associated to an abelian extension F/k of totally real number fields to the annihilators over the group ring ,[G (F/k)] of the even Quillen K -groups K2n,2 (OF) associated to the ring of integers OF of the top field F. In the same paper, Coates and Sinnott essentially prove the ,, -adic étale cohomological version of their conjecture, in which K2n,2(OF) is replaced by H2et(OF [1/,, ], ,(n)), for all primes ,, > 2, under the hypothesis that k = ,. Refinements of this result for k = ,, involving Fitting ideals rather than annihilators of H2et(OF [1/,,], ,,,(n)), were obtained in particular cases by Cornacchia,Østvaer [7] and in general by Kurihara [14]. More recently, Burns and Greither [3] proved the same type of refinements (involving Fitting ideals of étale cohomology groups) for arbitrary totally real base fields k, but working under the very strong hypothesis that the Iwasawa , -invariants ,F,,, vanish for all odd primes ,,. In this paper, we study a class of abelian extensions of an arbitrary totally real base field k including, for example, subextensions of real cyclotomic extensions of type k (,)+/k, where p is an odd prime. For this class of extensions, we prove similar refinements of the étale cohomological version of the Coates,Sinnott conjecture, under no vanishing hypotheses for the Iwasawa ,-invariants in question. Our methods of proof are different from the ones employed in [3], [14] and [7]. We build upon ideas developed by Greither in [10] and Wiles in [23] and [22], in the context of Brumer's Conjecture. If the Quillen,Lichtenbaum Conjecture is proved (and a proof seems tobe within reach), then we have canonical ,,,[G (F/k)]-module isomorphisms for all n , 2, all i = 1,2, and all primes ,, > 2, and all these results will yield proofs of the original K -theoretic version of the Coates,Sinnott Conjecture, in the cases and under the various hypotheses mentioned above (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Taxonomic revision of Mecyclothorax Sharp (Coleoptera, Carabidae) of Hawaii Island: abundant genitalic variation in a nascent island radiation

MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE IN BERLIN-DEUTSCHE ENTOMOLOGISCHE ZEITSCHRIFT, Issue 1 2008
James K. Liebherr
Abstract The Hawaii Island fauna of Mecyclothorax Sharp, 1903 is taxonomically revised and found to comprise 30 species, 18 newly described: M. gagnei sp. n., M. nitidus sp. n., M. maunakukini sp. n., M. punakukini sp. n., M. kaukukini sp. n., M. perivariipes sp. n., M. aa sp. n., M. giffini sp. n., M. hephaestus sp. n., M. funebris sp. n., M. granulipennis sp. n., M. rufipennis sp. n., M. blackburnianus sp. n., M. swezeyi sp. n., M. sinuosus sp. n., M. williamsi sp. n., M. purpuripennis sp. n., and M. footei sp. n. New synonymies include: Mecyclothorax parvus Britton, 1948 = M. subunctus (Perkins), 1917; Thriscothorax munroi Perkins, 1937 = M. karschi (Blackburn), 1882; Thriscothorax gracilis Sharp, 1903 and Mecyclothorax proximus Britton, 1948 = M. konanus Sharp, 1903; Mecyclothorax terminalis Britton, 1948 = M. discedens (Sharp) 1903. Mecyclothorax vulcanus (Blackburn) was described from a mixed series, with the cryptic sibling species M. hephaestus newly described to correct the partial misidentification. Species delimitation for the highly variable M. konanus is achieved using a hierarchical analysis based on infraspecifically variable attributes. Extensive male genitalic variation is documented within M. konanus and M. deverilli (Blackburn), and also among the cryptic sibling species pair M. variipes (Blackburn) and M. perivariipes. The observed variation is consistent with various hypotheses of sexual selection, but not with the genitalic lock and key hypothesis. Areas of endemism are tentatively proposed based on the most restricted distributions of Hawaii Island Mecyclothorax, with various flanks of Mauna Kea and Mauna Loa volcanoes identified as distinctive areas. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


The FliK protein and flagellar hook-length control

PROTEIN SCIENCE, Issue 5 2007
Richard C. Waters
Abstract The bacterial flagellum is a highly complex prokaryotic organelle. It is the motor that drives bacterial motility, and despite the large amount of energy required to make and operate flagella, motile organisms have a strong adaptive advantage. Flagellar biogenesis is both complex and highly coordinated and it typically involves at least three two-component systems. Part of the flagellum is a type III secretion system, and it is via this structure that flagellar components are exported. The assembly of a flagellum occurs in a number of stages, and the "checkpoint control" protein FliK functions in this process by detecting when the flagellar hook substructure has reached its optimal length. FliK then terminates hook export and assembly and transmits a signal to begin filament export, the final stage in flagellar biosynthesis. As yet the exact mechanism of how FliK achieves this is not known. Here we review what is known of the FliK protein and discuss the evidence for and against the various hypotheses that have been proposed in recent years to explain how FliK controls hook length, FliK as a molecular ruler, the measuring cup theory, the role of the FliK N terminus, the infrequent molecular ruler theory, and the molecular clock theory. [source]


A review of p53 expression and mutation in human benign, low malignant potential, and invasive epithelial ovarian tumors

CANCER, Issue 2 2003
Leanne M. Kmet M.Sc.
Abstract BACKGROUND In the current study, the authors present pooled data from studies that investigated p53 protein expression and/or mutation in human epithelial ovarian tumors. METHODS The English literature in the MEDLINE, PubMed, and Ingenta databases was searched to the end of the year 2000 to identify relevant studies. Data were pooled across eligible studies, and the prevalence of p53 expression and mutation among benign, low malignant potential (LMP), and invasive tumors was determined. Prevalence estimates by tumor histology, International Federation of Gynecology and Obstetrics (FIGO) stage, and grade also were calculated. RESULTS The pooled prevalence estimate for p53 overexpression among epithelial ovarian carcinomas was 51% (95% confidence intervals [95% CI], 50,53%) compared with 17% (95% CI, 15,20%) among LMP tumors and 7% (95% CI, 5,10%) among benign tumors. p53 mutation prevalence estimates were 45% (95% CI, 42,47%), 5% (95% CI, 2,9%), and 1% (95% CI, 0,5%), respectively, for invasive, LMP, and benign tumors. The prevalence of these p53 abnormalities was found to be associated positively with increasing tumor grade and stage. Differences based on histologic subtype also were found. CONCLUSIONS Although these pooled estimates might appear to offer support for various hypotheses regarding the role of p53 in ovarian carcinoma, the limitations inherent in these data hamper the interpretation of the significance of any of the findings. Future studies will require innovative methods to address the limitations of many previous investigations and more comprehensive investigation into defective tumor suppression mechanisms. Cancer 2003;97:389,404. © 2003 American Cancer Society. DOI 10.1002/cncr.11064 [source]