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Proposed Hypotheses (proposed + hypothesis)
Selected AbstractsTesting abundance-range size relationships in European carabid beetles (Coleoptera, Carabidae)ECOGRAPHY, Issue 5 2003D. Johan Kotze Four of the eight hypotheses proposed in the literature for explaining the relationship between abundance and range size (the sampling artifact, phylogenetic non-independence, range position and resource breadth hypotheses) were tested by using atlas data for carabid beetles (Coleoptera, Carabidae) from Belgium, Denmark and the Netherlands. A positive relationship between abundance and partial range size was found in all three countries, and the variation in abundance was lower for widespread species. Analysis of the data did not support three of the proposed hypotheses, but did support the resource breadth hypothesis (species having broader environmental tolerances and being able to use a wider range or resources will have higher local densities and be more widely distributed than more specialised species). Examination of species' characteristics revealed that widespread species are generally large bodied, generalists (species with wide niche breadths occurring in a variety of habitat types) and are little influenced by human-altered landscapes, while species with restricted distributions are smaller bodied, specialists (species with small niche breadths occurring in only one or two habitat types), and favour natural habitat. Landscape alteration may be an important factor influencing carabid abundance and range size in these three countries with a long history of human-induced environmental changes. [source] Size-Related Advantages for Reproduction in a Slightly Dimorphic Raptor: Opposite Trends between the SexesETHOLOGY, Issue 12 2007Fabrizio Sergio Despite many comparative analyses and more than 20 proposed hypotheses, there is still little consensus over the factors promoting the evolution of reversed sexual dimorphism (RSD) in raptorial species. Furthermore, intrapopulation studies, which may elucidate how RSD is maintained once evolved, have been surprisingly scarce and only focused on a handful of species with medium to high dimorphism. We examined the reproductive advantages associated with body size and condition, measured in the pre-laying period, in a diurnal raptor with low sexual dimorphism, the black kite (Milvus migrans). The study population was essentially monomorphic in size. For females, there was an evidence of reproductive benefits associated with larger size and/or with better body condition. Larger females had also access to higher quality partners and territories, consistent with the ,intrasexual selection' hypothesis, by which members of the larger sex enjoy size-related advantages in intrasexual competition over a scarce resource, the smaller sex. Opposite trends emerged for males: smaller, leaner males had higher breeding output, consistent with the ,small efficient male' hypothesis. Overall, the fact that we observed in an essentially monomorphic population the same selection pressures previously found in species with marked dimorphism suggests that such reproductive advantages may be counterbalanced in our study model by opposite selection pressures during other stages of the life cycle. This casts some doubts on the evolutionary significance of studies focusing exclusively on reproduction and calls for the need of more comprehensive analyses incorporating trait-mediated differentials in survival and recruitment. [source] In-situ oxygen profiling and lignin modification in guts of wood-feeding termitesINSECT SCIENCE, Issue 3 2010Jing Ke Abstract, Reports on the capability of wood-feeding termites (WFTs) in degrading wood particles and on the existence of aerobic environment in the localized guts suggest that their high efficiency of cellulose utilization is not only caused by cellulase, but also by biochemical factors that pretreat lignin. We thus extend the hypothesis that for highly efficient accessibility of cellulose, there should be direct evidence of lignin modification before the hindgut. The lignin degradation/modification is facilitated by the oxygenated environment in intestinal microhabitats. To test our hypothesis, we conducted experiments using a dissolved oxygen microelectrode with a tip diameter < 10 ,m to measure oxygen profiles in intestinal microhabitats of both Coptotermes formosanus (Shiraki) and Reticulitermes flavipes (Kollar). Lignin modification during passage through their three gut segments was also analyzed with pyrolysis gas chromatography/mass spectrometry. The data showed relatively high levels of oxygen in the midgut that could have promoted lignin oxidation. Consistent with the oxygen measurements, lignin modifications were also detected. In support of previously proposed hypotheses, these results demonstrate that lignin disruption, which pretreats wood for cellulose utilization, is initiated in the foregut, and continues in the midgut in both termites. [source] Biogeographical patterns of genetic differentiation in dung beetles of the genus Trypocopris (Coleoptera, Geotrupidae) inferred from mtDNA and AFLP analysesJOURNAL OF BIOGEOGRAPHY, Issue 7 2004Loredana Carisio Abstract Aim, To examine the phylogeography and population structure of three dung beetle species of the genus Trypocopris (Coleoptera, Geotrupidae). We wanted to test whether genetic differences and genealogies among populations were in accordance with morphologically described subspecies and we aimed to establish times of divergence among subspecies to depict the appropriate temporal framework of their phylogeographical differentiation. We also wished to investigate the historical demographic events and the relative influences of gene flow and drift on the distribution of genetic variability of the different populations. Location, Europe (mostly Italy). Methods, We collected adult males from dung pats from 15 Italian localities over the period 2000,2002. For sequence analysis, some dried specimens from Albania, Croatia, Slovakia and Spain were also used. We applied cytochrome oxidase I mitochondrial DNA sequencing and the amplified fragment length polymorphism (AFLP) technique to determine whether phylogeographical patterns within the three species support the proposed hypotheses of subspecies designations, and to detect further structure among populations that might mediate diversification. Results and main conclusions, The results show a high concordance between the distribution of mtDNA variation and the main morphological groups recognized as subspecies, which thus may represent independent evolutionary units. The degree of mitochondrial divergence suggests that speciation events occurred during the Pliocene, while diversification of the main subspecific lineages took place in the Pleistocene, from c. 0.3 to 1.5 Ma. Mitochondrial and nuclear data also reveal that there is phylogeographical structuring among populations within each of the main groups and that both contemporary and historical processes determined this pattern of genetic structure. Geographical populations form monophyletic clades in both phylogenetic and network reconstructions. Despite the high levels of intrapopulational diversity, FST values indicate moderate but significant genetic differentiation among populations, and a Bayesian clustering analysis of the AFLP data clearly separates the geographical populations. Nucleotide and gene diversity estimates reveal interspecific differences in the degree of diversification among populations that may be related to the different ecological requirements of the three species. [source] Evolutionary transitions among dioecy, androdioecy and hermaphroditism in limnadiid clam shrimp (Branchiopoda: Spinicaudata)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 9 2009S. C. WEEKS Abstract Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: dioecy to hermaphroditism. A fruitful approach to studying this latter transition can be sought by studying clades in which transitions between dioecy and hermaphroditism have occurred multiple times. Freshwater crustaceans in the family Limnadiidae comprise dioecious, hermaphroditic and androdioecious (males + hermaphrodites) species, and thus this family represents an excellent model system for the assessment of the evolutionary transitions between these related breeding systems. Herein we report a phylogenetic assessment of breeding system transitions within the family using a total evidence comparative approach. We find that dioecy is the ancestral breeding system for the Limnadiidae and that a minimum of two independent transitions from dioecy to hermaphroditism occurred within this family, leading to (1) a Holarctic, all-hermaphrodite species, Limnadia lenticularis and (2) mixtures of hermaphrodites and males in the genus Eulimnadia. Both hermaphroditic derivatives are essentially females with only a small amount of energy allocated to male function. Within Eulimnadia, we find several all-hermaphrodite populations/species that have been independently derived at least twice from androdioecious progenitors within this genus. We discuss two adaptive (based on the notion of ,reproductive assurance') and one nonadaptive explanations for the derivation of all-hermaphroditism from androdioecy. We propose that L. lenticularis likely represents an all-hermaphrodite species that was derived from an androdioecious ancestor, much like the all-hermaphrodite populations derived from androdioecy currently observed within the Eulimnadia. Finally, we note that the proposed hypotheses for the dioecy to hermaphroditism transition are unable to explain the derivation of a fully functional, outcrossing hermaphroditic species from a dioecious progenitor. [source] An Empirical Investigation of Knowledge-Sharing in NetworksJOURNAL OF SUPPLY CHAIN MANAGEMENT, Issue 4 2005Stephan M. Wagner Summary Given the growing importance of knowledge-sharing, the primary purpose of this research is to develop and test a series of hypotheses regarding interorganizational knowledge-sharing with different actors in networks. Findings, based on responses from 182 firms, reveal that a firm's degree of knowledge-sharing with research institutions and customers is positively influenced by the firm's resource commitment. As expected, the firms' satisfaction is positively related to the frequency of communication. Consistent with the proposed hypotheses, knowledge tacitness diminishes the effect sharing knowledge with suppliers has on satisfaction. Contrary to expectations, tacitness positively moderates the effect sharing knowledge with customers has on satisfaction. Overall, this paper establishes the foundation for a more fine-grained analysis of knowledge-sharing with customers, suppliers and research institutions in a network setting. [source] Phylogeographical structure and temporal complexity in American sweetgum (Liquidambar styraciflua; Altingiaceae)MOLECULAR ECOLOGY, Issue 17 2008ASHLEY B. MORRIS Abstract Eastern North American plant biogeography has traditionally focused on two primary issues: (i) the location of temperate Pleistocene refugia and their proximity to the southern margin of the ice sheet during the last glacial maximum, and (ii) the origin of the temperate element of northern Latin America. While numerous population genetic and phylogeographical studies have focused on the first issue, few (if any) have considered the second. We addressed these issues by surveying 117 individuals from 24 populations of Liquidambar styraciflua (American sweetgum; Altingiaceae) across the southeastern USA, eastern Mexico, and Guatemala, using more than 2200 bp of chloroplast DNA sequence data. To specifically address the issue of timing, we estimated intraspecific divergence times on the basis of multiple fossil-based calibration points, using taxa from Altingiaceae (Liquidambar and Altingia) and Hammamelidaceae (Hamamelis) as outgroups. More than half of the sampled localities exhibited multiple haplotypes. Remarkably, the greatest variation was observed within the USA, with Mexico and Guatemala sharing widespread haplotypes with Texas, Mississippi, Kentucky, Ohio, and northern Virginia. This lack of differentiation suggests shared ancestral polymorphisms, and that the genetic signal we observed is older than the disjunction itself. Our data provide support for previously proposed hypotheses of Pleistocene refugia in peninsular Florida and along the eastern Atlantic, but also for deeper divergences (~8 million years ago) within the USA. These patterns reflect a dynamic biogeographical history for eastern North American trees, and emphasize the importance of the inclusion of a temporal component in any phylogeographical study. [source] Testing co-evolutionary hypotheses over geological timescales: interactions between Mesozoic non-avian dinosaurs and cycadsBIOLOGICAL REVIEWS, Issue 1 2009Richard J. Butler Abstract The significance of co-evolution over ecological timescales is well established, yet it remains unclear to what extent co-evolutionary processes contribute to driving large-scale evolutionary and ecological changes over geological timescales. Some of the most intriguing and pervasive long-term co-evolutionary hypotheses relate to proposed interactions between herbivorous non-avian dinosaurs and Mesozoic plants, including cycads. Dinosaurs have been proposed as key dispersers of cycad seeds during the Mesozoic, and temporal variation in cycad diversity and abundance has been linked to dinosaur faunal changes. Here we assess the evidence for proposed hypotheses of trophic and evolutionary interactions between these two groups using diversity analyses, a new database of Cretaceous dinosaur and plant co-occurrence data, and a geographical information system (GIS) as a visualisation tool. Phylogenetic evidence suggests that the origins of several key biological properties of cycads (e.g. toxins, bright-coloured seeds) likely predated the origin of dinosaurs. Direct evidence of dinosaur,cycad interactions is lacking, but evidence from extant ecosystems suggests that dinosaurs may plausibly have acted as seed dispersers for cycads, although it is likely that other vertebrate groups (e.g. birds, early mammals) also played a role. Although the Late Triassic radiations of dinosaurs and cycads appear to have been approximately contemporaneous, few significant changes in dinosaur faunas coincide with the late Early Cretaceous cycad decline. No significant spatiotemporal associations between particular dinosaur groups and cycads can be identified , GIS visualisation reveals disparities between the spatiotemporal distributions of some dinosaur groups (e.g. sauropodomorphs) and cycads that are inconsistent with co-evolutionary hypotheses. The available data provide no unequivocal support for any of the proposed co-evolutionary interactions between cycads and herbivorous dinosaurs , diffuse co-evolutionary scenarios that are proposed to operate over geological timescales are plausible, but such hypotheses need to be firmly grounded on direct evidence of interaction and may be difficult to support given the patchiness of the fossil record. [source] Occupancy frequency distributions: patterns, artefacts and mechanismsBIOLOGICAL REVIEWS, Issue 3 2002MELODIE A. McGEOCH ABSTRACT Numerous hypotheses have been proposed to explain the shape of occupancy frequency distributions (distributions of the numbers of species occupying different numbers of areas). Artefactual effects include sampling characteristics, whereas biological mechanisms include organismal, niche-based and metapopulation models. To date, there has been little testing of these models. In addition, although empirically derived occupancy distributions encompass an array of taxa and spatial scales, comparisons between them are often not possible because of differences in sampling protocol and method of construction. In this paper, the effects of sampling protocol (grain, sample number, extent, sampling coverage and intensity) on the shape of occupancy distributions are examined, and approaches for minimising artefactual effects recommended. Evidence for proposed biological determinants of the shape of occupancy distributions is then examined. Good support exists for some mechanisms (habitat and environmental heterogeneity), little for others (dispersal ability), while some hypotheses remain untested (landscape productivity, position in geographic range, range size frequency distributions), or are unlikely to be useful explanations for the shape of occupancy distributions (species specificity and adaptation to habitat, extinction,colonization dynamics). The presence of a core (class containing species with the highest occupancy) mode in occupancy distributions is most likely to be associated with larger sample units, and small homogenous sampling areas positioned well within and towards the range centers of a sufficient proportion of the species in the assemblage. Satellite (class with species with the lowest occupancy) modes are associated with sampling large, heterogeneous areas that incorporate a large proportion of the assemblage range. However, satellite modes commonly also occur in the presence of a core mode, and rare species effects are likely to contribute to the presence of a satellite mode at most sampling scales. In most proposed hypotheses, spatial scale is an important determinant of the shape of the observed occupancy distribution. Because the attributes of the mechanisms associated with these hypotheses change with spatial scale, their predictions for the shape of occupancy distributions also change. To understand occupancy distributions and the mechanisms underlying them, a synthesis of pattern documentation and model testing across scales is thus needed. The development of null models, comparisons of occupancy distributions across spatial scales and taxa, documentation of the movement of individual species between occupancy classes with changes in spatial scale, as well as further testing of biological mechanisms are all necessary for an improved understanding of the distribution of species and assemblages within their geographic ranges. [source] Possible involvement of epidermodysplasia verruciformis human papillomaviruses in the immunopathogenesis of psoriasis: a proposed hypothesisEXPERIMENTAL DERMATOLOGY, Issue 6 2003Slawomir Majewski Abstract:, We have shown previously in psoriasis a very high prevalence of epidermodysplasia verruciformis-associated human papillomavirus 5 (EVHPV5) DNA and antibodies to human papillomavirus 5 (HPV5) virus-like particle (VLP)L1, and we suggested that this benign hyperproliferative disorder could be a reservoir for EVHPVs. Here we provide new data confirming the expression of EVHPVs in psoriasis and present our hypothesis on their possible involvement in the immunopathogenesis of the disorder. The new important finding was detection by a radioimmunoprecipitation assay of a very high prevalence of antibodies to E6/E7 HPV5 oncoproteins, known to enhance keratinocyte proliferation. More recently, EV genes were identified, EVER1 and EVER2, whose mutations are responsible for epidermodysplasia verruciformis. Epidermodysplasia verruciformis-associated human papillomaviruses are harmless to the general population as a result of genetic restriction, which in psoriasis appears to be partly alleviated, and this may allow the viral gene expression. We hypothesize that induction of keratinocyte proliferation in psoriasis by various stimuli initiates the EVHPV life cycle with expression of early (E6/E7) and late (L1) viral proteins. The early proteins may, in turn, enhance the keratinocyte proliferation, and the late proteins could serve as a target for specific B- and T-cell-mediated responses. Immune responses against the viral antigens in the epidermis may result in chemoattraction of leukocytes and Munro abscess formation, as well as in production of proinflammatory cytokines, leading to self perpetuation of the psoriatic process. The novel immunomodulatory therapies could also inhibit immune responses against EVHPV proteins, leading to decreased cytokine production, keratinocyte proliferation and EVHPV expression. Thus the beneficial effect of these therapies is not discordant with the proposed hypothesis of possible involvement of EVHPVs in the immunopathogenesis of psoriasis. [source] Stable Blue Emission from a Polyfluorene/Layered-Compound Guest/Host Nanocomposite,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2006E. Aharon Abstract In this study a blue-light-emitting conjugated polymer, poly(9,9-dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS2, and semiconducting SnS2. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X-ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or ,,, interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100,°C for 7,h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light-emitting devices fabricated with a polymer-intercalated SnS2 nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required. [source] Uropygial gland size correlates with feather holes, body condition and wingbar size in the house sparrow Passer domesticusJOURNAL OF AVIAN BIOLOGY, Issue 3 2010Gregorio Moreno-Rueda The uropygial gland is an organ exclusive of birds that secretes an oily substance, the uropygial secretion, the functions of which are still debated. One of the proposed hypothesis is its possible action against chewing lice (order Phthiraptera), a group of avian ectoparasites that feed on feathers, causing different types of harm. However, this hypothesis lacks support. The present study analyses the relationship between uropygial gland size and the number of feather holes (which is correlated with the load of chewing lice) in the house sparrow Passer domesticus. Moreover, the relationship between the uropygial gland size and different aspects of sparrow health (body condition, immunocompetence and haematocrit), as well as sexually selected traits in males (badge and wingbar size), is tested. The results show a negative correlation between uropygial gland size and number of feather holes, a result found both years of the study. This result supports the hypothesis that uropygial secretion is used against chewing lice. Uropygial gland size also correlated positively with body condition (residuals of body mass relative to tarsus length) and immunocompetence, being therefore related to bird health. After a year in captivity, with resources provided ad libitum, no correlation was found between individual uropygial gland size and body condition or haematocrit, perhaps because the negative effect that chewing lice exert on bird health was offset by captivity conditions. Uropygial gland size was not correlated with badge size, but it was correlated with wingbar size, which furthermore supports the contention that this sexually selected signal acts as an indicator of lice resistance in the house sparrow. In summary, this study supports the idea of a positive relationship between uropygial gland and bird health in the house sparrow, the gland secretion affording resistance against chewing lice. [source] A contribution to the discussion of biota dispersal with drift ice and driftwood in the North AtlanticJOURNAL OF BIOGEOGRAPHY, Issue 1 2001S. Johansen Aim The present work aims to review the early proposed hypothesis of biota dispersal by driftwood and drift ice. Location The North Atlantic region. Methods New knowledge gained about drift ice patterns and sources and transport routes of ice-rafted debris and dendrochronologically dated driftwood is used to investigate chance dispersal of diaspores. In addition, the extremely disjunct distribution patterns of some vascular plants in Scandinavia and East Greenland are examined in the light of this new data. Results Both drift ice and driftwood are thought to be important in the chance dispersal of diaspores from Siberia and North-west Russia to parts of the North Atlantic region, in the Late Weichselian or early Holocene. It is proposed that the extremely disjunct distribution of some vascular plants in northern Scandinavia and East Greenland (e.g. Draba sibirica, Oxytropis deflexa ssp. norvegica, Potentilla stipularis and Trisetum subalpestre) are examples of this type of long-distance dispersal. Main conclusions The concentration of extremely disjunct distributed vascular plant species in parts of northern Norway and East Greenland is suggested to relate to the Late Weichselian ice free conditions and the topography and exposure of the coastline in these areas, allowing accumulation of ice-rafted debris and driftwood. A systematic survey of debris samples obtained from drift ice and driftwood trees is needed to evaluate the significance of these vectors for dispersal of biota to the North Atlantic region. [source] | ||||||||||