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Limited Potential (limited + potential)
Selected AbstractsParasitism by the mite Trombidium breei on four U.K. butterfly speciesECOLOGICAL ENTOMOLOGY, Issue 6 2002L. Conradt Abstract 1. The incidence of parasitism by larvae of the mite species Trombidium breei was reported in one population of the lycaenid butterfly Polyommatus icarus, four populations of the satyrine butterfly Maniola jurtina, one population of the satyrine butterfly Aphantopus hyperanthus, and two populations of the satyrine butterfly Pyronia tithonus, as well as on one specimen of the dipteran Alophorus hemiptera. A considerable proportion of butterflies (11-50%) was infested in all study populations. 2. The pattern of infestation was examined in detail in M. jurtina. Males had a significantly higher incidence of infestation than females, and middle-aged butterflies had a higher incidence of infestation than old or young butterflies. The incidence of infestation peaked in the middle of the flight season, and this seasonal effect was independent of the effect of butterfly age. 3. Using a model based on capture-recapture data, it was estimated that a hypothetical ideal male M. jurtina that lives exactly the mean expected lifespan of 9-10 days has an approximately 75% chance of becoming infested with mites at least once during its lifetime, a mean time to first infestation of 3-4 days, and an average infestation persistence time of 2-3 days. 4. Capture-recapture data failed to show any effect of mite infestation on the lifespan or within-habitat movement rate of M. jurtina. 5. In experiments in which individual butterflies were taken out of their normal habitat and released, M. jurtina and P. tithonus that were infested with mite larvae did not differ from uninfested individuals in the efficiency with which they returned to suitable habitat. Thus, parasitism by T. breei larvae had no detectable effects on flight performance or orientation ability. 6. The results suggest that trombidiid mite larvae have limited potential in the biological control of insect pests. [source] Structural and functional insights into Erwinia carotovora l -asparaginaseFEBS JOURNAL, Issue 17 2008Anastassios C. Papageorgiou Bacterial l -asparaginases are enzymes that catalyze the hydrolysis of l -asparagine to aspartic acid. For the past 30 years, these enzymes have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. Their intrinsic low-rate glutaminase activity, however, causes serious side-effects, including neurotoxicity, hepatitis, coagulopathy, and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side-effects in leukemia therapy. To gain detailed insights into the properties of E. carotovora asparaginase, combined crystallographic, thermal stability and cytotoxic experiments were performed. The crystal structure of E. carotovoral -asparaginase in the presence of l -Asp was determined at 2.5 Å resolution and refined to an Rcryst of 19.2 (Rfree = 26.6%) with good stereochemistry. Cytotoxicity measurements revealed that E. carotovora asparaginase is 30 times less toxic than the Escherichia coli enzyme against human leukemia cell lines. Moreover, denaturing experiments showed that E. carotovora asparaginase has decreased thermodynamic stability as compared to the E. coli enzyme and is rapidly inactivated in the presence of urea. On the basis of these results, we propose that E. carotovora asparaginase has limited potential as an antileukemic drug, despite its promising low glutaminase activity. Our analysis may be applicable to the therapeutic evaluation of other asparaginases as well. [source] Genetic population structure of the net-winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south-western Cape, South Africa: implications for dispersalFRESHWATER BIOLOGY, Issue 1 2003M. J. Wishart SUMMARY 1.,The net-winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net-winged midge should exhibit a high degree of population sub-structuring. 2.,Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south-western Cape of South Africa. 3.,Twenty-five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour-joining tree revealed two highly divergent clades (,5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units. 4.,The distribution of genetic variation was examined using analysis of molecular variance (amova). This showed most of the variation to be distributed among the two ranges (,80%), with a small percentage (,15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001). 5.,Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra-generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna. 6.,The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi. [source] Using historical ecology to understand patterns of biodiversity in fragmented agricultural landscapesJOURNAL OF BIOGEOGRAPHY, Issue 11 2005Ian D. Lunt Abstract Aim, To enhance current attempts to understand biodiversity patterns by using an historical ecology approach to highlight the over-riding influence of land-use history in creating past, current and future patterns of biodiversity in fragmented agricultural landscapes. Methods, We develop an integrative conceptual framework for understanding spatial and temporal variations in landscape patterns in fragmented agricultural landscapes by presenting five postulates (hypotheses) which highlight the important role of historical, anthropogenic disturbance regimes. We then illustrate each of these postulates with examples drawn from fragmented woodlands in agricultural areas of south-eastern Australia, and discuss these findings in an international context. Location examples are drawn from agricultural areas in south-eastern Australia. Results, We conclude that there is limited potential to refine our understanding of patterns of biodiversity in human-modified landscapes based on traditional concepts of island biogeography, or simple assumptions of ongoing destruction and degradation. Instead, we propose that in agricultural landscapes that were largely cleared over a century ago: (1) present-day remnant vegetation patterns are not accidental, but are logically arrayed due to historic land-use decisions, (2) historic anthropogenic disturbances have a major influence on current ecosystem conditions and diversity patterns, and (3) the condition of remnant ecosystems is not necessarily deteriorating rapidly. Main conclusions, An historical ecology approach can enhance our understanding of why different species and ecosystem states occur where they do, and can explain internal variations in ecological conditions within remnant ecosystems, too often casually attributed to the ,mess of history'. This framework emphasizes temporal changes (both past and future) in biotic patterns and processes in fragmented agricultural landscapes. Integration of spatially and temporally explicit historical land-use information into ecological studies can prove extremely useful to test hypotheses of the effects of changes in landscape processes, and to enhance future research, restoration and conservation management activities. [source] Predictive value of clinical and microbiological parameters for the treatment outcome of scaling and root planingJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 7 2005P. F. Brochut Abstract Objectives: To compare the clinical and microbiological outcome of non-surgical periodontal therapy after 6 months with data obtained after hygienic phase or 6 weeks after completion of non-surgical therapy, in order to evaluate the value of clinical and microbiological parameters to predict treatment success. Material and Methods: Clinical and microbiological data were available from 271 sites in 10 systemically healthy non-smokers with moderate-to-advanced chronic periodontal disease (24,32 sites per individual). Subgingival plaque samples were tested for the presence of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Tannerella forsythensis and Treponema denticola using RNA probes. Results: Stepwise multiple linear regression analysis revealed a significant impact of the number of sites with visible plaque index >1 after hygienic phase on the bleeding tendency of a subject at month 6 (p<0.01). Furthermore, an association could be demonstrated between the number of residual pockets (PD>3 mm) 6 months after therapy and the number of bleeding sites and suppurating sites after hygienic phase (p=0.016). Six weeks after therapy, the mean total bacterial loads had a significant impact on the bleeding tendency of a subject at month 6 (p<0.01). Although the average numbers of sites with persisting P. gingivalis, A. actinomycetemcomitans, T. forsythensis and T. denticola seemed to be very similar 6 weeks and 6 months after therapy, large variations were noted between subjects, and therefore the microbiological status of a subject at week 6 could not predict the status at month 6. Conclusions: The present study showed a limited potential of microbiological tests, performed after hygienic phase or shortly after non-surgical periodontal therapy, to predict the clinical outcome 6 months later, but confirmed the importance of an establishment of perfect oral hygiene before non-surgical therapy. [source] Ligament creep recruits fibres at low stresses and can lead to modulus-reducing fibre damage at higher creep stresses: a study in rabbit medial collateral ligament modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2002G. M. Thornton Ligaments are subjected to a range of loads during different activities in vivo, suggesting that they must resist creep at various stresses. Cyclic and static creep tests of rabbit medial collateral ligament were used as a model to examine creep over a range of stresses in the toe- and linear-regions of the stress,strain curve: 4.1 MPa (n =7), 7.1 MPa (n = 6), 14 MPa (n = 9) and 28 MPa (n = 6). We quantified ligament creep behaviour to determine if, at low stresses, modulus would increase in a cyclic creep test and collagen fibres would be recruited in a static creep test. At higher creep stresses, a decrease in measured modulus was expected to be a potential marker of damage. The increase in modulus during cyclic creep and the increase in strain during static creep were similar between the three toe-region stresses (4.1, 7.1, 14 MPa). However, at the linear-region stress (28 MPa), both these parameters increased significantly compared to the increases at the three toe-region stresses. A concurrent crimp analysis revealed that collagen fibres were recruited during creep, evidenced by decreased area of crimped fibres at the end of the static creep test. Interestingly, a predominance of straightened fibres was observed at the end of the 28 MPa creep test, suggesting a limited potential for fibre recruitment at higher, linear-region stresses. An additional 28 MPa (n = 6) group had mechanically detectable discontinuities in their stress,strain curves during creep that were related to reductions in modulus and suggested fibre damage. These data support the concept that collagen fibre recruitment is a mechanism by which ligaments resist creep at low stresses. At a higher creep stress, which was still only about a third of the failure capacity, damage to some ligaments occurred and was marked by a sudden reduction in modulus. In the cyclic tests, with continued cycling, the modulus increased back to original values obtained before the discontinuity suggesting that other fibres were being recruited to bear load. These results have important implications for our understanding of how fibre recruitment and stress redistribution act in normal ligament to minimize creep and restore modulus after fibre damage. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Temporal patterns of genetic variation across a 9-year-old aerial seed bank of the shrub Banksia hookeriana (Proteaceae)MOLECULAR ECOLOGY, Issue 13 2005LUKE G. BARRETT Abstract The pattern of accumulation of genetic variation over time in seed banks is poorly understood. We examined the genetic structure of the aerial seed bank of Banksia hookeriana within a single 15-year-old population in fire-prone southwestern Australia, and compared genetic variation between adults and each year of a 9-year-old seed bank using amplified fragment length polymorphism (AFLP). B. hookeriana is well suited to the study of seed bank dynamics due to the canopy storage of its seeds, and because each annual crop can be identified. A total of 304 seeds from nine crop years and five maternal plants were genotyped, along with 113 plants from the adult population. Genetic variation, as assessed by the proportion of polymorphic markers (Pp) and Shannon's index (I), increased slightly within the seed bank over time, while gene diversity (Hj), did not change. Pp, I, and Hj all indicated that genetic variation within the seed bank quickly approached the maximal level detected. Analysis of molecular variance revealed that less than 4% of variation could be accounted for by variation among seeds produced in different years, whereas there was greater differentiation among maternal plants (12.7%), and among individual seeds produced by different maternal plants (83.4%). With increasing population age, offspring generated each year were slightly more outbred, as indicated by an increase in the mean number of nonmaternal markers per offspring. There were no significant differences for Hj or I between adults and the seed bank. Viability of seeds decreased with age, such that the viability of 9-year-old seeds was half that of 2-year-old seeds. These results suggest that variable fire frequencies have only limited potential to influence the amount of genetic variation stored within the seed bank of B. hookeriana. [source] The dynamics of gene products fluctuation during bovine pre-hatching developmentMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 8 2009Isabelle Gilbert Early embryonic development, spanning fertilization to blastocyst hatching, is a very dynamic developmental window that is characterized, especially in large mammals, by a period of transcriptional incompetence that ends during the maternal to embryonic transition (MET). Prior to the MET, the first cell cycles are supported by stored RNA and proteins pools accumulated during oogenesis. Therefore, RNA and protein content are different between developmental stages. It is also known that the stability of the stored mRNA and the mechanisms for translation recruitment are partly controlled by the length of the poly(A) tail. To date, little is known about RNA and protein content fluctuations during the pre-hatching period. In this report we present measurements of total RNA, mRNA, poly(A) bearing mRNA and protein contents, as well as estimations of the proportions of both mRNA fractions to total RNA contents within these developmental stages. We found that while the ontogenic profiles of the different transcript contents were expected, their amounts were considerably lower than the reported values. Additionally, low 28S rRNA abundance and a tendency for diminishing protein content prior to the MET, suggest a limited potential for ribosomal turnover and translation. We consider the overall fluctuations in RNA and protein contents to be reference points that are essential for downstream interpretation of gene expression data across stages whether it be through candidates or high throughput approaches. Mol. Reprod. Dev. 76: 762,772, 2009. © 2009 Wiley-Liss, Inc. [source] Land resources potential and sustainable land management: an overviewNATURAL RESOURCES FORUM, Issue 2 2000A. Parviz Koohafkan Abstract Land degradation continues to be a major threat to local and national food security. With limited potential to develop new land, any increase in agricultural production must be sought largely through the better use of land already under cultivation. Concerns for the global environment associated with agriculture worldwide have also increased in recent years and require more coordinated efforts at global and national levels with decentralisation of activities at the local level. This article presents an overview of land resources potential for food production, the processes and extent of land degradation and its economic and environmental costs and impacts, and highlights some macro-economic policies and institutional measures for the prevention of land degradation and rehabilitation of degraded lands. A people-centred programme is presented as a basis for decentralising activities for sustainable land use and land management. Finally, the need for better coordinated efforts of concerned UN, multinational agencies and NGOs for the implementation of Agenda 21 and related conventions is stressed. [source] Managing arable weeds for biodiversityPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 6 2007Jonathan Storkey Abstract As a result of the recent intensification of crop production, the abundance and diversity of UK arable weeds adapted to cultivated land have declined, with an associated reduction in farmland birds. A number of questions need to be addressed when considering how these declines can be reversed. Firstly, can the delivery of crop production and biodiversity be reconciled by spatially separating cropping from designated wildlife areas? A number of subsidised environmental schemes in the UK take this approach and are focused on establishing vegetation cover on uncropped land. However, because of the lack of regular disturbance in these habitats, they are dominated by perennials and they therefore have limited potential for promoting the recovery of annual weed populations. A number of farmland bird species also rely on the provision of resources in field centres, and it is therefore likely that the recovery of their populations will rely on weed management options targeted at the cropped areas of the field. This raises two further questions. Firstly, is it possible to identify beneficial weed species that are relatively poor competitors with the crop and also have biodiversity value? Secondly, are the tools available to manage these species at acceptable levels while controlling pernicious weeds? A number of approaches are being employed to answer these questions, including predicting yield loss from weed competition models and exploiting herbicide selectivity. The further development of these tools is crucial if farmer opposition to managing weeds in crops is to be overcome. Copyright © 2007 Society of Chemical Industry [source] Practitioner Review: The assessment of language pragmaticsTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 8 2002Catherine Adams Background: The assessment of pragmatics expressed in spoken language is a central issue in the evaluation of children with communication impairments and related disorders. A developmental approach to assessment has remained problematic due to the complex interaction of social, linguistic, cognitive and cultural influences on pragmatics. Method: A selective review and critique of current formal and informal testing methods and pragmatic analytic procedures. Results: Formal testing of pragmatics has limited potential to reveal the typical pragmatic abnormalities in interaction but has a significant role to play in the assessment of comprehension of pragmatic intent. Clinical assessment of pragmatics with the pre-school child should focus on elicitation of communicative intent via naturalistic methods as part of an overall assessment of social communication skills. Assessments for older children should include a comprehensive investigation of speech acts, conversational and narrative abilities, the understanding of implicature and intent as well as the child's ability to employ contextual cues to understanding. Practical recommendations are made regarding the choice of a core set of pragmatic assessments and elicitation techniques. The practitioner's attention is drawn to the lack of the usual safeguards of reliability and validity that have persisted in some language pragmatics assessments. Conclusions: A core set of pragmatic assessment tools can be identified from the proliferation of instruments in current use. Further research is required to establish clearer norms and ranges in the development of pragmatic ability, particularly with respect to the understanding of inference, topic management and coherence. [source] The latex capacity of opium poppy capsules is fixed early in capsule development and is not a major determinant in morphine yieldANNALS OF APPLIED BIOLOGY, Issue 2 2009T. Harvest Abstract This study found that the latex capacity (mg latex mg,1 dry weight capsule) of opium poppy capsules is fixed early in capsule development. Latex capacity, which represents the proportion of the capsule wall allocated to laticifers (specialised cells for latex storage), had peaked in the capsule at 1 week after flowering. In contrast, the morphine content of capsules continued to increase with capsule development until commercial harvest. Morphine content was correlated with capsule mass and total latex mass, but there was no correlation between latex capacity and morphine yield. The most important morphological characteristic in terms of morphine end yield (commercial harvest stage) was capsule mass. The findings of this study demonstrate that although latex yield per plant is a highly heritable morphological characteristic, it may have limited potential for use in a breeding strategy aimed at increasing the morphine yield from capsules. [source] | |||||||||||||