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PubMed2004

Responses of invertebrate natural enemies to complex-structured habitats: a meta-analytical synthesis.

The structural complexity of habitats has been espoused as an important factor influencing natural-enemy abundance and food-web dynamics in invertebrate-based communities, but a rigorous synthesis of published studies has not heretofore been conducted. We performed a meta-analytical synthesis of the density response of natural enemies (invertebrate predators and parasitoids) to experimental increases and decreases in the structural complexity of their habitats using data from 43 published studies, reporting 62 independent taxa. Studies varied in structural complexity at two spatial scales (habitat and within-plant architecture) and comprised a diverse array of natural-enemy taxa (natural-enemy assemblage at large, the entire spider assemblage, hunting spiders, web-building spiders, mites, hemipterans, coccinellid beetles, carabid beetles, ants, and parasitoids). For all taxa combined, increasing habitat structure resulted in a large and significant increase in natural enemy abundance. Similarly, decreasing habitat structure significantly diminished natural enemy abundance. Separate meta-analyses at two spatial scales (habitat and within-plant architecture) found that increasing habitat complexity resulted in significant increases in abundance. In particular, manipulating levels of detritus at the habitat spatial scale had the strongest effect on natural enemy abundance. In general, most guilds of natural enemies were significantly affected when the structural complexity of the habitat was altered. Seven of nine natural enemy guilds were more abundant under conditions of increased habitat complexity, with hunting spiders and web-building spiders showing the strongest response followed by hemipterans, mites, and parasitoids. Spiders in particular were negatively affected when habitat structure was simplified. The mechanisms underlying the accumulation of natural enemies in complex-structured habitats are poorly known. However, refuge from intraguild predation, more effective prey capture, and access to alternative resources (alternative prey, pollen, or nectar), are possible candidates. Our analysis was unable to confirm that predators aggregate in complex-structured habitats because prey (mostly herbivores) are more abundant there. The results of this meta-analysis support the view that basal resources mediate top-down impacts on herbivores, and provide encouragement that manipulations of habitat complexity can be made in agroecosystems that will enhance the effectiveness of the natural enemy complex for more effective pest suppression.

Agriculture↗
PubMed2003

Virtual screening on natural products for discovering active compounds and target information.

Natural products, containing inherently large-scale structural diversity than synthetic compounds, have been the major resources of bioactive agents and will continually play as protagonists for discovering new drugs. However, how to access this diverse chemical space efficiently and effectively is an exciting challenge for medicinal chemists and pharmacologists. While virtual screening, which has shown a great promise in drug discovery, will play an important role in digging out lead (active) compounds from natural products. This review focuses on the strategy of virtual screening based on molecular docking and, with successful examples from our laboratory, illustrates the efficiency of virtual screening in discovering active compounds from natural products. On the other hand, the sequencing of the human genome and numerous pathogen genomes has resulted in an unprecedented opportunity for discovering potential new drug targets. Chemogenomics has appeared as a new technology to initiate target discovery by using active compounds as probes to characterize proteome functions. Natural products are the ideal probes for such research. Binding affinity fingerprint is a powerful chemogenomic descriptor to characterize both small molecules and pharmacologically relevant proteins. Therefore, this review also discusses binding affinity fingerprint strategy for identifying target information from the genomic data by using natural products as the probes.

Biological Products↗
PubMedDate not supplied

Benefiting from networks by occupying central positions: an empirical study of the Taiwan health care industry.

At issue is whether network resources imply some resources available to all members in networks or available only to those occupying structurally central positions in networks. In this article, two conceptual models, the additive and interaction models of the firm, are empirically tested regarding the impact of hospital resources, network resources, and centrality on hospital performance in the Taiwan health care industry. The results demonstrate that: (1) in the additive model, hospital resources and centrality independently affect performance, whereas network resources do not; and (2) no evidence supports the interaction effect of centrality and resources on performance. Based on our findings in Taiwanese practices, the extent to which the resources are acquired externally from networks, we suggest that while adopting interorganizational strategies, hospitals should clearly identify those important resources that reside in-house and those transferred from network partners. How hospitals access resources from central positions is more important than what network resources can hospitals acquire from networks. Hospitals should improve performance by exploiting its in-house resources rather than obtaining network resources externally. In addition, hospitals should not only invest in hospital resources for better performance but should also move to central positions in networks to benefit from collaborations.

Efficiency, Organizational↗
PubMed2004

Comparative genomic structure of prokaryotes.

Recent advances in DNA-sequencing technologies have made available an enormous resource of data for the study of bacterial genomes. The broad sample of complete genomes currently available allows us to look at variation in the gross features and characteristics of genomes while the detail of the sequences reveal some of the mechanisms by which these genomes evolve. This review aims to describe bacterial genome structures according to current knowledge and proposed hypotheses. We also describe examples where mechanisms of genome evolution have acted in the adaptation of bacterial species to particular niches.

Bacteria↗
PubMedDate not supplied

A bi-directional theory of addiction: examining coping and the factors related to substance relapse.

The results from this study supported a bi-directional theory of addiction for a sample of Black, inner-city, working-class, male substance abusers. Using structural equations modeling, at 6 months posttreatment we found that (a) the reciprocal effect emotional and psychological distress and substance relapse had on one another existed within the context of their bi-directional relationship with social instability, and (b) effective coping skills and resources moderated the negative effects that emotional and psychological distress, social structure, and substance relapse had on one another. These findings led us to three suggestions treatment professionals can use to counteract recidivism.

Adaptation, Psychological↗
PubMed2005

A haplotype map of the human genome.

Inherited genetic variation has a critical but as yet largely uncharacterized role in human disease. Here we report a public database of common variation in the human genome: more than one million single nucleotide polymorphisms (SNPs) for which accurate and complete genotypes have been obtained in 269 DNA samples from four populations, including ten 500-kilobase regions in which essentially all information about common DNA variation has been extracted. These data document the generality of recombination hotspots, a block-like structure of linkage disequilibrium and low haplotype diversity, leading to substantial correlations of SNPs with many of their neighbours. We show how the HapMap resource can guide the design and analysis of genetic association studies, shed light on structural variation and recombination, and identify loci that may have been subject to natural selection during human evolution.

Chromosomes, Human, Y↗
PubMed2006

The interaction of disturbances and small mammal community dynamics in a lowland forest in Belize.

1. Three floods (July 2000, August 2002, September 2003) and a hurricane (October 2001) that occurred in a lowland forest in the southern Maya Mountains of Belize presented an opportunity to evaluate the influence of these disturbances on the structure of a small mammal assemblage. 2. Four terrestrial and four primarily scansorial/arboreal species were trapped July 2000-March 2005 in six grids over 14 irregularly spaced trapping periods. 3. Community dynamics were characterized more by changes in species composition than changes in diversity. The dynamics were driven by species-specific variation in abundance, with changes in composition generally, but not exclusively, due to the occurrence or disappearance of species at low abundance. Despite the disturbances, species richness remained relatively constant. Evenness within the assemblage was consistently low, primarily as a result of dominance by one species, Heteromys desmarestianus. 4. Effects of flooding on community structure were direct but relatively brief (< 1 year), and varied with the duration and intensity of flooding. Effects from the hurricane were indirect but long-lasting and strongly related to severely reduced food resources. 5. This study suggests that long-term dynamics in the structure of many animal communities in the tropics often results from interactions between direct and indirect effects of disturbance. It also suggests that community resistance will depend on variation in disturbance type and regime, but resilience will be determined by the life-history characteristics of each species.

Animals↗
PubMed2005

Predicted secondary structure for 28S and 18S rRNA from Ichneumonoidea (Insecta: Hymenoptera: Apocrita): impact on sequence alignment and phylogeny estimation.

We utilize the secondary structural properties of the 28S rRNA D2-D10 expansion segments to hypothesize a multiple sequence alignment for major lineages of the hymenopteran superfamily Ichneumonoidea (Braconidae, Ichneumonidae). The alignment consists of 290 sequences (originally analyzed in Belshaw and Quicke, Syst Biol 51:450-477, 2002) and provides the first global alignment template for this diverse group of insects. Predicted structures for these expansion segments as well as for over half of the 18S rRNA are given, with highly variable regions characterized and isolated within conserved structures. We demonstrate several pitfalls of optimization alignment and illustrate how these are potentially addressed with structure-based alignments. Our global alignment is presented online at (http://hymenoptera.tamu.edu/rna) with summary statistics, such as basepair frequency tables, along with novel tools for parsing structure-based alignments into input files for most commonly used phylogenetic software. These resources will be valuable for hymenopteran systematists, as well as researchers utilizing rRNA sequences for phylogeny estimation in any taxon. We explore the phylogenetic utility of our structure-based alignment by examining a subset of the data under a variety of optimality criteria using results from Belshaw and Quicke (2002) as a benchmark.

Animals↗
PubMed2006

An analysis of the Sargasso Sea resource and the consequences for database composition.

BACKGROUND: The environmental sequencing of the Sargasso Sea has introduced a huge new resource of genomic information. Unlike the protein sequences held in the current searchable databases, the Sargasso Sea sequences originate from a single marine environment and have been sequenced from species that are not easily obtainable by laboratory cultivation. The resource also contains very many fragments of whole protein sequences, a side effect of the shotgun sequencing method.These sequences form a significant addendum to the current searchable databases but also present us with some intrinsic difficulties. While it is important to know whether it is possible to assign function to these sequences with the current methods and whether they will increase our capacity to explore sequence space, it is also interesting to know how current bioinformatics techniques will deal with the new sequences in the resource. RESULTS: The Sargasso Sea sequences seem to introduce a bias that decreases the potential of current methods to propose structure and function for new proteins. In particular the high proportion of sequence fragments in the resource seems to result in poor quality multiple alignments. CONCLUSION: These observations suggest that the new sequences should be used with care, especially if the information is to be used in large scale analyses. On a positive note, the results may just spark improvements in computational and experimental methods to take into account the fragments generated by environmental sequencing techniques.

Amino Acid Sequence↗
PubMed1999

The mutual effects between job resources and mental health: a prospective study among Dutch youth.

The current study construes the relation between job resources (such as job autonomy, skill utilization, and variety) and mental health as a reciprocal process. Following conservation of resources theory (S. E. Hobfoll, 1989), the author expected job resources to have a positive effect on mental health. Poor mental health was assumed to impede workers' attempts to maintain or enhance their job resources either by changing the content of their jobs or attempting to find another (less distressing) job. Longitudinal data from a representative sample of 699 Dutch youth were analyzed with analysis of variance and covariance structure modeling. The results provided good support for the proposition that job resources and mental health mutually influence each other. Limitations and implications of the study are discussed.

Adult↗
PubMed1986

Do semantic memory deficiencies underlie learning disabled readers' encoding processes?

This study investigates the extent to which learning disabled readers' atypical encoding relates to their deficiencies in semantic memory. Inferences related to ability group performance were based on the assumption that encoding involves the matching of incoming information against a featural representation of that information in semantic memory. To this end, learning disabled and nondisabled readers in two age groups were compared on dichotic listening recall tasks that included orienting and nonorienting instructions. Orienting instructions directed children's attention toward semantic, phonemic, or structural word features. Dependent measures were lateralization, free recall, retrieval organization, and selective attention. The efficiency of allocating attentional resources was inferred from correlations between central and incidental recall. Primary results included the following: Disabled and nondisabled readers' ear asymmetry differences were dependent upon age, orienting instructions, and type of word list; disabled readers' recall and organization scores were lower than skilled readers'; however, both ability groups benefitted from orienting instructions compared to nonorienting instructions; during orienting instructions, disabled readers were less able than skilled readers to divide their attention between target and nontarget word features, especially during interhemispheric processing conditions; and the relative efficiency of allocating attentional resources differed qualitatively between the two ability groups. The results suggest that ability group variations reflect the structure of the memory trace in interaction with ear presentation and encoding processes. It is inferred that disabled readers' inferior memory traces reflect the quantity and internal coherence of information stored in semantic memory as well as the means by which such information is accessed.

Attention↗
PubMed2005

Development and application of high throughput plasma stability assay for drug discovery.

Plasma stability plays an important role in drug discovery and development. Unstable compounds tend to have rapid clearance and short half-life, resulting in poor in vivo performance. This paper examines the variables that affect the plasma stability assay results, including substrate concentration, %DMSO, plasma concentration, enzyme activity upon incubation and batch variation. The results show that plasma stability can accommodate a wide range of experimental conditions. Relatively minor differences in results are produced with major differences in conditions. Significant batch-to-batch variations were observed for rat plasma. We selected the following conditions: 1 microM substrate concentration, 2.5% DMSO, and 50% dilution of plasma in pH 7.4 buffer. Plasma stability can be used as a diagnostic assay when compounds are unexpectedly rapidly cleared, as a special assay when structural classes contain groups that may be susceptible to plasma enzyme hydrolysis, or as general screen for compounds if resources are available. Plasma stability assay has many applications in drug discovery: to alert teams to labile structural motifs, to prioritize compounds for in vivo studies and to screen prodrugs and antedrugs.

Animals↗
PubMed2006

Mutualistic stability in the arbuscular mycorrhizal symbiosis: exploring hypotheses of evolutionary cooperation.

The 450-million-year-old symbiosis between the majority of land plants and arbuscular mycorrhizal fungi (AMF) is one of the most ancient, abundant, and ecologically important mutualisms on Earth. Yet, the evolutionary stability of mycorrhizal associations is still poorly understood, as it follows none of the constraints thought to stabilize cooperation in other well-known mutualisms. The capacity of both host and symbiont to simultaneously interact with several partners introduces a unique dilemma; detecting and punishing those exploiting the mutualism becomes increasingly difficult if these individuals can continue to access resources from alternative sources. Here, we explore four hypotheses to explain evolutionary cooperation in the arbuscular mycorrhizal symbiosis: (1) pseudo-vertical transmission and spatial structuring of plant and fungal populations leading to local adaptation of partners; (2) luxury resource exchange in which plants trade surplus carbon for excess fungal nutrients; (3) partner choice allowing partners to associate with better cooperators; and (4) host and symbiont sanctions which actively reward good partners and punish less cooperative ones. We propose that mycorrhizal cooperation is promoted by an exchange of surplus resources between partners and enforced through sanctions by one or both partners. These mechanisms may allow plant and fungal genotypes to discriminate against individuals employing exploitative strategies, promoting patterns of partner choice. Together these selection pressures provide a framework for understanding the stabilization of mycorrhizal cooperation over evolutionary time.

Biological Evolution↗
PubMed1991

[Importance of the family as a resource in social support in Puerto Rico].

In this article we examine the role of the family in the provision of social support by studying the identity of persons which the participants consider available for providing support. We define social support as that human relationship in which socio-emotional (closeness, intimacy counseling), instrumental (goods and services) and recreational (companionship for recreation) resources are interchanged. Based on a probabilistic sample of the adult (17-68 yrs.) population, 912 persons were successfully interviewed (response rate = 90.4%) using a structured interview schedule. Results indicate that close relatives (parents, brothers/sisters, sons/daughters) are the main resource of all types of support, not only of the general population but also of specific demographic groups defined by their gender, age (17-39, 40-68) and schooling (0-11, 12 + yrs). The marital partner was also identified as an important support resource, especially emotional and recreational; more distant relatives were also important for providing instrumental support. Although the compared groups showed many similarities, they also differed in various aspects both when individually and jointly analyzed. It is concluded that the family is very important in the provision of social support in Puerto Rico (PR).

Adolescent↗
PubMed1998

Upstairs downstairs: vertical integration of a pediatric service.

BACKGROUND: The combined effects of recent changes in health care financing and training priorities have compelled academic medical centers to develop innovative structures to maintain service commitments yet conform to health care marketplace demands. In 1992, a municipal hospital in the Bronx, New York, affiliated with a major academic medical center reorganized its pediatric service into a vertically integrated system of four interdependent practice teams that provided comprehensive care in the ambulatory as well as inpatient settings. One of the goals of the new system was to conserve inpatient resources. OBJECTIVE: To describe the development of a new vertically integrated pediatric service at an inner-city municipal hospital and to test whether its adoption was associated with the use of fewer inpatient resources. DESIGN: A descriptive analysis of the rationale, goals, implementation strategies, and structure of the vertically integrated pediatric service combined with a before-and-after comparison of in-hospital resource consumption. METHODS: A before-and-after comparison was conducted for two periods: the period before vertical integration, from January 1989 to December 1991, and the period after the adoption of vertical integration, from July 1992 to December 1994. Four measures of inpatient resource use were compared after adjustment for case mix index: mean certified length of stay per case, mean number of radiologic tests per case, mean number of ancillary tests per case, and mean number of laboratory tests per case. Difference-in-differences-in-differences estimators were used to control for institution-wide trends throughout the time period and regional trends in inpatient pediatric practice occurring across institutions. Results. In 1992, the Department of Pediatrics at the Albert Einstein College of Medicine reorganized the pediatric service at Jacobi Medical Center, one of its principal municipal hospital affiliates, into a vertically integrated pediatric service that combines ambulatory and inpatient activities into four interdependent practice teams composed of attending pediatricians, allied health professionals, house officers, and social workers. The new vertically integrated service was designed to improve continuity of care for patients, provide a model of practice for professional trainees, conserve scarce resources, and create a clinical research infrastructure. The vertically integrated pediatric service augmented the role of attending pediatricians, extended the use of allied health professionals from the ambulatory to the inpatient sites, established interdisciplinary practice teams that unified the care of pediatric patients and their families, and used less inpatient resources. Controlling for trends within the study institution and trends in the practice of pediatrics across institutions throughout the time period, the vertical integration was associated with a decline in 0.6 days per case, the use of 0.62 fewer radiologic tests per case, 0.21 fewer ancillary tests per case, and 2.68 fewer laboratory tests per case. CONCLUSIONS: We conclude that vertical integration of a pediatric service at an inner-city municipal hospital is achievable; conveys advantages of improved continuity of care, enhanced opportunities for primary care training, and increased participation of senior clinicians; and has the potential to conserve significant amounts of inpatient resources.

Academic Medical Centers↗
PubMed2000

A model of burnout and life satisfaction amongst nurses.

This study, among 109 German nurses, tested a theoretically derived model of burnout and overall life satisfaction. The model discriminates between two conceptually different categories of working conditions, namely job demands and job resources. It was hypothesized that: (1) job demands, such as demanding contacts with patients and time pressure, are most predictive of exhaustion; (2) job resources, such as (poor) rewards and (lack of) participation in decision making, are most predictive of disengagement from work; and (3) job demands and job resources have an indirect impact on nurses' life satisfaction, through the experience of burnout (i.e., exhaustion and disengagement). A model including each of these relationships was tested simultaneously with structural equations modelling. Results confirm the strong effects of job demands and job resources on exhaustion and disengagement respectively, and the mediating role of burnout between the working conditions and life satisfaction. These findings contribute to existing knowledge about antecedents and consequences of occupational burnout, and provide guidelines for interventions aimed at preventing or reducing burnout among nurses.

Adult↗
PubMed2001

The organisational and human resource challenges facing primary care trusts: protocol of a multiple case study.

BACKGROUND: The study is designed to assess the organisational and human resource challenges faced by Primary Care Trusts (PCTs). Its objectives are to: specify the organisational and human resources challenges faced by PCTs in fulfilling the roles envisaged in government and local policy; examine how PCTs are addressing these challenges, in particular, to describe the organisational forms they have adopted, and the OD/HR strategies and initiatives they have planned or in place; assess how effective these structures, strategies and initiatives have been in enabling the PCTs to meet the organisational and human resources challenges they face; identify the factors, both internal to the PCT and in the wider health community, which have contributed to the success or failure of different structures, strategies and initiatives. METHODS: The study will be undertaken in three stages. In Stage 1 the key literature on public sector and NHS organisational development and human resources management will be reviewed, and discussions will be held with key researchers and policy makers working in this area. Stage 2 will focus on detailed case studies in six PCTs designed to examine the organisational and human resources challenges they face. Data will be collected using semi-structured interviews, group discussion, site visits, observation of key meetings and examination of local documentation. The findings from the case study PCTs will be cross checked with a Reference Group of up to 20 other PCG/Ts, and key officers working in organisational development or primary care at local, regional and national level. In Stage 3 analysis of findings from the preparatory work, the case studies and the feedback from the Reference Group will be used to identify practical lessons for PCTs, key messages for policy makers, and contributions to further theoretical development.

Decision Making, Organizational↗
PubMed2004

Trade-offs during the development of primary and secondary sexual traits in a horned beetle.

Resource allocation trade-offs during development affect the final sizes of adult structures and have the potential to constrain the types and magnitude of evolutionary change that developmental processes can accommodate. Such trade-offs can arise when two or more body parts compete for a limited pool of resources to sustain their growth and differentiation. Recent studies on several holometabolous insects suggest that resource allocation trade-offs may be most pronounced in tissues that grow physically close to each other. Here we examine the nature and magnitude of developmental trade-offs between two very distant body parts: head horns and genitalia of males of the horned scarab beetle Onthophagus taurus. Both structures develop from imaginal disklike tissues that undergo explosive growth during late larval development but differ in exactly when they initiate their growth. We experimentally ablated the precursor cells that normally give rise to male genitalia at several time points during late larval development and examined the degree of horn development in these males compared to that of untreated and sham-operated control males. We found that experimental males developed disproportionately larger horns. Horn overexpression was weakest in response to early ablation and most pronounced in males whose genital disks were ablated just before larvae entered the prepupal stage. Our results suggest that even distant body parts may rely on a common resource pool to sustain their growth and that the relative timing of growth may play an important role in determining whether, and how severely, growing organs will affect each other during development. We use our findings to discuss the physiological causes and evolutionary consequences of resource allocation trade-offs.

Animals↗