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Significant Clustering (significant + clustering)
Selected AbstractsThe fate of an intentional introduction of Formica lugubris to North America from EuropeJOURNAL OF APPLIED ENTOMOLOGY, Issue 4 2008A. J. Storer Abstract Red wood ants (Formica s.str.) are not prevalent in the forests of North America, but commonly occur in conifer and mixed conifer forests in northern Europe and Asia. In 1971, a European red wood ant species, Formica lugubris, was intentionally established in a 35-year-old predominantly mixed conifer plantation approximately 30 km north of QC, Canada. The purpose of its introduction was to evaluate the potential of this species as a biological control agent against conifer-defoliating Lepidoptera species. This red wood ant introduction was monitored periodically for about 5 years after establishment, but its long-term fate has not been reported. We visited this field site in 2005 and found that this species was well established, and we could locate some of the nests that resulted from the original release. We mapped and measured over 100 nests around the site of original release, which ranged from 5 cm in height to over 1 m. We estimated the population of introduced ants to have grown to over 8 million in the last 34 years. Significant clustering of nests suggests that these nests may be one supercolony. F. lugubris has become a dominant understory arthropod in this mixed forest, and is likely to have ecological impacts, including effects at the community and ecosystem level. [source] Hepatitis C virus infection among drug injectors in St Petersburg, Russia: social and molecular epidemiology of an endemic infectionADDICTION, Issue 11 2009Elijah Paintsil ABSTRACT Aims To understand the epidemiology and transmission patterns of hepatitis C virus (HCV), the predominant blood borne-pathogen infecting injection drug users (IDUs), in a part of the former Soviet Union. Design Cross-sectional respondent-driven sample of IDUs. Setting St Petersburg, Russia. Participants A total of 387 IDUs were recruited in late 2005 and throughout 2006. Measurements Participants were surveyed to collect demographic, medical and both general and dyad-specific drug injection and sexual behaviors. A blood sample was collected to detect antibodies to hepatitis C and to amplify viral RNA for molecular analysis. The molecular data, including genotypes, were analyzed spatially and linkage patterns were compared to the social linkages obtained by respondent-driven sampling (RDS) for chains of respondents and among the injection dyads. Findings HCV infection was all but ubiquitous: 94.6% of IDUs were HCV-seropositive. Among the 209 viral sequences amplified, genotype 3a predominated (n = 119, 56.9%), followed by 1b (n = 61, 29.2%) and 1a (n = 25, 11.9%). There was no significant clustering of genotypes spatially. Neither genotypes nor closely related sequences were clustered within RDS chains. Analysis of HCV sequences from dyads failed to find associations of genotype or sequence homology within pairs. Conclusions Genotyping reveals that there have been at least five unique introductions of HCV genotypes into the IDU community in St Petersburg. Analysis of prevalent infections does not appear to correlate with the social networks of IDUs, suggesting that simple approaches to link these networks to prevalent infections, rather than incident transmission, will not prove meaningful. On a more positive note, the majority of IDUs are infected with 3a genotype that is associated with sustained virological response to antiviral therapy. [source] Involvement of the inferior frontal junction in cognitive control: Meta-analyses of switching and Stroop studiesHUMAN BRAIN MAPPING, Issue 1 2005Jan Derrfuss Abstract There is growing evidence that a specific region in the posterior frontolateral cortex is involved intimately in cognitive control processes. This region, located in the vicinity of the junction of the inferior frontal sulcus and the inferior precentral sulcus, was termed the inferior frontal junction (IFJ). The IFJ was shown to be involved in the updating of task representations and to be activated commonly in a within-subject investigation of a task-switching paradigm, the Stroop task, and a verbal n-back task. Here, we investigate the involvement of the IFJ in cognitive control by employing a meta-analytic approach. Two quantitative meta-analyses of functional magnetic resonance imaging (fMRI) studies were conducted. One meta-analysis included frontal activations from task-switching, set-shifting, and stimulus,response (S,R) reversal studies, the other included frontal activations from color,word Stroop studies. Results showed highly significant clustering of activations in the IFJ in both analyses. These results provide strong evidence for the consistent involvement of the IFJ in both switching and Stroop paradigms. Furthermore, they support our concept of areal specialization in the frontolateral cortex, which posits that it is not only the middorsolateral part that plays an important role in cognitive control, but also the IFJ. Finally, our results demonstrate how quantitative meta-analyses can be used to test hypotheses about the involvement of specific brain regions in cognitive control. Hum Brain Mapp 25:22,34, 2005. © 2005 Wiley-Liss, Inc. [source] Spatial clustering of childhood cancer in Great Britain during the period 1969,1993INTERNATIONAL JOURNAL OF CANCER, Issue 4 2009Richard J.Q. McNally Abstract The aetiology of childhood cancer is poorly understood. Both genetic and environmental factors are likely to be involved. The presence of spatial clustering is indicative of a very localized environmental component to aetiology. Spatial clustering is present when there are a small number of areas with greatly increased incidence or a large number of areas with moderately increased incidence. To determine whether localized environmental factors may play a part in childhood cancer aetiology, we analyzed for spatial clustering using a large set of national population-based data from Great Britain diagnosed 1969,1993. The Potthoff-Whittinghill method was used to test for extra-Poisson variation (EPV). Thirty-two thousand three hundred and twenty-three cases were allocated to 10,444 wards using diagnosis addresses. Analyses showed statistically significant evidence of clustering for acute lymphoblastic leukaemia (ALL) over the whole age range (estimate of EPV = 0.05, p = 0.002) and for ages 1,4 years (estimate of EPV = 0.03, p = 0.015). Soft-tissue sarcoma (estimate of EPV = 0.03, p = 0.04) and Wilms tumours (estimate of EPV = 0.04, p = 0.007) also showed significant clustering. Clustering tended to persist across different time periods for cases of ALL (estimate of between-time period EPV = 0.04, p =0.003). In conclusion, we observed low level spatial clustering that is attributable to a limited number of cases. This suggests that environmental factors, which in some locations display localized clustering, may be important aetiological agents in these diseases. For ALL and soft tissue sarcoma, but not Wilms tumour, common infectious agents may be likely candidates. © 2008 Wiley-Liss, Inc. [source] Wet and dry summers in Europe since 1750: evidence of increasing droughtINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2009K. R. Briffa Abstract Moisture availability across Europe is calculated based on 22 stations that have long instrumental records for precipitation and temperature. The metric used is the self-calibrating Palmer Drought Severity Index (scPDSI) which is based on soil moisture content. This quantity is calculated using a simplified water budget model, forced by historic records of precipitation and temperature data, where the latter are used in a simple parameterization for potential evaporation. The precipitation and temperature records are updated to include the 2003 summer and all records, except for one, span at least 200 years, with the record for Kew going back to 1697. The Kew record shows a significant clustering of dry summers in the most recent decade. When all the records are considered together, recent widespread drying is clearly apparent and highly significant in this long-term context. By substituting the 1961,1990 climatological monthly mean temperatures for the actual monthly means in the parameterization for potential evaporation, an estimate is made of the direct effect of temperature on drought. This analysis shows that a major influence on the trend toward drier summer conditions is the observed increase in temperatures. This effect is particularly strong in central Europe. Based on the 22 scPDSI records, a gridded scPDSI dataset covering a large part of Europe has been constructed and compared to a recent high-resolution scPDSI dataset spanning the twentieth century only. We again observe that a major cause for the large areal extent of summer drought in the last two decades is high temperatures. Temperatures in the 12 months preceding and including the summer of 2003 explain an increase in the areas experiencing slightly dry (or worse) conditions of 11.1%. Copyright © 2009 Royal Meteorological Society [source] Geographical clustering of eating disordered behaviors in U.S. high school students,,INTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 3 2008Valerie L. Forman-Hoffman PhD Abstract Objective: The aim of this study was to determine if eating disorder behaviors geographically clustered among U.S high school students. Method: Our sample consisted of 15,349 high school students who responded to the 1999 Youth Risk Behavior Study (YRBS). Weight control and eating disordered behaviors under investigation included dieting, exercising, fasting, using diet pills, and purging to control weight in the last 30 days. We calculated pairwise odds ratios (PWORs) to determine the degree of within-county clustering. Results: Among all participants, adjusted analyses revealed that having any weight control or eating disorder symptom, severe restricting, dieting, exercising, and diet pill use each showed significant clustering (p < .05). Purging did not significantly cluster by county. The magnitude of clustering was stronger for female students than male students. Conclusion: The significant clustering of weight control and eating disorder behavior in U.S. high school students confirms evidence of a social contagion effect of eating disorders. © 2007 by Wiley Periodicals, Inc. Int J Eat Disord 2008 [source] Characterization of hepatitis B virus reverse transcriptase sequences in Chinese treatment naive patientsJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 8 2009Yue Han Abstract Background and Aims:, The hepatitis B virus (HBV) reverse transcriptase (RT) plays an important role in viral replication. The aim of the present study was to characterize profiles of the RT region and to construct a database for further studies. Methods:, Serum samples were obtained from 328 treatment naive patients chronically infected with HBV in five Chinese cities. Mutation status, genotypes and deep sequence analysis were carried out by amplifying and sequencing the RT region. Results:, The base usage in the RT region differed at the mono- and dinucleotide level and thymidine dominated. The higher the variability of the strain was, the more it replicated. No significant clustering was found between our HBV RT sequences and those isolated 10 years ago (achieved from genebank). Nucleotide analogue resistance related mutants exist. The M204V/I mutation was found in 1.8% of the strains, 1.2% had L180M+ M204V/I, 0.6% had A181T/V, and only one had all three mutations. Minor strain mutants were found in 9.3% of the samples studied. The genotype B patients made up 36.6% (88.7% B2) and were mostly found in southern China, 63.4% (92.2% C2) were genotype C, and only one was genotype D. The average age of HBeAg positive genotype B patients was 29.5 ± 10.4 years, for genotype C it was 36.1 ± 10.9 (P < 0.001). Conclusion:, Primarily antiviral resistance related mutant strains do exist in treatment naïve patients. Without antiviral pressure, HBV strains evolved at a normal speed. In depth sequence analysis implied that viral replication might be correlated with its variability, which needs to be further investigated. [source] Patterns of vegetative growth and gene flow in Rhizopogon vinicolor and R. vesiculosus (Boletales, Basidiomycota)MOLECULAR ECOLOGY, Issue 8 2005ANNETTE M. KRETZER Abstract We have collected sporocarps and tuberculate ectomycorrhizae of both Rhizopogon vinicolor and Rhizopogon vesiculosus from three 50 × 100 m plots located at Mary's Peak in the Oregon Coast Range (USA); linear map distances between plots ranged from c. 1 km to c. 5.5 km. Six and seven previously developed microsatellite markers were used to map the approximate size and distribution of R. vinicolor and R. vesiculosus genets, respectively. Genetic structure within plots was analysed using spatial autocorrelation analyses. No significant clustering of similar genotypes was detected in either species when redundant samples from the same genets were culled from the data sets. In contrast, strong clustering was detected in R. vesiculosus when all samples were analysed, but not in R. vinicolor. These results demonstrate that isolation by distance does not occur in either species at the intraplot sampling scale and that clonal propagation (vegetative growth) is significantly more prevalent in R. vesiculosus than in R. vinicolor. Significant genetic differentiation was detected between some of the plots and appeared greater in the more clonal species R. vesiculosus with ,ST values ranging from 0.010 to 0.078*** than in R. vinicolor with ,ST values ranging from ,0.002 to 0.022** (*P < 0.05, **P < 0.01, ***P < 0.001). When tested against the null hypothesis of no relationship between individuals, parentage analysis detected seven likely parent/offspring pairs in R. vinicolor and four in R. vesiculosus (, = 0.001). Of these 11 possible parent/offspring pairs, only two R. vinicolor pairs were still supported as parent/offspring when tested against the alternative hypothesis of being full siblings (, = 0.05). In the latter two cases, parent and offspring were located at approximately 45 m and 28 m from each other. Challenges to parentage analysis in ectomycorrhizal fungi are discussed. [source] Informatic and genomic analysis of melanocyte cDNA libraries as a resource for the study of melanocyte development and functionPIGMENT CELL & MELANOMA RESEARCH, Issue 3 2007Laura L. Baxter Summary As part of the RIKEN mouse encyclopedia project, two cDNA libraries were prepared from melanocyte-derived cell lines, using techniques of full-length clone selection and subtraction/normalization to enrich for rare transcripts. End sequencing showed that these libraries display over 83% complete coding sequence at the 5, end and 96,97% complete coding sequence at the 3, end. Evaluation of the libraries, derived from B16F10Y tumor cells and melan-c cells, revealed that they contain clones for a majority of the genes previously demonstrated to function in melanocyte biology. Analysis of genomic locations for transcripts revealed that the distribution of melanocyte genes is non-random throughout the genome. Three genomic regions identified that showed significant clustering of melanocyte-expressed genes contain one or more genes previously shown to regulate melanocyte development or function. A catalog of genes expressed in these libraries is presented, providing a valuable resource of cDNA clones and sequence information that can be used for identification of new genes important for melanocyte development, function, and disease. [source] Integration of AFLP markers into an RFLP-based map of durum wheatPLANT BREEDING, Issue 5 2000C. Lotti Abstract Amplified fragment length polymorphism (AFLP) is a powerful technique which can readily be applied to a wide range of species for mapping purposes. AFLPs were added to a linkage map of durum wheat constructed using restriction fragment length polymorphisms (RFLPs). The mapping population included 65 recombinant inbred lines derived from a cross between the durum wheat cultivar ,Messapia' and accession ,MG4343' of the wild Triticum turgidum ssp. dicoccoides (Körn.). Genomic DNA was digested with MseI (4-cutter) and Sse83871 (8-cutter). Using a silver-staining protocol, 14 primer combinations revealed 421 clearly scorable amplicons including 100 polymorphisms. The presence of nine pairs of bands linked in repulsion phase with each pair generated by one primer combination suggested the presence of codominant alleles; sequence analysis of four band pairs confirmed their codominant nature. The integration of 80 AFLP loci extended the map in several telomeric regions, reduced the size of four large gaps present in the previous map, and eliminated one gap. The new map obtained after the inclusion of the 80 AFLP loci and eight additional RFLP loci spans 2063cM which represent a 52.6% increment compared with the previous map. Compared with the distribution of RFLPs, no significant clustering of AFLP markers was observed. [source] Protoclusters associated with distant radio galaxiesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006B. P. Venemans Abstract The results of a large program conducted with the Very Large Telescope and the Keck telescope to search for forming clusters of galaxies near powerful radio galaxies at 2 < z < 5.2 are presented. Deep narrow- and broad-band images of eight radio galaxies and their surroundings were obtained. In the images a total of 335 candidate Ly, emitting galaxies at the redshift of the radio galaxies were selected. Subsequently, follow-up spectroscopy was performed to obtain redshifts for the candidate Ly, emitters. In at least six of eight fields (75%) an overdensity of Ly, emitters is found near the radio galaxy. Taken together with a significant clustering in redshift space of the emitters, we argue that we have discovered six forming clusters of galaxies (protoclusters). Based on the estimated masses and the volume density, we conclude that the observed structures are the likely progenitors of present-day massive (,1015 M,) clusters of galaxies. Finally, we compare the observed galaxy overdensities with numerical simulations of the development of large scale structure in the Universe. The preliminary results of this comparison provide strong additional evidence for the hypothesis that the radio galaxy protoclusters are forming massive clusters. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatial distribution of communal nests in a colonial breeding bird: benefits without costs?AUSTRAL ECOLOGY, Issue 5 2008URS CHRISTIAN GIEßELMANN Abstract The spatial organization of individuals, or groups of individuals, within a population can provide valuable information about social organization and population dynamics. We analysed the spatial distribution of nests of the sociable weaver (Philetairus socius) on two farms in the Kalahari. Sociable weavers build large communal nests on big savannah trees, forming a pattern of trees with and without nests. We used two spatial statistics, Ripley's K and the pair correlation function, to describe characteristics of the point patterns over a range of distances. (i) At distances of 200 and 300 m, communal nests were clustered. (ii) At distances greater than 1000 m, communal nests were regularly distributed. These findings are independent of the spatial distribution of trees. Furthermore, we used Moran's I to analyse spatial autocorrelation of nest sizes. We expected negative autocorrelation because of competition between nests. But on both farms there was no significant autocorrelation of nest sizes for any distance class. The regular distribution observed at larger distances may indicate competition and/or territoriality among different nests, but the lack of spatial autocorrelation between nest sizes suggests that these interactions may happen between nest clusters rather than between single nests. This was confirmed by significant clustering of nests on small scales. We thus suggest, that colonies of P. socius consist of several nests on adjacent trees forming a cluster of subcolonies. The question why sociable weavers establish subcolonies instead of adding more chambers to the natal nest, could not simply be answered by limitation of nesting space. We suggest a strategy to avoid costs due to increasing colony size. [source] A Class of Multiplicity Adjusted Tests for Spatial Clustering Based on Case,Control Point DataBIOMETRICS, Issue 1 2007Toshiro Tango Summary A class of tests with quadratic forms for detecting spatial clustering of health events based on case,control point data is proposed. It includes Cuzick and Edwards's test statistic (1990, Journal of theRoyal Statistical Society, Series B52, 73,104). Although they used the property of asymptotic normality of the test statistic, we show that such an approximation is generally poor for moderately large sample sizes. Instead, we suggest a central chi-square distribution as a better approximation to the asymptotic distribution of the test statistic. Furthermore, not only to estimate the optimal value of the unknown parameter on the scale of cluster but also to adjust for multiple testing due to repeating the procedure by changing the parameter value, we propose the minimum of the profile p-value of the test statistic for the parameter as an integrated test statistic. We also provide a statistic to estimate the areas or cases which make large contributions to significant clustering. The proposed methods are illustrated with a data set concerning the locations of cases of childhood leukemia and lymphoma and another on early medieval grave site locations consisting of affected and nonaffected grave sites. [source] | |||||||||||||