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Significant Variation (significant + variation)
Selected AbstractsSoil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlandsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2005J. B. Yavitt Summary Rates of organic carbon mineralization (to CO2 and CH4) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid-boreal Alberta, Canada, two were in low-boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH4 production varied significantly as a function of peat type, transplant site, and the type,site interaction. All four peat soils had very small rates of CH4 production (< 20 nmol g,1 day,1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH4 production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH4 production (4000 nmol g,1 day,1) correlated with large holocellulose content, a large concentration of p -hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO2 production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO2 production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH4 and CO2 in Sphagnum -derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future. [source] Functional biodiversity of macroinvertebrate assemblages along major ecological gradients of boreal headwater streamsFRESHWATER BIOLOGY, Issue 9 2005JANI HEINOArticle first published online: 3 AUG 200 Summary 1. Biodiversity,environment relationships are increasingly well-understood in the context of species richness and species composition, whereas other aspects of biodiversity, including variability in functional diversity (FD), have received rather little rigorous attention. For streams, most studies to date have examined either taxonomic assemblage patterns or have experimentally addressed the importance of species richness for ecosystem functioning. 2. I examined the relationships of the functional biodiversity of stream macroinvertebrates to major environmental and spatial gradients across 111 boreal headwater streams in Finland. Functional biodiversity encompassed functional richness (FR , the number of functional groups derived from a combination of functional feeding groups and habit trait groups), FD , the number of functional groups and division of individuals among these groups, and functional evenness (FE , the division of individuals among functional groups). Furthermore, functional structure (FS) comprised the composition and abundance of functional groups at each site. 3. FR increased with increasing pH, with additional variation related to moss cover, total nitrogen, water colour and substratum particle size. FD similarly increased with increasing pH and decreased with increasing canopy cover. FE decreased with increasing canopy cover and water colour. Significant variation in FS was attributable to pH, stream width, moss cover, substratum particle size, nitrogen, water colour with the dominant pattern in FS being related to the increase of shredder-sprawlers and the decrease of scraper-swimmers in acidic conditions. 4. In regression analysis and redundancy analysis, variation in functional biodiversity was not only related to local environmental factors, but a considerable proportion of variability was also attributable to spatial patterning of environmental variables and pure spatial gradients. For FR, 23.4% was related to pure environmental effects, 15.0% to shared environmental and spatial effects and 8.0% to spatial trends. For FD, 13.8% was attributable to environmental effects, 15.2% to shared environmental and spatial effects and 5% to spatial trends. For FE, 9.0% was related to environmental variables, 12.7% to shared effects of environmental and spatial variables and 4.5% to spatial variables. For FS, 13.5% was related to environmental effects, 16.9% to shared environmental and spatial effects and 15.4% to spatial trends. 5. Given that functional biodiversity should portray variability in ecosystem functioning, one might expect to find functionally rather differing ecosystems at the opposite ends of major environmental gradients (e.g. acidity, stream size). However, the degree to which variation in the functional biodiversity of stream macroinvertebrates truly portrays variability in ecosystem functioning is difficult to judge because species traits, such as feeding roles and habit traits, are themselves strongly affected by the habitat template. 6. If functional characteristics show strong responses to natural environmental gradients, they also are likely to do so to anthropogenic environmental changes, including changes in habitat structure, organic inputs and acidifying elements. However, given the considerable degree of spatial structure in functional biodiversity, one should not expect that only the local environment and anthropogenic changes therein are responsible for this variability. Rather, the spatial context, as well as natural variability along environmental gradients, should also be explicitly considered in applied research. [source] Changes in Regional Variation of Medicare Home Health Care Utilization and Service Mix for Patients Undergoing Major Orthopedic Procedures in Response to Changes in Reimbursement PolicyHEALTH SERVICES RESEARCH, Issue 4 2009John D. FitzGerald Background. Significant variation in regional utilization of home health (HH) services has been documented. Under Medicare's Home Health Interim and Prospective Payment Systems, reimbursement policies designed to curb expenditure growth and reduce regional variation were instituted. Objective. To examine the impact of Medicare reimbursement policy on regional variation in HH care utilization and type of HH services delivered. Research Design. We postulated that the reimbursement changes would reduce regional variation in HH services and that HH agencies would respond by reducing less skilled HH aide visits disproportionately compared with physical therapy or nursing visits. An interrupted time-series analysis was conducted to examine regional variation in the month-to-month probability of HH selection, and the number of and type of visits among HH users. Subjects. A 100 percent sample of all Medicare recipients undergoing either elective joint replacement (1.6 million hospital discharges) or surgical management of hip fracture (1.2 million hospital discharges) between January 1996 and December 2001 was selected. Results. Before the reimbursement changes, there was great variability in the probability of HH selection and the number of HH visits provided across regions. In response to the reimbursement changes, though there was little change in the variation of probability of HH utilization, there were marked reductions in the number and variation of HH visits, with greatest reductions in regions with highest baseline utilization. HH aide visits were the source of the baseline variation and accounted for the majority of the reductions in utilization after implementation. Conclusions. The HH interim and prospective payment policies were effective in reducing regional variation in HH utilization. [source] Geographical variation in predictive seedling emergence in a perennial desert grassJOURNAL OF ECOLOGY, Issue 1 2000Steven E. Smith Summary 1,Mechanisms that link germination and emergence to environmental cues associated with seedling success (predictive germination) would be expected to evolve when seedlings have a greater mortality risk than seeds, but may be less important in perennial plants than in annual plants. 2,We investigated variation in predictive seedling emergence among divergent populations of a short-lived perennial desert grass, Digitaria californica, from sites that differed in climatic and edaphic factors. This species is native to environments in which the amount and duration of adequate soil moisture may control germination and seedling establishment success. 3,We utilized a special irrigation system that permits application of a range of amounts of water within a single experiment in a glasshouse. Emergence data were subjected to probit and survival analyses to describe differences among the populations in response to applied water. 4,Significant variation in predictive emergence was shown to exist among populations of D. californica when measured as amount of water required for 50% emergence following 3 days of water application, or as time required to achieve this level of emergence. Both climatic and soil characteristics were important with populations that originated from sites with less summer precipitation, and soils with higher water-holding capacity tended to have lower water requirements for emergence. 5,The report demonstrates the existence of subtle variation in predictive emergence among populations of a perennial grass representing a relatively narrow range of ecological amplitude. It also establishes the usefulness of line-source irrigation and probit analysis procedures in studying seedling emergence behaviour. [source] Temperature adaptation in a geographically widespread zooplankter, Daphnia magnaJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2000Mitchell Evidence for temperature adaptation in Daphnia magna was inferred from variation in the shape of temperature reaction norms for somatic growth rate, a fitness-related trait. Ex-ephippial clones from eight populations across Europe were grown under standardized conditions after preacclimation at five temperatures (17,29 °C). Significant variation for grand mean growth rates occurred both within populations (among clones) and between populations. Genetic variation for reaction norm shape was found within populations, with temperature-dependent trade-offs in clone relative fitness. However, the population average responses to temperature were similar, following approximately parallel reaction norms. The among-population variation is not evidence for temperature adaptation. Lack of temperature adaptation at the population level may be a feature of intermittent populations where environmentally terminated diapause can entrain the planktonic stage of the life-history within a similar range of temperatures. [source] Spatial and interannual patterns in growth of an exploited coral-reef fishJOURNAL OF FISH BIOLOGY, Issue 4 2007A. J. Williams Patterns of growth in an exploited reef fish Lethrinus miniatus were examined over 5 years (1995,1999) at two spatial scales: (1) among regions of the Great Barrier Reef (GBR) separated by >100 km and (2) among reefs within each of these regions, separated by ,10 km. Mean annual growth of L. miniatus varied significantly among years, but this variation was consistent among ages and regions, indicating that factors that influence temporal patterns in growth were not age-specific and operated at relatively large spatial scales. Significant variation in growth was also observed among some reefs within regions, although the greatest variation was among regions. The average maximum fork length () and average maximum mass (M,) varied significantly among regions, suggesting that productivity of L. miniatus is likely to vary among regions of the GBR. There was also significantly greater mass of fish for a given LF in two regions, which magnified the regional differences in M,. The observed temporal and spatial variation in growth highlighted the importance of a multi-scale approach to population studies and assessment of fish stocks. [source] Temperature Effects on Survival and DNA Repair in Four Freshwater Cladoceran Daphnia Species Exposed to UV RadiationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009Sandra J. Connelly The biological responses of four freshwater daphniid species, Daphnia middendorffiana, D. pulicaria, D. pulex and D. parvula, to a single acute dose of ultraviolet B radiation (UVB) were compared. In addition to survival, we compared the induction of DNA damage (i.e. cyclobutane pyrimidine dimers) between species as well as the ability to repair this damage in the presence or absence of photoreactivating light. All four species showed high levels of shielding against DNA damage when compared to damage induced in purified DNA dosimeters at the same time and dose. Significant variation in survival was observed between species depending on temperature and light conditions. Contrary to our expectations, all species showed significantly higher survival and light-dependent DNA damage removal rates at 10°C compared to 20°C, suggesting that the enhanced rate of photoenzymatic repair (PER) at the lower temperature contributed significantly to the recovery of these organisms from UVB. PER was highly effective in promoting survival of three of the four species at 10°C, but at 20°C it was only partially effective in two species, and ineffective in two others. None of the species showed significant dark repair at 20°C and only D. pulicaria showed a significant capacity at 10°C. Two species, D. middendorffiana and D. pulex, showed some short-term survival at 10°C in absence of PER despite their inability to repair any appreciable amount of DNA damage in the dark. All species died rapidly at 20°C in absence of PER, as predicted from complete or near-absence of nucleotide excision repair (NER). Overall, the protective effects of tissue structure and pigmentation were similar in all Daphnia species tested and greatly mitigated the absorption of UVB by DNA and its damaging effects. Surprisingly, the visibly melanotic D. middendorffiana was not better shielded from DNA damage than the three non-melanotic species, and in fact suffered the highest damage rates. Melanin content in this species was not temperature dependent under the experimental growth conditions, and so did not contribute to temperature-dependent responses. It is evident that different species within the same genus have developed diverse biological responses to UVB. Our data strongly suggest that DNA damage is lethal to Daphnia and that photoenzymatic repair is the primary mechanism for removing these lesions. In the absence of light, few species are capable of removing any DNA damage. Surprisingly, the single species in which significant excision repair was detected did so only at reduced temperature. This temperature-dependence of excision repair is striking and may reflect adaptations of certain organisms to stress in a complex and changing environment. [source] The Distribution of Ganglion Cells in the Equine Retina and its Relationship to Skull MorphologyANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2 2007K. E. Evans Summary It has recently been reported that a strong correlation exists between the distribution of retinal ganglion cells and nose length in the domestic dog. To determine if this phenomenon occurs in another domestic species with diverse skull morphology, the current study examined the distribution of retinal ganglion cells in 30 horses from a variety of breeds. There was a significant variation in the density of ganglion cells found across the retinae. Breed was a significant predictor for ganglion cell density within the visual streak. A strong positive correlation exists between the density of ganglion cells in the visual streak and nasal length. Significant variation was also seen in the area centralis but did not correlate with any of the recorded skull measurements. The findings of this study provide us with further understanding of the equine visual system and the level of variation that exists between individuals of the same species. [source] Telomerase activity and hTERT mRNA expression can be heterogeneous and does not correlate with telomere length in soft tissue sarcomasINTERNATIONAL JOURNAL OF CANCER, Issue 6 2002Pu Yan Abstract In a previous study, we showed that telomerase activity (TA) and human telomerase reverse transcriptase (hTERT) mRNA expression were undetectable in benign mesenchymal lesions and low-grade soft tissue sarcomas (STSs), but detectable in about 50% of intermediate-/high-grade STSs. We wondered if this lack of TA or hTERT mRNA expression could be related to the tumor sample examined and if there was a relationship between the former 2 parameters and telomere length. Two separate tumor samples from 37 STSs were examined for telomerase activity, using the telomerase repeat amplification protocol (TRAP) assay and for hTERT mRNA expression, using RT-PCR. Telomere length was determined in each tumor sample, using the terminal restriction fragments (TRF) technique. Significant variations in telomere length, TA and hTERT mRNA expression between 2 samples of the same tumor were observed in 27%, 11% and 27% of STSs, respectively. Telomere length did not correlate with TA or hTERT mRNA expression. Despite great intratumoral heterogeneity in telomere length, short and long telomeres were more often seen in the low/intermediate-grade and high-grade STS categories, respectively. Few STSs that showed a TRF pattern suggestive of alternative lengthening of telomeres (ALT) may contain ALT subpopulations. © 2002 Wiley-Liss, Inc. [source] We are all different: insights from osteoporosis research in AsiaINTERNATIONAL JOURNAL OF RHEUMATIC DISEASES, Issue 4 2008Swan Sim YEAP Abstract Osteoporosis only became a ,disease' entity in the 20th century. After the initial observations and definitions of osteoporosis based on Caucasian populations, systematic research in Asian populations started in the 1980s. Significant variations between different ethnic groups with respect to the rate of osteoporotic fractures, bone mineral density and disease risk factors emerged from the data; this article highlights some of the earlier important findings and the dissimilarities. Osteoporosis is therefore not a homogeneous disease across the world. [source] (A-)typical and (in-)secure?INTERNATIONAL SOCIAL SECURITY REVIEW, Issue 4 2008"non-standard" forms of employment in Europe, Social protection Abstract Atypical forms of employment (part-time work, mini-jobs, fixed-term contracts and solo self-employment) have gained in importance overall in recent years in many European countries. They are often part of an irregular career pattern and carry a high risk of unemployment. In a 6-country comparison (Germany, the United Kingdom, the Netherlands, Italy, Denmark and Poland) we consider whether and in what way national social protection laws cover the various forms of non-standard employment and the specific risks these entail. Significant variations were found in coverage standards and practices between countries as well as substantial variability within countries in their responses to different types of non-standard employment. A need for further and improved coordination of both social legislation and tax law is identified. [source] Microwave-Assisted Free Radical Copolymerizations of Styrene and Methyl MethacrylateMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2007Heiner Stange Abstract Free radical copolymerizations of styrene and MMA were performed in toluene and DMF as solvents using different peroxide initiators with and without microwave irradiation. A general trend showed significant solvent dependence of monomer conversion rate only for copolymerizations initiated by tert -butyl perbenzoate in DMF compared to toluene but nearly no impact for copolymerizations initiated by dicumyl peroxide and dibenzoyl peroxide. Significant variations in copolymer composition were not observed for reactions under conventional heating compared to microwave irradiation. It was concluded that enhanced initiator decomposition under microwave irradiation in DMF accelerate polymerization of styrene and MMA by formation of larger amount of initiator radicals. [source] Refined structures of placental alkaline phosphatase show a consistent pattern of interactions at the peripheral siteACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2010Boguslaw Stec In order to gain deeper insights into the functional sites of human placental alkaline phosphatase, the structures of the enzyme with the putative regulators l -Phe, pNPP and 5,-AMP [Llinas et al. (2005), J. Mol. Biol.350, 441,451] were re-refined. Significant variations in ligand positioning and identity were found compared with the previous report. The multiple corrections to the model improved the phases and the electron-density maps, allowing the modeling of omitted side chains and multiple disordered residues. These improvements led to a change in the position of l -Phe at the peripheral binding site, which appeared to be reversed. The structure with pNPP contained only p -nitrophenol in three distinct sites, while the structure with 5,-AMP contained the p -nitrophenyl group in two of the sites instead of 5,-AMP. Comparison of the re-refined models shows a consistent pattern of interactions at the peripheral site. [source] Hybridization, developmental stability, and functionality of morphological traits in the ground beetle Carabus solieri (Coleoptera, Carabidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2006STEPHANE GARNIER The assessment of developmental stability in hybrids can provide valuable information in the study of species formation because it allows an evaluation of the degree of incompatibility of genetic systems that control developmental processes. The present study assessed the impact of two hybridization events, assumed to have occurred at different times, on developmental instability in the ground beetle Carabus solieri. Developmental instability was estimated in 678 individuals from 27 populations from the fluctuating asymmetry (FA) levels of four morphological traits: the tibia length of middle and hind legs, which are functional structures, and the length and the proximal width of the hind wings, which are vestigial and thus nonfunctional structures. Significant variations of FA levels between populations were shown only for the wing width. For this trait, FA levels in hybrids were higher than in their parental entities for both hybridization events, indicating a significant divergence of the gene systems controlling development between the parental entities in the two hybridization cases. As expected, wing traits exhibited FA levels at least three times higher than leg trait. Finally, the potential interest of vestigial traits in the particular context of hybridization is discussed. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 151,158. [source] Variation in Pesticide Tolerance of Tadpoles among and within Species of Ranidae and Patterns of Amphibian DeclineCONSERVATION BIOLOGY, Issue 5 2000Christine M. Bridges Because variability exists among organisms in their sensitivity to environmental stressors, it is important to determine the degree of this variation when undertaking conservation efforts. We conducted both lethal (time-to-death) and sublethal (activity change) assays to determine the degree of variation in the sensitivity of tadpoles to a pesticide, carbaryl, at three hierarchical levels: among ranid species, among several populations of a single ranid species ( Rana sphenocephala), and within populations of R. sphenocephala. We observed significant variation in time to death among the nine ranid species and among the 10 R. sphenocephala populations we tested. Four out of eight R. sphenocephala populations exhibited significantly different times to death among families. The magnitude of the activity change in response to exposure to sublethal carbaryl levels was significantly different among species and within R. sphenocephala populations. Chemical contamination, at lethal or sublethal levels, can alter natural regulatory processes such as juvenile recruitment in amphibian populations and should be considered a contributing cause of declines in amphibian populations. Resumen: Existe una variación significativa entre y dentro de especies de anfibios con respecto a los reportes de disminuciones poblacionales; las especies en disminución son frecuentemente encontradas en ambientes que son fisiográficamente similares a ambientes donde las mismas especies están prosperando. Debido a que la variabilidad existe entre organismos en lo referente a su sensibilidad a estresores ambientales, es importante determinar el grado de esta variación cuando se lleven a cabo esfuerzos de conservación. Nosotros llevamos a cabo ensayos tanto letales (tiempo de muerte) como subletales (cambios de actividad) para determinar el grado de variación en la sensibilidad de renacuajos a un pesticida, carbaryl, en tres niveles jerárquicos: entre especies de ránidos, entre diversas poblaciones de una sola especie de ránido ( Rana sphenocephala) y dentro de poblaciones de R. sphenocephala. Observamos diferencias significativas en tiempo de muerte entre las nueve especies de ránidos y entre las 10 poblaciones de R. sphenocephala evaluadas. Cuatro de ocho poblaciones de R. sphenocephala exhibieron tiempos de muerte significativamente diferentes entre familias. La magnitud del cambio de actividad al ser expuestas a niveles subletales de carbaryl fue significativamente diferente entre especies y dentro de poblaciones de R. sphenocephala. La contaminación química, a niveles letales y subletales, puede alterar los procesos reguladores naturales (por ejemplo el reclutamiento de juveniles) en poblaciones de anfibios y debería ser considerado como una causa que contribuye a la disminución de poblaciones de anfibios. [source] Participation of children with cerebral palsy is influenced by where they liveDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 5 2004Donna Hammal MSc The study aimed to determine whether degree of participation of children with cerebral palsy (CP) is influenced by where they live, as predicted by the social model of disability. Ninety-two per cent children with CP resident in Northern England and born 1991-1996 were entered into the study. Participation was measured by the Lifestyle Assessment Score and its six component domain scores. Regression analysis was used to investigate variations in participation. There were 443 children (265 male, 178 female; mean age 4 years 8 months [SD1 year 1 month] at time of assessment) in the study. In the regression analysis the following factors remained significant with regard to level of participation: type of CP (167 with hemiplegia, and of those remaining 240 with bilateral spasticity); intellectual impairment (105 with IQ<50,113 with IQ 50 to 70, and 225 with IQ>70); presence of seizures (115 with active epilepsy); walking disability (114 unable to walk, 81 restricted and needing aids, 186 restricted but unaided, 62 unrestricted); communication problems (61 no formal communication, 51 use alternative formal methods, 126 some delay or difficulty, 205 no communication problems). After adjustment for these factors, there were significant variations with regard to level of participation in the Lifestyle Assessment Score by district of residence. The magnitude of these variations in Lifestyle Assessment Score between districts is similar to that accounted for by severe intellectual impairment. Similar models were obtained for four of the six domain scores. For one of these four, restriction of social interaction, the significant variation between districts was minimally influenced by the underlying type of CP, walking ability, or presence of seizures. Higher levels of participation among children with CP are associated with residence in certain districts. This is not attributable to variations in case-mix or functional capacity of the children. Participation of children with disability is partly a product of their environment. [source] Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic RegionDIVERSITY AND DISTRIBUTIONS, Issue 3 2002R. M. Cowling Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source] Cold tolerance in obligate and cyclical parthenogens of the peach-potato aphid, Myzus persicaeECOLOGICAL ENTOMOLOGY, Issue 4 2004Christoph Vorburger Abstract., 1. Many aphids form mixed populations of cyclical and obligate parthenogens. This is puzzling, because all else being equal, obligate parthenogens should outcompete cyclical parthenogens due to the two-fold cost of sex. Yet cyclical parthenogens produce frost-resistant, diapausing eggs in autumn, while obligate parthenogens spend the winter as active stages. Frost resistance thus represents a short-term advantage to sexual reproduction mediated by winter temperatures, which may promote this coexistence. 2. Because obligate parthenogens overwinter as active stages, there may be selection for increased cold tolerance compared to cyclical parthenogens. This has the potential to gradually erode the advantage of sexually producing eggs. 3. Four obligately and four cyclically parthenogenetic lines of Myzus persicae (Sulzer) (Hemiptera: Aphididae) were collected from each of two areas differing in winter severity, and their survival after exposure to a severe experimental frost (14 h at ,9 °C), as well as their reproductive performance at a low (10 °C) and a high (20 °C) temperature were compared. 4. There was significant variation among lines in survival after the experimental frost, but this variation was neither related to their reproductive mode, nor to their area of origin. Similarly, neither reproductive mode nor origin had a significant effect on reproductive performance, independent of temperature. The average slope of the response to variation in temperature was also similar for both reproductive modes, despite the fact that slopes differed significantly among lines. 5. Within the limits of extrapolating from laboratory experiments, it is concluded that in M. persicae, the active stages of obligate parthenogens are not better adapted to cold temperatures than those of cyclical parthenogens. [source] Color vision and macular recovery time in epileptic adolescents treated with valproate and carbamazepineEUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2006A. Verrotti Visual dysfunction has been reported in patients diagnosed with epilepsy. Some of these visual disturbances may be attributable to either the disease process, or the anticonvulsant therapy prescribed to control the seizures. The aims of our study were to evaluate whether color vision and macular function are impaired in epileptic adolescents, to study if the monotherapy with valproic acid (VPA) and carbamazepine (CBZ) can affect color vision and macular function and to determine the possible relationship between color vision, retinal function and antiepileptic drugs (AEDs) dosage and their serum concentrations. We examined 45 (16 male and 29 female, mean age ± SD, 15.71 ± 2.01 years) Caucasian epileptic patients suffering from various types of cryptogenic epilepsy before the beginning of therapy and after 1 year of VPA or CBZ monotherapy and 40 sex- and age-matched healthy controls. Color vision was assessed by Farnsworth Munsell (FM) 100-hue test and total error score (TES) was evaluated. This test consists of colored caps: the testee has to arrange the caps according to their colors macular function was assessed by nyctometry evaluating initial recovery time (IRT) and summation method (SM). This test evaluates visual acuity after a period of intense illumination of macula. Analysis of variance was used to evaluate the difference between controls and patients; moreover, Pearson's correlation test have been performed. Before the beginning of therapy, there were no differences in color vision and macular function between controls and epileptic patients. After 1 year, the patients, treated with VPA or CBZ, showed a deficit in FM 100-hue test. At nyctometry, all patients showed no significant variation of macular function between baseline evaluation and second evaluation at end of the follow-up. Our study demonstrates that, in our group of epileptic patients, epilepsy per se does not affect color vision and retinal function. In contrast, after 1 years of therapy with VPA and CBZ these patients showed a deficit in FM 100-hue test although nyctometry evaluation continued to be normal allowing to exclude an impairment in macular function. Further investigations are required to determine the pathophysiological alteration(s) that are at the basis of color perception defects. [source] Daytime variations of interleukin-1, in gingival crevicular fluidEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2008Angela Bergmann Interleukin-1, (IL-1,) is an important parameter in periodontal research because of its role in inflammation and bone resorption. One measure used to assess local IL-1, concentrations is analysis of its levels in gingival crevicular fluid (GCF). While studies on serum IL-1, concentrations indicate a circadian rhythm of this parameter, nothing is known about daytime variations of IL-1, in GCF. The present study thus aimed to analyse such variations. Daytime variations of GCF-IL-1, between 08:00 and 22:00 h were assessed, with a time resolution of 2 h, in 28 periodontally healthy subjects. The data showed a significant variation throughout the day, with the lowest concentrations and total amounts in the morning and the highest in the evening. The effect sizes of comparisons between morning and evening samples were medium to high and corresponded in magnitude to those reported in other published research comparing healthy sites and those affected by periodontitis. The smallest daytime variations were found to occur between 12:00 h and 18:00 h. It is concluded that daytime variations in GCF-IL-1, are large enough to be able to mimic or mask differences caused by clinical factors. [source] Corrosion of Pure Mg as a Function of Grain Size and Processing Route,ADVANCED ENGINEERING MATERIALS, Issue 6 2008C. op't Hoog This study is a discrete effort towards optimization of microstructure for enhanced corrosion resistance by understanding the largely unknown corrosion , grain size relationship for magnesium. This is particularly important for magnesium that commonly displays poor corrosion resistance. A significant variation in corrosion resistance with grain size exists, which is of key significance; however these trends were strongly dependent upon the specific thermo-mechanical processing route used to prepare the specimens. [source] NATURAL SELECTION ALONG AN ENVIRONMENTAL GRADIENT: A CLASSIC CLINE IN MOUSE PIGMENTATIONEVOLUTION, Issue 7 2008Lynne M. Mullen We revisited a classic study of morphological variation in the oldfield mouse (Peromyscus polionotus) to estimate the strength of selection acting on pigmentation patterns and to identify the underlying genes. We measured 215 specimens collected by Francis Sumner in the 1920s from eight populations across a 155-km, environmentally variable transect from the white sands of Florida's Gulf coast to the dark, loamy soil of southeastern Alabama. Like Sumner, we found significant variation among populations: mice inhabiting coastal sand dunes had larger feet, longer tails, and lighter pigmentation than inland populations. Most striking, all seven pigmentation traits examined showed a sharp decrease in reflectance about 55 km from the coast, with most of the phenotypic change occurring over less than 10 km. The largest change in soil reflectance occurred just south of this break in pigmentation. Geographic analysis of microsatellite markers shows little interpopulation differentiation, so the abrupt change in pigmentation is not associated with recent secondary contact or reduced gene flow between adjacent populations. Using these genetic data, we estimated that the strength of selection needed to maintain the observed distribution of pigment traits ranged from 0.0004 to 21%, depending on the trait and model used. We also examined changes in allele frequency of SNPs in two pigmentation genes, Mc1r and Agouti, and show that mutations in the cis -regulatory region of Agouti may contribute to this cline in pigmentation. The concordance between environmental variation and pigmentation in the face of high levels of interpopulation gene flow strongly implies that natural selection is maintaining a steep cline in pigmentation and the genes underlying it. [source] EVOLUTIONARY ANALYSIS OF A KEY FLORAL TRAIT IN AQUILEGIA CANADENSIS (RANUNCULACEAE): GENETIC VARIATION IN HERKOGAMY AND ITS EFFECT ON THE MATING SYSTEMEVOLUTION, Issue 7 2007Christopher R. Herlihy The mating system of flowering plant populations evolves through selection on genetically based phenotypic variation in floral traits. The physical separation of anthers and stigmas within flowers (herkogamy) is expected to be an important target of selection to limit self-fertilization. We investigated the pattern of phenotypic and genetic variation in herkogamy and its effect of self-fertilization in a broad sample of natural populations of Aquilegia canadensis, a species that is highly selfing despite strong inbreeding depression. Within natural populations, plants exhibit substantial phenotypic variation in herkogamy caused primarily by variation in pistil length rather than stamen length. Compared to other floral traits, herkogamy is much more variable and a greater proportion of variation is distributed among rather than within individuals. We tested for a genetic component of this marked phenotypic variation by growing naturally pollinated seed families from five populations in a common greenhouse environment. For three populations, we detected a significant variation in herkogamy among families, and a positive regression between parental herkogamy measured in the field and progeny herkogamy in the greenhouse, suggesting that there is often genetic variation in herkogamy within natural populations. We estimated levels of self-fertilization for groups of flowers that differed in herkogamy and show that, as expected, herkogamy was associated with reduced selfing in 13 of 19 populations. In six of these populations, we performed floral emasculations to show that this decrease in selfing is due to decreased autogamy (within-flower selfing), the mode of selfing that herkogamy should most directly influence. Taken together, these results suggest that increased herkogamy should be selected to reduce the production of low-quality selfed seed. The combination of high selfing and substantial genetic variation for herkogamy in A. canadensis is enigmatic, and reconciling this observation will require a more integrated analysis of how herkogamy influences not only self-fertilization, but also patterns of outcross pollen import and export. [source] PLASTICITY IN QUEEN NUMBER AND SOCIAL STRUCTURE IN THE INVASIVE ARGENTINE ANT (LINEPITHEMA HUMILE)EVOLUTION, Issue 10 2002Krista K. Ingram Abstract., In many polygynous social insect societies, ecological factors such as habitat saturation promote high queen numbers by increasing the cost of solitary breeding. If polygyny is associated with constrained environments, queen number in colonies of invasive social insects should increase as saturation of their new habitat increases. Here I describe the variation in queen number, nestmate relatedness, and nest size along a gradient of time since colonization in an invading population of Argentine ants (Linepithema humile) in Haleakala, Hawaii. Nest densities in this population increase with distance from the leading edge of the invasion, reaching a stable density plateau approximately 80 m from the edge (> 2 years after colonization). Although the number of queens per nest in Haleakala is generally lower than previously reported for Argentine ants, there is significant variation in queen number across this population. Both the observed and effective queen numbers increase across the density gradient, and nests in the center of the population contain queen numbers three to nine times higher than those on the edge of the invasion. The number of workers per nest is correlated with queen number, and nests in the center are six times larger than nests at the edge. Microsatellite analysis of relatedness among nestmates reveals that all nests in the Haleakala population are characterized by low relatedness and have evidence of multiple reproducing queens. Relatedness values are significantly lower in nests in the center of the population, indicating that the number of reproducing queens is greater in areas of high nest density. The variation in queen number and nestmate relatedness in this study is consistent with expectations based on changes in ecological constraints during the invasion of a new habitat, suggesting that the social structure of Argentine ant populations is strongly influenced by ecological factors. Flexibility in social structure may facilitate persistence in variable environments and may also confer significant advantages to a species when introduced into new areas. [source] Infiltrating cells and related cytokines in lesional skin of patients with chronic idiopathic urticaria and positive autologous serum skin testEXPERIMENTAL DERMATOLOGY, Issue 5 2003M. Caproni Abstract:, In approximately one-third of patients with chronic idiopathic urticaria (CIU), autoantibodies against the high-affinity IgE receptor and/or against IgE can be detected and a wheal-and-flare response can be provoked by the intradermal injection of autologous serum (ASST). In this study we aimed to further characterize the inflammatory response observed in the subgroup of CIU patients with positive ASST and serum-evoked histamine-release in vitro from basophils in comparison with unaffected skin and healthy donors. An immunohistochemical analysis of infiltrating cells (CD4, MPO, EG1, EG2, tryptase), cytokines (IL-4, IL-5, IFN-,), chemokines and chemokine receptors (IL-8, CCR3, CXCR3), and adhesion molecules (ICAM-1, VCAM-1, ELAM-1) was performed on seven selected patients (four males and three females; median age: 45 years; range: 22,57) and five healthy donors. Cytokine evaluation was also performed in five psoriatic patients to obtain an additional control. In spontaneous wheals we observed an increased number of CD4+ T lymphocytes when compared with the controls, and an increased number of neutrophils and eosinophils, whereas mast cells did not show a significant variation. A significant expression for IL-4 and IL-5 could only be observed in lesional skin, while IFN-, showed a slight expression in the same site. Chemokine receptors CCR3 and CXCR3 did not show a defined polarized response in either lesional or unaffected skin. An increased expression of all cellular adhesion molecules (CAMs) studied was detected in spontaneous wheals. The lack of a significant difference in the expression of tryptase + mast cells, T lymphocytes, IL-8, CXCR3 and CCR3, a few CAMs between the lesional and unaffected skin of CIU patients suggests a wide immunological activation that involves not only lesional tissues, but possibly extends to the whole of the skin's immune system. [source] Effects of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2005Z. B. SAJURI ABSTRACT Load-controlled fatigue tests were performed at 20 and 50 °C using two relative humidity levels of 55 and 80% to characterize the influence of humidity and temperature on the fatigue behaviour of an extruded AZ61 magnesium alloy. Fatigue tests were also conducted at 150 °C. No significant variation in fatigue properties was noticed with respect to temperature over the range from 20 to 50 °C for both the humidity levels. Fatigue limits in the range 140,150 MPa were observed for relative humidity of 55%. Fatigue strength decreased significantly with increase in temperature to 150 °C. Further, a significant reduction in fatigue strength with a fatigue limit of ,110 MPa was observed with increase in relative humidity to 80% at 20 and 50 °C. The crack initiation and propagation remained transgranular under all test conditions. The fatigue fracture at low stress amplitudes and high relative humidity of 80% results from the formation of corrosion pits at the surface and their growth to a critical size for fatigue-crack initiation and propagation. The observed reduction in fatigue strength at high humidity is ascribed to the effects associated with fatigue,environment interaction. [source] Characterization of the aroma-active compounds in five sweet cherry cultivars grown in Yantai (China)FLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2010Shu Yang Sun Abstract This study was conducted to determine the aroma-active compounds of five sweet cherry cultivars grown in Yantai region, China, viz. ,Lapins', ,Rainier', ,Stella', ,Hongdeng' and ,Zhifuhong'. The samples were extracted by headspace solid phase microextraction (HS,SPME) and analysed by gas chromatography,mass spectrometry (GC,MS) on DB-wax and DB-5 columns. A total of 52 volatiles were identified. Among these, hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexen-1-ol, benzaldehyde and benzyl alcohol were the main volatile compounds in the five cherries. Furthermore, the aroma compounds of five cherry samples were evaluated using a combination of HS,SPME and GC,olfactometry (GC,O) dilution analysis, and a total of 40 aroma-active compounds were identified. The results suggested that hexanal, (E)-2-hexenal, (Z)-3-hexenal, nonanal, benzaldehyde and geranylacetone (FD , 16), responsible for the green, orange, almond and floral characters of the cherries, were the potentially important common odorants in these cherry cultivars. Benzyl alcohol and linalool were significant aroma compounds in most cherries, with the exception of ,Stella' and ,Rainier'. In addition, (E,Z)-2,6-nonadienal (cucumber-like odour) could be important to ,Hongdeng' and ,Zhifuhong', and (E,E)-2,4-nonadienal (fatty odour) probably made great contributions to the aromas in ,Lapins' and ,Stella'. From the present result, it was concluded that the aroma profiles were similar in the five cherry cultivars, but significant variation was found in the contributions of these compounds to each cherry. Copyright © 2010 John Wiley & Sons, Ltd. [source] Population genetic structure of three freshwater mussel (Unionidae) species within a small stream system: significant variation at local spatial scalesFRESHWATER BIOLOGY, Issue 8 2007DAVID J. BERG Summary 1. Unionid mussels are highly threatened, but little is known about genetic structure in populations of these organisms. We used allozyme electrophoresis to examine partitioning of genetic variation in three locally abundant and widely distributed species of mussels from a catchment in Ohio. 2. Within-population variation was similar to that previously reported for freshwater mussels, but genotype frequencies exhibited heterozygote deficiencies in many instances. All three species exhibited significant among-population variation. Evidence of isolation-by-distance was found in Elliptio dilatata and Ptychobranchus fasciolaris, while Lampsilis siliquoidea showed no geographical pattern of among-population variation. 3. Our results suggest that the isolating effects of genetic drift were greater in L. siliquoidea than in the other species. Differentiation of populations occurred at a much smaller spatial scale than has previously been found in freshwater mussels. Differences among species may reflect differences in the dispersal abilities of fishes that serve as hosts for the glochidia larvae of mussels. 4. Based on our results, we hypothesise that species of mussels that are common to large rivers exhibit relatively large amounts of within-population genetic variation and little differentiation over large geographical distances. Conversely, species typical of small streams show lower within-population genetic variation and populations will be more isolated. If this hypothesis can be supported, it may prove useful in the design of conservation strategies that maintain the genetic structure of target species. [source] Transgenerational plasticity for sexual reproduction and diapause in the life cycle of monogonont rotifers: intraclonal, intraspecific and interspecific variation in the response to crowdingFUNCTIONAL ECOLOGY, Issue 3 2004T. SCHRÖDER Summary 1In monogonont rotifers parthenogenetic reproduction allows population growth, and mictic (sexual) reproduction leads to the production of diapausing eggs. When amictic females are exposed to a mixis stimulus, they produce mictic daughters, whose eggs develop into males or, if fertilized, into diapausing eggs. Experiments showed that mictic offspring production is initiated by crowding in females of Brachionus angularis Gosse 1851, Epiphanes senta (O.F. Müller 1773) and Rhinoglena frontalis Ehrenberg 1853, just as it is in Brachionus calyciflorus Pallas 1766 and B. plicatilis Müller 1786. 2In B. calyciflorus, B. angularis, E. senta and R. frontalis, the propensity of amictic females to respond to crowding by producing mictic female offspring is low in the stem female hatching from a diapausing egg, but then increases after some generations. In many cases, only few mictic offspring are produced by crowded females of the second to the fifth generation, but the maximal response occurs only in later generations. Delayed sexual reproduction in early generations from the resting egg may be advantageous, because it first favours rapid population growth and later on maximizes resting egg production. However, it may be disadvantageous, if unpredictable environmental variation causes a population decline when sexual reproduction is still suppressed. 3The extent to which sexual reproduction is delayed varies among and within species. When strains from populations in temporary and permanent habitats were compared, sexual reproduction was significantly delayed in strains from temporary habitats in all species, whereas in B. calyciflorus and R. frontalis mixis was not significantly delayed in strains from permanent habitats. In E. senta mixis was significantly delayed in clones from both habitat types. 4Within all strains there was significant variation among clones in the propensity to produce mictic offspring, the extent to which sexual reproduction was delayed in the first generations after the stem female hatched, or both. [source] Three-dimensional seismic structure beneath the Australasian region from refracted wave observationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000Y. Kaiho The earthquakes in the seismicity belt extending through Indonesia, New Guinea, Vanuatu and Fiji to the Tonga,Kermadec subduction zone recorded at the 65 portable broad-band stations deployed during the Skippy experiment from 1993,1996 provide good coverage of the lithosphere and mantle under the Australian continent, Coral Sea and Tasman Sea. The variation in structure in the upper part of the mantle is characterized by deter-mining a suite of 1-D structures from stacked record sections utilizing clear P and S arrivals, prepared for all propagation paths lying within a 10° azimuth band. The azimuth of these bands is rotated by 20° steps with four parallel corridors for each azimuth. This gives 26 separate azimuthal corridors for which 15 independent 1-D seismic velocity structures have been derived, which show significant variation in P and S structure. The set of 1-D structures is combined to produce a 3-D representation by projecting the velocity values along the ray path using a turning point approximation and stacking into 3-D cells (5° by 50 km in depth). Even though this procedure will tend to underestimate wave-speed perturbations, S -velocity deviations from the ak135 reference model exceed 6 per cent in the lithosphere. In the uppermost mantle the results display complex features and very high S -wave speeds beneath the Precambrian shields with a significant low-velocity zone beneath. High velocities are also found towards the base of the transition zone, with highS -wave speeds beneath the continent and high P -wave speeds beneath the ocean. The wave-speed patterns agree well with independent surface wave studies and delay time tomography studies in the zones of common coverage. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||