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Selective Agents (selective + agent)
Selected Abstracts1,3-Dibromo-5,5-dimethylhydantoin [DBDMH] as an Efficient and Selective Agent for the Oxidation of Thiols to Disulfides in Solution or under Solvent-Free Conditions.CHEMINFORM, Issue 19 2005Ardeshir Khazaei Abstract For Abstract see ChemInform Abstract in Full Text. [source] Do past experience and competitive ability influence foraging strategies of parasitoids under interspecific competition?ECOLOGICAL ENTOMOLOGY, Issue 6 2008CECILE LE LANN Abstract 1.,In solitary parasitoids, several species can exploit the same host patch and competition could potentially be a strong selective agent as only one individual can emerge from a host. In cereal crops, Aphidius rhopalosiphi and A. ervi share the grain aphid Sitobion avenae as host. 2.,The present work studied foraging strategies of both species on patches already exploited by the other species. The study analysed larval competition in multi-parasitised hosts and compared the foraging behaviour of females with and without previous experience. 3.,It was found that A. ervi wins larval competition three times more often than A. rhopalosiphi. Both species spent less time on patches exploited by a heterospecific than on unexploited ones. When they foraged on heterospecifically exploited patches, experienced females induced less mortality in aphids than inexperienced ones. 4.,Although A. rhopalosiphi is a specialist on cereal aphids and is the most abundant species due to its early appearance in the season, S. avenae is still a profitable host for A. ervi, because: (i) A. rhopalosiphi leaves patches partially exploited, (ii) A. ervi wins larval competition in three out of four multi-parasitised hosts, and (iii) A. ervi is only slightly deterred by the cornicular secretions of the host and can thus easily parasitise hosts. [source] Scaling up evolutionary responses to elevated CO2: lessons from ArabidopsisECOLOGY LETTERS, Issue 5 2004Joy K. Ward Abstract Results from norm of reaction studies and selection experiments indicate that elevated CO2 will act as a selective agent on natural plant populations, especially for C3 species that are most sensitive to changes in atmospheric CO2 concentration. Evolutionary responses to CO2 may alter plant physiology, development rate, growth, and reproduction in ways that cannot be predicted from single generation studies. Moreover, ecological and evolutionary changes in plant communities will have a range of consequences at higher spatial scales and may cause substantial deviations from ecosystem level predictions based on short-term responses to elevated CO2. Therefore, steps need to be taken to identify the plant traits that are most likely to evolve at elevated CO2, and to understand how these changes may affect net primary productivity within ecosystems. These processes may range in scale from molecular and physiological changes that occur among genotypes at the individual and population levels, to changes in community- and ecosystem-level productivity that result from the integrative effects of different plant species evolving simultaneously. In this review, we (1) synthesize recent studies investigating the role of atmospheric CO2 as a selective agent on plants, (2) discuss possible control points during plant development that may change in response to selection at elevated CO2 with an emphasis at the primary molecular level, and (3) provide a quantitative framework for scaling the evolutionary effects of CO2 on plants in order to determine changes in community and ecosystem productivity. Furthermore, this review points out that studies integrating the effects of plant evolution in response to elevated CO2 are lacking, and therefore more attention needs be devoted to this issue among the global change research community. [source] Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1, levels, and energy metabolismJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2007Jeanne Bourdeau-Heller Cancer cells are able to tolerate levels of O2 that are damaging or lethal to normal cells; we hypothesize that this tolerance is the result of biochemical plasticity which maintains cellular homeostasis of both energy levels and oxidation state. In order to examine this hypothesis, we used different O2 levels as a selective agent during long-term culture of DU145 prostate cancer cells to develop three isogenic cell lines that grow in normoxic (4%), hyperoxic (21%), or hypoxic (1%) O2 conditions. Growth characteristics and O2 consumption differed significantly between these cell lines without changes in ATP levels or altered sensitivity to 2-deoxy- D -glucose, an inhibitor of glycolysis. O2 consumption was significantly higher in the hyperoxic line as was the level of endogenous superoxide. The hypoxic cell line regulated the chemical gradient of the proton motive force (PMF) independent of the electrical component without O2 -dependent changes in Hif-1, levels. In contrast, the normoxic line regulated Hif-1, without tight regulation of the chemical component of the PMF noted in the hypoxic cell line. From these studies, we conclude that selection of prostate cancer cells by long-term exposure to low ambient levels of O2 resulted in cells with unique biochemical properties in which energy metabolism, reactive oxygen species (ROS), and HIF-1, levels are modulated to allow cell survival and growth. Thus, cancer cells exhibit remarkable biochemical plasticity in response to various O2 levels. J. Cell. Physiol. 212:744,752, 2007. © 2007 Wiley-Liss, Inc. [source] Increased body size confers greater fitness at lower experimental temperature in male Drosophila melanogasterJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2000Reeve Genetic variation of body size along latitudinal clines is found globally in Drosophila melanogaster, with larger individuals encountered at higher latitudes. Temperature has been implicated as a selective agent for these clines, because the body size of laboratory populations allowed to evolve in culture at lower temperatures is larger. In this study, we investigated the hypothesis that larger size is favoured at lower temperature through natural selection on adult males. We measured life-span and age-specific fertility of males from lines of flies artificially selected for body size at two different experimental temperatures. There was an interaction between experimental temperature and body size selection for male fitness; large-line males were fitter than controls at both temperatures, but the difference in fitness was greater at the lower experimental temperature. Smaller males did not perform significantly differently from control males at either experimental temperature. The results imply that thermal selection for larger adult males is at least in part responsible for the evolution of larger body size at lower temperatures in this species. The responsible mechanisms require further investigation. [source] Growth of pure cultures of Verocytotoxin-producing Escherichia coli in a range of enrichment mediaJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2008C.L. Baylis Abstract Aims:, This study compared the growth of different strains of Verocytotoxin-producing Escherichia coli (VTEC) in a range of selective enrichment media. Methods and Results:, Turbidometric and impedance methods were used to determine the growth of VTEC in pure culture in different enrichment media. Ten strains failed to grow in buffered peptone water + vancomycin, cefsulodin, cefixime at 42°C and some failed to grow, or grew poorly in E. coli (EC) medium supplemented with 20 mg l,1 novobiocin and modified EC supplemented with 20 mg l,1 novobiocin at 37°C and 42°C. Individual VTEC strains were sensitive to the selective agents in some media. Statistical analysis of the conductance detection times of 10 strains showed no overall effect of temperature alone (P = 0·66) but there were significant (P < 0·001) effects as a result of the combination of medium and temperature and these two factors were influenced by strain. Conclusions:, Growth of VTEC during enrichment is dependent on different factors alone or in combination. These include medium type, presence of certain selective agents or antibiotics, incubation temperature and the initial population of VTEC. Sensitivity to these conditions can be strain related. Significance and Impact of the Study:, This study highlighted differences in the ability of some enrichment media to support the growth of VTEC, making them unsuitable for the isolation of VTEC, especially low numbers of non-O157 strains. [source] Colour polymorphism in birds: causes and functionsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2003P. Galeotti Abstract We studied polymorphism in all species of birds that are presently known to show intraspecific variation in plumage colour. At least three main mechanisms have been put forward to explain the maintenance of polymorphism: apostatic, disruptive and sexual selection. All of them make partly different predictions. Our aims were to investigate evolutionary causes and adaptive functions of colour polymorphism by taking into account a number of ecological and morphological features of polymorphic species. Overall, we found 334 species showing colour polymorphism, which is 3.5% of all bird species. The occurrence of colour polymorphism was very high in Strigiformes, Ciconiiformes, Cuculiformes and Galliformes. Phylogenetically corrected analysis using independent contrasts revealed that colour polymorphism was maximally expressed in species showing a daily activity rhythm extended to day/night, living in both open and closed habitats. All these findings support the hypothesis that colour polymorphism probably evolved under selective pressures linked to bird detectability as affected by variable light conditions during activity period. Thus, we conclude that selective agents may be prey, predators and competitors, and that colour polymorphism in birds may be maintained by disruptive selection. [source] Dispersion patterns of parasites in 0+ year three-spined sticklebacks: a cross population comparisonJOURNAL OF FISH BIOLOGY, Issue 6 2002M. Kalbe Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an ,individual parasitation index' (IPI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks. [source] Pathogens as potential selective agents in the wildMOLECULAR ECOLOGY, Issue 22 2009MÉLANIE DIONNE Pathogens are considered a serious threat to which wild populations must adapt, most particularly under conditions of rapid environmental change. One way host adaptation has been studied is through genetic population structure at the major histocompatibility complex (MHC), a complex of adaptive genes involved in pathogen resistance in vertebrates. However, while associations between specific pathogens and MHC alleles or diversity have been documented from laboratory studies, the interaction between hosts and pathogens in the wild is more complex. As such, identifying selective agents and understanding underlying co-evolutionary mechanisms remains a major challenge. In this issue of Molecular Ecology, Evans & Neff (2009) characterized spatial and temporal variation in the bacterial parasite community infecting Chinook salmon (Oncorhynchus tshawytscha) fry from five populations in British Columbia, Canada. They used a 16S rDNA sequencing-based approach to examine the prevalence of bacterial infection in kidney and looked for associations with MHC class I and II genetic variability. The authors found a high diversity of bacteria infecting fry, albeit at low prevalence. It was reasoned that spatial variability in infection rate and bacterial community phylogenetic similarity found across populations may represent differential pathogen-mediated selection pressures. The study revealed some evidence of heterozygote advantage at MHC class II, but not class I, and preliminary associations between specific MHC alleles and bacterial infections were uncovered. This research adds an interesting perspective to the debate on host,pathogen co-evolutionary mechanisms and emphasizes the importance of considering the complexity of pathogen communities in studies of host local adaptation. [source] Latest news and product developmentsPRESCRIBER, Issue 10 2008Article first published online: 3 JUN 200 Glitazones more than double fracture risk An analysis of the UK General Practice Research Database has found that both glitazones increase the risk of fracture more than two-fold (Arch Intern Med 2008;168:820-5). Compared with nonusers, the odds ratio for fracture (mostly hip and wrist) was 2.59 for pioglitazone and 2.38 for rosiglitazone. The risk increased with dose but was unrelated to age and sex. Reduce antipsychotics in dementia patients Antipsychotics should be prescribed for patients with dementia only as a last resort at times of severe distress or critical need, the All-Party Parliamentary Group on Dementia has concluded. Its inquiry (available at www.alzheimers.org.uk) found that antipsychotics are being prescribed for patients with mild behavioural symptoms and for prolonged periods despite the limited benefits they offer and the risk of serious adverse effects such as stroke. Contributory factors include lack of training for staff, inadequate leadership and exclusion of family and friends from decisions about treatment. High-dose atorvastatin in chronic kidney disease High-dose atorvastatin (Lipitor) reduces cardiovascular events in patients with chronic kidney disease (CKD) more than a low dose , despite similar reductions in LDL-C (J Am Coll Cardiol 2008;51:1448-54). A post hoc subgroup analysis of the Treating-to-New-Targets study involving 10 001 patients with CHD, with or without CKD, found that atorvastatin 10 and 80mg per day reduced LDLC and triglycerides to similar levels; there was no change in HDL-C. After a median follow-up of five years, the incidence of cardiovascular events in patients with CKD was 9.3 per cent at 80mg per day and 13.4 per cent at 10mg per day (number needed to treat to prevent one event, NNT, 24). In patients with no CKD, the corresponding figures were 7.9 vs 9.2 per cent (NNT 74). There was no difference in all-cause mortality; adverse events were more frequent at the higher dose. COX-2 NSAIDs not more cost-effective An economic analysis of COX-2 selective NSAIDs has concluded that they are not more cost effective than older agents plus a proton pump inhibitor (PPI) in the treatment of osteoarthritis and rheumatoid arthritis (Health Technology Assessment 2008;12:No. 11). The analysis concluded that selective and nonselective NSAIDs were similarly effective but selective agents were associated with a lower risk of upper GI events and a higher risk of cardiovascular events. However, the available evidence includes only low numbers of events and further studies are needed. Compared with ibuprofen or diclofenac plus a PPI, the COX-2 selective NSAIDs look ,generally unattractive from a cost effectiveness point of view', even in high-risk patients with a history of peptic ulcer. There were insufficient data to allow a reliable comparison within the COX-2s. Naftidrofuryl helps intermittent claudication Naftidrofuryl increases pain-free walking distance (PFWD) in patients with intermittent claudication, a new Cochrane review has shown (Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD001368. DOI: 10.1002/ 14651858.CD001368.pub3; also see page 49 in this issue). The meta-analysis of six trials involving a total of 1083 patients found that, compared with placebo, naftidrofuryl increased PFWD by over a third with a proportion successfully treated of 20 per cent (NNT 4.5). Coversyl Arginine To clarify any confusion following our recent news item (Perindopril brand switch, 19 April issue, page 12), Servier has asked us to reiterate that the new formulations Coversyl Arginine 2.5, 5 and 10mg are equivalent to 2, 4 and 8mg of the discontinued Coversyl formulation. Coversyl Arginine contains perindopril arginine, a salt that offers greater stability and a longer shelf-life. Prescriptions for the Coversyl brand of perindopril must in future be written as Coversyl Arginine in its revised strengths. Coversyl Plus has also been replaced by Coversyl Arginine Plus and the same revised dosages apply. Generic formulations of perindopril remain unaffected. Copyright © 2008 Wiley Interface Ltd [source] The evolution of egg colour and patterning in birdsBIOLOGICAL REVIEWS, Issue 3 2006R. M. Kilner ABSTRACT Avian eggs differ so much in their colour and patterning from species to species that any attempt to account for this diversity might initially seem doomed to failure. Here I present a critical review of the literature which, when combined with the results of some comparative analyses, suggests that just a few selective agents can explain much of the variation in egg appearance. Ancestrally, bird eggs were probably white and immaculate. Ancient diversification in nest location, and hence in the clutch's vulnerability to attack by predators, can explain basic differences between bird families in egg appearance. The ancestral white egg has been retained by species whose nests are safe from attack by predators, while those that have moved to a more vulnerable nest site are now more likely to lay brown eggs, covered in speckles, just as Wallace hypothesized more than a century ago. Even blue eggs might be cryptic in a subset of nests built in vegetation. It is possible that some species have subsequently turned these ancient adaptations to new functions, for example to signal female quality, to protect eggs from damaging solar radiation, or to add structural strength to shells when calcium is in short supply. The threat of predation, together with the use of varying nest sites, appears to have increased the diversity of egg colouring seen among species within families, and among clutches within species. Brood parasites and their hosts have probably secondarily influenced the diversity of egg appearance. Each drives the evolution of the other's egg colour and patterning, as hosts attempt to avoid exploitation by rejecting odd-looking eggs from their nests, and parasites attempt to outwit their hosts by laying eggs that will escape detection. This co-evolutionary arms race has increased variation in egg appearance both within and between species, in parasites and in hosts, sometimes resulting in the evolution of egg colour polymorphisms. It has also reduced variation in egg appearance within host clutches, although the benefit thus gained by hosts is not clear. [source] | ||||||||||