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Generation Time (generation + time)
Kinds of Generation Time Selected AbstractsPARASITISM OF PHOTOSYNTHETIC DINOFLAGELLATES BY THREE STRAINS OF AMOEBOPHRYA (DINOPHYTA): PARASITE SURVIVAL, INFECTIVITY, GENERATION TIME, AND HOST SPECIFICITY1JOURNAL OF PHYCOLOGY, Issue 3 2002D. Wayne Coats Amoebophrya ceratii (Koeppen) Cachon is an obligate parasite of dinoflagellates and may represent a species complex. However, little is known about the biology and host range of different strains of Amoebophrya Cachon. Here, we determined parasite generation time and dinospore infectivity, survival, and ability to infect nonprimary hosts for strains of Amoebophrya from Akashiwo sanguinea (Hirasaka) G. Hansen et Moestrup, Gymnodinium instriatum (Freudenthal et Lee) Coats comb. nov., and Karlodinium micrum (Leadbeater et Dodge) J. Larsen. Akashiwo sanguinea was readily infected, with parasite prevalence reaching 100% in dinospore:host inoculations above a 10:1 ratio. Parasitism also approached 100% in G. instriatum, but only when inoculations exceeded a 40:1 ratio. Karlodinium micrum appeared partially resistant to infection, as parasite prevalence saturated at 92%. Parasite generation time differed markedly among Amoebophrya strains. Survival and infectivity of dinospores decreased over time, with strains from G. instriatum and A. sanguinea unable to initiate infections after 2 and 5 days, respectively. By contrast, dinospores from Amoebophrya parasitizing K. micrum remained infective for up to 11 days. Akashiwo sanguinea and G. instriatum were not infected when exposed to dinospores from nonprimary Amoebophrya strains. Karlodinium micrum, however, was attacked by dinospores of Amoebophrya from the other two host species, but infections failed to reach maturity. Observed differences in host,parasite biology support the hypothesis that Amoebophrya ceratii represents a complex of host-specific species. Results also suggest that Amoebophrya strains have evolved somewhat divergent survival strategies that may encompass sexuality, heterotrophy during the "free-living" dinospore stage, and dormancy. [source] Infection of Gymnodinium sanguineum by the Dinoflagellate Amoebophryasp.: Effect of Nutrient Environment on Parasite Generation Time, Reproduction, and InfectivityTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 5 2000WONHO YIH ABSTRACT. Preliminary attempts to culture Amoebophrya sp., a parasite of Gymnodinium sanguineum from Chesapeake Bay, indicated that success may be influenced by water quality. To explore that possibility, we determined development time, reproductive output, and infectivity of progeny (i.e. dinospores) for Amoebophrya sp. maintained on G. sanguineum grown in four different culture media. The duration of the parasite's intracellular growth phase showed no significant difference among treatments; however, the time requiredfor completion of multiple parasite generations did, with elapsed time to the middle of the third generation being shorter in nutrient-repletemedia. Parasites of hosts grown in nutrient-replete medium also produced three to four times more dinospores than those infectinghosts under low-nutrient conditions, with mean values of 380 and 130 dinospores/host, respectively. Dinospore production relative tohost biovolume also differed, with peak values of 7.4 per 1,000 ,m3 host for nutrient-replete medium and 4.8 per 1,000 ,m3 host fornutrient-limited medium. Furthermore, dinospores produced by "high-nutrient" parasites had a higher success rate than those formedby "low-nutrient" parasites. Results suggest that Amoebophrya sp. is well adapted to exploit G. sanguineum populations in nutrient-enrichedenvironments. [source] In Vitro Determination of Generation Times for Entodinium exiguum, Ophryoscolex purkynjei and Eudiplodinium maggiiTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2004BURK A. DEHORITY ABSTRACT. Most previously reported generation times for rumen ciliate protozoa are longer than would be required to prevent their being flushed out of the rumen. In an earlier study from this lab, using a sequential transfer procedure, generation times between 12 and 13 h were determined for both Epidinium caudatum and Entodinium caudatum. This would permit these species to be maintained in a rumen with a fluid volume turnover rate as rapid as twice a day. In this study, generation times were estimated for Entodinium exiguum (13.2 h), Eudiplodinium maggii (26.8 h), and Ophryoscolex purkynjei (29 h), by sequential transfer at both 12 and 24 h time periods. The generation time for E. exiguum is lower than reported for this and other Entodinium species as determined by logarithmic growth from a small inoculum, but similar to that obtained for Ent. caudatum using sequential transfer. Eudiplodinium maggii and O. purkynjei generation times are similar to previous estimates of 24- and 24,48 h, respectively. However, it was observed that after an adaptation period of 36 to 48 h (generally 3,4 transfers) cell concentrations decreased and generation times were markedly decreased, i.e. 12.2 h for Ent. exiguum, 15.0 h for E. maggii and 12.8 h for O. purkynjei. In a separate study, varying both the concentration of Epidinium and the quantity of substrate fed per cell had no effect on generation time. [source] Which demographic traits determine population growth in the invasive brown seaweed Sargassum muticum?JOURNAL OF ECOLOGY, Issue 4 2009Aschwin Engelen Summary 1Life-history traits commonly associated with plant invasiveness are vegetative reproduction or r -selected traits such as short generation times and high rates of reproduction and individual growth. 2We used matrix modelling to assess which demographic traits are important for the population growth of an invasive seaweed lacking vegetative reproduction and whether demographic and life-history strategies shift with increased dominance of the invader. The vital rates of one of the most successful invading seaweeds, Sargassum muticum, were investigated monthly for 2 years in intertidal pools dominated by the native brown seaweed Cystoseira humilis and by S. muticum, respectively. In order to speculate about the demographic mechanisms that determine invasiveness of S. muticum, and as the study sites were recently colonized, we assumed that C. humilis and S. muticum pools are proxies for early and late phases of invasion, respectively. 3Both deterministic and stochastic matrix models showed positive rates of population growth, and rates were significantly higher in the pools dominated by S. muticum than in the ones dominated by C. humilis, indicating demographic changes with invader dominance. The variability of population growth rates and of reproductive and elasticity values of S. muticum was higher in the pools dominated by C. humilis, suggesting invader-driven stabilization of environmental conditions. Generation times of the species increased with invader dominance, supporting invader-stabilized environmental conditions. 4Elasticity analyses revealed that the most important demographic trait for population growth rate at both levels of invader dominance was the persistence of the non-fertile adult fronds rather than reproduction or growth. No major shifts in the life-history strategy of S. muticum between levels of invader dominance were detected. 5Synthesis. This study suggests that the invasiveness of S. muticum, a perennial invader without vegetative reproduction, relies on K - rather than r -selected traits and without drastic changes in life-history strategy between phases of invasion. [source] Rapid evolution in introduced species, ,invasive traits' and recipient communities: challenges for predicting invasive potentialDIVERSITY AND DISTRIBUTIONS, Issue 4 2008Kenneth D. Whitney ABSTRACT The damaging effects of invasive organisms have triggered the development of Invasive Species Predictive Schemes (ISPS). These schemes evaluate biological and historical characteristics of species and prioritize those that should be the focus of exclusion, quarantine, and/or control. However, it is not clear how commonly these schemes take microevolutionary considerations into account. We review the recent literature and find that rapid evolutionary changes are common during invasions. These evolutionary changes include rapid adaptation of invaders to new environments, effects of hybridization, and evolution in recipient communities. Strikingly, we document 38 species in which the specific traits commonly associated with invasive potential (e.g. growth rate, dispersal ability, generation time) have themselves undergone evolutionary change following introduction, in some cases over very short (, 10 year) timescales. In contrast, our review of 29 ISPS spanning plant, animal, and microbial taxa shows that the majority (76%) envision invading species and recipient communities as static entities. Those that incorporate evolutionary considerations do so in a limited way. Evolutionary change not only affects the predictive power of these schemes, but also complicates their evaluation. We argue that including the evolutionary potential of species and communities in ISPS is overdue, present several metrics related to evolutionary potential that could be incorporated in ISPS, and provide suggestions for further research on these metrics and their performance. Finally, we argue that the fact of evolutionary change during invasions begs for added caution during risk assessment. [source] Life table and heat tolerance of Acyrthosiphon pisum (Hemiptera: Aphididae) in subtropical TaiwanENTOMOLOGICAL SCIENCE, Issue 3 2008Wei-Nung LU Abstract The effect of temperature on the life table of Acyrthosiphon pisum reared on Pisum sativum was evaluated under laboratory conditions using temperatures of 10, 15, 20, 25, 30, and 35°C. The development time of juvenile A. pisum decreased with increasing temperature (from 21.3 days at 10°C to 4.7 days at 35°C). Adult longevity also decreased with increasing temperature (from 53.2 days at 10°C to 2.3 days at 35°C). Interestingly, 70% and 25% of A. pisum nymphs reared at 30°C and 35°C, respectively, successfully developed into adults. These temperatures have previously been considered unsuitable for A. pisum development. However, adult aphids reared at 30°C and 35°C failed to reproduce. Linear regression analysis revealed that the lower development threshold of A. pisum was 153.1 degree-days above 1.9°C. Maximal average reproductive capability was observed at 10°C for A. pisum adults, with each adult producing more than 120 nymphs. The intrinsic rate of increase (rm) of A. pisum increased from 0.124/day at 10°C to 0.337/day at 25°C, whereas opposite trends were observed for the net reproductive rate (R0) and the mean generation time (GT). At 20°C and 25°C, the intrinsic rate of increase of A. pisum was significantly higher than at 10°C and 15°C (P < 0.0001), indicating that 20°C and 25°C are within the optimal range for the growth of A. pisum, and that 30°C is beyond the upper threshold limit for reproduction, which involves a temperature range that is narrower than that of the survival range (upper limit is unknown, but above 35°C). [source] Techniques for continuous rearing and assessing host preference of a multivoltine leaf-mining moth, Acrocercops transecta (Lepidoptera: Gracillariidae)ENTOMOLOGICAL SCIENCE, Issue 3 2005Issei OHSHIMA Abstract Techniques for rearing the leaf-mining moth Acrocercops transecta successively over several generations are described. Based on continuous rearing, some life historical parameters in A. transecta were determined. Because of its short generation time, successive rearing makes the moth suitable for mating experiments and a model organism to elucidate the mechanism of host-associated speciation. [source] A STATISTICAL TEST OF UNBIASED EVOLUTION OF BODY SIZE IN BIRDSEVOLUTION, Issue 12 2002Folmer Bokma Abstract., Of the approximately 9500 bird species, the vast majority is small-bodied. That is a general feature of evolutionary lineages, also observed for instance in mammals and plants. The avian interspecific body size distribution is right-skewed even on a logarithmic scale. That has previously been interpreted as evidence that body size evolution has been biased. However, a procedure to test for unbiased evolution from the shape of body size distributions was lacking. In the present paper unbiased body size evolution is defined precisely, and a statistical test is developed based on Monte Carlo simulation of unbiased evolution. Application of the test to birds suggests that it is highly unlikely that avian body size evolution has been unbiased as defined. Several possible explanations for this result are discussed. A plausible explanation is that the general model of unbiased evolution assumes that population size and generation time do not affect the evolutionary variability of body size; that is, that micro- and macroevolution are decoupled, which theory suggests is not likely to be the case. [source] Subaqueous hydrochory: open-channel hydraulic modelling of non-buoyant seed movementFRESHWATER BIOLOGY, Issue 11 2008SCOTT H. MARKWITH Summary 1. Subaqueous transport may be a significant dispersal and migration mechanism of non-buoyant seeds of aquatic and riparian plants, and also secondary transport of seeds once they have lost buoyancy, but the efficiency of this difficult to observe process is largely unexamined. This study uses hydraulic modelling to establish the discharges that move the non-buoyant seeds of Hymenocallis coronaria as bedload or suspended load; uses stream gauge data to examine the frequency of effective discharges from late June to late September, the seed maturation and germination period; and the potential transport distance of the seeds. 2. The results show that the majority of non-buoyant seeds of H. coronaria can be transported as bedload through entire modelled stream reaches of lengths 10.8, 18 and 14.4 km with the 0.5 year return interval flow. Bedload apparently has the ability to move seeds over great distances, and may be a substantial factor determining the genetic structure, demography and dynamics of populations and communities. However, prolonged movement of non-buoyant seeds in suspension appears to be quite rare. 3. Although insect mediated pollination and biochory occur concurrently with bedload transport, bedload transport alone may be sufficient to account for the established gene flow rate of H. coronaria. The potential transport distance of many of the seeds exceed that between populations, and migration may occur more frequently than the species' generation time. 4. This is the first known study to use open-channel hydraulic modelling and sediment transport analysis to determine the effectiveness of non-buoyant seed transport. This method of analysis shows promise for application in other contexts, and especially where flow management is a critical issue for maintenance of rare species. [source] Growth and reproduction of three cladoceran species from a small wetland in the south-eastern U.S.A.FRESHWATER BIOLOGY, Issue 4 2003A. M. Lemke SUMMARY 1.,Growth, reproduction and life-history parameters were measured for three cladoceran species from a small south-eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources. 2.,Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49,72% day,1) and Diaphanosoma (21,91% day,1) than for Scapholeberis (11,45% day,1). Multiple regression equations were developed which predict temperature- and mass-specific growth rates for each species. 3.,Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28,92 eggs per female) than for Simocephalus (18,25 eggs per female) and Diaphanosoma (1,41 eggs per female), and was related to differences in reproductive strategy and survival. 4.,Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R0) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R0 values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma. 5.,This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics. [source] Can the evolutionary-rates hypothesis explain species-energy relationships?FUNCTIONAL ECOLOGY, Issue 6 2005K. L. EVANS Summary 1There is growing consensus that much of the marked broad-scale spatial variation in species richness is associated with variation in environmental energy availability, but at least nine principal mechanisms have been proposed that may explain these patterns. 2The evolutionary-rates hypothesis suggests that high environmental energy availability elevates rates of molecular evolution, promoting faster speciation, so that more species occur in high-energy areas because more evolve there. Direct tests of this hypothesis are rare and their conclusions inconsistent. Here we focus on assessing the support for its underlying assumptions. 3First, the evolutionary-rates hypothesis assumes that high energy levels promote mutation. There is certainly evidence that high levels of ultraviolet radiation increase mutation rates. High temperatures may also reduce generation times and elevate metabolic rates, which may promote mutation. On balance, data support a link between rates of metabolism and mutation, but a link between the latter and generation time is more equivocal and is particularly unlikely in plants. 4Second, the evolutionary-rates hypothesis assumes that mutation rates limit speciation rates. This may be true if all else was equal, but correlations between mutation and speciation are probably very noisy as many other factors may influence rates both of sympatric and allopatric speciation, including the occurrence of physical isolation barriers, the magnitude of selection and population size. 5Third, the evolutionary-rates hypothesis assumes that there is a strong correlation between current and historical energy levels. Factors such as tectonic drift may weaken such relationships, but are likely to have had negligible effects over the time period during which the majority of extant species evolved. 6Fourth, the evolutionary-rates hypothesis assumes that changes in species ranges following speciation do not sufficiently weaken the correlation between the rate of speciation in an area and species richness. The ranges of many species appear to alter dramatically following speciation, and this may markedly reduce the strength of the relationship, but to what extent is unclear. 7In sum, the degree to which the evolutionary-rates hypothesis can explain spatial variation in species richness remains surprisingly uncertain. We suggest directions for further research. [source] Environmental change and the phenology of European aphidsGLOBAL CHANGE BIOLOGY, Issue 8 2007RICHARD HARRINGTON Abstract Aphids, because of their short generation time and low developmental threshold temperatures, are an insect group expected to respond particularly strongly to environmental changes. Forty years of standardized, daily data on the abundance of flying aphids have been brought together from countries throughout Europe, through the EU Thematic Network ,EXAMINE'. Relationships between phenology, represented by date of first appearance in a year in a suction trap, of 29 aphid species and environmental data have been quantified using the residual maximum likelihood (REML) methodology. These relationships have been used with climate change scenario data to suggest plausible changes in aphid phenology. In general, the date of first record of aphid species in suction traps is expected to advance, the rate of advance varying with location and species, but averaging 8 days over the next 50 years. Strong relationships between aphid phenology and environmental variables have been found for many species, but they are notably weaker in species living all year on trees. Canonical variate analysis and principal coordinate analysis were used to determine ordinations of the 29 species on the basis of the presence/absence of explanatory variables in the REML models. There was strong discrimination between species with different life cycle strategies and between species feeding on herbs and trees, suggesting the possible value of trait-based groupings in predicting responses to environmental changes. [source] Effect of recombinant factor VIIa variant (NN1731) on platelet function, clot structure and force onset time in whole blood from healthy volunteers and haemophilia patientsHAEMOPHILIA, Issue 5 2007D. F. BROPHY Summary., NN1731 is a novel variant of recombinant factor VIIa (rFVIIa) that binds to activated platelets, but has greater enzymatic activity than rFVIIa in generating FXa and thrombin. The effect of NN1731 on clot structure and platelet function was characterized ex vivo in whole blood from healthy volunteers and haemophilic patients. Blood samples from six healthy volunteers, nine haemophilia A patients with and without inhibitors and one acquired haemophilia A patient, were spiked with increasing concentrations (0.32, 0.64 and 1.28 ,g mL,1) of rFVIIa and NN1731. Platelet contractile force (PCF) or platelet function, clot elastic modulus (CEM) or clot structure, and force onset time (FOT) or the thrombin generation time (TGT) were determined using the Hemodyne Hemostasis Analysis System (HASÔ). Baseline PCF, CEM and FOT values in patients were abnormal compared to healthy volunteers' baseline values. Overall, haemophilia blood samples with or without inhibitors spiked with NN1731 had significantly greater PCF, CEM and shorter FOT values relative to samples spiked with corresponding doses of rFVIIa. The variability in response to treatment between patients was greater with rFVIIa compared to NN1731. At 1.28 ,g mL,1 (90 ,g kg,1), NN1731 normalized PCF, CEM and FOT in nine of 10 patients, while rFVIIa normalized these parameters in four of 10 patients. Increasing in vitro concentrations of NN1731 normalized platelet function, clot structure and thrombin generation consistently in haemophilia blood with or without inhibitors. NN1731 may be a promising haemostatic agent for patients with bleeding disorders. These results should be confirmed in an in vivo study. [source] EFFECTS OF TEMPERATURE ON CERTAIN POPULATION PARAMETERS OF LIRIOMYZA SATIVAE BLAN-CHARD (DIPTERA: AGROMYZIDAE)INSECT SCIENCE, Issue 2 2000ZHANG Run-jie Abstract, Effects of temperature on population parameters and the intrinsic rate of natural increase of the leafminer, Liriomyza sativae Blanchard, were studied at constant temperatures, 15, 20, 25, 30 and 3593 80% RH and a photoperiod of 12:12 (L:D) in the laboratory with Phaseolus vulgaris as the host plant. Developmental time of the immature stage decreased from 38 d at 15C to lld at 3593 Regression equations relating temperature (t) to development rates (y) for egg, larval and pupal stages, were y = 1.7862t - 13.841, y = 1.162t - 4.946 and y= 0.634t - 5.146, respectively. Longevity of female adult decreased from 20 d at 15°C to 9 d with temperature up to 35C The most favorable temperature range for reproduction was 20°C - 30oC in which the fecundity ranged from 158 to 282 eggs per female. The lowest total mortality was 9% at 25oC and the highest was 49% at 35 93 High intrinsic rate of natural increase (rm) was 0.27 and high net reproductive rate (R0) was 116.8 at temperature range between 25 t and 30 t indicating that this range was optimal for population growth and that population density might increase 117 times per generation under this temperature condition. Mean generation time (T) and time for population to double (t) decreased as temperature increased, showing a negative linear trend with temperature. The relationship between finite rate of increase (A) and temperature, however, was a positive linear regression. [source] Ontogenetic Shifts in the Ability of the Cladoceran, Moina macrocopa Straus and Ceriodaphnia cornuta Sars to Utilize Ciliated Protists as Food SourceINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2008Ram Kumar Abstract The ontogenetic diet shifts and age specific ability of the two cladoceran species Moina macrocopa and Ceriodaphnia cornuta to derive energy from ciliated protists have been investigated in laboratory. The postembryonic developmental rates and life table demography (longevity, age and size at first reproduction, fecundity and intrinsic rate of natural increase) of the cladocerans have been elucidated on algae (Chlorella vulgaris) and the ciliated protists (Tetrahymena pyriformis, Colpoda (c.f.) steini) as food. For either of the cladoceran, the somatic growth rate and average body size at first reproduction were higher with algal diet. During initial stages of development (0,5 days), either cladoceran realized higher rate of somatic growth on algal diet, subsequently ciliated protists supported significantly higher growth rate than the alga. Algal and ciliate diets did not differ in maximum body size (C. cornuta: 539,554 ,m; M. macrocopa: 1274.8,1309 ,m) reached by either of the cladocerans. The maximum body sizes were larger than size at first reproduction with either of the ciliated protists, however, with algal diet the maximum body sizes did not differ from the size at first reproduction in each case. In case of C. cornuta the generation time (20.5 ± 0.3 days on ciliate; 15.6 ± 0.17 days on algal diet), reproductive rates (net reproductive rate: 20.05 ± 3.2 on ciliate; 15.5 ± 1.2 on algal diet), and average life expectancy at hatching (27 ± 0.8 days on ciliate; 22.7 ± 0.71 days on alga) were higher, whereas the size at first reproduction (482 ,m on ciliate; 521 ,m on alga) was smaller with the ciliate than with an algal diet. The algal and the ciliate diets did not differ in survival (life expectancy at hatching: 9.2 ± 0.7 days) and fecundity (NRR: 23.6 ± 2.4) for M. macrocopa. The two ciliates used in the experiment did not differ in their performance as food source for either cladoceran species. Our results suggest that both the cladoceran species are able to utilize smaller ciliate (e.g., T. pyriformis, C. (c.f.) steini) as food; however with differential ability to derive energy from the ciliate diet and this ability is size and age structured in both cases. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Selective harvest of sooty shearwater chicks: effects on population dynamics and sustainabilityJOURNAL OF ANIMAL ECOLOGY, Issue 4 2005CHRISTINE M. HUNTER Summary 1Selectivity of harvest influences harvest sustainability because individuals with different characteristics contribute differently to population growth. We investigate the effects of selection based on chick weight on a traditional harvest of the sooty shearwater Puffinus griseus by Rakiura Maori in New Zealand. 2We develop a periodic stage-structured matrix population model and incorporate seasonal harvest of three weight classes of chicks. Intensity and selectivity of harvest are defined in terms of weight-specific hazard functions. 3We investigate the effect of harvest intensity and selectivity on population growth rate, ,, and the chick exploitation rate, E. We also consider the interaction of chick harvest and adult mortality. 4, decreases and E increases as harvest intensity increases. At low harvest intensities, selection has little effect on ,. At high harvest intensities, , increases as selectivity increases because of the non-linear relationship between harvest intensity and the probability of being harvested. 5, is determined almost completely by E, irrespective of the combination of harvest selectivity and intensity producing E. This is true for both general patterns of selectivity and specific patterns estimated from empirical data. 6The elasticities of ,, the net reproductive rate and the generation time are unaffected by selectivity and show only small responses to harvest intensity. 7Adult sooty shearwaters are killed as bycatch in long-line and driftnet fisheries. Such mortality of adults has an effect on , about 10-fold greater than an equivalent level of chick harvest. 8The sustainability of any combination of chick harvest and adult mortality depends on the resulting reduction in ,. We explore these results in relation to indices of sustainability, particularly the United States Marine Mammal Protection Act (MMPA) standards. [source] Experimental and mathematical study of the influence of growth factors on the growth kinetics of adult human articular chondrocytes,JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2005Andrea Barbero This study aimed at determining how kinetic parameters of adult human articular chondrocytes (AHAC) growth are modulated by the growth factor combination TGF,1, FGF-2, and PDGF BB (TFP), recently shown to stimulate AHAC proliferation. AHAC, isolated from cartilage biopsies of three individuals, were cultured in medium without (CTR) or with TFP. For growth curves, AHAC were seeded at 1,000 cells/cm2 and cultured for 12 days, with cell numbers measured fluorimetrically in the same wells every 12 h. For microcolony tests, AHAC were seeded at 2.5 cells/cm2 and cultured for 6 days, with cell numbers determined for each microcolony by phase contrast microscopy every 8 h. A mathematical model combining delay and logistic equations was developed to capture the growth kinetic parameters and to enable the description of the complete growth process of the cell culture. As compared to CTR medium, the presence of TFP increased the number of cells/well starting from the fifth day of culture, and a four-fold larger cell number was reached at confluency. For single microcolonies, TFP reduced the time for the first cell division by 26.6%, the time for subsequent cell divisions (generation time) by 16.8%, and the percentage of quiescent cells (Qc) by 42.5%. The mathematical model fitted well the experimental data of the growth kinetic. Finally, using both microcolony tests and the mathematical model, we determined that prolonged cell expansion induces an enrichment of AHAC with shorter first division time, but not of those with shorter generation time. © 2005 Wiley-Liss, Inc. [source] Detection of delayed density dependence in an orchid populationJOURNAL OF ECOLOGY, Issue 2 2000M. P. Gillman Summary 1,Annual censuses of Orchis morio (green-winged orchid) flowering spikes have been taken over a 27-year period in a replicated factorial experiment on the effects of fertilizer application. Census data, combined by block or treatment, were used in time,series analyses to test for density dependence. 2,Partial autocorrelation functions revealed the importance of positive correlations at lag 1 and negative correlations at lag 5. Stepwise multiple regressions provided evidence of delayed density dependence, again with a delay of about 5 years, with no evidence of direct (first-order) density dependence. 3,First-order autocorrelations and delayed density dependence were considered in the light of the known stage structure and generation time of the plant and the possibility of density dependence at different points in the life history. 4,Model structure affects the detection of density dependence, increasing the propensity for type I errors. [source] INDICATOR AND PATHOGENIC BACTERIA IN GUACAMOLE AND THEIR BEHAVIOR IN AVOCADO PULPJOURNAL OF FOOD SAFETY, Issue 4 2001SOFÍ M. ARVIZU-MEDRANO ABSTRACT The presence of some indicator microorganisms and pathogenic bacteria in guacamole sampled from restaurants and street vendors, and the behavior of Salmonella spp., Staphylococcus aureus, and Escherichia coli O157:H7 were studied in avocado pulp. Coliform, yeast and mold populations showed a wide dispersion, in agreement with the diversity of sanitary conditions observed among places sampled. The frequency of Salmonella spp., Listeria monocytogenes, and E. coli were 1.3, 16.0, and 60.0 %, respectively; with higher numbers among street vendors. Populations of E. coli ranged from 29 to 3800 NMP/g and S. aureus from 2.95 to 5.35 log CFU/g. Thirteen out of 16 hemolytic L. monocytogenes strains were pathogenic for mice. In avocado pulp Salmonella spp. and E. coli O157:H7 showed a lag phase close to 3 h, and a generation time of 54 min and 1.23 h, respectively. No growth of pathogens was observed in avocado pulp stored at 4-7C. [source] Growth and Survival of Escherichia coli O157:H7 in Different Types of Milk Stored at 4 °C or 20 °CJOURNAL OF FOOD SCIENCE, Issue 8 2003Y. Mamani ABSTRACT: Samples of ultra heat-treated (UHT) milk (whole, semiskimmed, and skimmed milk, whole milk with cinnamon and lemon flavors, and semiskimmed milk with cocoa) were collected. Growth of E. coli O157:H7 was detected in whole milk at 4 °C (generation time 0.89 d) and in all milks at 20 °C during the first 24 h. Growth of nonpathogenice. coli was detected in milk samples without flavors during the same period of time. The fastest death time of E. coli O157:H7 was detected in whole milk with cinnamon and lemon at 4 °C (,1.35 d) The nonpathogenic strain showed the fastest death time in skimmed milk at 20 °C. [source] ULTRASTRUCTURAL CHARACTERIZATION OF THE LYTIC CYCLE OF AN INTRANUCLEAR VIRUS INFECTING THE DIATOM CHAETOCEROS CF. WIGHAMII(BACILLARIOPHYCEAE) FROM CHESAPEAKE BAY, USA,JOURNAL OF PHYCOLOGY, Issue 4 2009Yoanna Eissler Numerous microalgal species are infected by viruses that have the potential to control phytoplankton dynamics by reducing host populations, preventing bloom formation, or causing the collapse of blooms. Here we describe a virus infecting the diatom Chaetoceros cf. wighamii Brightw. from the Chesapeake Bay. To characterize the morphology and lytic cycle of this virus, we conducted a time-course experiment, sampling every 4 h over 72 h following viral inoculation. In vivo fluorescence began to decline 16 h after inoculation and was reduced to <19% of control cultures by the end of experiment. TEM confirmed infection within the first 8 h of inoculation, as indicated by the presence of virus-like particles (VLP) in the nuclei. VLP were present in two different arrangements: rod-like structures that appeared in cross-section as paracrystalline arrays of hexagonal-shaped profiles measuring 12 ± 2 nm in diameter and uniformly electron-dense hexagonal-shaped particles measuring , 22,28 nm in diameter. Nuclei containing paracrystalline arrays were most prevalent early in the infection cycle, while cells containing VLP increased and then declined toward the end of the cycle. The proportion of nuclei containing both paracrystalline arrays and VLP remained relatively constant. This pattern suggests that rod-like paracrystalline arrays fragmented to produce icosahedral VLP. C. cf. wighamii nuclear inclusion virus (CwNIV) is characterized by a high burst size (averaged 26,400 viruses per infected cell) and fast generation time that could have ecological implications on C. cf. wighamii population control. [source] PARASITISM OF PHOTOSYNTHETIC DINOFLAGELLATES BY THREE STRAINS OF AMOEBOPHRYA (DINOPHYTA): PARASITE SURVIVAL, INFECTIVITY, GENERATION TIME, AND HOST SPECIFICITY1JOURNAL OF PHYCOLOGY, Issue 3 2002D. Wayne Coats Amoebophrya ceratii (Koeppen) Cachon is an obligate parasite of dinoflagellates and may represent a species complex. However, little is known about the biology and host range of different strains of Amoebophrya Cachon. Here, we determined parasite generation time and dinospore infectivity, survival, and ability to infect nonprimary hosts for strains of Amoebophrya from Akashiwo sanguinea (Hirasaka) G. Hansen et Moestrup, Gymnodinium instriatum (Freudenthal et Lee) Coats comb. nov., and Karlodinium micrum (Leadbeater et Dodge) J. Larsen. Akashiwo sanguinea was readily infected, with parasite prevalence reaching 100% in dinospore:host inoculations above a 10:1 ratio. Parasitism also approached 100% in G. instriatum, but only when inoculations exceeded a 40:1 ratio. Karlodinium micrum appeared partially resistant to infection, as parasite prevalence saturated at 92%. Parasite generation time differed markedly among Amoebophrya strains. Survival and infectivity of dinospores decreased over time, with strains from G. instriatum and A. sanguinea unable to initiate infections after 2 and 5 days, respectively. By contrast, dinospores from Amoebophrya parasitizing K. micrum remained infective for up to 11 days. Akashiwo sanguinea and G. instriatum were not infected when exposed to dinospores from nonprimary Amoebophrya strains. Karlodinium micrum, however, was attacked by dinospores of Amoebophrya from the other two host species, but infections failed to reach maturity. Observed differences in host,parasite biology support the hypothesis that Amoebophrya ceratii represents a complex of host-specific species. Results also suggest that Amoebophrya strains have evolved somewhat divergent survival strategies that may encompass sexuality, heterotrophy during the "free-living" dinospore stage, and dormancy. [source] Thrombin generation time is a novel parameter for monitoring enoxaparin therapy in patients with end-stage renal diseaseJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2006D. F. BROPHY Summary.,Background:,Patients with end-stage renal disease (ESRD) who receive enoxaparin are at increased risk for adverse bleeding episodes. This phenomenon appears to occur despite judicious monitoring of antifactor Xa (aFXa) activity. Better monitoring parameters are needed to quantify the anticoagulant effects of enoxaparin in the ESRD population. Objectives:,The objective of this study was to determine the utility of using thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM) to monitor the degree of anticoagulation in ESRD subjects, and to compare these results to aFXa activity, the current gold-standard monitoring parameter. Methods:,Eight healthy volunteers without renal dysfunction and eight ESRD subjects were enrolled into this study. Subjects received a single dose of enoxaparin 1 mg kg,1 subcutaneously, and blood samples were obtained for the determination of aFXa activity, TGT, PCF and CEM at baseline, 4, 8, and 12 h postdose. Results:,Baseline, 4, 8, and 12-h aFXa activity concentrations were not different between groups. However, the corresponding TGT at 8 and 12 h was significantly prolonged in the ESRD group (P = 0.04, and P = 0.008, respectively). The 4-h peak TGT trended toward significance (P = 0.06). There were no differences in PCF or CEM across time. Conclusions:,These data suggest that the parameter aFXa activity is a poor predictor of the anticoagulant effect of enoxaparin in patients with ESRD. Thrombin generation time appears to be more sensitive to the antithrombotic effects of enoxaparin in this population. Further large-scale trials are needed to corroborate these data. [source] Acquisition of iron from human transferrin by Porphyromonas gingivalis: a role for Arg- and Lys-gingipain activitiesMOLECULAR ORAL MICROBIOLOGY, Issue 2 2001V. Brochu Porphyromonas gingivalis, a key causative agent of adult periodontitis, is known to produce a variety of virulence factors including proteases. The aim of this study was to evaluate the participation of Arg- and Lys-gingipain activities of P. gingivalis in the acquisition of iron from human transferrin and its subsequent utilization in growth. Iron-saturated transferrin was found to support the long-term growth of P. gingivalis. Our results indicated that P. gingivalis does not produce siderophore and does not possess ferric reductase and transferrin-binding activities. Incubating transferrin with P. gingivalis resulted in degradation of the protein, a step that may be critical for the acquisition of iron from transferrin. Spontaneous and site-directed mutants of P. gingivalis deficient in one or several proteases were used to demonstrate the key role of specific enzymes in degradation of transferrin and subsequent utilization for growth. The lack of both Arg- and Lys-gingipain activities (mutants M1 and KDP128) was associated with an absence of degradation of transferrin and the incapacity of bacteria to grow in the presence of transferrin as the sole source of iron. It was also found that the Lys-gingipain activity is more critical than the Arg-gingipain activity since the mutant KDP112 (deficient in Arg-gingipain A and B) could grow whereas the mutant KDP129 (deficient in Lys-gingipain) could not. The fact that growth of mutant KDP112 was associated with a lower final optical density and a generation time much longer compared with the parent strain suggests that the Arg-gingipain activity also participates in the acquisition of iron from transferrin. Selected inhibitors of cysteine proteases (TLCK, leupeptin and cathepsin B inhibitor II) were tested for their capacity to reduce or inhibit the growth of P. gingivalis under different iron conditions. All three inhibitors were found to completely inhibit growth of strain ATCC 33277 in a medium supplemented with transferrin as the source of iron. The inhibitors had no effects when the bacteria were grown in a medium containing hemin instead of transferrin. The ability of P. gingivalis to cleave transferrin may be an important mechanism for the acquisition of iron from this protein during periodontitis. [source] Stage, age and individual stochasticity in demographyOIKOS, Issue 12 2009Hal Caswell Demography is the study of the population consequences of the fates of individuals. Individuals are differentiated on the basis of age or, in general, life cycle stages. The movement of an individual through its life cycle is a random process, and although the eventual destination (death) is certain, the pathways taken to that destination are stochastic and will differ even between identical individuals; this is individual stochasticity. A stage-classified demographic model contains implicit age-specific information, which can be analyzed using Markov chain methods. The living stages in the life cycles are transient states in an absorbing Markov chain; death is an absorbing state. This paper presents Markov chain methods for computing the mean and variance of the lifetime number of visits to any transient state, the mean and variance of longevity, the net reproductive rate R0, and the cohort generation time. It presents the matrix calculus methods needed to calculate the sensitivity and elasticity of all these indices to any life history parameters. These sensitivities have many uses, including calculation of selection gradients. It is shown that the use of R0 as a measure of fitness or an invasion exponent gives erroneous results except when R0=,=1. The Markov chain approach is then generalized to variable environments (deterministic environmental sequences, periodic environments, iid random environments, Markovian environments). Variable environments are analyzed using the vec-permutation method to create a model that classifies individuals jointly by the stage and environmental condition. Throughout, examples are presented using the North Atlantic right whale (Eubaleana glacialis) and an endangered prairie plant (Lomatium bradshawii) in a stochastic fire environment. [source] Role of IscS in Fe-S cluster assembly in Trypanosoma bruceiTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005O. SMÍD Despite the significance of proteins containing iron-sulfur cluster (Fe,S proteins), the processes of Fe,S cluster assembly and maturation of Fe,S proteins are poorly understood. However, several key proteins involved in the assembly have been identified, notably IscS, a cystein desulfurase, which provides sulfur for Fe,S cluster and IscU, a metallochaperone acting as a scaffold for cluster assembly. In this work, we studied the process of Fe,S cluster biosynthesis in Trypanosoma brucei by identifying the homologue of IscS in the T. brucei (TbIscS). To address the function of TbIscS, we inhibited its expression by means of RNA interference (RNAi). After RNAi induction, generation time of the TbIscS knock-down cell line was significantly prolonged. All types of mitochondrial ATP production in the cells were severely affected. Analysis of glucose metabolism end products determined pyruvate as major excreted metabolite of the induced cells, while the uninduced cells produced only small amount of this glycolytic end product. These data demonstrate that mitochondrial metabolism is impaired in cells with TbIscS knocked down. To test whether the observed phenomena were results of Fe,S cluster assembly disruption, we examined the Fe,S cluster-dependent activity of aconitase. This enzyme is localized in its active form in mitochondrion as well as in cytosol of T. brucei. After RNAi induction we observed the reduction of aconitase activity in both compartments (approx. 70% reduction in cytosol, approx. 30% in mitochondria). Western blots together with the EPR analysis showed that the reduction in cytosolic activity was due to impaired Fe,S cluster formation, while decrease in aconitase activity in mitochondria corresponded to the reduced level of the protein. [source] In Vitro Determination of Generation Times for Entodinium exiguum, Ophryoscolex purkynjei and Eudiplodinium maggiiTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2004BURK A. DEHORITY ABSTRACT. Most previously reported generation times for rumen ciliate protozoa are longer than would be required to prevent their being flushed out of the rumen. In an earlier study from this lab, using a sequential transfer procedure, generation times between 12 and 13 h were determined for both Epidinium caudatum and Entodinium caudatum. This would permit these species to be maintained in a rumen with a fluid volume turnover rate as rapid as twice a day. In this study, generation times were estimated for Entodinium exiguum (13.2 h), Eudiplodinium maggii (26.8 h), and Ophryoscolex purkynjei (29 h), by sequential transfer at both 12 and 24 h time periods. The generation time for E. exiguum is lower than reported for this and other Entodinium species as determined by logarithmic growth from a small inoculum, but similar to that obtained for Ent. caudatum using sequential transfer. Eudiplodinium maggii and O. purkynjei generation times are similar to previous estimates of 24- and 24,48 h, respectively. However, it was observed that after an adaptation period of 36 to 48 h (generally 3,4 transfers) cell concentrations decreased and generation times were markedly decreased, i.e. 12.2 h for Ent. exiguum, 15.0 h for E. maggii and 12.8 h for O. purkynjei. In a separate study, varying both the concentration of Epidinium and the quantity of substrate fed per cell had no effect on generation time. [source] Morphometric changes in a strain of the lineage ,Nevada', belonging to the Brachionus plicatilis (Rotifera) complexAQUACULTURE RESEARCH, Issue 8 2009Venetia Kostopoulou Abstract The rotifer Brachionus plicatilis is an important component of aquaculture as a larval feed. Its taxonomic status has been recently re-defined as a species complex, consisting of at least 14 new species/lineages. This study deals with the lineage Brachionus,Nevada', which has been shown to occur in European hatcheries. A strain of B. ,Nevada' was mass cultured using two commonly applied feeding regimes and analysed in terms of its morphometry. A new formula was proposed for the calculation of volume, which can be used as an index of adequacy of rotifers as feed for fish larvae. The results were related to life cycle parameters. The pre-reproductive and reproductive phases were divided into distinct size groups. Differences were also found between the two diets in morphometry and demography. Rotifers of a larger size (yeast-based diet) showed a lower growth rate and a longer reproductive period, lifespan and mean generation time compared with smaller-sized rotifers (Culture Selco® -based diet). In terms of lorica length, the present study's strain of B. ,Nevada' (238.5 ,m) was intermediate between values reported for Brachionus ibericus (193.5 ,m) and B. plicatilis sensu stricto (299 ,m). [source] Use of gene transfer technology for functional studies in grapevineAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2010J.R. VIDAL Abstract The understanding of the genetic determinism of plant phenotypes requires the functional annotation of genes governing specific traits including the characterisation of their regulatory networks. A striking feature of the grapevine genome and proteome lies in the existence of large families related to wine attributes that have a higher gene copy number than in other sequenced plants. During speciation, the appearance of new adaptive functions is often based on the evolution of orthologous genes eventually associated with duplication (paralogous sequences) leading to new proteins and expression profiles. The presence of original features in grapevine, including perennial status, vegetative architecture, inflorescence/tendril, flower organisation (corolla), and fleshy fruit of considerable acidity with various flavonoid compounds, makes functional genomics an essential approach to link a gene to a trait. For grapevine, the current lack of high throughput genetic techniques (e.g. induced mutant collections) and the difficulties associated with genetic mapping (allele diversity, chimerism, generation time) highlights the critical role of transgenic technology for characterising gene function. Different techniques are available to obtain information about gene functioning, but the choice of a particular approach depends on the process investigated (e.g. metabolism, developmental, pathogen response) and the experimental purpose (e.g. induction of ectopic functions, promoter studies, subcellular localisation). After a brief overview of the development of grapevine biotechnology, this paper reviews the state-of-the-art gene transfer technology for grapevine and detailed examples of where transgenic technology has proven useful for studying gene function. [source] Metabolic effects of static magnetic fields on streptococcus pyogenesBIOELECTROMAGNETICS, Issue 6 2007A.C. Morrow Abstract This study aimed to develop a simple experimental system utilising bacterial cells to investigate the dose responses resulting from exposures to static magnetic flux densities ranging from 0.05 to 0.5 T on viability, bacterial metabolism and levels of DNA damage in Streptococcus pyogenes. Exposure of S. pyogenes to a field of 0.3 T at 24 °C under anaerobic conditions resulted in a significant (P,<,0.05) decrease in growth rate, with an increased mean generation time of 199,±,6 min compared to the control cells at 165,±,6 min (P,<,0.05). Conversely, exposure to magnetic fields of 0.5 T significantly accelerated the growth rate at 24 °C compared to control cells, with a decreased mean generation time of 147,±,4 min (P,<,0.05). The patterns of metabolite release from cells incubated in phosphate buffered saline (PBS) at 24 °C and exposed to different magnetic flux densities (0.05,0.5 T) were significantly (P,<,0.05) altered, compared to non-exposed controls. Concentrations of metabolites, with the exception of aspartic acid (r,=,0.44), were not linearly correlated with magnetic flux density, with all other r,<,0.20. Instead, "window" effects were observed, with 0.25,0.3 T eliciting the maximal release of the majority of metabolites, suggesting that magnetic fields of these strengths had significant impacts on metabolic homeostasis in S. pyogenes. The exposure of cells to 0.3 T was also found to significantly reduce the yield of 8-hydroxyguanine in extracted DNA compared to controls, suggesting some possible anti-oxidant protection to S. pyogenes at this field strength. Bioelectromagnetics 28:439,445, 2007. © 2007 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||