THE EFFECT OF WATER QUALITY ON OVIPOSITION IN BIOMPHALARIA GLABRATA (SAY, 1818) (PLANORBIDAE), AND A DESCRIPTION OF THE STAGES OF THE EGG-LAYING PROCESS

With the overall goal of developing a method to reliably induce ovipositionin the freshwater pulmonate Biomphalaria glabrata, the effectsof water quality on female reproductive physiology were examined.Groups of snails were subjected to controlled experimental conditionsconsisting of a daily regimen of feeding and water change. Aftera period of acclimatiz-ation, egg mass (EM) output under theseconditions was relatively stable, and snails laid a majority(82.5%) of their EM during the initial 4 h following daily waterchange. When this regimen was perturbed by halting water changefor 24 h (dirty-water treatment), EM output was significantly inhibited.When water change was resumed, EM output returned to previouslevels within 4 h post-water change (PWC). This dirty-water treatmentfollowed by water change also resulted in a significant increasein mean EM size during the 4 h PWC when compared to controls.To better describe the events preceding egg-laying in B. glabrata,we then used these experimental manipulations to induce ovipositionin groups of snails, and dissected them during the 4 h followingwater change. Observations of the reproductive tracts of stimulatedsnails allowed us to divide the egg-laying process, from ovulationto oviposition, into discrete stages, after de Jong-Brink, Koop,Roos & Bergamin-Sassen (1982). Stage I was characterized bythe presence of ova in the hermaphroditic duct and carrefour,and fertilized, packaged eggs in the oviduct and muciparousgland. Stage II was characterized by the presence of packagedeggs in the othecal gland embedded in a mucous layer, constitutingthe egg mass to be laid on the substratum. No packaging eventswere occurring in the carrefour/albumen gland region duringthis stage. When snails were dissected immediately after oviposition(Stage III), unpackaged ova were observed in the hermaphroditicduct, carrefour, and oviduct. The mean time it took for snailsto reach Stage III was 120 6 49 min (SD), and this value wasstatistically different from the mean time to Stages I and II,showing that our induction protocol results in a temporal progressionthrough the egg- laying process. Gonadal oocyte density (oocytes/mm²of ovotestis) was quantified as a function of these stages ofthe reproductive cycle, and was found to be significantly lowerduring Stage II (fully formed egg mass in othecal gland) thanall other stages examined. Taken together, these results showthat female reproductive activity can be experimentally controlledthrough the manipulation of water quality, and that such a protocolis a valuable tool for addressing specific questions regardingthe reproductive physiology of B. glabrata. The implicationsof these results as they pertain to the regulation of femalereproductive activity in B. glabrata are discussed. (Received 15 January 1999; accepted 17 May 1999)     

Cost-Effectiveness of Aspirin Adjuvant Therapy in Early Stage Colorectal Cancer in Older Patients

Background & Aims

Recent observational studies showed that post-operative aspirin use reduces cancer relapse and death in the earliest stages of colorectal cancer. We sought to evaluate the cost-effectiveness of aspirin as an adjuvant therapy in Stage I and II colorectal cancer patients aged 65 years and older.

Methods

Two five-state Markov models were constructed separately for Stage I and II colorectal cancer using TreeAge Pro 2014. Two hypothetical cohorts of 10,000 individuals at a starting age of 65 years and with colorectal cancer in remission were put through the models separately. Cost-effectiveness of aspirin was evaluated against no treatment (Stage I and II) and capecitabine (Stage II) over a 20-year period from the United States societal perspective. Extensive one-way sensitivity analyses and multivariable Probabilistic Sensitivity Analyses (PSA) were performed.

Results

In the base case analyses, aspirin was cheaper and more effective compared to other comparators in both stages. Sensitivity analyses showed that no treatment and capecitabine (Stage II only) can be cost-effective alternatives if the utility of taking aspirin is below 0.909, aspirin’s annual fatal adverse event probability exceeds 0.57%, aspirin’s relative risk of disease progression is 0.997 or more, or when capecitabine’s relative risk of disease progression is less than 0.228. Probabilistic Sensitivity Analyses (PSA) further showed that aspirin could be cost-effective 50% to 80% of the time when the willingness-to-pay threshold was varied from USD20,000 to USD100,000.

Conclusion

Even with a modest treatment benefit, aspirin is likely to be cost-effective in Stage I and II colorectal cancer, thus suggesting a potential unique role in secondary prevention in this group of patients.     

Temporal and regional variation in the copepod community in the central Barents Sea during spring and early summer 1988 and 1989

In this study, we examined a 3000 km² area to the southeastof Bear Island in the central Barents Sea with respect to copepodabundance and depth distribution at nine stations in March,April and May of 1988 and 1989. In order to describe the populationdynamics of the most prominent species in the area during theperiod of study, the annual ascent and abundance of Calanusfinmarchicus, Metridia longa and Calanus glacialis are shown.Stage abundance, vertical distribution and cohort developmentdid vary between species and years at one site. The number ofspecies and the complexity of the data for the entire area studiedhave encouraged us to search for more significant and persistentpatterns by using a canonical correlation analysis (CCA). Weincluded a total of 27 species and stage categories, latitude,salinity and sigma from the nine stations in 1989 We performedthis analysis for 1989. since we only have environmental data(CTD) available from the same stations in that year The species-environmentrelationship showed that the zooplankton community could notbe grouped according to area (latitude) or environmental (sigma,salinity) conditions during March–May in 1989. This meansthat the differences in environmental conditions in the areaof study in 1989 do not mediate any consistent gradient in thezooplankton community. When comparing the copepod data for bothyears. the largest differences are associated with the depthand month vectors. The largest interannual variation is seenin the copepod community in the depth strata from 100 to 400m. and is related to a lesser degree of similarity among thespecies and stages found in this depth interval throughout thestudy. Two species were particularly responsible for the interannualdifferences: Pseudocalanus acuspes CV and females, and C glacialisCV and adults. Changes in these two species are clearly relatedto major shifts in the hydrographic conditions between the 2years, where 1988 was generally colder compared to 1989.     

Somatic Embryogenesis in Cassava: The Anatomy and Morphology of the Regeneration Process

Anatomical and morphological studies demonstrated that somaticembryos developed similarly on mature seed and clonal leaf explantsof cassava (Manihot esculenta Crantz) cultured for 20–24d on Murashige and Skoog (MS2) basal medium supplemented with4.0 mg l^–1 2,4-D (Stage 1) before transfer to MS2 basalmedium supplemented with 0–01 mg l^–1 2,4-D and 0–1mg l^–1 6-benzylaminopurine (Stage II medium). Within 7d of inoculation onto Stage I medium, cell divisions occurredin the adaxial tissues of cotyledon-piece and leaf-lobe explants,and associated with this was the development of embryogeneticprotusions and ridges on the adaxial surface. Foliose structuresand somatic embryo initials developed from these tissues oncotyledon, embryonic axis and leaf-lobe explants and, when cultureswere transferred to Stage II medium, further somatic embryodevelopment occurred. Somatic embryos apparently originatedfrom groups of cells and were identified by the presence ofa closed root axis, a shoot axis and cotyledons of similar shapeand venation to those of zygotic embryos. Somatic embryos hadno vascular connection with parental cultures. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, anatomy, morphology, morphogenesis     

Copepod populations during the spring bloom in an Alaskan subarctic embayment

Copepod population and biomass was monitored in Auke Bay, Alaska,during the spring bloom from 1987 to 1989. The most abundantspecies were Pseudocalanus spp., Oithona similis and Centropagesabdominalis, with Acartia clausi reaching high concentrationsin the surface waters. Although populations of Pseudocalanuswere similar during all three years, C.abdominalis and O.similisconcentrations were significantly higher in 1988 and lower in1989 than in 1987. The population differences may have resultedfrom warmer temperatures during early spring in 1988. Substantialcontributions to biomass resulted from advection of adult Calanusmarshallae and Metridia ochotensis and late stage Neocalanusplumchrus into the bay. While copepod populations in Auke Bayappear to be more sensitive to factors influencing the timingand development rate of various cohorts, biomass is substantiallyaltered by water mass movements.     

Modification of flag leaf senescence and yield characters in barley (Hordeum vulgare L.) by gibberellic acid and kinetin

Barley plants (Hordeum vulgare L.) received foliar applications of 10^?4 M gibberellic acid (GA₃) and Kinetin (KN) individually and in combination at one or more of three growth stages: flag leaf appearance (I), ear emergence (II), and the first stage of senescence initiation in the flag leaf (III). Both plant growth regulators (PGR) hastened onset of senescence when sprayed at Stage I and/or Stage II. Treatment at Stage III, either alone or in combination with treatments at the other stages, tended to postpone senescence. Yield components also showed stage-dependent response: Stage I treatment increased the formation of total and bearing tillers, and Stage III treatment improved grain number and weight. However, while GA₃ proved more effective than KN, the two together acted antagonistically.     

Modification of flag leaf senescence and yield characters in barley (Hordeum vulgare L.) by gibberellic acid and kinetin

Barley plants (Hordeum vulgare L.) received foliar applications of 10^–4 M gibberellic acid (GA₃) and Kinetin (KN) individually and in combination at one or more of three growth stages: flag leaf appearance (I), ear emergence (II), and the first stage of senescence initiation in the flag leaf (III). Both plant growth regulators (PGR) hastened onset of senescence when sprayed at Stage I and/or Stage II. Treatment at Stage III, either alone or in combination with treatments at the other stages, tended to postpone senescence. Yield components also showed stage-dependent response: Stage I treatment increased the formation of total and bearing tillers, and Stage III treatment improved grain number and weight. However, while GA₃ proved more effective than KN, the two together acted antagonistically.     

The swimming behavior of the copepod Metridia pacfica

The swimming behavior of the copepod Metridia pacifica was studied.Animals exposed to algae showed lower average swimming speedand fewer high-speed bursts. Animals exposed to Artemia naupliialone exhibited no change in swimming behavior.     

Salinity and in vitro Ageing Effects on Primary Photosynthetic Processes of Thylakoids Isolated from Pisum sativum and Spinacia oleracea

The effects of in vitro ageing and salinity of the reactionmedium on the primary photochemistry of photosystem II and thepattern of energy distribution within the photochemical apparatusof thylakoids isolated from Pisum sativum and Spinacia oleraceaare described. Analyses of the low temperature induction curvesof fluorescence emission at 695 and 735 nm and of low temperatureabsorption and fluorescence emission spectra were used to examinethese processes. In vitro ageing over short periods reducedthe photochemical activity and changed the energy distributionwithin thylakoids of P. sativum, but had little effect on thylakoidsof S. oleracea. A synergistic effect of in vitro ageing andsalinity of the reaction medium was observed for P. sativumthylakoids. Ageing effects could be minimized by addition of100 mM NaCl to the resuspension medium. Changes in NaCl concentrationin the reaction medium produced large and similar changes inthe primary photochemical functioning of thylakoids from P.sativum and S. oleracea, which could be attributed mainly tothe cation species, Na^$; however, experiments using mannitolto produce osmotic stress indicated some small osmotically inducedchanges in photofunction of the thylakoids. Optimal primaryphotochemical activity of photosystem II, for both species,was observed with 200 mM NaCl. Cation-induced regulation ofexciton distribution appears to be facilitated by controllingthe degree of energy coupling between the light-harvesting chlorophylla/b complex and the two photosystems, I and II, and not by regulationof coupling between photosystems I and II.     

Somatic Embryogenesis from Clonal Leaf Tissues of Cassava

Leaf lobes were isolated from palmate leaves of clonal cassava(Manihot esculenta Crantz) material growing in vitro or in glasshouseconditions and subjected to a two-stage culture procedure involvingincubation on Murashige and Skoog (MS2) basal medium supplementedwith 2–12 mg l^–1 2,4-D for 20 d (Stage I) beforetransfer to MS2 basal medium supplemented with 0.01 mg l^–12,4-D and 0.1 mg l^–1 6-benzylamino purine (BAP) (StageII medium). Embryogenetic tissues, foliose structures and somatic embryosdeveloped from leaf lobes at all Stage I 2,4-D concentrations,except on those explants isolated from shoot-tip cultures incubatedon MS2 basal medium supplemented with 0.1 mg l^–1 NAA and1.0 mg l^–1 BAP. Leaf lobes isolated directly from glasshouse plants showed optimalembryogenetic competence when subjected to a Stage I cultureperiod of 17 d, although foliose structure initiation was optimalwith shorter Stage I durations. Leaf lobes of 2–4 mm lengthand those isolated from phyllotaxic leaf numbers 4 and 5 showedthe greatest embryogenetic competence. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, morphogenetic competence     

Localization of Purothionins and Genome Expression in Wheat Plants

The leaves, steins and ears of tetraploidal wheat, Triticumdurum (genomes AABB) harvested two weeks after heading wereanalyzed for purothionins. There were considerable amounts oftwo iso-purothionins (Pu-1 and Pu-2) in the young kernels ofthe ears, but not in the leaves and stems. The amino acid compositionsof Pu-1 and Pu-2 were in good agreement with those of Pu I andPu II from hexaploidal wheat. As diploidal wheat, T. monococcum(genome AA) is known to produce only Pu I [Fernandez de Caleyaet al. (1976) Genetics 83: 687], we conclude that the threeiso-purothionins, Pu I, Pu II and Pu III in hexaploidal wheat,T. aestivum (genomes AABBDD), are encoded by the genes of genomesA, B and D, respectively. (Received June 28, 1982; Accepted September 24, 1982)     

Potential novel candidate polymorphisms identified in genome-wide association study for breast cancer susceptibility

Previous genome-wide association studies (GWAS) have shown several risk alleles to be associated with breast cancer. However, the variants identified so far contribute to only a small proportion of disease risk. The objective of our GWAS was to identify additional novel breast cancer susceptibility variants and to replicate these findings in an independent cohort. We performed a two-stage association study in a cohort of 3,064 women from Alberta, Canada. In Stage I, we interrogated 906,600 single nucleotide polymorphisms (SNPs) on Affymetrix SNP 6.0 arrays using 348 breast cancer cases and 348 controls. We used single-locus association tests to determine statistical significance for the observed differences in allele frequencies between cases and controls. In Stage II, we attempted to replicate 35 significant markers identified in Stage I in an independent study of 1,153 cases and 1,215 controls. Genotyping of Stage II samples was done using Sequenom Mass-ARRAY iPlex platform. Six loci from four different gene regions (chromosomes 4, 5, 16 and 19) showed statistically significant differences between cases and controls in both Stage I and Stage II testing, and also in joint analysis. The identified variants were from EDNRA, ROPN1L, C16orf61 and ZNF577 gene regions. The presented joint analyses from the two-stage study design were not significant after genome-wide correction. The SNPs identified in this study may serve as potential candidate loci for breast cancer risk in a further replication study in Stage III from Alberta population or independent validation in Caucasian cohorts elsewhere.     

Chromatic Regulation of Photosystem Composition in the Photosynthetic System of Red and Blue-Green Algae

A chromatic adaptation in the photosynthetic quantum yield forthe light mainly absorbed by chlorophyll a (Chl a light) firstfound by Yocum (1951) was studied with one red and three blue-greenalgal strains. When the cells were grown under a weak Chl alight, the quantum yield in all the strains increased. Comparisonof photosystem (PS) compositions, including phycobilin (PBP)and Chl a antennae, reaction centers I and II, in the cellsgrown under the light mainly absorbed by PBP and Chl a revealedthat changes in quantum yield could be attributed to changesin the ratio of PS I/II; PS I/II becomes larger than 1 underPBP light but decreases to 1 in most cases under Chl a light.The change in the PS I/II ratio is due solely to the changesin the PS I population in the cell; PS II remains constant.These results are similar to the intensity-dependent responsein PS composition. A common hypothesis for both the chromatic and intensity-inducedregulation of PS composition was proposed based on the ideaof balance between the electron flow from H₂O to NADP drivenby PS I and II and the cyclic one driven by PS I. (Received May 16, 1985; Accepted September 4, 1985)     

Oogenesis in Xenopus laevis (Daudin). I. Stages of oocyte development in laboratory maintained animals

Oogenesis in the anuran Xenopus laevis can be divided into six stages based on the anatomy of the developing oocyte. Stage I consists of small (50 to 100 μ) colorless oocytes whose cytoplasm is transparent. Their large nuclei and mitochondrial masses are clearly visible in the intact oocyte. Stage II oocytes range up to 450 μ in diameter, and appear white and opaque. Stage I and II are both previtellogenic. Pigment synthesis and yolk accumulation (vitellogenesis) begins during Stage III. Vitellogenesis continues through Stage IV (600 to 1000 μ), the oocytes grow rapidly, and the animal and vegetal hemispheres become differentiated. By Stage V (1000 to 1200 μ) the oocytes have nearly reached their maximum size and yolk accumulation gradually ceases. Stage VI oocytes are characterized by the appearance of an essentially unpigmented equatorial band. They range in size from 1200 to 1300 μ, are postivtellogenic and ready for ovulation. These stages of oocyte development have been correlated with physiological and biochemical data related to oogenesis in Xenopus.     

The ecology of the Calanus ponticus population in the deeper layer of its concentration in the Black Sea

The layer of daytime concentration of Calanus ponticus (VC andVI C) performing daily vertical migrations and the layer of‘winter stock’ aggregation are confined to the depthof maximal gradient of the main pycnocline under an unusuallysharp oxycline. The concentration layer thickness ranges from2 to 20–30 m and the Calanus concentration in it is >250ind. m^–3, sometimes being 3500 ind. m^–3 and evenmore. The population in the concentration layer is divided intotwo ecological groups: I, feeding and migrating specimens ofcopepodite stages V and VI, their body lipid contents being25–60 µg min.^–1; and II, non-feeding and non-migratingspecimens of copepodite stage V, their body lipid contents being100–150 µg ind.^–1. The relationship with oxygenconcentration was studied in both ecogroups. The experimentsshow that specimens of ecogroup II can exit at an oxygen concentrationof 0.06 ml 1^–1, but at such concentration falling intoanabiosis. They die at 0.04 ml O₂ 1^–1. Estimates of respirationof the group II specimens (‘winter stock’) showthat lipids they store are sufficient for 7 months' survival.Depth of Calanus concentration is determined by water densityrather than concentration of oxygen.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Flow Cytometric Determination of Nuclear Replication Stage in Seed Tissues

Flow cytometric determination of DNA levels in embryos of fullymatured seeds of various plant species revealed large amountsof 2C DNA signals, indicating that most cells had arrested thecell cycle at the presynthetic G₁ phase of nuclear division.The accumulation of cells at G₁ was found both in orthodox andin recalcitrant (i.e. Castanea sativa) seed species. As recalcitrantseeds are characterized by the absence of maturation drying,the arrest of the cell cycle in the presynthetic phase may notbe linked to the seed water status. Apart from the 2C signal, 4C values were found in the embryoof some seed species (e.g. Raphanus sativus) indicating thatcells were arrested in G₂ Cells arrested in G₂ were primarilylocated in the root-tip region of the embryo. In addition, combinationsof higher C values (i.e. 8C, 12C, 16C and 64C) were observedin the endosperm of Solanum melongena and Lycopersicon esculentum,and in the root-tip cells of Phaseolus vulgaris and Spinaciaoleracea. These mixtures of polyploid nuclei (also called 'polysomaty')may arise from a developmentally controlled cellular endoreduplicationand indicates that in each cell type of the seed the amountof DNA is regulated both spatially and temporally.Copyright1993, 1999 Academic Press Endive, Cichorium endiva, lettuce, Lactuca sativa, egg-plant, Solanum melongena, pepper, Capsicum annuum, tomato, Lycopersicon esculentum, radish, Raphanus sativus, bean Phaseolus vulgaris, spinach, Spinacia oleracea, chestnut, Castanea sativa, beech, Fagus sylvatica, pine, Pinus nigra, DNA content, flow cytometry, seed, nuclear replication stage, C levels, storage     

Mesozooplankton community structure and grazing impact in the region of the Subtropical Convergence south of Africa

Mesozooplankton distribution and community structure in theregion of the Subtropical Convergence (STC) south of Africawere investigated during the SAAMES III cruise in austral winter(June–July) 1993. Both the STC and an associated warm-coreeddy (WCE) exhibited enhancements in zooplankton abundance,compared to the Subantarctic waters. Particularly, elevatedzooplankton densities were found in the centre of the STC andin the region north of it as well as at the edge of the WCE.Copepods (mainly Pleuromamma abdominalis and Metridia lucens),euphausiids (Euphausia spinifera, E.similis and E.recurva),pteropods (Limacina spp.) and chaetognaths (Eukrohnia hamataand Sagitta spp.) dominated numerically and accounted for >60     

The life history and vertical distribution of the chaetognath, Sagitta elegans, in Dabob Bay, Washington

Seasonal changes in the population structure and patterns ofvertical distribution and migration of the dominant chaetognath,Sagitta elegans, in a fjord off Puget Sound were determinedwith samples collected at approximately semi-monthly intervalsfrom November 1972 to November 1973. S. elegans bred continuouslyfrom March through August, with major recruitment in June andJuly. Seasonal changes in the vertical distribution of the populationand in the proportion of the population that vertically migratedreflected the stage of maturity and size of the individuals.Small chaetognaths were non-migratory and distributed in thetop 100 m. Stage II individuals were dispersed throughout thewater column; some did migration was evident. Breeding stageswere restricted to a layer between SO and 100 m during the dayand migrated to the surface layer at night, enhancing the probabilityof successful reproduction.     

Regulation of Electron Transport Composition in Cyanobacterial Photosynthetic System: Stoichiometry among Photosystem I and II Complexes and Their Light-Harvesting Antennae and Cytochrome b6/fComplex

This study was done to confirm our previous observation withthe pattern of changes in electron transport composition inducedby an imbalance of the electron transport state. Contents ofphotosystem (PS) I and II complexes and their antennae and Cytb₆/f complex were determined for systems of cyanobacterium SynechocystisPCC 6714 of different PS I/PS II ratios. The results indicatedthat (1) the observed changes in the PS I/PS II ratio are not-dueto regulation of the activities of the respective PS's but tochanges in their contents, (2) the molar ratio between PS IIand Cyt b₆/f complexes was fairly constant when marked changesoccurred in the PS I content, and (3) the PS II and Cyt b₆/fcontents per cell remained fairly constant while the PS I contentchanged markedly. These findings agree with our previous observationwith autotrophic cells of Anacystis nidulans Tx 20 and supportour argument that in cyanobacterial and red algal electron transportsystems, the content of the terminalcomponent(s), such as PSI complex, is regulated in order to maintain a balance betweenthe electron influx by PS II action to the system and the effluxby PS I action from it. (Received June 3, 1987; Accepted September 20, 1987)