bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of short-range forces on wall-slip in microgel pastes
Authors: Seth Jyoti R. , Cloitre Michel , Bonnecaze Roger T.
Published: August 2008

Concentrated suspensions of soft deformable particles, e.g., polymer microgel pastes and compressed emulsions, display a generic slip behavior [Meeker et al., J. Rheol. 92, 18302 (2004a); Meeker et al., J. Rheol. 48, 1295–1320 (2004b)]. When sheared with smooth surfaces, they exhibit apparent motion due to slip at the wall. Wall-slip stops at a sliding yield stress the value of which is much lower than the bulk yield stress. The physical mechanism of slip at low stresses and the origin of the sliding yield stress have so far been unresolved issues. We propose that the paste-wall interactions control the wall-slip behavior and determine the occurrence of the sliding yield point. We present experiments performed with different shearing surfaces. Two distinct slip behaviors are identified: depending on whether the interaction between the microgel particles and the wall is attractive or repulsive, wall-slip can be either suppressed or promoted. We provide an extension to the elastohydrodynamic slip model of Meeker and co-workers by incorporating attractive or repulsive interactions between the slipping paste particle and the wall. The interplay of various short range forces due to van der Waals, hydrophobic/hydrophilic, and/or electrostatic interactions and elastohydrodynamics is used to explain the influence of the shearing surface on wall-slip. The model encompasses the different slip regimes observed in our experiments and can predict the slip behavior accurately for well characterized surfaces.
Wall slip and spurt flow of polybutadiene
Authors: Park Hee Eon , Lim Sung Taek , Smillo Fabricio , Dealy John M. , Robertson Christopher G.
Published: August 2008

Spurt occurs in the flow of entangled melts in a capillary rheometer in which the driving pressure is controlled. As the driving pressure increases, at a critical value there is a sudden increase in flow rate, often called spurt. This discontinuity is followed by another regime of smoothly increasing flow rate. A phenomenon that may contribute to this instability is a curve of wall shear stress versus slip velocity that has a maximum followed by a minimum, and there are models that predict such behavior. We used a sliding plate rheometer (SPR) to study wall slip for a highly entangled, linear polybutadiene at 1atm and at 46MPa. By varying the plate speed, we were able to explore the entire curve of shear stress versus slip velocity. This curve exhibited a maximum and a minimum in the stress, providing support for theories predicting this behavior and an explanation for the spurt effect in capillary rheometry. The spurt flow of the same polymer was also observed, and slip velocities were estimated and compared with those determined using the SPR. The slip velocities obtained using the two instruments were in good agreement.
A study of the nonlinear rheology of complex fluids using diffusing wave spectroscopy
Authors: Raudsepp Allan , Callaghan Paul , Hemar Yacine
Published: August 2008

Diffusing wave spectroscopy’s (DWS) sensitivity to local shear rate has been used to investigate the nonlinear rheology of (1) a doped shear thinning, semidilute polymer solution measured in the cone-plate and parallel-plate geometries and of (2) doped shear banding wormlike micelles solutions measured in the cylindrical-Couette geometry. DWS measurements of the semidilute polymer solution in the cone-plate geometry under stress controlled conditions were used to construct a flow curve for the material, the expected radial dependence of the local shear rate being demonstrated in the parallel-plate geometry. The method is shown to be sensitive to shear banding in semidilute wormlike micelles in the cylindrical-Couette geometry under strain controlled conditions, and DWS correlation functions were quantitatively interpreted using a heterogeneous shear flow model. Flow curves and shear rate profiles were inferred from these measurements.
New drug targets for pulmonary hypertension: Rho GTPases in pulmonary vascular remodelling
Authors: Wojciak-Stothard B
Published: August 2008

Rho GTPases, key regulators of actin dynamics, play a major role in vascular processes such as endothelial permeability, cell motility, angiogenesis, nitric oxide production, smooth muscle contractility, cell proliferation and differentiation. In the lung, Rho GTPases control pulmonary vascular tone and remodelling. Their basal activity is important in fetal lung development and vascular adaptation to changes in oxygen levels, but their continuous activation in neonatal or adult lung leads to the development of pulmonary hypertension (PH), a condition characterised by excessive remodelling and hyperconstriction of pulmonary arteries. This review, based on recent molecular, cellular and animal studies, focuses on the current understanding of Rho GTPases signalling in pulmonary vascular physiology and pathophysiology. It also discusses the existing and prospective treatments targeting Rho GTPases in the management of PH.
Lung cancer mimicking left atrial mass
Authors: Kadappu K K , Rajaratnam R , Kachwalla H , Nguyen P D
Published: August 2008

Cardiac involvement in lung cancer is found in up to 25% of autopsy cases. However, despite the considerable mortality and morbidity associated with cardiac metastasis, antemortem diagnosis is unusual. A rare case of lung cancer presenting as a left atrial mass is reported.
See one, do one, then what? Faculty development in postgraduate medical education
Authors: Swanwick T
Published: August 2008

Interest in the development of medical educators working in the postgraduate sector is running high. Driven by three interlinked trends—the professionalisation of medical education, increasing accountability, and the pursuit of educational excellence—there is a growing need for high quality and sustained faculty development programmes across the network of education providers. Postgraduate medical education has a number of unique features that set it apart from undergraduate medicine, to which faculty development programmes need to cater. The key issue for the future will be how to engage the service in the business of education. Widespread cultural change is required and this will require effective and sympathetic leadership from postgraduate training institutions, hospitals and health authorities.
Forest fires in the Muddus National Park (northern Sweden) during the past 600 years
Authors: Engelmark Ola
Published: August 2008

The occurrence of forest fires in the Muddus National Park (area, 50 000 ha), just north of the Arctic Circle in northern Sweden, was investigated on 75 separate sample plots. Between 1413 and the present, evidence of 47 fire years was obtained by dating the fire scars on living Scots pines (Pinus sylvestris), the oldest of which had germinated in 1274. The fire traces found on the sample plots were fire scars on living or dead trees or charcoal fragments in the humus layer. Plots lacking all traces of former forest fires were mainly those situated on sites surrounded by extensive mires. Forest fires were shown to have occurred in the five different types of forest investigated. The commonest frequencies of fires in the pine forests occurred with the interval 81–90 years, while the mean frequency was 110 years. The mean interval of time elapsed since the last forest fire occurred in the pine forests was 144 years. Some of the major fire years in the Muddus area coincide with forest fires in other parts of northern Sweden, in the taiga of western Russia, and in central Siberia.
Low root temperatures and nitrogenase activity in soybean
Authors: Layzell D. B. , Rochman P. , Canvin D. T.
Published: August 2008

A continuously flowing open gas exchange system was used to monitor the rates of CO2 evolution, C2H2 reduction, and H2 evolution from intact nodulated soybean ('Harosoy 63') roots, while root temperatures were dropped from the growing temperature (25 °C) to 10 °C at the rate of 5 °C/h. Four Rhizobium japonicum inoculants were used, three of which (type S (Nitragin Co.), USDA 16, USDA 35) displayed net H2 evolution while the fourth (USDA 110) did not evolve H2. Between 25 and 15 °C, values for Q10 in the H2-evolving symbioses ranged from 2.0 to 2.7 for CO2 evolution. 1.3 to 2.4 for C2H2 reduction, and 3.2 to 3.7 for H2 evolution. Nodulated roots of USDA 110 displayed the highest Q10 values for both CO2 evolution (Q10 = 2.9) and C2H2 reduction (Q10 = 15.2). The temperature profiles of these gas exchange measurements were used to calculate both the relative efficiency (RE = 1 − (H2 evolution/C2H2 reduction)) of N2 fixation and the ratio between CO2 evolution and C2H2 reduction at temperatures between 10 and 25 °C. The effect of short-term changes on the CO2/C2H2 ratio varied with symbiotic association. In the type-S symbiosis, long-term (96 h) treatments at low root temperature (9.5 °C) decreased the amount of CO2 evolved per C2H2 reduced to 35% of the value obtained at 25 °C. This study did not determine whether these observed changes were associated with N2 fixation or growth and maintenance of the nodulated root. In all H2-evolving symbioses, the RE increased from ca. 0.6 to 0.9 in response to a temperature drop from 25 to 10 °C. Studies of net H2 uptake and 3H2 exchange at 25 and 15 °C indicated that the observed changes in relative efficiency were due to variations in electron allocation by nitrogenase rather than a relative increase in uptake hydrogenase activity. The increase in RE above 0.75 suggested that lower temperatures may have altered the minimal nitrogenase electron allocation to less than one H2 per N2 fixed. This observed increase in RE with lower temperatures indicated that, in the symbioses studied, H2 evolution may have provided a buffer which permitted the maintenance of high levels of N2 fixation during short-term or diurnal fluctuations in soil temperature.
Le pneumatode chez Phoenix dactylifera. II. Ultrastructure de la paroi de la cellule aérifère chez des pneumatodes jeunes provenant de cultures axeniques
Authors: Belarbi-Halli Rosa , Dexheimer Jean , Mangenot François
Published: August 2008

The pneumatode in Phoenix dactylifera is composed of air-filled cells with multilayered walls. Three main layers, L1, L2, and L3, have a pectic, polysaccharide, and proteic composition. When ageing, the last layer gives rise to wall outgrowths which are covered with a thin lamella (L4) essentially polysaccharidic in nature as are the wall and all material of intercellular spaces. Inwards, there appears a thin layered deposit (L0) that might correspond to beginning suberisation. The wall outgrowths are warts composed of juxtaposed vesicles. Every vesicle is constituted by a thin envelope and a matrix with a central globule inside. In the intercellular spaces, between young cells with still smooth walls, a fibrillar material is visible among a mosaïc of polysaccharidic and proteic matter. When vesicles appear, they release an homogenous-appearing material.
Antagonism of isolates of Bacillus subtilis to Phytophthora cactorum
Authors: Utkhede R. S.
Published: August 2008

Twenty-one isolates of the bacterium Bacillus subtilis isolated from local and exotic sclerotia of Sclerotium cepivorum were tested on cornmeal agar (CMA) for antagonism to six isolates of Phytophthora cactorum, causal agent of apple crown rot. All bacterial isolates produced diffusible antibiotics antagonistic to growth of all P. cactorum isolates on CMA. Antagonists were further evaluated in a replicated greenhouse trial for their ability to control crown rot infection on McIntosh apple seedlings in sterile soil. Six isolates of B. subtilis provided statistically significant reductions of infection on McIntosh seedlings. No correlation was observed between width of inhibition zone in vitro and protection from P. cactorum infections in McIntosh apple seedlings in a greenhouse trial. Significant negative correlations were observed between percent seedling infection and root weight.
Relationships between free carbohydrate levels and resistance or susceptibility of Capsicum annuum to Phytophthora capsici
Authors: Bounias Michel , Coulomb Claude , Coulomb Philippe J.
Published: August 2008

The chromatographic analysis of the free carbohydrate content of leaves and stems of pepper showed 19 major fractions which were gathered in 8 structural classes. A number of correlations were found between the respective carbohydrate levels of two varieties of pepper, one susceptible and the other resistant to downy mildew, and also between those of healthy and inoculated tissues. Some cases of departures from the established correlations were observed and discussed with respect to their hypothetical involvement in the character of resistance and susceptibility to the infection. The concentrations of free carbohydrates of the dideoxyhexose group are increased in inoculated leaves of both susceptible and resistant varieties and those of the rhamnose group are depressed in inoculated leaves of the sole susceptible variety. Sucrose strongly increases in inoculated stems but decreases in the inoculated leaves of the sole resistant variety; concomitantly glucose and fructose also increase in inoculated stems, whereas they decrease in inoculated leaves of both susceptible and resistant strains. The results suggest a number of hypotheses concerning the molecular mechanisms of the host resistance to infection in relation to the cellular pathways of sugar translocation.
Conversion of mature leaves into sinks on the dicotyledonous C4 plants Amaranthus caudatus and Gomphrena globosa
Authors: Blechschmidt-Schneider Sabine
Published: August 2008

The effect of an artificially created sink leaf on translocation of 14C-labeled assimilates from a source leaf of the C4 plants Amaranthus caudatus L. and Gomphrena globosa L. was studied with autoradiography. Anatomical studies showed that the vasculature of two successive leaves within a given orthostichy is directly connected by stem bundles. Therefore, in an intact plant, much of the acropetally translocated 14C-labeled assimilates from a mature source leaf moved into the next younger leaf directly above. When such a young leaf on an otherwise illuminated plant was kept under sink conditions (dark, CO2-free air), its increased sink demand resulted in a clearly higher 14C-import, compared with a control. Even a mature leaf of Gomphrena subjected to the similar sink conditions developed sufficient sink demand to import a certain amount of basipetally transported 14C-labeled assimilates from a younger source leaf. In Amaranthus, there was no basipetal translocation from a younger source leaf and, consequently, no 14C-import into a mature leaf under sink conditions occurred. A complete conversion of a mature leaf into a sink was attained only with a pruned source–sink transport system of both plants under source and sink limitation. This conversion from the source to the sink status caused a change in the direction of assimilate flow within the petiolar and stem bundles. The data indicate that a mature leaf under sink conditions can be characterized as a sink with regard to assimilate translocation, although no growth or storage processes are involved in controlling this sink activity.
Geoperception in primary and lateral roots of Phaseolus vulgaris (Fabaceae). II. Intracellular distribution of organelles in columella cells
Authors: Ransom J. Steven , Moore Randy
Published: August 2008

A morphometric analysis of the ultrastructures of columella cells in primary and lateral roots of Phaseolus vulgaris was performed to determine the precise location of cellular components in these cells. Roots were fixed in situ to preserve the in vivo ultrastructure of the cells. All cellular components in columella cells of both types of roots were distributed asymmetrically. The nucleus and vacuome were located primarily in the middle third of both types of columella cells. Dictyosomes, mitochondria, and amyloplasts were most abundant in the lower third of the columella cells in both types of roots. The distribution of amyloplasts was the most asymmetrical of all cellular components examined, with the lower third of the columella cells containing approximately 90% of the relative volume of amyloplasts in both types of roots. The distribution of cellular components in columella cells of primary roots was not significantly different from that of columella cells of lateral roots. These results indicate that differences in georesponsiveness of primary and lateral roots of P. vulgaris are probably due to factors other than the ultrastructures of their individual columella cells.
Axenic culture of rose rust fungus, Phragmidium tuberculatum
Authors: Rahbar-Bhatti M. H.
Published: August 2008

The development of axenic culture of Phragmidium tuberculatum was achieved by seeding urediniospores on agar medium. Urediniosporelike and teliosporelike structures developed in older cultures. Urediniospores and hyphae failed to infect detached leaflets of rose cultivar 'Elizabeth of Glamis.'
Oxygen Transport in Salmon Spawning Gravels
Authors: Johnson R. A.
Published: August 2008

The importance of understanding transport characteristics of flow through gravel media is discussed from the viewpoint of salmonid enhancement programs. A summary of the important features of the incubation process with respect to mass transport is provided along with applicable theories describing flow through porous media. Data obtained from experiments described herein are used to assess the accuracy of existing correlations for predicting pressure drops across gravel substrates. It is found that available hydraulic relations can be used to predict flow velocity magnitudes in gravel media with an accuracy of ± 50% over a twofold range of flow rates, providing one measurement of head loss is available at one flow rate. An adaptation of the Carman–Kozeny equation is found to be suitable for calculating the influence of fines on permeability. The importance of air entrapment on flow resistance is confirmed experimentally and modeled using available correlations. Lastly, the applications of these results for calculating oxygen transport to incubating salmon eggs and minimum water flows in hatcheries are discussed.Key words: Salmon enhancement, oxygen transport, permeability, gravel, incubation, hatcheries
Factors Controlling Oxygen Depletion in Ice-Covered Lakes
Authors: Mathias Jack A. , Barica Jan
Published: August 2008

Winter oxygen depletion rates from four sets of Canadian lakes (prairie, southeastern Ontario, Arctic, and Experimental Lakes Area) differing in morphometry and trophic state, were analyzed. An inverse relationship was found between oxygen depletion rate and mean depth. The effect of lake trophic status on oxygen depletion rate was demonstrable after the influence of basin morphometry was removed by regression of oxygen depletion rate against the sediment area: lake volume ratio. The sediments of eutrophic lakes consumed oxygen about 3 times faster (0.23 g∙m−2∙d−1) than those of oligotrophic lakes (0.08 g∙m−2∙d−1), but water column respiration was about the same (0.01 g∙m−3∙d−1) for both groups of lakes. Data from prairie lakes showed that the winter oxygen consumption was limited by oxygen supply below an average whole-lake oxygen concentration of 3.8 mg∙L−1. The rate of eddy diffusion near the sediments in ice-covered prairie lakes was 3.72 ± 1.41 × 10−3 cm2∙s−1. Implications for lake management during the winter are discussed.Key words: oxygen, depletion, respiration, lakes, ice-covered, winter, sediments, model, consumption
Mortality, Hematocrit, Osmolality, Electrolyte Regulation, and Fat Depletion of Young-of-the-Year Freshwater Fishes under Simulated Winter Conditions
Authors: Toneys Michael L. , Coble Daniel W.
Published: August 2008

In laboratory experiments young-of-the-year green sunfish, Lepomis cyanellus, largemouth bass, Micropterus salmoides, brook trout, Salvelinus fontinalis, and yellow perch, Perca flavescens, were held for 4 mo under simulated winter conditions (2–4 °C; photoperiod of 9 h light: 15 h dark) in solutions of various osmotic strengths, from 90% distilled water to 1.0% NaCl. Mortality in three of five experiments often was greater in salt solutions, indicating that NaCl did not increase survival. Survival was greater for larger yellow perch than smaller but was not related to size in the other species. Hematocrit was depressed below control levels in all solutions at the end of experiments. The fish generally were able to regulate plasma osmotic concentration in all solutions except the highest NaCl concentrations, where plasma osmolality was often significantly higher than in the control at the end of experiments. Plasma Na+ and Cl− typically decreased and then recovered at low temperatures. Presence of Na+ and Cl− in the external medium tended to alleviate their loss from plasma. Changes in plasma Na+ and Cl− were not related to mortality in hypoionic solutions but usually did correspond to changes in plasma osmolality. Fat content of survivors declined and water content increased for all species, but the losses and gains were not related to osmolality of solutions. Low fat content probably was not a cause of death.Key words: Mortality, electrolyte regulation, osmolality, hematocrit, fat depletion, winter conditions, green sunfish, largemouth bass, brook trout, yellow perch, sodium, chloride
Influence of Secondarily Treated Kraft Mill Effluent on the Accumulation Rate of Attached Algae in Experimental Continuous-Flow Troughs
Authors: Bothwell Max L. , Stockner John G.
Published: August 2008

In three seasonal experiments in 1977, increases in the rate of attached algal accumulation were normally found with each additional increment of secondarily treated kraft mill effluent (KME). The effect of KME on the instantaneous accumulation coefficients of algae were 1.2–2.8 times greater in the summer than in the autumn or spring at all dilutions tested. At higher concentrations (5 and 25% v/v KME) an inhibition of accumulation was usually observed during the first 5–6 d of exposure; after this period diatom biomass increased sharply. Succession of diatom taxa to different forms, rather than physiological adaptation by usually predominant species occurred. No inhibition was noted at lower concentrations (0.5, 1, and 2% v/v) of KME. Relatively high levels (20–30 μg∙L−1) of soluble reactive phosphorus (SRP) and low concentrations of nitrate + nitrite–nitrogen (5–10 μg∙L−1) and ammonia–nitrogen (2–20 μg∙L−1) in the river dilution water suggested that nitrogen was the primary limiting nutrient. Ammonium uptake tests for nitrogen deficiency confirmed nitrogen limitation in algae grown in unenriched river water compared to algae exposed to KME for 6 d. Differences in chlorophyll a: ATP ratios among periphyton communities of the different treatments were minimal after 9 d.Key words: kraft mill effluent, algal growth, nutrient enrichment, benthic algae, river, chlorophyll a
Harvesting Strategies and Parameter Estimation for an Age-Structured Model
Authors: Deriso R. B.
Published: August 2008

An age-structured model with knife-edge recruitment describes the dynamics of exploited, seasonally breeding populations. For management strategy, an equation is derived that characterizes the economic optimal state of exploitation of a modeled stock. A further generalization is derived to account for those species where recruitment to the mature stock occurs over many age-categories. Since the parameters all have phenomenological definitions, they can be estimated from information independent of the model. These parameters can also be estimated by regression of the model to catch and effort data. Test regressions of the general model are made on catch and effort data from three exploited fish stocks: the yellowtail flounder of New England, the Pacific halibut of Area II, and the haddock of Georges Bank; the corresponding R2 values are 0.75, 0.87, and 0.86. Although the confidence intervals for individual parameter estimates are very large, the estimates compare favorably with published parameter values. Since only certain combinations of parameters from the general model appear to have low sensitivity to small perturbations to the data, some guiding suggestions are made that may lead to an improved robustness in the statistical procedures.Key words: age-structured model, optimal harvesting strategy, spawner–recruit curves, parameter estimation
Sex Determination of the Ommastrephid Squid Illex illecebrosus Using Beak Morphometries
Authors: Mercer M. C. , Misra R. K. , Hurley G. V.
Published: August 2008

The beak morphometrics of the ommastrephid squid Illex illecebrosus were analyzed as possible criteria for determining sex composition of beak samples taken from predator stomachs. A multivariate analytical procedure was adopted to elucidate the course of discriminant analysis needed in this study. The discriminant functions presented here can be employed usefully in identifying the sex of an unknown individual from either the upper or lower beak morphometrics.Key words: squid, Illex, beak, morphometrics, multivariate, discriminant analysis, sex determination
Chromosome Complement of the Marine Worm Neanthes arenaceodentata (Polychaeta: Annelida)
Authors: Pesch Gerald G. , Pesch Carol E.
Published: August 2008

The chromosome complement for the marine worm Neanthes arenaceodentata consists of nine pairs; one pair has a median centromere, seven pairs have submedian centromeres, and one pair is polymorphic with either a subterminal or terminal centromere. A technique for studying polychaete chromosomes is described. This species was selected as a model for studying cytogenetic effects of toxicants in marine environments because it has a suitable karyotype, is easily cultured, and as a benthic organism it is representative of an ecologically important group of organisms.Key words: polychaete, chromosomes, karyotype
Techniques for Exploring and Presenting Data Applied to Lake Phosphorus Concentration
Authors: Reckhow K. H.
Published: August 2008

Water quality sampling and data analysis are undertaken to acquire and convey information. Therefore, when data are presented, the form of this presentation should be such that information transfer is high. For example, a graph or table of average values is often an inadequate summary of batches of data. As an alternative, a technique is presented (that was developed for exploratory data analysis purposes) that can be used to display several sets of data on a single graph, indicating median, spread, skew, size of data set, and statistical significance of the median. This technique is useful in the study of phosphorus concentration variability in lakes. Additions to, and modifications of, this procedure are easily made and will often enhance the analysis of a particular problem. Some suggestions are made for useful modifications of the plots in the study and display of phosphorus lake data and models.Key words: limnology, exploratory data analysis, statistics, phosphorus, water quality, models, lakes
Changes in Fish Mercury Concentrations in an Intensively Fished Lake
Authors: Verta Matti
Published: August 2008

A small polyhumic lake inhabited by northern pike (Esox lucius), burbot (Lota lota), perch (Perca fluviatilis), roach (Rutilus rutilus), and eel (Anguilla anguilla) was fished intensively during spring 1984 and 1985 to lower the high mercury levels in the top predator, northern pike. A total catch of 29.5 kg∙ha−1 (74% roach) was removed which represented about 50% of the total fish biomass. Mercury concentrations in burbot, large pike, and small roach had decreased by 1987 and 1988, but increased in young pike and some perch. Northern pike had the clearest increase in growth rate, while that of perch and roach levelled off within 3 yr at the prefishing level. Only a small increase in growth rate of burbot occurred. The yearly accumulation of mercury in northern pike remained constant, and the decrease in [Hg] was apparently due to growth dilution. The decrease in [Hg] of burbot and roach is explained by a switch to a diet with lower [Hg] or a decrease in water methylmercury concentrations. The amount of methylmercury removed from the lake by fishing was equivalent to several years of calculated mercury methylation and accumulation in the fish. Overfishing may be a feasible means of lowering methylmercury levels in this type of oligotrophic lake.
Acoustic Observations of Gas Bubble Release by Pacific Herring (Clupea harengus pallasi)
Authors: Thorne Richard E. , Thomas G. L.
Published: August 2008

Evidence is given to show that Pacific herring (Clupea harengus pallasi) release gas bubbles during diel vertical migration and while holding in strong currents. The evidence includes hydroacoustic observations of echoes from both fish concentrations and gas bubbles. The fish are identified as herring on the basis of historical fisheries data and, in some cases, direct capture. Echoes from objects emanating form the fish concentrations are attributed to gas bubbles based on similarity to acoustic observations of gas bubbles in many other circumstances, as well as direct observation of bubbles at the surface in some cases. Since conclusive evidence exists that herring do not have gas secretion capability, two alternative hypotheses are presented to explain the source of the gas. One hypothesis is that the gas results from fermentation in the gut. A second is that herring gulp gas at the surface prior to descent to daytime depths. One consequence of differing amounts of gas would be changes in the acoustic target strength of herring, which is a critical parameter in acoustic assessment techniques.
Additional Evidence Supporting Demic Behaviour of a Yellow Perch (Perca flavescens) Population
Authors: Aalto S. K. , (Buck) Newsome G. E.
Published: August 2008

To test the hypothesis that yellow perch (Perca flavescens) return to their natal location to spawn, the following experimental manipulations were performed. During the years 1978 through 1989, the egg-masses deposited by females along isobathic transects at a number of sites in Lochaber Lake were counted. During the years 1984 through 1987, egg-masses were removed from one of the sites in the lake during the spawning seasons. There was a statistically significant reduction in the proportion of egg-masses deposited within the boundaries of the site from which the egg-masses were removed. The analysis strongly suggests that the model of perch spawning behaviour which assumes that any perch selects a spawning site independently of its natal site may be rejected. This result provides additional support for the hypothesis that yellow perch exhibit demic behaviour.
Enzyme Heterozygosity and Fecundity in a Naturalized Population of Brook Trout (Salvelinus fontinalis)
Authors: Liskauskas Arunas P. , Ferguson Moira M.
Published: August 2008

Relationships between heterozygosity at 7 enzyme loci and components of fecundity as well as female size were examined in a naturalized population of brook trout, Salvelinus fontinalis, from Algonquin Park, Ontario. A significant positive regression between the number of heterozygous loci per fish and estimated egg number per female was detected. Multilocus heterozygosity (summing heterozygosity across all loci) was positively associated with total ovulated egg weight. When adjustments were made for female weight, multilocus heterozygosity did not explain a significant amount of variation in either total ovulated egg weight or other components of fecundity. A marginally significant (P = 0.055) linear relationship existed between multilocus heterozygosity and female weight but not length. Treating each locus separately rather than summing heterozygosity across all loci improved the predictive value of heterozygosity on estimated egg number per female, female weight, and length. Individuals heterozygous at Aat-1,2 had more eggs than homozygotes whereas heterozygotes at G3p-1, were heavier or longer than homozygotes.
Optimization of Insecticide Treatments in Rivers: an Application of Graph Theory for Planning a Black Fly Larvae Control Program
Authors: Chalifour Alain , Boisvert Jacques , Back Christian
Published: August 2008

Combining a model of susceptibility of black fly larvae to commercial formulations of Bacillus thuringiensis var. israelensis and a one-dimensional transport equation in a river, the quantity of larvicide that should be applied at a given site in order to achieve a given mortality downstream can be calculated. The obtained relation, a function of biological and hydrological parameters, allowed us to calculate the costs related to the treatment of a section of river. It is then possible to determine an optimal strategy of treatment which minimizes the quantity of an insecticide applied and the logistic movement between injection sites. Optimal solution is found with the aid of a well known algorithm developed in operations research theory to solve this combinatorial problem. An experimental treatment conducted in the Onchocerciasis Control Program in West Africa is analyzed as an example of the model's application to illustrate the savings of insecticide, time, and money using this approach.
Direct and Indirect Effects of Consumers on Benthic Algae in Isolated Pools of an Ephemeral Stream
Authors: McCormick Paul V.
Published: August 2008

Artificial pools were used to test for interactions among dominant consumer and producer populations that coexist in isolated pools of an ephemeral stream each summer. Nitrogen and/or phosphorus were supplied to one set of pools; herbivorous snails and crayfish and a predaceous centrarchid were added in different combinations to other pools. Algal growth was measured inside and outside wire cages placed in pools to exclude herbivores and/or predators. Algal biomass and the abundance of most algal species were increased by nitrogen enrichment. Algal biomass was also enhanced by addition of consumers. There were few differences in structure between algal assemblages inside and outside cages in any treatment. Under conditions of nitrogen limitation, moderate levels of herbivory can enhance algal growth. Positive effects are greatest at the microsite level and may depend on the ability of algal species to resist digestion by grazers. Predators may affect the algal assemblage indirectly by reducing herbivore survival or activity and directly by converting nutrients stored in herbivore biomass into a form available for algal growth. Because the importance of different trophic connections may vary among ecosystems, experimentation must consider all those that are potentially important.
Daily Growth Rates as Indicated by Valve Ridges in Postlarval Giant Scallop (Placopecten magellanicus) (Bivalvia: Pectinidae)
Authors: Parsons G. Jay , Robinson Shawn M. C. , Roff John C. , Dadswell Michael J.
Published: August 2008

Postlarval giant scallop (Placopecten magellanicus) were examined for daily growth ridges and growth rates by marking the dissoconch shell with Alizarin red dye. The surface of the left valve of postlarvae was composed of concentric ridges, each consisting of a series of irregularly shaped raised nodules. Ridges were clear and distinct in newly settled scallop between ≈0.25 and 2.0 mm shell height. The shell of postlarvae >2 mm was pigmented and ribbed and ridges were no longer distinguishable. Estimated age was significantly correlated with actual age, suggesting that growth ridges were produced daily, under the environmental conditions of Passamaquoddy Bay. Mean growth rate ranged from 32 to 57 μm∙d−1 and was proportional to size and age, but growth of individual scallop showed no coherence in their daily growth patterns. The short-term growth ridges in postlarval giant scallop can be used to determine age and can be applied to comparative growth, mortality, and recruitment studies of newly settled individuals <2.0 mm (≈40 d old postsettlement). The high accuracy and precision of age determination for postlarval scallop differs from studies of short-term internal growth increments of bivalve shells and larval fish otoliths.
Prerelease Stratification in Tag-Recovery Models with Time Dependence
Authors: Dorazio Robert M.
Published: August 2008

A statistical model is developed for estimating time-dependent survival and recovery rates of tagged populations that are stratified into groups at release. For populations of fish, the groups might include different sexes or stocks, or they might be distinguished by the location or method of capture. In the model developed here, survival and recovery rates are formulated as linear combinations of parameters that include the effects of time, group, and time–group interactions. Methods of testing the statistical significance of these potential sources of variation are described and illustrated with the recoveries of different stocks of anadromous striped bass (Morone saxatilis). For the striped bass data, elimination of time- and stock-specific sources of variation substantially improved the precision of survival estimates without introducing important bias. During 1988–89 the average survival of both stocks was 0.78 (SE = 0.04). Calculations of statistical power indicate that stock-specific differences in survival of ± 0.2 could have been detected about 50% of the time, given the low rates of recovery and numbers of fish released.
Smolt-to-AduIt Survival Patterns of Sockeye Salmon (Oncorhynchus nerka): Effects of Smolt Length and Geographic Latitude when Entering the Sea
Authors: Koenings Jeffery P. , Geiger Harold J. , Hasbrouck James J.
Published: August 2008

Variations in smolt-to-adult survival (SAS) of sockeye salmon (Oncorhynchus nerka) relative to smolt length and age and latitude of the nursery lake outlet were explored for six stocks in Canada, Russia, and Alaska (W. E. Ricker. 1962. J. Fish. Res. Board Can. 19: 531–560) and 12 Alaskan populations. SAS values ranged from <1 to 68% for age 1., 2., and 3. smolt populations of 54–200 mm in mean length. The common pattern underlying the SAS to smolt size relationship, determined by nonparametric regression (loess), was nonlinear with functionally distinct zones. SAS of smaller smolts increased (0.3–0.5 (%) SAS∙mm−1) with size, but SAS of smolts >90–100 mm (6–8 g) did not. Variation in SAS was explained by smolt size (30%) and a south to north dine of nursery lakes (21%) indexed by latitude. SAS of about 3 and 13% for threshold-sized age 1. smolts (60–65 mm) from southern and northern nursery lakes were consistent with sockeye biostandards for Canada (4.7%) and Alaska (12%), respectively. The combined effects of latitude and smolt length on SAS resulted in larger smolts at higher (>60°N) latitudes having seven times the SAS of smaller smolts at lower (<55°N) latitudes.
Mitochondrial DNA Variation in Lake Sturgeon (Acipenser fulvescens) from the St. Lawrence River and James Bay Drainage Basins in Quebec, Canada
Authors: Guénette S. , Fortin R. , Rassart E.
Published: August 2008

Restriction fragment length pattern analysis of mitochondrial DNA (mtDNA) was used to assess genetic differentiation in sympatric lake sturgeon (Acipenser fulvescens) from the St. Lawrence River drainage basin (St. Lawrence and Ottawa rivers and Lac des Deux Montagnes) and in sturgeon from the Waswanipi River (James Bay drainage basin). Using 14 restriction enzymes on mtDNA from 82 specimens, the genetic divergence was relatively low (d = 0.219–0.744%), as only three genotypes were found. Genotype 1 is present at all sites whereas genotype 2 is present only in Lac des Deux Montagnes and the Ottawa and Waswanipi rivers. The St. Lawrence River sturgeon form a homogeneous genotypic group that was not found significantly different from sturgeon from Lac des Deux Montagnes. The genetic heterogeneity seemed higher in the James Bay drainage population than in the St. Lawrence drainage populations that probably have been more significantly influenced by overfishing and man-made habitat changes.
Variation in the size and position of Hymenolepis diminuta (Cestoda: Cyclophyllidea) within the rat intestine
Authors: Mettrick D. F. , Dunkley Lorna C.
Published: August 2008

Data on the dry weight of 410 worms from both male and female rats is shown not to differ significantly from the normal (Gaussian) frequency distribution. This finding justified the use of statistics based on this function.Host body weight is shown to have a highly significant (P < 0.01) effect upon worm dry weight. The heavier the rat, the smaller the worms. An experimental design taking rat body weight into consideration is shown to be up to 36% more efficient in demonstrating differences between groups than one that ignores this source of variation. The point of scolex attachment behind the pyloric sphincter also has a significant effect (P < 0.05) upon worm dry weight. The nearer the scolex is to the stomach, the smaller the worm.The distribution of worm biomass in the intestine does not follow a normal (Gaussian) frequency, but is both asymmetrical (P < 0.001) and flattened (P < 0.001). Over 50% of the parasite biomass lies within the second quarter of the intestine. The distribution of the median points of worm strobilae in the rat intestine is also asymmetrical (P < 0.01) with a peak in the zone which represents a distance of 30–35% from the stomach.The migration of H. diminuta within the rat intestine results in the greater part of the parasite body lying in the second quarter of the intestine. The median points of the strobilae are concentrated at the junction of the first and second quarters of the intestine. This region of the rat intestine appears to offer the optimum site for the growth of H. diminuta.
The genus Zealeuctra and its position in the family Leuctridae (Plecoptera, Insecta)
Authors: Ricker W. E. , Ross H. H.
Published: August 2008

Zealeuctra Ricker 1952 (type Leuctra claasseni (Frison 1929)) contains seven known species, of which six are newly described: arnoldi, fraxina, hitei, narfi, wachita, and warreni. All the species occur in the central Mississippi valley region of the United States, with only a little overlap into adjacent watersheds in Texas and West Virginia. Zealeuctra occupies a fairly central position in the general scheme of evolution among Leuctridae, but the large epiproct and basally undivided subanal probe are primitive characters. Its seven species are all closely allied to each other, and are very different from other genera.
The embryology of Lytta viridana Le Conte (Coleoptera:Meloidae). V. The blastoderm, germ layers, and body segments
Authors: Rempel J. G. , Church N. S.
Published: August 2008

This study deals with the formation of the blastoderm, germ layers, and body segments in Lytta viridana. It comprises the period of development from 16 h to 65 h. In the blastoderm the germ rudiment appears ventrally and the serosa dorsally. Two clusters of cells in the germ rudiment become visibly differentiated from the neighboring blastoderm cells. They are considered to be the endoderm. They assume later the function of secondary vitellocytes and become the centers around which are formed the yolk polyhedra. They do not give rise to the enteron rudiments. The latter arise as ectodermal outgrowths from the blind ends or the stomodaeum and proctodaeum. What is generally called gastrulation results in the inward movement of presumptive mesoderm. The view is expressed that the germ layer theory is applicable in Lytta. During development pronounced morphogenetic movements affect the blastema, the blastoderm, the germ rudiment, and segmentation. The mesoderm becomes segmented before the ectoderm. The following somites are found: labral, antennal, intercalary, 3 gnathal, 3 thoracic, and 11 abdominal. All but the last somite have coelomic sacs. The labral mesoderm is preoral from the beginning. The suboesophageal body arises as an ectodermal invagination between the intercalary and the mandibular segments. Three invaginations in the roof of the stomodaeum form the anlagen of the stomatogastric nervous system.
Activity of Microtus pennsylvanicus related to moon phase and moonlight revealed by the sand transect technique
Authors: Doucet G. J. , Bider J. R.
Published: August 2008

Activity of Microtus pennsylvanicus was recorded as the number of crossings per day over a sand transect during four consecutive summers. Appropriate samples were selected to test the effects of both moon phases and moonlight on activity. Initially the results of tests comparing new moon to full moon phases showed that the voles were more active during new moon in only 3 of 10 discreet paired samples tested. However, when the effects of sampling sequence, phenology of population growth, date at which moon phases occurred, and, finally, the effect of climate were all considered as factors which could have affected the above results, it seemed reasonable to conclude that the new moon phase tended to be associated with higher activity. To establish if moonlight by itself, independent of phases, was a factor affecting the activity, tests were made during brightest and darkest nights of the lunar month and results indicated that moonlight did not affect the differences in activity found in the moon phase tests.
The harp seal, Pagophilus groenlandicus (Erxleben, 1777). V. Levels of haemoglobin, iron, certain metabolites and enzymes in the blood
Authors: Vallyathan N. V. , George J. C. , Ronald K.
Published: August 2008

The normal levels of haemoglobin, iron, certain metabolites (glucose, fat, and cholesterol) and enzymes (amylase, aldolase, lactic dehydrogenase, and lipase/esterase) in the blood of the harp seal were estimated. All values except for the lipase (esterase), were considerably higher than those recorded for other animals, including man. The elevated level of lactic dehydrogenase activity as a normal characteristic of the blood is attributed to the role of the enzyme in the oxidation of lactic acid to pyruvate as an adaptation in a diving animal. The extremely low level of lipase (esterase) activity in the blood is suggested to be indicative of the fact that fat is not the favored metabolite for muscular energy in a diving animal.
The development of Trypanosoma canadensis of Rana pipiens in Placobdella sp.
Authors: Woo Patrick T. K.
Published: August 2008

Trypanosoma canadensis Woo 1969, from Rana pipiens, developed to the metacyclic stage in Placobdella sp. The metacyclic stage was reached in 20 days at 22–24 °C. Epimastigotes and transitional stages occurred in the crop and gastric caeca and had fine yellow granules in the posterior part of the body. Epimastigotes divided evenly and metacyclic stages were found mainly in the crop.
Effects of temperature on brain tissue oxygen consumption in salmonid fishes
Authors: Peterson R. H. , Anderson J. M.
Published: August 2008

The oxygen consumption of brain tissue from Atlantic salmon and brook trout was determined at temperatures ranging from 6 °C to 30 °C for fish acclimated to 6° and 18 °C. In sucrose medium, oxygen consumption of brain homogenate was higher at all test temperatures for the 6 °C acclimated fish than for the 18 °C acclimated ones. Preparing brain tissue as a mince in saline medium markedly reduced the thermal acclimation effect. The latter preparation had much higher respiratory rates than did homogenate preparations. These differences were ascribed largely to an increase in ATPase activity in the ionic medium.