bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of renal hyporesponsiveness to ANP in heart failure
Authors: Charloux A. , Piquard F. , Doutreleau S. , Brandenberger G. , Geny B. 
Published: August 2003

AbstractThe atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP.Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down‐regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP‐dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium‐retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin‐angiotensin‐aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin‐converting enzyme and angiotensin‐receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP‐induced natriuresis.To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.
The distribution of aquatic invertebrate egg masses in relation to physical characteristics of oviposition sites at two Victorian upland streams
Authors: Reich Paul , Downes Barbara J. 
Published: August 2003

Summary1. Various physical variables were measured at rocks potentially used by lotic macroinvertebrates as oviposition sites at multiple locations on two occasions along the Acheron and Little Rivers, south‐eastern Australia. The associations between these parameters and the presence/absence and abundance of aquatic insect egg masses were explored as well as the small‐scale distribution of egg masses on individual rocks.2. Physical features that characterise oviposition sites of 17 different aquatic taxa are presented. No obvious differences in patterns of oviposition site selectivity were apparent between multiple sampling times or locations. For some common taxa, multivariate analyses revealed that measurements of rock size and local current speed were positively related to the likelihood of an egg mass being present. However there were no consistent relationships between the abundance of egg masses and either of these variables.3. The small‐scale distribution of egg masses on individual rocks revealed patterns in relation to surfaces that clearly differed as oviposition habitat, such as the underside, upstream and downstream surfaces. Presumably, these patterns are the result of small‐scale variation in flow conditions that characterise these particular rock surfaces.4. The results of this study indicate that the oviposition strategies of a number of aquatic taxa may be reasonably predictable based on measurable physical parameters. These findings have important implications for future studies wanting to incorporate the adult and egg life history stages of lotic insects into studies of population dynamics.
Local disturbance history affects patchiness of benthic river algae
Authors: Matthaei Christoph D. , Guggelberger Cornelia , Huber Harald 
Published: August 2003

Summary1. Recent research has shown that high‐flow events in streams leave a small‐scale mosaic of bed patches that have experienced scouring, sediment deposition (fill), or remained stable. Few studies have investigated if this ‘local disturbance history’ contributes to the patchy distribution of benthic organisms in streams and rivers.2. In the present research, we demonstrate that local disturbance history in a mid‐sized river can have both short‐ and long‐term effects on epilithic algae. Chains buried vertically in the substratum of the river bed (236 in a 800‐m reach) indicated that two floods (return periods ≤1 year) caused a mosaic of bed patches with different disturbance histories. Once after the first and twice after the second flood, we sampled epilithic algae (mainly diatoms) in replicate patches that had been scoured, filled, or remained stable during the respective event. Algal biomass and cell density per substratum area were determined.3. Three months after the first flood, algal biomass, total diatom density, diatom taxon richness, and densities of six of nine most common taxa were highest in fill patches. Six days after the second flood, biomass was highest in stable patches, indicating a refugium function of these patches. The refugium patches consisted of average‐sized stones, in contrast to previous studies of flood refugia for benthic algae in which these refugia were always large and/or immobile substrata. Four weeks after the second flood, diatoms tended to be most abundant in scour patches. With one exception, these differences between patch types could not be attributed to differences in local near‐bed current velocity or water depth.4. The effects of disturbance history were more complex than a simple refugium function of stable patches because algal patterns changed with time since the last disturbance, possibly depending on the successional state of the algal mats.
Breakdown of tussock grass in streams along a gradient of agricultural development in New Zealand
Authors: Niyogi Dev K. , Simon Kevin S. , Townsend Colin R. 
Published: August 2003

Summary 1. We measured the breakdown rate of tussock grass in 12 New Zealand streams in catchments that provided a gradient of agricultural development. We also examined the microbial and invertebrate communities associated with decomposing tussock litter.2. Pristine streams in the study had low concentrations of dissolved inorganic nitrogen (<10 μg L−1) and dissolved reactive phosphate (<3 μg L−1), whereas streams in the most developed catchments had high concentrations of nitrate (>2500 μg L−1) and phosphate (35 μg L−1), as well as greater amounts of suspended sediment and fine sediment covering the streambed.3. Breakdown rate and microbial respiration were significantly related across the sites, and both were positively related to concentrations of nitrate and phosphate. Fungal biomass, measured as ergosterol, was positively related to microbial respiration and was also higher at sites with higher concentrations of nutrients. Total and shredding invertebrates were most abundant at the sites with high nutrient concentrations, but abundance of shredding invertebrates was not significantly related to breakdown rate. Amphipods were the most common shredding invertebrate at most sites, but probably did not contribute greatly to high rates of breakdown in streams in agricultural catchments.4. With the exception of one site, nutrients from agricultural development appeared to have larger positive effects on litter breakdown than negative effects from sedimentation. Litter breakdown can serve as a functional measure of ecosystem health in streams, but caution should be exercised when a stress, such as land use, can have both positive (nutrients) and negative (sedimentation) effects.
A landscape approach to examining spatial patterns of limnological variables and long‐term environmental change in a southern Canadian lake district
Authors: Quinlan Roberto , Paterson Andrew M. , Hall Roland I. , Dillon Peter J. , Wilkinson Anna N. , Cumming Brian F. , Douglas Marianne S. V. , Smol John P. 
Published: August 2003

Summary1. We explored patterns of limnological variables (physical, chemical and biological) with relation to landscape position (expressed as lake order) in 86 study lakes located on shield bedrock in south‐central Ontario, Canada.2. Using anovas with lake order as the categorical variable, landscape position explained significant amounts of variation in major ion chemistry, physical and catchment characteristics, hypolimnetic oxygen, and community composition in algal (diatom, chrysophyte) and invertebrate (chironomid) assemblages preserved in surficial sediments. Several nutrient variables (TP, total phosphorus and TN, total nitrogen) and dissolved organic carbon did not have significant relationships with lake order.3. The strongest relationships with lake order (as a fraction of variation explained in anovas) included silica concentrations (r2 = 0.40) and SO4 (r2 = 0.29) concentrations, surface area (r2 = 0.50) and hypolimnetic oxygen (r2 = 0.29).4. Bedrock geology (carbonate metasedimentary versus non‐carbonate bedrock) had strong influences on spatial gradients of pH and major ion chemistry. It was difficult to separate geological influences from spatial influences on limnological variables in this study, as drainage patterns in the region are highly influenced by surface features of underlying geological formations because of the very thin glacial till or exposed bedrock that exists in most catchments.5. Patterns of limnological variables indicated that low‐order, headwater lakes had the lowest concentrations of major ions, and, from algal inferences of pH change, had been most susceptible to acidic deposition. High‐order, downstream lakes were larger and deeper, and had higher concentrations of hypolimnetic oxygen, indicating that optimal lake trout habitat was primarily located in high‐order lakes.6. Variance partitioning analyses indicated that lake order as a metric of landscape position explained comparable portions of community variation in algal and invertebrate assemblages compared with geographic position (latitude, longitude) and Cartesian coordinate position (e.g. x, y, x2, y2, etc.) metrics. Lake order explained more community variation in chironomid assemblages compared with other landscape metrics, possibly because of the strong relationships between lake order and lake morphometry variables.
Interspecific interference and the functional response of four species of carnivorous stoneflies
Authors: Elliott J.M. 
Published: August 2003

Summary1. A previous study compared the functional responses to their prey and intraspecific interference in mature larvae ofPerlodes microcephalus,Isoperla grammatica,Dinocras cephalotesandPerla bipunctata. The present study extends this work by assessing interspecific interference between pairs of these species in equal numbers (one, two or three larvae per species) to provide total predator densities of two, four or six larvae.Baetislarvae as prey were replaced as they were eaten, and their density per predator was varied between 20 and 200 larvae.2. The number of prey eaten by each competing species increased curvilinearly with prey density, the relationship being well described by a Type II model. Of the two constants in the model, handling time varied considerably between species, mean values being shortest forPerlodes,slightly higher forIsoperla,and much higher forDinocrasandPerla. It was not affected significantly either by predator density or the identity of the competing species.3. Attack rate also varied between species and decreased with predator density. This decrease was slight forPerlodes,and also forDinocrasandPerlain competition withIsoperla. The decrease inDinocrasandPerlawas similar to that for intraspecific interference.4. The decrease in attack rate was described by a convex curve forPerlodeswith the other three species and forDinocras/PerlawithIsoperla,but by a concave curve (negative power function) forIsoperlacompeting with the other three species, and for bothDinocrasandPerlain competition withPerlodes. Prey consumption also decreased with predator density, the severity of competition with different species reflecting that for attack rate.5. A comparison with previous results for intraspecific interference showed that the latter was dominant forPerlodesin all contests and forDinocrasorPerlacompeting withIsoperla,whilst interspecific interference dominated forIsoperlain all contests and forDinocrasandPerlacompeting withPerlodes. Both types of interference were applicable to competition betweenDinocrasandPerla.Isoperlawas the least, andPerlodesthe most, aggressive of the four species withDinocrasandPerlaintermediate.
Toxin production of cyanobacteria is increased by exposure to zooplankton
Authors: Jang Min‐Ho , Ha Kyong , Joo Gea‐Jae , Takamura Noriko 
Published: August 2003

Summary1. Cyanobacterial toxin production in response to direct and indirect zooplankton feeding activity was examined using four strains of Microcystis aeruginosa, of which three were previously reported to be toxic to zooplankton and one non‐toxic. Direct (Microcystis cultured with zooplankton) and indirect effects (Microcystis cultured with filtered zooplankton culture media, ZCMF) were tested for the zooplankton species, Moina macrocopa, Daphnia magna or D. pulex.2. With direct exposure to zooplankton, increased mass‐specific microcystin productions occurred in all Microcystis strains, with mean microcystin concentrations up to five times greater (61.5–177.3 μg g−1 dry cell) than the controls.3. With indirect exposure, mass‐specific microcystin production increased over controls in three strains of M. aeruginosa. Mean maximum concentrations of microcystin during the experiment were 92.6–125.7 μg g−1 dry cell.4. These results suggest that several strains of Microcystis aeruginosa increased toxin production in response to direct and indirect exposure to herbivorous zooplankton of several species, and support the hypothesis that this response is an induced defence mediated by the release of info‐chemicals from zooplankton.
Stay cool: habitat selection of a cyclopoid copepod in a north temperate oligotrophic lake
Authors: Makino Wataru , Yoshida Takehito , Sakano Hiroyuki , Ban Syuhei 
Published: August 2003

Summary1. We studied the vertical distributions of Cyclops cf. sibiricus in Lake Toya, a north temperate oligotrophic lake. During the winter circulation period, their distribution was vertically homogeneous both day and night. During the summer stratification period, C. cf. sibiricus stayed below the thermocline. Diel vertical migration (DVM) was pronounced in advanced developmental stages, although the upper limit of the migration became deeper as the thermocline gradually descended. This seasonal change was observed throughout the 4‐year study period, implying that thermal structure is the primary determinant of C. cf. sibiricus distribution.2. In a field experiment, C. cf. sibiricus incubated in the summer epilimnion, which most of the population never experience, developed faster and grew better than in their original habitat. We consider that trans‐thermocline DVM would not have evolved because of possible disadvantages such as the cost of migration offset the benefit observed in the field experiment. The rapid temperature change at the thermocline may act as a swimming‐cost estimator for the copepod.3. Low food availability in deep water during the summer stratification period seemed to determine the lower limit of C. cf. sibiricus distribution, and the copepod minimised the risks of predation by fish via DVM. These results suggest that C. cf. sibiricus modified their distribution seasonally to obtain maximum benefit in terms of individual fitness.
Ontogenetic shifts in habitat use by the endangered Roanoke logperch (Percina rex)
Authors: Rosenberger Amanda , Angermeier Paul L. 
Published: August 2003

Summary1. Conservation of the federally endangered Roanoke logperch (Percina rex, Jordan and Evermann) necessitates protection of habitat that is critical for all age classes. We examined habitat use patterns of individual logperch to determine: (1) if age classes of logperch in the Nottoway and Roanoke Rivers exhibit habitat selectivity, (2) if age classes differ in habitat use, and (3) if ontogenetic patterns of habitat use differ between the Roanoke and Nottoway river populations.2. In the summers of 2000 and 2001, we observed 17 young‐of‐year (YOY) logperch [<4 cm total length (TL)], 13 subadult logperch (4–8 cm TL), and 49 adult logperch (>8 cm TL) in the upper Roanoke River, and 40 subadult and 39 adult logperch in the Nottoway River, Virginia.3. All size classes of Roanoke logperch demonstrated habitat selectivity and logperch used a wide range of habitats in the Roanoke and Nottoway rivers during ontogeny. Habitat use by logperch varied among age classes and between rivers.4. In the Roanoke River, adult and subadult logperch primarily preferred run and riffle habitat, often over gravel substrate. Subadults were found in lower water velocities and slightly more embedded microhabitats than adults. YOY logperch were found in shallow, stagnant backwaters and secondary channels. In the Nottoway River, both adult and subadult logperch were found over sand and gravel in deep, low‐velocity pools and runs. Subadults were observed in slightly more silted, lower velocity habitat than adults. Shifts in habitat use were more distinct between age classes in the Roanoke River than the Nottoway River.5. Successful conservation of this species will involve sound understanding of spatial variation in habitat use over logperch life history and preservation of the ecological processes that preserve required habitat mosaics.
Conversion of leaf litter to secondary production by a shredding caddis‐fly
Authors: González J.M. , Graça M.A.S. 
Published: August 2003

Summary 1. The aim of this study was to estimate the amount of leaf litter ingested by the shredder caddis‐fly Sericostoma vittatum in a small stream in central Portugal. The study combined field data on population dynamics and laboratory experiments to determine the effect of temperature (9, 12, 15 and 18 °C), leaf species (Alnus glutinosa, Castanea sativa, Populus × canadensis and Quercus andegavensis) and animal mass on growth and consumption rates of the larvae.2. Sericostoma vittatum had two overlapping cohorts, each of which needed about 1 year to complete development. Mean annual density and biomass were 115 individuals m−2 and 83 mg m−2, respectively. Secondary production was 0.44 g m−2 year−1 and production/biomass ratio was 4.9–5 year−1.3. Consumption rates of larvae increased with temperature up to the optimal temperature for growth which varied between 13.7 and 16.7 °C depending on the diet.4. Consumption rate was positively related to larval mass but growth rate was negatively related with larval mass. Larvae fed on A. glutinosa and P. × canadensis had higher consumption and growth rates than those fed on C. sativa or Q. andegavensis.5. Annual leaf litter consumption by S. vittatum was estimated as 14–22 g m−2 depending on the diet. No relationship was observed between the amount of detritus consumed by the population of this caddis‐fly in the field and either water temperature, the stock of detritus on the stream bottom, or larval abundance. Instead, the temporal dynamics of leaf litter consumption by S. vittatum were controlled by its life history.6. This study highlights the influence of factors such as animal size and water temperature on the invertebrate energetics. Models explaining how these variables affect invertebrate production efficiency may be very important for obtaining accurate estimates of the role of shredders in the energy flow across stream ecosystems.
Predator‐induced phenotypic plasticity in the exotic cladoceran Daphnia lumholtzi
Authors: Dzialowski Andrew R. , Lennon Jay T. , O'Brien W.J. , Smith Val H. 
Published: August 2003

Summary1. The exotic cladoceran Daphnia lumholtzi has recently invaded freshwater systems throughout the United States. Daphnia lumholtzi possesses extravagant head spines that are longer than those found on any other North American Daphnia. These spines are effective at reducing predation from many of the predators that are native to newly invaded habitats; however, they are plastic both in nature and in laboratory cultures. The purpose of this experiment was to better understand what environmental cues induce and maintain these effective predator‐deterrent spines. We conducted life‐table experiments on individual D. lumholtzi grown in water conditioned with an invertebrate insect predator, Chaoborus punctipennis, and water conditioned with a vertebrate fish predator, Lepomis macrochirus.2. Daphnia lumholtzi exhibited morphological plasticity in response to kairomones released by both predators. However, direct exposure to predator kairomones during postembryonic development did not induce long spines in D. lumholtzi. In contrast, neonates produced from individuals exposed to Lepomis kairomones had significantly longer head and tail spines than neonates produced from control and Chaoborus individuals. These results suggest that there may be a maternal, or pre‐embryonic, effect of kairomone exposure on spine development in D. lumholtzi.3. Independent of these morphological shifts, D. lumholtzi also exhibited plasticity in life history characteristics in response to predator kairomones. For example, D. lumholtzi exhibited delayed reproduction in response to Chaoborus kairomones, and significantly more individuals produced resting eggs, or ephippia, in the presence of Lepomis kairomones.
In situexperiments on the effects of increased sediment loads on littoral rocky shore communities in Lake Tanganyika, East Africa
Authors: Donohue Ian , Verheyen Erik , Irvine Kenneth 
Published: August 2003

Summary1. Twoin situexperiments investigated the responses to artificially increased sediment loads of the gastropod and fish communities, and of the whole benthos, of the rocky shores of Lake Tanganyika. Sediments were emptied once onto randomly selected quadrats using SCUBA, with control quadrats receiving no addition of sediment. Quadrats were monitored up to 6 months after sediment addition.2. While the abundance ofLavigeria grandis(Mollusca; Gastropoda) was reduced greatly by the addition of sediment, low abundance and biomass of the whole gastropod community on sediment‐impacted quadrats 6 months after sediment addition suggests more general impacts of inundation in the longer term.3. Benthic invertebrate communities inundated by sediment had significantly fewer individuals and numbers of taxa than control communities. No significant community recovery was recorded on sediment‐impacted quadrats within the timescale of the experiment. A short‐term period of high turbidity brought about by the emptying of sediments onto sediment‐impacted quadrats also caused severe decreases in benthic invertebrate abundance on controls 10 days after sediment addition. This suggests that even short‐term pulses of sediment may have significant detrimental effects on littoral communities.4. Although significant impacts of sediment on fish community dynamics were found, and a significant reduction in the number of benthic algivorous species was recorded immediately after sediment addition, littoral fish communities showed strong resistance overall to the addition of sediments. This apparent resistance, however, may be a consequence of the small scale at which the experiment took place. Littoral fish communities were also shown to be more dynamic than indicated previously.