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1.
MacNeil C Fielding NJ Hume KD Dick JT Elwood RW Hatcher MJ Dunn AM 《International journal for parasitology》2003,33(1):57-64
In a river survey, Gammarus pulex amphipods both unparasitised and parasitised with the acanthocephalan Echinorhynchus truttae were distributed similarly with respect to flow regimen, tending to be more abundant in faster, shallower, riffle patches. However, there was a higher prevalence of parasitism in faster, shallower areas than in slower, deeper areas and abundance correlated with macrophyte coverage for unparasitised but not parasitised amphipods, indicating subtle differences in habitat usage. A laboratory 'patch' simulation indicated that parasitism influenced micro-distribution. There were higher proportions of unparasitised amphipods in/under stone substrates and within weed. In contrast, there were higher proportions of parasitised amphipods in the water column and at the water surface. As the experiment progressed, unparasitised but not parasitised amphipod habitat usage shifted from those micro-habitats above the substrate and in the water column to those in/under the substrates. Experiments also demonstrated that parasitised amphipods were more active and had a greater preference for illumination. Previous studies of the effects of acanthocephalan parasitism of amphipod hosts have focussed on how drift behaviour is altered, now we show that subtle differences in micro-habitat usage could translate to greatly increased vulnerability to fish predation. We discuss how aggregation of parasitised individuals within specific habitats could promote parasite transmission. 相似文献
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D. A. WRIGHT 《Freshwater Biology》1980,10(6):571-579
SUMMARY. Adult Gammarus pulex lose about 42% body calcium into solution over a 2–3-day period preceding the moult. A further 54% body calcium is lost with the exuviae, leaving c . 4% in the newly moulted animal.
Nearly all of the body calcium in a stage A (post moult) animal is contained in the hepatopancreas and a transient increase in the calcium content of this tissue is seen in some individuals. The haemolymph calcium compartment is heavily depleted at this stage. In stage B animals the hepatopancreas calcium level has returned to, or even fallen below, the intermoult level while the haemolymph calcium concentration remains lower than in intermoult animals.
Animals switch from a strongly negative calcium balance to a state of rapid calcium uptake immediately following moult. Uptake at 10°C proceeds at a rate of between 3 and 10 μmol g−1 h−1 depending on the calcium concentration of the external medium. The lower rate is found in starved animals in 0.1 mM calcium and this concentration is probably close to a minimum for the satisfactory restoration of body calcium. Recalcification is completed in 10–14 days in 0.1 mM calcium and is apparently enhanced by the presence of food in the form of a portion of oak leaf together with the cast exuviae. In 1.0 mM calcium the recalcification period is shortened to 3–4 days. This is considerably longer than the time recorded for French populations of this species (Vincent, 1969), although reasons for this are offered. 相似文献
Nearly all of the body calcium in a stage A (post moult) animal is contained in the hepatopancreas and a transient increase in the calcium content of this tissue is seen in some individuals. The haemolymph calcium compartment is heavily depleted at this stage. In stage B animals the hepatopancreas calcium level has returned to, or even fallen below, the intermoult level while the haemolymph calcium concentration remains lower than in intermoult animals.
Animals switch from a strongly negative calcium balance to a state of rapid calcium uptake immediately following moult. Uptake at 10°C proceeds at a rate of between 3 and 10 μmol g
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K. G. Andersson C. Brönmark J. Herrmann B. Malmqvist C. Otto P. Sjörström 《Hydrobiologia》1986,133(3):209-215
Introduction of sculpins into a stream previously devoid of these predators significantly reduced drift rate of Gammarus pulex. The drift of insect larvae was not affected. High amounts of exudates after implantation of sculpins were probably responsible for the low number of drifting G. pulex specimens. Laboratory experiments confirmed reduced locomotory activity of G. pulex when exposed to caged sculpins, an observation that excludes reduced drift activity as a result only of predation.The average size of drifting G. pulex specimens was larger during the night than during the day. This result is in accordance with the hypothesis that large individuals should, in relation to small ones, turn nocturnal because of greater predation risk during daytime. Presence of sculpins did not alter the size composition of drifting G. pulex. 相似文献
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We characterized the first microsatellite markers for Gammarus fossarum. Eight loci gave satisfactory amplification patterns in two stream populations (Southern France) with number of alleles ranging from 2 to 10 and expected heterozygosity from 0.076 to 0.857. We performed cross-amplification in two closely related gammarid species, Gammarus pulex and Gammarus orinos. Among the eight tested microsatellite loci, four correctly amplified in G. pulex and three in G. orinos. 相似文献
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Acanthocephalan parasites are known to alter the reproductive biology and physiology of their hosts in various ways. In this study we investigated the influence of two acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on the fecundity and pairing success of female Gammarus pulex. The results show that P. laevis and P. minutus affect female intermediate host reproduction in different ways. Females infected with P. minutus were totally castrated, whereas those infected with P. laevis only showed reduced fecundity. The oocytes of P. laevis-infected females showed a similar structure to those of uninfected females, although infected females had a higher proportion of oocytes that had failed to reach complete maturity. In comparison, the oocytes of P. minutus-infected females demonstrate a clearly altered structure that suggests a major disruption to the process of vitellogenesis. In the field, males paired more frequently with uninfected females than with infected ones, and is a stronger effect for P. minutus-infected females than P. laevis-infected females. We suggest that the difference in pairing success of P. minutus-infected and P. laevis-infected females is a direct result of the different effects that the two parasites have on female fecundity. 相似文献
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Life-cycle, drift and production of Gammarus pulex L. (Amphipoda) in a Danish spring 总被引:2,自引:0,他引:2
SUMMARY. Gammarus pulex L. was studied at three sites in a Danish spring. Breeding took place during the summer and therefore cohorts could be followed. Sexual maturity was not reached until the next summer and maximum age appeared to be two years.
Changes in population size differed between stations and was tentatively related to differences in drift and numbers of predators. Generally the drift was non-selective between cohorts and within cohorts.
Yearly production estimated from production curves was 2.6 g dry weight m−2 (the young cohort) and 1.2 g dry weight (the old cohort) at Station 1. The respective P / ratios were 3.35 and 1.22. Production of the youngest cohort at the three stations in the period September-May was 0.9–1.3 g m−2 and P / ratios were 2.14–2.31. Total yearly production at the three stations was estimated at 4–7 g dry weight m−2 . 相似文献
Changes in population size differed between stations and was tentatively related to differences in drift and numbers of predators. Generally the drift was non-selective between cohorts and within cohorts.
Yearly production estimated from production curves was 2.6 g dry weight m
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The mutual predatory behaviour between Gammarus pulex (Linnaeus, 1758) and Gammarus duebeni celticus (Stock & Pinkster, 1970) is described. The implications of the predatory nature of these species are discussed in terms of the feeding ecology of Gammarus and other amphipods. Predation rates by males on moulted congeneric females are assessed and compared. When males are present at the moult of a congeneric female, 100%of females are eaten in both species/sex combinations. When females are allowed to recover from moulting prior to presentation to a congeneric male, predation rates are significantly reduced in both species. However, significantly more G. d. celticus females are eaten by G. pulex males compared with the reciprocal situation. The predatory 'clumping' behaviour of both species is described and shown to be a form of feeding frenzy upon congenerics. Clumping behaviour also results in significantly higher rates of congeneric predation on G. d. celticus females than on G. pulex females. Support is thus given to the hypothesis that differential predation by males on moulted females may be the primary mechanism by which the introduced G. pulex has displaced the native Irish species G. d. celticus . The implications of amphipod congeneric predation are discussed in terms of observed patterns of interspecific coexistence and exclusion. 相似文献
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Gammarus pulex and Asellus aquaticus generally occupy different zones in rivers; the former occurs in upper reaches but is replaced by the latter in lower reaches. Microdistribution and life-history patterns of G. pulex and A. aquaticus in sympatry and allopatry, were analyzed. Both species exhibited similar patterns of microhabitat selection, with larger individuals associated predominantly with large-sized substratum particles, and juveniles with weed. Coexisting populations of G. pulex and A. aquaticus had similar densities and population dynamics. Within each species, differences in population dynamics of allopatric and sympatric populations were observed. Although variation in population dynamics of G. pulex may be explained in terms of competition between the two species, the evidence is weak and equivocal. Differences in the dynamics of the two A. aquaticus populations were possibly a consequence of coal-mine and organic pollution, reducing the survival of offspring in the allopatric population. 相似文献
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Andy P. Dedecker Peter L. M. Goethals Tom D’heygere Niels De Pauw 《Aquatic Ecology》2006,40(2):249-261
Ecological models can act as interesting tools to support decision-making in river restoration management. In particular models which are capable of predicting the habitat requirements of species are of considerable importance to ensure that the planned actions have the desired effects on the aquatic ecosystem. To this end, Artificial Neural Network (ANN) models were tested and optimized for the prediction of the habitat suitability for Gammarus pulex, a relevant indicator species in water quality assessment. Although ANN models are in general quite robust with a rather high predictive reliability, the model performance had to be increased with regard to simulations for river restoration management. In particular, it has been shown that spatial and temporal expert-rules could possibly be included. Migration dynamics of downstream drift and upstream migration of the organisms and migration barriers along the river (weirs, culverted river sections,␣...) might indeed deliver important additional information on the effectiveness of the restoration plans, and also on the timing of the expected effects. In this context, an additional in-stream migration model for Gammarus pulex was developed. This migration model, implemented in a Geographical Information System (GIS), has been used to simulate a practical river restoration scenario for a river in Flanders, Belgium. The case study illustrated that the removal of a weir, at a particular site, resulted in the improvement of the habitat suitability for Gammarus pulex. The ANN models predicted that after restoration the habitat was suitable again for Gammarus pulex. The migration model indicated that the restored parts of the river would be recolonized within about 2 months. In this way, decision makers can have an idea whether and when a restoration option will have a desired effect. 相似文献
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SUMMARY. 1. The toxicity to the freshwater amphipod Gammarus pulex (L.) of soft water (pH6.0) with three concentrations of XAD-extracted aquatic humus was treated in the laboratory.
2. Exposure to pH6.0 water without humus added resulted in 92% mortality after 3 weeks. Humus, added at concentrations of 7 and 20 g Cm3 , decreased the mortality to 80% and 64% in the same period.
3. Surviving animals kept at pH6.0 had a lower growth rate, lower food conversion efficiency and higher body water content than animals kept at pH 7.3.
4. Humus had no significant effects on growth, food conversion or body composition of G. pulex kept at pH 6.0. However, there was a tendency for growth and food conversion to increase, and for body water content to decrease with increased humus concentration. The effects of humus on growth and food conversion of G. pulex observed in this study do not support the contention that humus acts as a free coupler to lower metabolic efficiency. On the contrary, humus tended to benefit food conversion.
5. It is suggested that low concentrations of humus can be directly beneficial to organisms in acidified water in ways other than by complexing toxic metals. 相似文献
2. Exposure to pH6.0 water without humus added resulted in 92% mortality after 3 weeks. Humus, added at concentrations of 7 and 20 g Cm
3. Surviving animals kept at pH6.0 had a lower growth rate, lower food conversion efficiency and higher body water content than animals kept at pH 7.3.
4. Humus had no significant effects on growth, food conversion or body composition of G. pulex kept at pH 6.0. However, there was a tendency for growth and food conversion to increase, and for body water content to decrease with increased humus concentration. The effects of humus on growth and food conversion of G. pulex observed in this study do not support the contention that humus acts as a free coupler to lower metabolic efficiency. On the contrary, humus tended to benefit food conversion.
5. It is suggested that low concentrations of humus can be directly beneficial to organisms in acidified water in ways other than by complexing toxic metals. 相似文献
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Gut passage times in Gammarus pulex (Crustacea, Amphipoda) were calculated by counting and measuring voided faecal pellets. Following feeding on elm leaves conditioned in a stream, or summer fine detritus from the same source, calculated gut passage times were usually short, about 2 h or less at 15 °C. Using harder oak and beech leaves, not previously conditioned in the stream, apparent gut passage times were much longer, 8–48 h, but since intermittent feeding occurred these figures are not comparable to the others.In connection with summer feeding of the animal in the stream, the microbiological status of the fine detritus there was studied. It contained fungal hyphae, which were mostly empty, viable fungal spores of terrestrial derivation, and bacteria, all largely carried on fragments of vascular plant tissues. In experiments, such fungal spores (of Aureobasidium pullulans and of Mucor sp.), incorporated into fine detritus, were not digested by the animal. The bacterium Bacillus cereus was present in the fine detritus and when the latter was consumed it survived passage through the gut of the animal. Using B. cereus as a proportion marker it was concluded that other unicellular bacteria in the fine detritus were not digested either. In other experiments, not immediately related to the summer season, nutrient extraction by the animal from hyphae of the fungus Nectria lugdunensis was examined; it probably occurs through sub-microscopic pores connecting the cells. This mode of extraction may apply when the animal consumes vascular plant tissues. 相似文献
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Exposure to contaminants below lethal concentrations may affect the performance of organisms, resulting in measurable differences in behavior. We measured the response of the benthic invertebrate Gammarus pulex (Crustacea, Amphipoda) to sublethal concentrations of three pharmaceuticals, fluoxetine, ibuprofen and carbamazepine, and the cationic surfactant cetyltrimethylammonium bromide (CTAB). Responses in behavior during exposure were analyzed using the multivariate method of Principal Response Curves (PRC). The PRC results show that exposure to low pharmaceutical concentrations (range 1–100 ng/l) resulted in increased ventilation, whereas exposure to control or to high concentrations (1 μ g/l–1 mg/L) resulted in increased locomotion. Exposure to CTAB resulted in decreased locomotion and increased ventilation at increasing concentrations. The results of our experiments indicate that increased ventilation can be used as a general sign of stress, but not necessarily an early warning signal for mortality. 相似文献
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This study examines the cannibalistic behaviour of the freshwater amphipods Gammarus duebeni celticus Stock & Pinkster, 1970 and G. pulex (L., 1758). In the first experiment, interactions were staged among all combinations of single adult males, single adult females, adults in the precopulatory mate-guarding phase and juveniles. Cannibalism by inter-moult individuals on newly moulted conspecifics occurred in all interaction categories in both species. Gammarus d. celticus , however, were significantly more cannibalistic than G. pulex. Cannibalism between and within sex and size categories (males > females > juveniles) was facilitated by the vulnerability of individuals at moult. Individuals of smaller size categories, however, did not cannibalize newly moulted conspecifics of larger size categories. Males were less cannibalistic on newly moulted females than on newly moulted males and juveniles and, when in the precopulatory condition, appeared to defend females from cannibalistic attacks. In a second experiment, stream conditions were simulated in the laboratory and replicated populations monitored for nine weeks. High levels of cannibalism, and the species and sex differences in cannibalism identified in the first experiment, were confirmed under these heterogeneous conditions. Cannibalism by males on their newly moulted female mating partners, termed 'reversed' sexual cannibalism, was further investigated. When males were deprived of foraging opportunities, cannibalism of precopulatory partners was significantly more frequent. The occurrence of 'reversed' sexual cannibalism is thus interpreted as a conflict between motivation to feed and motivation to mate. 相似文献