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1.
Coosen J. Twisk F. van der Tol M. W. M. Lambeck R. H. D. van Stralen M. R. Meire P. M. 《Hydrobiologia》1994,282(1):381-395
The edible cockle (Cerastoderma edule L.) is a dominant suspension feeder in the Oosterschelde, a 351 km2 tidal bay in the SW Netherlands. To establish its role in the benthic foodweb, and to assess the impact of human activities, data on density, age composition, biomass and growth were collected from several tidal flats in the Oosterschelde between 1980 and 1990.To estimate the overall biomass development of the cockle, a simple model was used, in which three growing seasons are defined for the cockle population. A standard individual growth curve was constructed. A negative exponential mortality function was assumed to estimate the number of recruits. By combining the estimated number of recruits, the estimated specific mortality rate and the standard individual growth curve, numbers and biomass of each age group in the Oosterschelde population were estimated. Average biomass (including shell organics) per m2 of tidal flat in August varied from 140 g AFDW in 1980 to 21 g AFDW in 1989, implying a total cockle stock on all tidal flats of 19 170 to 2350 tonnes AFDW (72 × 103 to 9 × 103 tonnes flesh), respectively.A comparison of results from field surveys and the reconstructed stock estimations showed large deviations. However, an uncertainty analysis performed on the model showed that most field data fitted within the minimum and maximum biomass calculated.Total biomass is largely dependent on the strength of certain year classes. In this respect, the year classes 1979, 1982, and 1985 were good. Effects of the construction of the storm-surge barrier and the compartmentalisation dams could not be demonstrated.The year-to-year variation in cockle stocks, assessed in the way described in this paper should be regarded as relative, because a systematic survey of the intertidal flats was not performed every year, but population dynamics from selected stations were used instead. 相似文献
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Moore H.H. Niering W.A. Marsicano L.J. Dowdell M. 《Wetlands Ecology and Management》1999,7(4):177-191
Changes in hydrology, water quality and vegetation were evaluated in four palustrine emergent wetland pairs, each including created and reference sites. Located along interstate highways, they were initially sampled in 1988 (Confer and Niering, 1992) and again in 1996. Overall, created sites showed significant decreases in open water and water depth between 1989 and 1996 compared to more stable conditions in reference sites. Total nitrogen was generally higher in created sites compared to reference sites, as was specific conductivity, with chloride levels exceeding 800 mg/L, apparently related to road salt. Emergent plant cover increased from 30 to 39% at three created sites, and decreased at a fourth, whereas reference sites remained relatively stable. Wetland species richness also increased from 31 to 39 species at created sites and 35 to 42 species at reference wetlands between the surveys. By 1996 there was an increase in invasive species, particularly Phragmites australis (common reed) and Lythrum salicaria (purple loosestrife). Phragmites increased from <1 to 15% at created sites, while Lythrum increased at one reference site from <1 to 16%. Typha latifolia (common cattail), dominant in the created wetlands in 1988, decreased from 16 to 5% while Typha angustifolia (narrow-leaved cattail) increased from 2 to 10%. At two created sites experiencing increased sedimentation, Phragmites is now dominant or co-dominant with Typha spp., whereas Carex stricta (tussock sedge) and T. latifolia continue to dominate at reference sites. At the one created, permanent flow-through-hydrology wetland, a three-fold decrease in T. latifolia and an eight-fold increase in Phragmites cover have occurred, the latter correlated with sedimentation from road culverts. Increases in alien or invasive species such as Phragmites and Lythrum can serve as indicators of wetland disturbance. Although these created wetlands provide the services of sediment retention, flood storage, and wildlife habitat, a greater range of wetland functions should be possible by constructing two-tiered systems that remove excess sediments and nutrients upstream of the wetland designed to compensate for wetland loss. 相似文献
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FrontiersofProteinStructureandFunctionMarch2631,2000SanFrancisco,California,USADr.RobertGennisDept.ofBiochemistry,UniversityofIllinois600SouthMathewsAvenue,Urbana,IL618013364,USATel:+12173339075;Fax:+12172443186;Email:rgennis@uiuc.edu13thInterna… 相似文献
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Acidification of lakes in Šumava (Bohemia) and in the High Tatra Mountains (Slovakia) 总被引:5,自引:5,他引:0
Acidification of lakes takes place when pH of rainwater is less than 4.5 and the catchments lie on sensitive geology. Both
conditions are met for most lakes in Bohemia and Slovakia. Since 1978 we have studied mountain lakes in the Sumava and in
the High Tatra Mountains.
In Šumava the three lakes under study are of glacial origin. The catchments are small, with steep sides covered by spruce.
The bedrocks are biotite-rich paragneiss, together with gneiss, quartzite and granite. In summer 1936 surface pH was 5.7–6.9
in the Lake Čertovo and 6.9–7.0 in the Lake Černé. Now the pH values are 4.3–4.8 in the two lakes and in the Lake Prášilské
as well. Old reports on zooplankton are from the years 1871, 1892–96, 1935–37, 1947 and 1960. Since 1979 we have not found
any planktonic Crustacea in the lakes Černé and Čertovo. Lake Prášilské is inhabited by Daphnia longispina and Cyclops abyssorum. In July 1989 the pH values were 4.4, 4.7 and 4.7, concentrations of labile monomeric Al were 0.83, 0.68 and 0.24 mg l-1 in the lakes Čertovo, Černé and Prašilské, respectively. High levels of toxic Al compounds might be responsible for the extinction
of planktonic Crustacea in the lakes Čertovo and Černé. All the three lakes are void of fish at present.
In the High Tatra Mts. we examined more than 40 lakes above timberline in altitudes 1612–2145 m. They are all clearwater,
naturally fishless lakes. The bedrock is granite. Owing to different levels of calcium the lakes are now in different stages
of acidification. According to recent changes in the zooplankton they can be divided into three groups: (1) Species composition
of planktonic Crustacea has not changed. (2) Planktonic Crustacea were present until 1973 but are absent now. (3) From the
original species of Crustacea only Chydorus sphaericus is present.
The three groups are well separated along the gradients of calcium, ANC and pH. They can be identified with the Henriksen's
bicarbonate (our group 1), intermediate (our group 2) and acid (our group 3) lakes. We suppose that in the process of acidification
the lakes of the group (2) have been shifted from oligotrophy to ultraoligotrophy. 相似文献
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The syncytium formed by Utricularia is extremely unusual and perhaps unique among angiosperm syncytia. All typical plant syncytia (articulated laticifers, amoeboid tapetum, the nucellar plasmodium of river weeds) are formed only by fusion of sporophytic cells which possess the same genetic material, unlike Utricularia in which the syncytium possesses nuclei from two different sources: cells of maternal sporophytic nutritive tissue and endosperm haustorium (both maternal and paternal genetic material). How is this kind of syncytium formed and organized and is it similar to other plant syncytial structures? We used light and electron microscopy to reconstruct the step-by-step development of the Utricularia syncytia. The syncytia of Utricularia developed through heterotypic cell fusion involving the digestion of the cell wall, and finally, heterokaryotic multinucleate structures were formed, which possessed different-sized nuclei that were not regularly arranged in the cytoplasm. We showed that these syncytia were characterized by hypertrophy of nuclei, abundant endoplasmic reticulum and organelles, and the occurrence of wall ingrowths. All these characters testify to high activity and may confirm the nutritive and transport functions of the syncytium for the developing embryo. In Utricularia, the formation of the syncytium provides an economical way to redistribute cell components and release nutrients from the digested cell walls, which can now be used for the embryo, and finally to create a large surface for the exchange of nutrients between the placenta and endosperm. 相似文献
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Ariane Payne Maria Laura Boschiroli Eric Gueneau Jean Louis Moyen Thomas Rambaud Barbara Dufour Emmanuelle Gilot-Fromont Jean Hars 《European Journal of Wildlife Research》2013,59(3):331-339
In France, several surveillance programmes have been carried out to monitor the presence of bovine tuberculosis (bTB) in badgers in regions where cattle or wildlife show high bTB prevalence (Seine-Maritime, Côte d’Or, Dordogne/Charente). Diagnostic methods include post-mortem examination, polymerase chain reaction (PCR) and/or microbiological culture. The frequency of visible lesions was significantly higher in Dordogne/Charente (14/283, 4.9 %) than in Côte d’Or (19/1146, 1.7 %) and Seine-Maritime (2/160, 1.25 %) (Fisher’s exact test, p?<?0.001). Lesions were mainly located in cephalic and thoracic lymph nodes with one badger showing generalised tuberculosis. Near infected cattle farms or pastures, Mycobacterium bovis was detected using the culture method in roughly 1 % (1/103) of the badgers sampled in Seine-Maritime and in 5.6 % (49/878) of the badgers sampled in Côte d’Or. In Dordogne/Charente, the prevalence determined by PCR was 13.3 % (29/218). M. bovis was not found in badgers trapped in areas where there are no infected cattle. Spoligotyping and multiple locus variable number tandem repeat analysis showed that all M. bovis strains isolated from badgers were of the same genotype as those isolated from cattle in the vicinity, demonstrating an epidemiological link between both species. These are the first cases of bTB in badgers reported in France. Further surveys and research are needed to investigate the role badgers play in the epidemiology of bTB. 相似文献
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DCMU inhibits in vivo nitrate reduction in illuminated barley (C(3)) leaves but not in maize (C(4)): a new mechanism for the role of light? 总被引:1,自引:0,他引:1
The leaves of C(4) plants possess a superior metabolic efficiency not only in terms of photosynthetic carbon assimilation, but also in terms of inorganic nitrogen assimilation, when compared to C(3)plants. In vivo nitrate assimilation efficiency of leaves is dependent on light, but the obligatory presence of light has been debated and its role remains confounded. This problem has not been addressed from the standpoint of the C(3) vs. C(4) nature of the species investigated, which may actually hold the key to resolve the controversy. Here, we present the first report providing evidence for differential photo-regulation of leaf nitrate reduction in barley ( Hordeum vulgare L.) vs. maize ( Zea mays L.) plants, which may help explain the superior nitrogen-use efficiency (and hence superior productivity) of maize plants. The novel finding that carbohydrate-depleted maize leaves were able to reduce nitrate when photosynthesis was inhibited by 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea (DCMU) in the presence of light, raises a very important question about the possibilities of a new photo-regulatory mechanism for supporting nitrate reduction in maize leaves operating independently of photosynthetic carbon dioxide fixation. On the other hand, leaves of barley could not carry out any in vivo nitrate assimilation, whatsoever, under these conditions. We find another fundamental difference between the two species in terms of differential regulation of nitrate reductase (NR; EC 1.6.6.1). In barley leaves, NR activity and activation state remained unaffected due to DCMU, but in sharp contrast, both were appreciably upregulated in maize. Collectively, the results indicate that enzyme capacity is not limiting for nitrate reduction in leaves, as the NR activity was higher in barley than in maize. The maize leaves may have had a selective advantage due to C(4) morphology/metabolism in terms of maintaining a better reductant/carbon skeleton supply for nitrate reduction. 相似文献
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Summary Weeds and among themAmbrosia are probably the most important vascular plants related to pollinosis in Hungary. Sampling was carried out in central (Budapest) and in southern (Paks, Szeged) Hungary. The results of two years (1989–1990) of aerobiological study onAmbrosia airborne pollen are reported. The highest percentage of airborne pollen was found in the mid-August to mid-September period, having a good correlation with clinical data on pollinosis. The implications of these results are considered in the context of forecasting and prevention of seasonal ragweed pollinosis. 相似文献
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For the years 1972–1981, 7 333 isolates of dermatophytes belonging to 14 species were obtained from glabrous skin (32%), feet (28%), groin (19%), scalp (8%), toenails (7%), fingernails (3%) and beard (1%)., T. rubrum represented 50% of all the isolates and was the most frequent species on glabrous skin, groin and nails. T. mentagrophytes (24%) was mainly obtained from the feet, E. floccosum (9%) from the groin and T. megninii (4%) from uncovered areas of the skin, fingernail and beard. These 4 species predominated in men. M. canis was the commonest agent on the scalp and in children up to 11 years.
T. violaceum, previously the main cause of tinea capitis, and T. tonsurans have been decreasing for the period of this study, just as T. schoenleinii for the years 1962–71.The rising prevalence of T. rubrum was observed since 1962. In the whole it seems stable after 1969, but the analysis of the main sites involved shows that in the glabrous skin this species increased from 1962 to 1974; in the groin it was gone up from 30% during 1962–1965, to 64% in the years 1969–1971; in the feet the evolution was slower and only in 1980 T. rubrum became more frequent than T. mentagrophytes.The increase in certain species, whereas others become rare, lacks a satisfactory explanation.
Résumé Depuis 1972 jusqu'à 1981, 7 333 isolements de dermatophytes concernant 14 espèces ont été obtenus de la peau glabre (32%), des pieds (28%), des plis inguinaux (19%), des ongles des orteils (7%), des ongles des mains (3%) et de la barde (1%). T. rubrum a réprésenté 50% de tous les isolements, étant l'espèce la plus fréquente dans la peau glabre, aux plis inguinaux et dans les ongles. T. mentagrophytes (24%) a été isolé surtout des pieds; E.floccosum (9%) des plis inguinaux; et T. megninii (4%) des régions découvertes de la peau, des ongles de la main et de la barbe. Ces 4 espèces ont prédominé chez des adultes du sexe masculin. M. canis a été l'agent le plus commun dans le cuir chevelu et chez des enfants jusqu'à 11 ans. T. violaceum (auparavant la cause principale des teignes du cuir chevelu) et T. tonsurans sont devenus beaucoup moins fréquents pendant cette étude, comme d'ailleurs T. schoenleinii était devenu rare au cours d'une enquête anterieur (1962–1971).La prévalence de T. rubrum s'est beaucoup elevée dès 1962. Dans l'ensemble, elle parait stabilisée depuis 1969, mais l'analyse des principales localisations de la maladie démontre que dans la peau glabre cette espèce a augmenté depuis 1962 jusqu'à 1974; aux plis inguinaux elle a changé de 30% en 1962–1965 pour 64% en 1969–1971; aux pieds l'évolution a été moins rapide et seulement dès 1980 T. rubrum est devenu plus fréquent que T. mentagrophytes.L'augmentation de certaines espèces tandis que d'autres deviennent rares n'a pas trouvée une interpretation satisfaisante.相似文献
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Lene H. Petersen Shelby L. Needham Mark L. Burleson Matthew D. Overturf Duane B. Huggett 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2013,164(2):291-300
Currently, we have little information concerning the involvement of β3-adrenergic receptors (AR) in cardiovascular regulation in fishes. The goal of this study was to investigate the effect of β3-AR ligands on in vivo cardiovascular function in larval and adult rainbow trout (Oncorhynchus mykiss). In adult fish, injection of BRL37344 (β3-AR agonist) resulted in an increase in heart rate (fH) (~ 31%) while stroke volume (Sv) was reduced (? 25.9%). Injection of SR59230A (β3-AR antagonist) and propranolol (β1/β2-AR antagonist) resulted in increases in dorsal aorta blood pressure (PDA) with differing effect on cardiac variables (fH and Sv). To confirm specificity of the results, BRL37344 was injected following sequential injections of phentolamine (α1-AR antagonist), atropine (muscarinic antagonist), propranolol and SR59230A. While phentolamine had no effect on BRL37344, atropine completely abolished the influence of BRL37344 on fH, Sv and cardiac output (Q). In larval trout, BRL37344 (10 and 100 μM) induced a significant concentration-dependent increase in fH while SR59230A (1 and 10 μM) and propranolol (1 and 10 μM) separately caused a significant concentration-dependent decrease. These data suggest that β3-ARs have an important role in regulation of cardiovascular function, and provide evidence for a potential interaction between muscarinic and adrenergic receptors in rainbow trout. 相似文献
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An analysis of long-term changes in abundance of hibernating bats as revealed from the annual monitoring programme conducted
in four mountain regions of the Western Carpathians (Muránska planina Mts, Revúcka vrchovina Mts, Slovensky kras Mts, Štiavnické
vrchy Mts) during the period 1992–2009 is providing in the paper. Data from 52 hibernacula were analysed. Among 18 bat species
recorded, an apparent population increase of three most abundant thermophilous and originally cave dwelling species of bats,
Rhinolophus hipposideros, R. ferrumequinum, Myotis myotis, was observed. In other bat species (e.g., R. euryale, M. emarginatus, M. mystacinus, M. dasycneme, Barbastella barbastellus), population trends could not be detected and because of data scarcity, they should be evaluated from more extensive datasets
obtained from a wide range of hibernacula or from a completely different type of evidence. 相似文献
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In homeothermic vertebrates inhabiting temperate latitudes, it is clear that the seasonal changes in daylength are decoded by the master circadian clock, which through secondary messengers (like pineal melatonin secretion) entrains rhythmic physiology to local conditions. In contrast, the entrainment and neuroendocrine regulation of rhythmic physiology in temperate teleosts is not as clear, primarily due to the lack of understanding of the clock gene system in these species. In this study, we analyzed the diel expression of the clock‐genes in brains of Atlantic salmon, a species that is both highly photoperiodic and displays robust clock‐controlled behavior. Atlantic salmon parr were acclimated to either long‐day (LD) or short‐day (SD) photoperiods for one month and thereafter sampled at 4 h intervals over a 24 h cycle. Clock, Bmal1, Per2, and Cry2 were all actively expressed in salmon brain homogenates and, with the exception of Per2, all displayed rhythmic expression under SD photoperiods that parallels that reported in zebrafish. Interestingly, daylength significantly altered the mRNA expression of all clock genes studied, with Clock, Bmal1, and Per2 all becoming arrhythmic under the LD compared to SD photoperiod, while Cry2 expression was phase delayed under LD. It is thus proposed that the clock‐gene system is actively expressed in Atlantic salmon, and, furthermore, as has been reported in homeothermic vertebrates, it appears that clock expression is daylength‐dependent. 相似文献
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Klaas J. Hellingwerf Pieter W. Postma Jan Tommassen Hans V. Westerhoff 《FEMS microbiology reviews》1995,16(4):309-321
Abstract: The molecular basis of many forms of signal transfer in living organisms is provided via the transient phosphorylation of regulatory proteins by transfer of phosphoryl groups between these proteins. The dominant form of signal transduction in prokaryotic microorganisms proceeds via so-called two-component regulatory systems. These systems constitute phosphoryl transfer pathways, consisting of two or more components. Most of these pathways are linear, but some converge and some are divergent. The molecular properties of some of the well-characterised representatives of two-component systems comply with the requirements to be put upon the elements of a neural network: they function as logical operators and show the phenomenon of autoamplification. Because there are many phosphoryl transfer pathways in parallel and because there also appears to be cross-talk between these pathways, the total of all two-component regulatory systems in a single prokaryotic cell may show the typical characteristics fo a 'phospho-neural network'. This may wel lead to signal amplification, associative responses and memory effects, characteristics which are typical for neural networks. One of the main challenges in molecular microbial physiology is to determine the extent of the connectivity of the constituting elements of this presumed 'phospho-neural network', and to outline the extent of intelligence-like behaviour this network can generate. Escherichia coli is the organism of choice for this characterization. 相似文献