Food preference of freshwater invertebrates: comparing fresh and decomposed angiosperm and a filamentous alga

1. Fresh and decomposed Mougeotia sp. (a filamentous green alga) and Elodea nuttallii (a vascular plant) were offered as food to three species of aquatic macroinvertebrates (Lymnaea peregra, Asellus meridianus and Endochironomus albipennis) to test: (i) if filamentous algae are preferred to aquatic higher plants (hereafter, called ‘macrophytes’) and (ii), as is known for higher plants, if decomposition also results in greater palatability of filamentous algae. 2. Compared with the alga, the macrophyte in both states was of higher nutritional value. Conditioning improved the nutritional value of both food types, but especially of the macrophyte. 3. Both fresh alga and fresh macrophyte were eaten little by all animals except A. meridianus feeding upon the macrophyte. Consumption was higher for both plants in their decomposed state. However, L. peregra consumed more decomposed macrophyte than the decomposed alga. Both decomposed plants were eaten most by E. albipennis followed by A. meridianus and L. peregra. 4. Digestibility of both plants, but especially of the macrophyte, increased significantly after decomposition. The assimilation efficiencies of all animals on the fresh E. nuttallii were higher than on fresh Mougeotia sp. After decomposition, the efficiency increased significantly only on the alga. Consequently, both decomposed plants were assimilated with similar efficiency by all test animals. 5. Amongst aquatic macrophytes, the increase of their consumption and digestibility upon decomposition has hitherto been known only for vascular plants but not for filamentous algae.     

Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone

1. Using 5‐m² field enclosures, we examined the effects of Elodea canadensis on zooplankton communities and on the trophic cascade caused by 4–5 year old (approximately 16 cm) roach. We also tested the hypothesis that roach in Elodea beds use variable food resources as their diet, mainly benthic and epiphytic macroinvertebrates, and feed less efficiently on zooplankton. Switching of the prey preference stabilises the zooplankton community and, in turn, also the fluctuation of algal biomass. The factorial design of the experiment included three levels of Elodea (no‐, sparse‐ and dense‐Elodea) and two levels of fish (present and absent). 2. During the 4‐week experiment, the total biomass of euplanktonic zooplankton, especially that of the dominant cladoceran Daphnia longispina, decreased with increase in Elodea density. The Daphnia biomass was also reduced by roach in all the Elodea treatments. Thus, Elodea provided neither a favourable habitat nor a good refuge for Daphnia against predation by roach. 3. The electivity of roach for cladocerans was high in all the Elodea treatments. Roach were able to prey on cladocerans in Elodea beds, even when the abundance and size of these prey animals were low. In addition to cladocerans, the diet of roach consisted of macroinvertebrates and detrital/plant material. Although the biomass of macroinvertebrates increased during the experiment in all Elodea treatments, they were relatively unimportant in roach diets regardless of the density of Elodea beds. 4. Euplanktonic zooplankton species other than Daphnia were not affected by Elodea or fish and the treatments had no effects on the total clearance rate of euplanktonic zooplankton. However, the chlorophyll a concentration increased with fish in all the Elodea treatments, suggesting that fish enhanced algal growth through regeneration of nutrients. Thus, our results did not unequivocally show that Elodea hampered the trophic cascade of fish via lowered predation on grazing zooplankton. 5. In treatments with dense Elodea beds (750 g FW m^?2), chlorophyll a concentration was always low suggesting that phytoplankton production was controlled by Elodea. Apparently, the top‐down control of phytoplankton biomass by zooplankton was facilitated by the macrophytes and operated simultaneously with control of phytoplankton production by Elodea.     

Methanol Accumulation in Maturing Seeds

During in vitro growth and maturation of soybean seeds, cessationof embryo growth and dry weight accumulation occurred in thepresence of abundant C and N nutrients. Axis followed by cotyledontissues changed from green to yellow, and post-harvest germinationpotential declined if cultured after yellowing of axis tissues.A tissue specific accumulat;on of methanol occurred during thein vitro culture of immature seeds (i.e. initially 50 to 70mg fresh weight) to maturity in liquid medium. Methanol accumulatedto 3.0 g m^–3 or 50 µg seed^–1 in the medium,while methanol decreased from 37 to about 3.0 µg g^–1fresh weight in cotyledons. By contrast, axis tissues increased20-fold in methanol concentration to 90 µg g^–1 during20 d in culture. Ethanol was present only in trace amounts inaxis tissues and medium. Addition of exogenous methanol vapourto in situ grown seeds during precocious maturation decreasedsubsequent seedling vigour and germination with increasing levelsof exposure. Methanol accumulation in axis tissues during thegermination phase was not correlated with high temperature andtissue water content treatments which simulated pre-harvestdeterioration of seeds. However, the accumulation of methanolduring in vitro seed development and maturation in liquid culturemay contribute to reduced post-harvest germination performance. Key words: Soybean, Glycine max, seed maturation, in vitro, methanol     

Low Pressure and Ethylene in Lettuce Seed Germination

The extent and manner of ethylene involvement in germination of lettuce (Lactuca Sativa L. cv. Mesa 659) seed at a moderate temperature (20°C) were investigated. Inhibition of germination at low pressure of 150 mmHg in an oxygen flow-through system was alleviated to a marked extent by ethylene. Carbon dioxide was ineffective by itself but caused further alleviation of inhibition in presence of ethylene and oxygen. Other seed treatments which partially alleviated the inhibition caused by low pressure included soaking in 10μM of fusicoccin and a prior treatment with acetone. Of the two ethylene adsorbents used, Purafil was more effective in inhibiting germination in a closed container. Although the ethylene biosynthesis inhibitor, 8-hydroxyquinoline (1.0 mM). showed no effect on ethylene production, it markedly inhibited germination and the effect was partially reversed by ethylene and GA₃. An ethoxy analog of rhizobitoxine, on the other hand, had little or no effect on germination but strongly inhibited the ethylene production. Although no causal relation of ethylene to germination was established, the evidence presented here implicates ethylene, together with other gases, in the regulation of germination.     

Phylogeny of the infraorder Culicomorpha (Diptera: Nematocera) based on 28S RNA gene sequences

Phylogenetic relationships between the families of the infraorder Culicomorpha were investigated by using partial 28S ribosomal RNA gene sequences. All families traditionally placed in this infraorder were investigated and confirmed as clades. On the other hand, some of the morphological relationships between these families were found to be in disagreement with phylogenies based on molecular characters. Our results did not support the generally accepted division of the Culicomorpha into two superfamilies, the Culicoidea (Culicidae + Corethrellidae + Chaoboridae + Dixidae) and the Chironomoidea (Chironomidae + Ceratopogonidae + Simuliidae + Thaumaleidae). Precisely, if the sister-group relationship between Culicidae, Chaoboridae and Corethrellidae was clearly confirmed, the Dixidae, traditionally considered as closely related to these two families, were not placed close to them on our trees. On the other hand, strong evidence was found for grouping together the Simuliidae and the Thaumaleidae, in spite of the cytological and morphological differences between these two families. The position of the Ceratopogonidae was uncertain, and the Chironomidae appeared as a possible sister group to the rest of Culicomorpha. The phylogenetic positions of the groups characterized by feeding on vertebrate blood or insect haemolymph (the Culicidae, Chaoboridae, Ceratopogonidae and Simuliidae) suggest that haematophagy has appeared at least twice in the evolution of Culicomorpha.     

Epidemiology and Pathogenesis of Staphylococcus Bloodstream Infections in Humans: a Review

Staphylococci are among the most frequent human microbiota components associated with the high level of bloodstream infection (BSI) episodes. In predisposed patients, there is a high risk of transformation of BSI episodes to sepsis. Both bacterial and host factors are crucial for the outcomes of BSI and sepsis. The highest rates of BSI episodes were reported in Africa, where these infections were up to twice as high as the European rates. However, there remains a great need to analyze African data for comprehensive quantification of staphylococcal BSI prevalence. The lowest rates of BSI exist in Australia. Asian, European, and North American data showed similar frequency values. Worldwide analysis indicated that both Staphylococcus aureus and coagulase-negative staphylococci (CoNS) are the most frequent BSI agents. In the second group, the most prevalent species was Staphylococcus epidermidis, although CoNS were not identified at the species level in many studies. The lack of a significant worldwide decrease in BSI episodes indicates a great need to implement standardized diagnostic methods and research etiological factors using advanced genetic methods.     

Studies on the Physiology of Hyacinth Bulbs (Hyacinthus orientalis L.): VI. HORMONAL ACTIVITIES IN HYACINTH BULBS DURING FLOWER FORMATION AND DORMANCY RELEASE

The activities of auxin, gibberellin, cytokinin, and abscisicacid were investigated, at 3-weekly intervals, in hyacinth /{Hyadnthusorientalis L.) bulbs during flower bud formation in dry storagefor 12 weeks at 25 /'b0C and during dormancy release in theperiod of 12 weeks of cold treatment at 3 /'b0C after planting.The formation of the flower bud coincided with a gradual increasein the activity of cytokinins and auxins in the bulbs, whereasthe level of abscisic acid was almost stable. Gibberellin activitywas not detectable in lifted bulbs, but it appeared after 6weeks of dry storage and declined in bulbs stored for 12 weeks.The cold storage of bulbs resulted in a gradual decrease ofabscisic acid and it was not detectable in the bulbs cooledfor 12 weeks. The content of auxins was highest in the bulbsduring their rooting in the first 3 weeks of cold treatmentand gradually decreased thereafter. The cytokinin activity declinedin the bulbs cooled for 6 weeks, while gibberellins appearedin them. In the bulbs cooled for a longer time a lack of gibberellinactivity and a gradual increase of cytokinin content was observed.     

Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.