Predator-induced bottom-up effects in oligotrophic systems

Five treatments (replication n=2) were applied to mesocosms in an oligotrophic lake (TP=6–10 µg 1^-1) to assess the effects of fish on planktonic communities. The treatments were: (1) high fish (30 kg ha^–1 Lepomis auritus, Linnaeus), (2) low fish (10 kg ha^–1), (3) high removal of zooplankton, (4) low removal of zooplankton and (5) control. Total phosphorus, chlorophyll a, zooplankton biomass, and species richness decreased from high fish > low fish > control > low removal > high removal treatments. The fish treatments were dominated by crustacean zooplankton, while rotifers outnumbered the other zooplankters in the removal treatments. Calculations of zooplankton grazing rates suggested that clearance rates seldom exceeded 2% of the enclosure volume d^–1 and were unlikely to have had much influence on phytoplankton biomass. Calculations from a phosphorus bioenergetics model revealed that when fish were present, their excretion rates were higher than the rates ascribed to zooplankton. Diet analysis showed that the fish derived most of their energy from the benthos and periphyton, and that fish excretion and egestion made significant contributions to the very oligotrophic pelagic phosphorus pool. In the absence of fish, zooplankton excretion was highest in the control treatments and lowest in the zooplankton removal treatments. Our results suggest that in oligotrophic systems, planktivorous fish can be significant sources of phosphorus and that fish and zooplankton induced nutrient cycling have significant impacts on planktonic community structure.     

The Gene for Human Glutaredoxin (GLRX) Is Localized to Human Chromosome 5q14

Glutaredoxin is a small protein (12 kDa) catalyzing glutathione-dependent disulfide oxidoreduction reactions in a coupled system with NADPH, GSH, and glutathione reductase. A cDNA encoding the human glutaredoxin gene (HGMW-approved symbol GLRX) has recently been isolated and cloned from a human fetal spleen cDNA library. The screening of a human genomic library in Charon 4A led to the identification of three genomic clones. Using fluorescencein situhybridization to metaphase chromosomes with one genomic clone as a probe, the human glutaredoxin gene was localized to chromosomal region 5q14. This localization at chromosome 5 was in agreement with the somatic cell hybrid analysis, using DNA from a human–hamster and a human–mouse hybrid panel and using a human glutaredoxin cDNA as a probe.     

Multiple fatal mycetism caused byAmanita virosa in Mexico

Mushroom poisonings caused by amatoxins are mostly lethal. Information about mycetisms caused by white species ofAmanita is scarce. The present paper describes a case of mushroom poisoning caused byA. virosa. A prolongated latency period (6–10 hours), followed by cholera-like, improvement and visceral complication phases confirmed the amatoxin poisoning. The consumption of about 3 pounds of the toadstool by seven persons caused the death of five. Two patients survive the ingestion.     

Typology of shallow lakes of the Salado River basin (Argentina), based on phytoplankton communities

The phytoplankton communities of eleven shallow lakes from Buenos Aires Province, Argentina, were studied seasonally from 1987 to 1989. Several physical and chemical properties were measured in each lake (pH, temperature, dissolved oxygen, transparency, nutrients), in order to interpret the structural and dynamic traits of the phytoplankton community.Important differences between the lakes studied were put in evidence by means of multivariate techniques (Cluster Analysis and PCA). The shallow lakes densely populated by macrophytes hosted lowest phytoplanktonic densities, with average values ranging from 690 to 16500 algae ml^–1. High species diversities were observed in these lakes (4.0–4.8). Lakes less colonized by macrophytes had higher phytoplankton densities. In some of them important blooms of Cyanophyceae were recorded, with between 60 000 and 179 000 algae ml^–1, and concomitant low diversities.The results of this investigation support the hypothesis that the phytoplankton community is strongly influenced by the macrophytes, by direct competition and/or by competition from periphytic algae associated with higher plants.     

A genetic approach to the identification of functional amino acids in protein p6 of Bacillus subtilis phage ?29

Protein p6 of the Bacillus subtilis phage ø29 is essential for in vivo viral DNA replication. This protein activates the initiation of ø29 DNA replication in vitro by forming a multimeric nucleoprotein complex at the replication origins. The N-terminal region of protein p6 is involved in DNA binding, as shown by in vitro studies with p6 proteins altered by deletions or missense mutations. We report on the development of an in vivo functional assay for protein p6. This assay is based on the ability of protein p6-producing B. subtilis non-suppressor (su ^–) cells to support growth of a ø29 sus6 mutant phage. We have used this trans-complementation assay to investigate the effect on in vivo viral DNA synthesis of missense mutations introduced into the protein p6 N-terminal region. The alteration of lysine to alanine at position 2 resulted in a partially functional protein, whereas the replacement of arginine by alanine at position 6 gave rise to an inactive protein. These results indicate that arginine at position 6 is critical for the in vivo activity of protein p6. Our complementation system provides a useful genetic approach for the identification of functionally important amino acids in protein p6.     

Endophytic fungi alter foraging and dispersal by desert seed-harvesting ants

Endophytic fungi are thought to interact mutualistically with host plants by producing alkaloid metabolites that deter herbivory. Since such fungi are transmitted via seed in some grasses, the presence of endophytes may also protect plants from seed predators. We conducted seed choice experiments for two dominant seed harvesting ants, Pogonomyrmex rugosus in the Sonoran desert and Pogonomyrmex occidentalis at a higher elevation, riparian zone in Arizona, USA. Non-infected fescue (Festuca arundinacea) seeds and seeds infected with the endophytic fungus, Acremonium coenophialum, were presented to ant colonies in three different populations. Infected seeds were harvested less frequently than non-infected seed for the two populations of Pogonomyrmex rugosus but not for the population of Pogonomyrmex occidentalis. We also a conducted seed dispersal experiment for one population of Pogonomyrmex rugosus. Of the seeds that were harvested, most of the colonies discarded more infected seeds into refuse piles than expected by chance. Seeds discarded into refuse piles have greater germination success than surrounding areas. The most important interaction of endophytes and grasses may be deterrence of seed predation and enhancing the probability of germinating in favorable sites, since these processes directly increase plant fitness.     

Effect of cytokinins on plastid development and photosynthetic polypeptides during organogenesis ofPinus ponderosa Dougl. cotyledons culturedin vitro

InPinus ponderosa Dougl., application of the cytokinins, benzyladenine and 2-isopentenyl adenine, to excised cotyledons, promoted thein vitro formation of meristematic centers which led to bud and shoot production. Meristematic cells showed plastids with poorly developed thylakoid membranes and rudimentary grana, whereas cells in non-meristematic tissues and in growth regulator free medium, had chloroplasts with well developed inner membranes, and more thylakoid membranes and grana than plastids of meristematic cells. Chlorophyll and six polypeptides associated with photosynthesis were present in lower concentrations in cytokinin-treated cotyledons than in those cultured in growth regulator free medium. Both benzyladenine and 2-isopentenyl adenine are effective in inhibiting the accumulation of at least two photosynthetic polypeptides in the first 24 h in culture. The ability of cotyledons to respond in this way to cytokinins is lost after three days in culture in growth regulator free medium prior to treatment with cytokinin.     

Effect of environmental pH on the fermentation balance of Lactobacillus reuteri

The influence of environmental pH on the regulation of glucose catabolism by Lactobacillus reuteri was examined in anaerobic batch cultures. Under acidic conditions both glucose consumption and end-products formation were low. Maximum biomass was reached at pH 5·0, with a specific growth rate of µ= 0·78 h^-1. The shift in pH values from 4.3 to 6.5 reflected an increase in glucose uptake as well as in the yield ( Y _p/x) of acetate, lactate and ethanol after 12 h of incubation. Ethanol was the major metabolite produced at all pH values assayed.     

Chemical structure and conformational features of cell-wall polysaccharides isolated from Aphanoascus mephitalus and related species

The structures of cell-wall mannans isolated from Aphamoascus mephitalus, A. Fulvescens, A. verrucosus, and A. reticulisporus have been investigated by chemical analyses and 1D and 2D ¹H and ¹³C NMR techniques. It was found that all of them consists of a relatively simple comb-like structure of the disaccharide repeating block {→ 6)-[-Man p-(1 → 2)]--Man p-(1 →}. The conformations around the -(1 → 2) and -(1 → 6) linkages in thes kinds of polymers were also studied by using molecular mechanics and dynamics calculations, together with NOE data. The results are similar to those found within the oligosaccharide chains of glycoproteins, with a well-defined conformation for the -(1 → 2) linkage and a certain restriction around the -(1 → 6) bonding imposed by the 2-substitution.     

Mechanisms of group-hunting in vertebrates

Group-hunting is ubiquitous across animal taxa and has received considerable attention in the context of its functions. By contrast much less is known about the mechanisms by which grouping predators hunt their prey. This is primarily due to a lack of experimental manipulation alongside logistical difficulties quantifying the behaviour of multiple predators at high spatiotemporal resolution as they search, select, and capture wild prey. However, the use of new remote-sensing technologies and a broadening of the focal taxa beyond apex predators provides researchers with a great opportunity to discern accurately how multiple predators hunt together and not just whether doing so provides hunters with a per capita benefit. We incorporate many ideas from collective behaviour and locomotion throughout this review to make testable predictions for future researchers and pay particular attention to the role that computer simulation can play in a feedback loop with empirical data collection. Our review of the literature showed that the breadth of predator:prey size ratios among the taxa that can be considered to hunt as a group is very large (<10⁰ to >10²). We therefore synthesised the literature with respect to these predator:prey ratios and found that they promoted different hunting mechanisms. Additionally, these different hunting mechanisms are also related to particular stages of the hunt (search, selection, capture) and thus we structure our review in accordance with these two factors (stage of the hunt and predator:prey size ratio). We identify several novel group-hunting mechanisms which are largely untested, particularly under field conditions, and we also highlight a range of potential study organisms that are amenable to experimental testing of these mechanisms in connection with tracking technology. We believe that a combination of new hypotheses, study systems and methodological approaches should help push the field of group-hunting in new directions.