Feeding of Sagitta enflata and vertical distribution of chaetognaths in relation to low oxygen concentrations

Zooplankton samples were collected in Mejillones Bay, northernChile (23°00'15'S, 70°26'43'W ). Sampling was conductedat 4 h intervals, for 24 h during three seasons, austral spring(October 2000), summer ( January 2001) and winter (August 2001)at three different strata (0–25, 25–50 and 50–100m). Five species of chaetognaths were collected. Sagitta enflatawas the most abundant species, representing up to 65% of allchaetognaths in total numbers, followed by Sagitta bierii, makingup 34% of the total abundance of chaetognaths. S. enflata wasdistributed mainly above the Oxygen Minimum Zone, while S. bieriiremained below this zone. Feeding rates were relatively constantwithin the upper layer (0–25 m depth), for each samplingdate, averaging 1.2 prey S. enflata day^–1, and decreasingwith depth. Gut content analyses demonstrated that predationwas principally focused on small copepods (<1500 µm),with greatest feeding activity occurring at night. The dailypredation impact on the total standing stock of small copepodsvaried seasonally between 6% in spring and 0.4% in winter. Thispercentage may represent a negligible impact on the entire copepodcommunity, but it is relevant at the species or genus level,since S. enflata removed more than 20% of the standing stockof Centropages brachiatus and Corycaeus sp. Thus, during someperiods of the year, chaetognaths may strongly influence theabundance and size distribution of copepods in coastal upwellingecosystems.     

A UNIQUELY CALCIFIED BROWN ALGA FROM HAWAII: NEWHOUSIA IMBRICATA GEN. ET SP. NOV. (DICTYOTALES,PHAEOPHYCEAE)1

An encrusting brown alga from subtidal habitats around the island of Oahu (Hawaiian Islands) represents only the second genus of the class Phaeophyceae to form calcium carbonate, which it deposits primarily as both extracellular and intracellular aragonite, admixed with small (3.3%) amounts of calcite. Plants form expanses 15–100+ cm in extent consisting of horizontally aligned imbricating tiers of distromatic blades 1–4 mm in diameter that are separated from one another by cementing layers of extracellular aragonite, the tiers forming stacks of dozens of laminae and anchored to coral substrata by a basement layer that adheres tightly without haptera or rhizoids. The hypodermal layer of each blade consists of lightly pigmented rectilinear cells bearing either one or two smaller deeply pigmented epidermal cells in cross‐sectional profiles and three or four in long‐sectional profiles, the cells of both layers becoming encased in rigid carbonate skeletons laid down in their outer wall matrices. The successive tiers become stacked by either overgrowing marginal proliferations or new blade primordia that arise from the hypodermal layer of surface laminae and initially spread centrifugally by means of continuous marginal meristems. Neither plurilocular nor unilocular reproductive structures are known. The alga is described as the new genus and species Newhousia imbricata Kraft, G.W. Saunders, Abbott et Haroun and is assigned on the basis of small subunit rDNA gene sequence analyses to the order Dictyotales, family Dictyotaceae, within a strongly supported monophyletic clade that includes Distromium, Lobophora, and Zonaria.     

Characterization of the hypotensive effect of S-nitroso-N-acetylcysteine in normotensive and hypertensive conscious rats.

S-Nitrosothiols (RSNOs) are potent vasodilators found naturally in vivo. A variety of synthetic RSNOs have been considered as potential nitric oxide (NO) donors for biomedical applications. We have characterized the hypotensive effect of the RSNO S-nitroso-N-acetylcysteine (SNAC) in normotensive and hypertensive conscious rats. SNAC reduced the medium arterial pressure in a dose-response manner in both normotensive and hypertensive animals. At the same doses (EC(50) of SNAC), SNAC showed a vasodilator effect in normotensive rats more potent and more prolonged than that of sodium nitroprusside (SNP). The hypotensive effect of SNAC was also more potent in methylene blue-treated rats, where the cGMP-dependent pathway had been blockaded. These data indicate that SNAC acts by both cGMP-dependent and cGMP-independent pathways. It was also shown that the thiol N-acetylcysteine (NAC) potentiates the action of SNP in hypertensive rats, pointing to the mediation of thiols in the vasodilator action of SNP in this condition. Such mediation may involve the formation of a more potent thiol complex with the nitroprusside anion or the transfer of NO to NAC, generating SNAC as a primary vasoactive species. The kinetic monitoring of the decomposition reactions of SNAC and SNP showed that both compounds are quite stable under the infusion conditions used. Therefore, their vasodilator action cannot be assigned to their breakdown with release of free NO in solution. As the two compounds are unlikely to cross the plasmalemma of smooth muscle cells, their actions are probably associated with the mediation of endogenous thiols in transnitrosation reactions.     

Novel methods improve prediction of species' distributions from occurrence data

Prediction of species' distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species' distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species' occurrence data. Presence-only data were effective for modelling species' distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.     

Absence of VanA- and VanB-Containing Enterococci in Poultry Raised on Nonintensive Production Farms in Brazil

We examined cloacal samples from poultry raised on nonintensive production farms in Brazil for the presence of vancomycin-resistant enterococci. No VanA- or VanB-containing enterococci were identified in a total of 200 cloacal swabs. The most prevalent species were Enterococcus gallinarum (vanC1; 13.0%) and E. casseliflavus (vanC2/3; 5.5%).     

EARLY TOXIC EFFECTS OF ZINC ON PSII OF SYNECHOCYSTIS AQUATILIS F. AQUATILIS (CYANOPHYCEAE)1

Zinc toxicity on photosynthetic activity in cells of Synechocystis aquatilis f. aquatilis Sauvageau was investigated by monitoring Hill activity and fluorescence. The oxygen‐evolving activity decreased to about 80% of the initial value after exposure to 0.1 mM ZnSO₄ for 1 h. The PSII activity was inhibited by 40% in the presence of zinc concentrations ranging from 0.5 to 5.0 mM, suggesting that the metal effect is limited by zinc uptake. The fluorescence capacity (F_max–F/F_max) decreased from 0.57 to 0.35 and 0.20 in Zn‐treated cells for 15 and 60 min, respectively, thus providing evidence for rapid inactivation of electron transport at PSII. Zinc treatment promoted a rapid increase in PSII fluorescence that was counteracted by addition of 1,4‐benzoquinone, indicating that electron transfer at the reducing side of the PSII reaction center is arrested by zinc. Furthermore, a decline in the fluorescence yield could be observed after 1 h of zinc treatment as well as when Zn‐treated cells were excited in presence of 3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethylurea. Under these conditions, zinc did not affect energy transfer from phycobilisomes to PSII, and the gradual quenching of PSII fluorescence may be due to a decrease in electron flow on the donor side of PSII. However, the 20% increase in the minimal fluorescence intensity (F_o) in parallel to the absence of changes in the maximal fluorescence intensity (F_max), observed in the first hour of zinc treatment, could also suggest a metal‐induced decline in the energy transfer from PSII‐chl a antenna to the PSII reaction center.     

Environmental implications of oncoids and associated sediments from the Remoredo Formation (Lower Jurassic) Mendoza, Argentina

Lower Jurassic deposits of the middle member (19 m) of the Remoredo Formation at Arroyo Montañesito, southwestern Mendoza Province (Neuquén Basin, Argentina), and its oncoids are described. Four lithofacies constitute the lacustrine deposits of the Remoredo Formation: (1) laminated green to gray calcareous shales; (2) laminated to massive dark gray mudstones; (3) massive to upward-coarsening dark gray oncolite wackestones; and (4) massive dark gray packstones with abundant macro-oncolites. According to layer configuration, two types of oncoids were recognized: (a) those having distinctly banded, well defined concentric and continuous lamination (Type I); and (b) those having a vertical arrangement of irregular and discontinuous laminae (Type I³–I). The continuous micritic laminations suggest growth during agitated conditions, and the discontinuous laminations reflect short periods of non agitation or tranquility in the water mass. The oncolites are associated with a well preserved faunal assemblage of ostracods (Darwinula sp. and possible members of the Subfamily Iliocypridinae) and some fragments of bivalves that are indicative of shallow water conditions. The facies association is a coarsening-upward sequence interpreted as the product of deposition in a shallow nearshore lacustrine environment, and a progressive infilling by pyroclastic subaereal flows.     

Effect of Membrane Lipid Composition on the Allosteric Inhibition by Sodium of the (Ca2+)-Adenosine Triphosphatase from Escherichia coli

The allosteric inhibition by sodium of the (Ca(2+))-adenosine triphosphatase (EC 3.6.1.3) from Escherichia coli was found to be dependent on the lipid composition of the cell membrane.     

Membrane lipid fatty acids and regulation of membrane-bound enzymes. Allosteric behaviour of erythrocyte Mg2+-ATPase, (Na+ + K2+)-ATPase and acetylcholineasterase from rats fed different fat-supplemented diets

Studies were carried out to determine the Hill coefficients for the inhibition by F^? of the erythrocyte membrane-bound Mg²⁺-ATPase, $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ and acetylcholinesterase from rats fed with seven different diets. Five groups were fed with different natural fats or oil supplements, one with a hydrogenated fat supplement and the other with fat-free diet. The responses of the red cell fatty acids to dietary fats were recorded. The value of $\text{n}$ for the inhibition by F^? of the three enzymes revealed a particular and different behaviour in each group. Correlations between the fatty acid compositions of erythrocyte membranes and cooperativity of each enzyme were calculated. The results indicate that neither the essential fatty acid family nor the non-essential ones are particularly involved in the allosteric phenomena. The increase of the double bond index/saturation ratio of fatty acids, which is taken as indicative of membrane fluidity, was accompanied in an inverse manner by changes in allosteric transitions of the $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ and acetylcholinesterase, whereas the Mg²⁺-ATPase was not dependent on this ratio. Diminution of membrane fluidity, carried out by in vitro increase of its cholesterol content, yields confirmatory results of this regulatory mechanism since the value of $\text{n}$ for acetylcholinesterase shifted as predicted.These facts indicate that the membrane fluidity is a physiological regulator for the allosteric behaviour of the membrane-bound enzymes and that each enzyme exhibits a particular behaviour in this phenomenon.