Population dynamics of two small pelagic fish in the central-south area off Chile: delayed density-dependence and biological interaction

It is widely believed that environmental variability is the main cause for fluctuations in commercially exploited small pelagic fish populations around the world. Nevertheless, density-dependent factors also can drive population dynamics. In this paper, we analyzed thirteen years of a relative abundance index of two clupeoids fish populations coexisting in the central-south area off Chile, namely the common sardine, Strangomera bentincki, and anchovy, Engraulis ringens. We applied the classical diagnostic tools of time series analysis to the observed time-series. Also, the realized per capita population growth rate was studied with the aim of detecting the feedback structure that is characterizing the population dynamics of the two species. The analysis suggests that population fluctuations of the two species have an important density-dependent component, displaying first-order (direct density-dependent) and second-order (delayed density-dependent) simultaneously. The density-dependent component explained 70.5 and 55.6 % of the realized per capita population growth rate of common sardine and anchovy, respectively. The deterministic skeleton model showed an asymptotic convergence to equilibrium density. In presence of a stochastic environment, fluctuations were reproduced for the species showing a component of fluctuation with a period of 4 year. The intrinsic dynamics of each species is typical of interacting species resulting from trophic interactions. It is postulated that the second-order dynamics of S. bentincki and E. ringens in central-south Chile, may be the result from interactions with a specialist predator (the fishing fleet), interacting with exogenous environmental factors.     

Ethylene and IAA interactions in the inhibition of photoperiodic flower induction of <Emphasis Type="Italic">Pharbitis nil</Emphasis>

It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis.     

The type IC hsd loci of the enterobacteria are flanked by DNA with high homology to the phage P1 genome: implications for the evolution and spread of DNA restriction systems

Eco R124I, Eco DXXI and Eco prrI are the known members of the type IC family of DNA restriction and modification systems. The first three are carried on large, conjugative plasmids, while Eco prrI is chromosomally encoded. The enzymes are coded by three genes, hsdR , hsdM and hsdS . Analysis of the DNA sequences upstream and downstream of the type IC hsd loci shows that all are highly homologous to each other and also to sequences present in the bacteriophage P1 genome. The upstream sequences include functional phd and doc genes, which encode an addiction system that stabilizes the P1 prophage state, and extend to and beyond pac , the site at which phage DNA packaging begins. Downstream of the hsd loci, P1 DNA sequences begin at exactly the same place for all of the systems. For Eco DXXI and Eco prrI the P1 homology extends for thousands of base pairs while for Eco R124I an IS 1 insertion and an associated deletion have removed most of the P1-homologous sequences. The significance of these results for the evolution of DNA restriction and modification systems is discussed.     

Acid phosphatase isoenzyme mapping in Leishmania

The profiles of acid phosphatase isoenzymes of several well defined species of the genus Leishmania were compared. The profiles were generated after isoelectric focusing of parasite extracts in polyacrylamide and incubation of the gels with an appropriate substrate coupled to an azo dye. Analysis of the zymograms showed that there is species-specificity of the acid phosphatase isoenzyme maps in Leishmania. It was also demonstrated that different strains of the same species present identical pattern of enzyme activity. The method even enabled the differentiation of closely related species which were previously difficult to identify. Some technical aspects of the isoelectric focusing procedure are discussed. The method described here can be used as an aid for species identification of Leishmania.     

Prostacyclin production by human endothelial and bovine smooth muscle cells in culture. Effect of repeated stimulation with arachidonic acid, thrombin and ionophore A23187

Prostacyclin (prostaglandin I2) is the major product of arachidonic acid metabolism in vascular cells. Its physiological role may be linked to the ability of the cells to respond continuously with prostaglandin I2 production to a variety of stimuli. We report that human endothelial cells or bovine smooth muscle cells in culture respond with prostaglandin I2 synthesis to a first but not to a second stimulation with arachidonic acid. The development of this refractoriness was independent of the arachidonic acid concentration used (6.6-25 microM) and lasted for about 6 h. The same time was required for the cells to recover completely after inhibition of cyclooxygenase activity by aspirin. Neither cis-polyunsaturated fatty acids (linoleic or oleic acids) nor stearic acid (a long-chain saturated fatty acid) prevented the generation of prostaglandin I2 by arachidonic acid. Similarly to arachidonic acid, thrombin and ionophore A23187 could elicit vascular prostaglandin I2 synthesis only once. Pretreatment of the cells with arachidonic acid rendered the cells unresponsive to any other stimulus. These results indicate that the mechanism of the refractoriness induced by arachidonic acid was different from that induced by the other stimuli. It is proposed that vascular cells cannot be stimulated continuously to produce prostaglandin I2, but this process is regulated by different feedback mechanisms.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.