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.     

Properties of herpes simplex virus type 1 and type 2 DNA polymerase

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) DNA polymerases were highly purified from infected HeLa BU cells by DEAE cellulose, phosphocellulose and DNA cellulose column chromatography. DNA exonuclease activity but not endonuclease activity was found associated with both types of DNA polymerase. Both DNA polymerase activities could be activated by salt in a similar fashion with the optimal activity in the range of ionic strength between 0.22 and 0.29 alpha. At an ionic strength of 0.14, spermidine and putrescine in the concentration range (0--5 mM) studied could mimic the action of KCI in stimulating DNA polymerase activity. Spermine, in the same concentration range, had a biphasic effect. At an ionic strength of 0.29 all three polyamines were inhibitory. HSV-1 and HSV-2 DNA polymerase are similar in their column chromatographic behavior, sedimentation rate in sucrose gradient centrifugation, and activation energy, but they differ in their heat stability at 45 degrees C with the HSV-2 enzyme more stable than the HSV-1 enzyme. Kinetic behavior of both enzymes is similar, with Km values for deoxyribonucleoside triphosphates in the range of 5 . 10(-7) to 1.8 . 10(-8) M. IdUTP and dUTP served as apparent competitive inhibitors with respect to dTTP, and AraATP acted as an apparent competitive inhibitor with respect to dATP. AraATP could not replace dATP in the DNA polymerization reaction; in contrast, IdUTP could replace TTP. Phosphonoformic acid behaved as an uncompetitive inhibitor with respect to DNA. The ID(50) value estimated was foind to be dependent on the purity of the DNA polymerase used and the ionic strength of the assay condition. Each DNA-polymerase associated DNA exonuclease had the same stability at 45 degrees C as its DNA polymerase. The associated DNAase activity was inhibited by phosphonoformic acid and high ionic strength of the assay condition.     

High-dose mode of death in Tribolium

This study reports the first demonstration within a single insect genus (Tribolium) of both the acute, or lethal-midlethal, dose-independent pattern of mortality, and the hyperacute, dose-dependent pattern, after appropriate doses of ionizing radiation. This demonstration provides resolution of apparently contradictory reports of insect responses in terms of doses required to cause lethality and those based on survival time as a function of dose. A dose-dependent mortality pattern was elicited in adult Tribolium receiving high doses, viz., 300 Gy or greater; its time-course was complete in 10 days, before the dose-independent mortality began. Visual observations of heavily-irradiated Tribolium suggested neural and/or neuromuscular damage, as had been previously proposed by others for lethally-irradiated wasps, flies, and mosquitoes. Results of experiments using fractionated high doses supported the suggestion that the hyperacute or high-dose mode of death is the result of damage to nonproliferative tissues. Relative resistance of a strain to the hyperacute or high-dose mode of death is not necessarily correlated with resistance to the midlethal mode, which is believed to be the result of damage to the proliferative cells of the midgut.

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Résumé Les résultats de nombreuses études des réactions des insectes adultes de différents groupes à l'irradiation s'opposent quant à l'importance de la dose provoquant la létalité et quant aux modalités de la mort. Les diptères et les guèpes impliquent des doses très élevées,-des centaines de Gy-, ne présentent aucune période caractérisant la mort par irradiation, et décèdent de plus en plus tôt avec l'augmentation des doses. Beaucoup d'autres insectes succombent à des doses (milétalelétale) beaucoup plus faibles,-de quelques Gy à des dizaines-, et quelle que soit la dose meurent au bout d'un temps voisin.Au cours de cette étude, nous avons pu observer que ces deux types de mortalité peuvent être provoqués chez le même genre d'insecte (Tribolium), avec des doses convenables d'irradiation . Un syndrôme caractéristique a été provoqué avec des doses très élevées, de 300 Gy ou plus,-à ces doses la mort est obtenue en 10 jours après l'irradiation. L'absence de syndrôme caractéristique se produit avec des doses inférieures ou égales à 80 Gy; la mort a lieu alors entre 10 et 16 jours en fonction de la dose.Les différences entre les deux types de décès indiquent deux processus de mort par irradiation. La manifestation d'une désorientation et d'une perte de coordination motrice chez les Tribolium fortement irradiés suggère des altérations neurales et/ou neuromusculaires comme cause/s de ce type de mort provoquée par des doses élevées. L'implication de tissus sans prolifération a été confortée par les résultats d'expériences utilisant de hautes doses fractionnées. Le type de mort milétal est considéré après de nombreuses observations indépendantes, comme le résultat d'atteintes à la prolifération des cellules de l'intestin moyen.Les données contradictoires sur les réactions des insectes aux irradiations proviennent d'abord de l'absence de connaissances sur le lieu des dégâts. Les diptères sont connus maintenant, après différentes études, comme perdant complètement l'aptitude au renouvellement cellulaire, et présentent ainsi un type de mort avec dose élevée. Beaucoup d'autres insectes adultes ont un renouvellement cellulaire de l'intestin moyen limité, et ainsi présentent le type de mort milétal. Le type de mort, dit haute dose, peut être induit dans cette dernière catégorie d'insectes par une irradiation suffisamment forte, et, dans le cas du Tribolium le déroulement de la mort se produit alors de deux façons bien distinctes.