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.     

Analysis of uric acid and oxypurines in normal subjects and in gout patients

The behavior of plasma and urine oxypurines (hypoxanthine and xanthine) and of uric acid has been studied in normal subjects and in gout patients. Oxypurines and uric acid were increased in the plasma of gout patients but only the urinary excretion of hypoxanthine was higher in this group. The interpretation of the observed variations is discussed.     

Purine metabolism: determination of PRPP-amidotransferase and PRPP-synthetase in lymphocytes from patients with chronic lymphatic leukemia (CLL)

Phosphoribosyl-1-pyrophosphate (PRPP) amidotransferase is the "key anabolic enzyme" of purine nucleotide synthesis; PRPP synthetase connects the pentose cycle with the same pathway. We have studied their behavior in 5 control subjects and in 8 affected by CLL. Determination of PRPP amidotransferase was carried out through the evaluation of 14C-glutamic acid (released by 14C-glutamine) in the incubation mixture. PRPP synthetase was followed by adding ATP and ribose 5-phosphate to the incubation mixtures, and by evaluating the PRPP formed through the release of CO2 in a coupled reaction. In the case of PRPP-amidotransferase, our values are in the range reported in the literature: in patients affected by CLL, the enzyme activity is much higher and the increase is more evident when values referred to the patients, than when to the cells. Our values of PRPP synthetase are consistent with those of Peters and Veerkamp, but no definite conclusion is possible in the case of leukemic patients.