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 use of restriction fragment length polymorphisms in paternity analysis.

This paper examines the utility of restriction fragment length polymorphisms (RFLPs) for paternity analysis. While, on the average, 99% of falsely accused males can be excluded with the standard battery of blood group antigens, red cell enzymes, serum proteins, and HLA antigens, there are still mother-child pairs for whom the exclusion probability is not high. It has been suggested that additional resolution would be available with RFLPs. We have examined the strategic aspects of using RFLPs for paternity analysis, comparing the efficacy and cost of a multimarker haplotypic set with those of a comparable set of unlinked RFLPs, using published frequencies for the beta-globin complex, the serum albumin region, and the growth hormone region. There are four major findings. (1) Greater resolution is obtained with a carefully chosen set of tightly linked RFLPs producing chromosomal haplotypes than with a comparable set (same allele frequencies) of unlinked markers, but only if it is possible to establish linkage phase unambiguously. (2) Assay of linked sets is cheaper than is the assay of unlinked markers, but the cost advantage is optimized with sets of no more than two or three linked markers. (3) Also, with more than two or three tightly linked markers, the haplotypic frequencies are too poorly estimated to provide a reliable measure of the probability of paternity for unexcluded males, given the sample sizes likely to be available in the near future. (4) Optimal resolution, minimal cost, and acceptable accuracy are obtained with several independent sets of no more than two or three tightly linked RFLP markers each. With current technology, RFLP analysis is more expensive for the same level of genetic resolution than is the standard battery, but gradual replacement of the latter can be anticipated as economies of scale reduce the cost of the DNA technology.     

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.