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Biomedical subjects

G Meszéna

Publications and source records attributed to G Meszéna.

5 recordsLinked to original sources
PubMed2006

Emergence of asymmetry in evolution.

We investigate symmetry-breaking bifurcation patterns in evolution in the framework of adaptive dynamics (AD). We define weak and strong symmetry. The former applies for populations where only the simultaneous reflection of all individuals is an invariant transformation. The symmetry is strong in populations where reflection of some, but not all, individuals leaves the situation unchanged. We show that in case of weak symmetry evolutionary branching can lead to the emergence of two asymmetric variants, which are mirror images of each other, and the loss of the symmetric ancestor. We also show that in case of strong symmetry, evolutionary branching can occur into a symmetric and an asymmetric variant, both of which survive. The latter, asymmetric branching differs from the generic branching patterns of AD, which is always symmetric. We discuss biological examples for weak and strong symmetries and a specific model producing the new kind of branching.

Animals↗
PubMed2003

Speciation in multidimensional evolutionary space.

Adaptive dynamics in two-dimensional phenotype space is investigated by computer simulation. The model assumes Lotka-Voltera-type competition and a stochastic mutation process. The carrying capacity has a single maximum in the origin of the strategy space and the competition coefficient decreases with strategy difference. Evolutionary branching, an asexual analog of adaptive speciation, is observed with suitable parameters. The branching at the singular point, which is a fixed point of the directional evolution, may occur into two or three, but not more, directions. Further branchings may occur after the initial separation. The probability of three-branching is studied as a function of several parameters. We conclude that the two-way branching is the predominant mode of adaptive speciation.

Adaptation, Physiological↗
PubMed1994

Trapping magnetically oriented chloroplast thylakoid membranes in gels for electric measurements.

Electrochromic absorbance change and light gradient photovoltage measurements were carried out in chloroplast thylakoid membranes embedded in different compositions of gels. The goal was to find a system suitable for determining the dependence of the amplitude of the anomalous light gradient photovoltage signal, with opposite sign with respect to the ordinary signal, on the alignment of membranes. We found that polyacrylamide gel drastically increased the permeability of membranes which rendered electric measurements impossible in this gel. Agarose gel was successfully used in electric measurements. We will show that the light gradient photovoltage induced by a 580 nm laser flash depends strongly on the alignment of membranes with respect to the direction of the excitation beam. With face-aligned membranes the amplitude of the anomalous (negative) signal was drastically diminished, and the ordinary (positive) signal became clearly discernible. The observed differences in the decay of the two signals are tentatively explained by differences in the rates of ionic equilibration between different subcompartments of the inner aqueous phase of the thylakoid membrane system.

Acrylamides↗
PubMed1982

Field concentration and temperature dependence of fluorescence polarization of magnetically oriented chloroplasts.

Chloroplasts in higher magnetic fields align with their equatorial plane perpendicular to the field. Because of the nonrandom orientation of the chromophores in the membrane the fluorescence radiation will be partially polarized. The chloroplast concentration, magnetic field, and temperature dependence of the fluorescence polarization has been investigated. The results are compared with a simplified model calculation. It is shown that the concentration dependence can be related to the linear dichroism of the fluorescence radiation and self-adsorption. Taking these effects into account results in the calculation of a higher fluorescence polarization (FP) ratio and higher inclination of chlorophyll dipoles to the membrane plane. Analyzing the magnetic field dependence of the FP ratio, we conclude that in a magnetic field not only will be chloroplasts be aligned, but the thylakoid stacks as well. A decrease in the FP ratio was observed around 20 degrees C. It is suggested that this decrease reflects a phase transition in the photosynthetic membrane.

Chloroplasts↗