Genetic structure of Pinus brutia stands exposed to wild fires

This study investigates the genetic structure of brutia pine (Pinus brutia Ten.) stands that were exposed to wild fires. A systematic investigation within the species distribution in Greece first identified areas of frequent wild forest fires and then located stands that had experienced ground fires about 20 years ago. In these stands it was possible to sample the pre-fire population that had survived the ground fire event (“mature” population) as well as the post-fire population that has reached reproductive capacity (“young” population). Gel electrophoresis was used in order to study isoenzyme variability in four such populations present in two sites (Kourteri, Lesvos island and Mytilineoi, Samos island). Results indicated absence of notable differences in genetic diversity among the remnant mature populations and the young populations after regeneration. No significant inbreeding was detected and genetic identity among young and mature stands was high. However, some differences were observed in the frequencies of rare alleles and in the presence of interspecific (P. brutia x halepensis) hybrids in the young populations. This paper discusses the above results in the context of the evolution of brutia pine and the maintenance of its genetic variation.     

The origin of variation in “wild”Raphanus sativus (Cruciferae) in California

Analyses of populations ofRaphanus growing in the central part of California, from the Sierra Nevada foothills to the Pacific coast, show that pureR. raphanistrum can be found only in the Central Valley, while over the remainder of the area populations of the so-called wild (weedy)R. sativus occur. More detailed morphological studies of a number of populations in this area have revealed that the populations of wildR. sativus originated by hybridization of the cultivated forms of this species (the radish) with another introduced species, already a weed,R. raphanistrum. The composition of each hybrid population with respect to the proportion of characters of the one or the other species depends upon the habitat it occupies and its geographic location. Populations in inland areas display a high proportion ofR. raphanistrum characters, while in those near the coastR. sativus characters predominate.Artificial hybrids betweenR. raphanistrum and a cultivated form ofR. sativus exhibited about 50% pollen fertility and were heterozygous for a reciprocal translocation. Examination of wild populations ofR. sativus revealed that plants heterozygous for a reciprocal translocation are present in varying proportions. Experimental evidence is produced to show that this translocation is identical with that separatingraphanistrum from cultivated forms ofsativus. Thus a cytological proof of the introgression is added to the morphological evidence. Introgression ofraphanistrum characters appears to have been a major factor in converting the erstwhile crop plant,R. sativus, into a highly successful weed in California.     

Information coding by ensembles of resonant neurons

In the present paper, we propose a novel neural procedure for signal processing and coding based on the subthreshold oscillations and resonance of the neural membrane potential that could be used by real neurons to perform frequency spectra analysis and information coding of incoming signals. Taking into account the biophysical properties of the neural membranes, we note that the subthreshold resonant behaviour they exhibit can be used to analyse incoming signals and represent them in the frequency domain. We study the reliability of the representation of signals depending on the biophysical parameters of the neurons, the fault-tolerance of this coding scheme and its robustness against noise and in the presence of spikes. The principal characteristics of our system are the use of the physical phenomenon of neural resonance (rarely considered in the literature for signal coding); it fits well with the biophysical parameters of most neurons that exhibit subthreshold oscillations; it is compatible with experimental data; and it can be easily integrated in a more general model of information processing and coding that includes communication between neurons based on spikes.