An analysis of age-and size-dependent flowering: A critical-production model

Three critical phenomena of flowering can be recognized in nature: critical age, critical initial size and critical switchover size. In order to understand the ecological significance of these flowering phenomena from the viewpoint of matter production, a simple model of flowering phenomean (critical-production model) was studied, assuming that plant flowering is controlled by the productive capacity of the plant (critical-production model, under the condition that plants forecast environmental conditions affecting matter production. Thus, we concluded that all three critical phenomena are various manifestation of the same critical-production principle. Then, using the model simulation, the reliability of each critical phenomenon for securing a given critical production was investigated in relation to the photosynthetic productivity of the habitat. The main predictions obtained from the simulation were as follows: 1) Only annual and biennial plants will show critical age phenomena, and most biennials will be facultative. 2) Among perennials, the critical initial size phenomenon will appear in low productive habitats, whereas in high productive habitats the critical switchover size phenomenon will be observed.     

Sequence and temperature effect on hydrogen bond disruption in DNA determined by a statistical analysis

We use the modified self-consistent phonon approximation theory to calculate temperature dependent interbase hydrogen bond disruption profiles for a number of six base pair repeating sequence infinite B-DNA polymers with various guanine-cytosine/adenine-thymine ratios. For comparison we also include results we have obtained in our earlier work on several B-DNA homopolymers, copolymers and a four-base-pair repeating sequence polymer. Our theory gives a statistical estimate of thermal fluctuational disruption probability of individual hydrogen bonds in individual base pairs in DNA as a function of temperature. The calculated probabilities show no sequence dependence at premelting temperatures, in agreement with proton exchange measurements. These probabilities however become very sensitive to base sequence at temperatures close to the observed melting temperatures. Multi-phasic critical transitions are found in which a portion of base pairs are disrupted at temperatures below the final disruption temperature. These transitions include localized as well as non-localized base pair opening. The localized transitions involve disruption of a few base-pairs at every other location without large scale base unstacking, and they may not appear in the observed UV curves with current resolution. On the other hand the overall disruption behavior is consistent with observations. The midpoint transition temperatures are close to the observed melting temperatures and these temperatures show the observed linear dependence on guanine-cytosine content. Our calculations indicate that our theory can be used effectively to calculate H-bond disruption behavior of different DNA sequences. Received: 20 February 1996 / Accepted: 2 May 1996     

The Bionic Anticipation of Natural Disasters

After major natural disasters, such as the recent earthquake-tsunami event in South Asia, reports appear about the mysterious ability of animals to anticipate and to escape the impending danger. This is an opportunity to recall the long history of this phenomenon in the traditions of different civilizations, to evaluate Chinese efforts, 30-40 years ago, to use this phenomenon for earthquake prediction, and to judge its state of acceptance in modem science. An effort is made to introduce this phenomenon as a research field of modem bionics. The timing is favorable since, increasingly, infrared thermal anomalies, monitored from satellite, suggesting litho-atmospheric processes, are found to precede earthquakes. They were unexpected by seismologists and are here suggested to essentially reflect the energy conversion patterns responsible for the signals monitored by animals. The aim is to learn from animals in the long term how natural disasters can better be anticipated, and how simple technical warning systems can be developed. Some challenges are analyzed. One is interpretation of the nature of energy release prior to the main earthquake disaster resulting in ＂macro-anomaly＂ precursors, another is better to understand the effect on animal senses. The role of non-linear cooperative phenomena including tsunamitype waves is emphasized.     

Is it advantageous for Atlantic salmon to be triploid at lower temperatures?

Marine organisms living at low temperatures tend to have larger genomes and larger cells which suggest that these traits can be beneficial in colder environments. In fish, triploidy (three complete sets of chromosomes) can be induced experimentally following fertilization, which provides a model system to investigate the hypothesis that larger cells and genomes offers a physiological advantage at low temperatures. We tested this hypothesis by measuring metabolic rates and swimming performance of diploid and triploid Atlantic salmon (Salmo salar) post smolts acclimated to 3 or 10.5 °C. At 10.5 °C, triploids had significantly lower maximum metabolic rates which resulted in a lower aerobic scope compared to diploids. In addition, triploids initiated ram ventilation at lower swimming speeds, providing further evidence of a reduced capacity to meet oxygen demands during strenuous activity at 10.5 °C. However, at 3 °C, metabolic rates and critical swimming speeds were similar between both ploidies, and as expected substantially lower than at 10.5 °C. Therefore, triploidy in colder environments did not provide any advantage over diploidy in terms of metabolic rate traits or swimming performance in Atlantic salmon. We therefore conclude that traits, other than aerobic scope and swimming performance, contribute to the trend for increased cell and genome size in marine ectotherms living in cold environments.