[An analytical study of the patterns of the survival curves of experimental objects in model experiments on Daphnia magna.]

The phenomenon of multiphase survival curves found in drosophila is confirmed in experiments on daphnia. Mathematical modeling showed that the multiphase nature of the daphnia survival curves reflects abrupt changes in the intensity of death of crustaceans during the transition from phase to phase. In intact daphnia there is no phase of a sharp increase in mortality observed at an early age in drosophila. It arises as a reaction to weak negative influences, which leads to a sharp decrease in the survival of young individuals. A logical conclusion was made about the readiness for reaction of each experimental individual. The effect was observed in a series of experiments posed in different years. It is proved that in daphnia, the predisposition to reaction persists for an indefinitely large number of generations. It is postulated that this reaction has an epigenetic nature. Previous experimental materials suggest that a reaction of this type is widespread in natural surroundings.

Heating stress patterns in Caenorhabditis elegans longevity and survivorship.

Survival data from Caenorhabditis elegans strain TJ1060 (spe-9; fer-15) following brief exposure to 35 degrees C have been investigated. Three experiments with 3-day-old worms were conducted with heat duration ranging between 0 and 12 hours. A statistically significant increase in life expectancy was observed in the groups heated for less than 2 hours, as compared to the unheated control groups. In different experiments P-values for the observed life spans under the hypothesis that heating has no influence on longevity were P < 0.004 after 0.5 hour heat, P < 0.012 after 1 hour heat and P < 0.055 after 2 hours of heating. A biphasic survival model with Gamma distributed frailty has been constructed to describe the survival of worms after heating. The increase in the remaining life expectancy is determined by more effective protection by heat-induced substances in the ages yanger than 27 days. The unheated control group demonstrated acquired heterogeneity of frailty with chronological age while the heat-induced substances defend the worms in a universal way and protect against the development of frailty.

Ageing and survival after different doses of heat shock: the results of analysis of data from stress experiments with the nematode worm Caenorhabditis elegans.

Stress experiments performed on a population of sterilised nematode worms (Caenorhabditis elegans) show a clear hormesis effect after short exposure and clear debilitation effects after long exposure to heat shock. An intermediate duration of exposure results in a mixture of these two effects. In this latter case the survival curves for populations in the stress and control groups intersect. In this paper we develop an adaptation model of stress and apply it to the analysis of survival data from three such stress experiments. We show that the model can be used to explain empirical age-patterns of mortality and survival observed in these experiments. We discuss possible biological mechanisms involved in stress response and directions for further research.