Life span variations in 128 successive generations of D. melanogaster. I. Evidence that the phenomenon exists and analysis of the variations mode.

Survival of Drosophila melanogaster was estimated in 128 successive generations for 5 years. The resultant 116 samples (58 for females and 58 for males) containing series of individual values of life span (LS; 50-90 values in each series) were analyzed. Each of 58 pairs of samples belonged to a definite generation in a continuous succession where every next generation was an offspring of the preceding one. In total, 10180 Drosophila flies (5100 females and 5080 males) were studied. The mean life span (MLS) was found to be considerably heterogeneous in the series of generations: in many pairs of consecutive generations, MLSs significantly differed within two errors of the mean (P<0.05), and the minimum and maximum MLSs in the series differed from each other almost twofold. The use of the nonparametric Kruskal-Wallis test made it possible to conclusively demonstrate highly significant (P<0.001) differences between LS distributions and their medians in the series of successive generations of D. melanogaster. Highly significant (P<0.0001) positive correlations (from 0.61 to 0.91) between the parameters characterizing the minimum (t(10)), mean, and maximum (t(90)) LSs were found. This indicates considerable consistency of the LS variations in successive generations of the same population, with the proportions of individuals with low and high LSs remaining about the same irrespective of the MLS. It was demonstrated with the use of mathematical simulation that the MLS changes in successive generations may be regarded as an oscillatory process and described as a sum of several (three to five) harmonic components. The calculated determination coefficients were high (93.51 and 88.93% for females and males, respectively). This indicates that the mathematical model used for simulation adequately described the observed variations in MLS. The results are discussed in terms of population gerontology and the problem of geroprotector effectiveness.