On the discontinuous character of annuity curves. III. Two forms of viability variation in Drosophila melanogaster

The validity of the two-component structure of annuity curves in Drosophila melanogaster (line Canton-S) observed in our previous studies has been confirmed. The structure is formed by a combination of a stable five-phase pattern and the variability of phase duration (the latter determines the variability of insect viability). Both the stable and the variable component were preserved over 60 generations of flies. The unconventional type of variability addressed in the present study exists along with the well-known type of variability related to the stochastic variation of the annuity curves. The variance of viability that characterizes the reaction norm remains unchanged in a series of generations as well. Thus, both types of variability can be classified as genetically determined phenomena.