Detecting early-life components in the determination of the age of death.

The non-heritable intrapopulation variability of lifespans can be used as a tool for studying the onset of expression of senescence. For this purpose, analytical methods are described and illustrated here. They are simple and applicable to any system including the limited clonal division potential of cells in culture (in vitro senescence). Using these methods, two questions can be posed: (1) when is lifespan first determined? and (2) are the pre-senescent events of life correlated with lifespan? The use of the analysis in answering these questions is exemplified with a few preliminary experiments. These are intended to be illustrative and provocative rather than definitive. The results suggest the following which show that the methods of this report can profitably be used to answer important questions concerning senescence. In the Oregon-R line of Drosophila melanogaster most if not all of the intrapopulation variability in lifespan is non-heritable, in support of the conclusion of Lints. The variability may instead indicate the stochastic action of the mechanism of senescence itself; other models are also considered. Experiments indicate that much of the variability to be expressed in lifespan may be present in latent form very early in life in Drosophila. Evidence is presented indicating that two pre-senescent events studied are correlated with lifespan and hence are landmarks of the progress of senescence. It is argued that such experimental results can place constraints on theories of senescence.