Quantitative measures of aging in the nematode Caenorhabditis elegans. I. Population and longitudinal studies of two behavioral parameters

As a first step in the quantitative characterization of senescence in the nematode Caenorhabditis elegans, we have studied movement wave frequency, defecation frequency, and whole-body water efflux as a function of age. Populations of C. elegans, strain N2, were cultured monoxenically on E. coli lawns at 20 degrees C. The median lifespan in such populations was approximately 12 days. Population mean movement wave frequency declined linearly with age (slope = -4.66 waves/minute per day). The decline in population mean defecation frequency (defecations per minute) was multiphasic, consisting of (1) a rapid decline (slope = -0.233 defecations/minute per day) from day 3 to day 6, (2) no apparent trend from day 6 to day 9, and (3) a gradual decline (slope = -0.089 defecations/minute per day) from 9 to day 14. Animals alive on or after day 15 were not observed to defecate. In longitudinal studies, individual animals exhibited linear declines in movement wave frequency and multiphasic declines in defecation frequency. For future population studies, the age-dependent declines in movement and defecation frequency appear sufficiently large and reproducible to a multiparametric description of senescence in C. elegans. One physiological parameter, 3H2O efflux, was found to be age-independent and to consist of two first-order rates. The half-times of the slow and fast efflux rates were approximately 15 and approximately 2.1 minutes, respectively. The two half-times and the fractions of 3H2O exhibiting the two half-times were invariant with age.