2-PARAMETER LOGISTIC AND WEIBULL EQUATIONS PROVIDE BETTER FITS TO SURVIVAL-DATA FROM ISOGENIC POPULATIONS OF CAENORHABDITIS-ELEGANS IN AXENIC CULTURE THAN DOES THE GOMPERTZ MODEL

We have fitted Gompertz, Weibull, and two- and three-parameter logisti c equations to suvival data obtained from 77 cohorts of Caenorhabditis elegans in axenic culture. Statistical analysis showed that the fitti ng ability was in the order three-parameter logistic > two-parameter l ogistic = Weibull > Gompertz Pooled data were better fit by the logist ic equations, which tended to perform equally well as population size increased, suggesting that the third parameter is likely to be biologi cally irrelevant. Considering restraints imposed by the small populati on sizes used, we simply conclude that the two-parameter logistic and Weibull mortality models for axenically grown C. elegans generally pro vided good fits to the data, whereas the Gompertz model was inappropri ate in many cases. The survival curves of several short- and long-live d mutant strains could be predicted by adjusting only the logistic cur ve parameter that defines mean life span. We conclude that life expect ancy is genetically determined. the life span-altering mutations repor ted in this study define a novel mean life span, but do not appear to fundamentally alter the aging process.