EVOLUTIONARY PATTERNS AMONG MEASURES OF AGING

Maximum lifespan has been one of the most common aging measures in com parative studies, while the Gompertz model has recently attracted both proponents and critics of its capacity to adequately describe the acc eleration of mortality in the oldest age classes. The Gompertz demogra phic model describes age-dependent mortality rate acceleration and age -independent mortality using the parameters a and A, respectively. Evo lutionary biologists have predominantly used average longevity in stud ies of aging. Little is known about the evolutionary relationships of these measures on the microevolutionary time scale. We have simultaneo usly compared Gompertz parameters, average longevity, and maximum long evity in 50 related populations of Drosophila melanogaster, many of wh ich have been selected for postponed aging. Overall, these populations have differentiated significantly for the A and a parameter of the Go mpertz equation, as well as average and maximum longevity. These indic es of aging appear to measure the same genetic changes in aging. Howev er, in some specific population comparisons, the relationships among t hese measures are more complex. In a second experiment, environmental manipulation of longevity had substantially different effects from gen etic differentiation, with the A parameter accounting for chances in o verall mortality. The adequacy of the maximum lifespan and the Gompert z equation as indices of aging in evolutionary studies is discussed.