Evolutionary patterns among measures of aging

Abstract

Maximum lifespan has been one of the most common aging measures in comparative studies, while the Gompertz model has recently attracted both proponents and critics of its capacity to adequately describe the acceleration of mortality in the oldest age classes. The Gompertz demographic model describes age-dependent mortality rate acceleration and age-independent mortality using the parameters alpha and A, respectively. Evolutionary biologists have predominantly used average longevity in studies of aging. Little is known about the evolutionary relationships of these measures on the microevolutionary time scale. We have simultaneously compared Gompertz parameters, average longevity, and maximum longevity in 50 related populations of Drosophila melanogaster, many of which have been selected for postponed aging. Overall, these populations have differentiated significantly for the A and alpha parameter of the Gompertz equation, as well as average and maximum longevity. These indices of aging appear to measure the same genetic changes in aging. However, in some specific population comparisons, the relationships among these measures are more complex. In a second experiment, environmental manipulation of longevity had substantially different effects from genetic differentiation, with the A parameter accounting for changes in overall mortality. The adequacy of the maximum lifespan and the Gompertz equation as indices of aging in evolutionary studies is discussed.