Abstract
Variation among individuals in robustness has been posed as a general explanation for the lack of increase in late-life mortality rates. Here, we test corollaries of this heterogeneity theory. One is that populations that have undergone strong laboratory selection for differentiated stress resistance should show significant differences in their late-life mortality schedules. To test this corollary, we employed 40 410 flies from three groups of Drosophila melanogaster populations that differ substantially in their resistance to starvation. No significant differences between these groups were found for late-life mortality. Another corollary of the heterogeneity theory is that there should be late-life plateaus in stress resistance that coincide with the plateau stage of the mortality curve. In 20 994 flies from six replicate outbred laboratory populations, we measured mortality rates every other day and starvation and desiccation resistance every 7 days. Both male and female starvation and desiccation resistance clearly decreased with time overall. There was no late-life plateau in male desiccation resistance. A late-life plateau in male starvation resistance may exist, however. Together, these two experiments generally constitute evidence against heterogeneity as a major contributor to the phenomenon of late-life mortality plateaus.
Highlights
IntroductionM.D. Drapeau et al / Experimental Gerontology 35 (2000) 71– 84 rates late in the life of Drosophila fruit flies and a number of other organisms, including medflies, wasps, nematodes, yeast, and humans (Charlesworth and Partridge, 1997; Vaupel et al, 1998)
Some evolutionary biologists, demographers, and gerontologists have directed their attention toward the well-documented plateau in age-specific mortalityM.D
With respect to the first test, the data presented here do not indicate any clear relationship between late-life mortality rates and large genetic differences in stress resistance
Summary
M.D. Drapeau et al / Experimental Gerontology 35 (2000) 71– 84 rates late in the life of Drosophila fruit flies and a number of other organisms, including medflies, wasps, nematodes, yeast, and humans (Charlesworth and Partridge, 1997; Vaupel et al, 1998). Because late-life plateaus in cohort mortality rates indicate that there is no “wall of death” past which no organism can survive, some individuals can theoretically live indefinitely. Late-life mortality plateaus seem to challenge current definitions and theories of aging (see Finch, 1990; Rose, 1991). Since 1992, some theorists have risen to this challenge of explaining late-life mortality plateaus by using population genetic theories of senescence (e.g., Mueller and Rose, 1996)
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