Cultural artifacts: A comparison of senescence in natural, laboratory-adapted and artificially selected lines of Drosophila melanogaster

When animals are kept in the laboratory in non-overlapping generations, a high load of mutations with late-acting effects can accumulate over time. This may lead, in turn, to a gradual but steady decline in life expectancy. Selection experiments designed to extend longevity in laboratory-adapted lines may, in fact, simply restore the vigour that was lost from the original lines after they were introduced to the laboratory environment. To test this idea, we compared longevity in virgin males from six strains in the fruit fly, Drosophila melanogaster, including a wild-caught strain recently obtained from the wild, a laboratory strain that has been housed in the laboratory with a 2 week generation time for almost a century, two lines that had been selected for long life span, and two lines that had served as controls in the longevity selection experiment. We found that life span in the wild-caught strain was almost identical to that of the line that had been under selection for long life span for nearly 20 years. Life span in the laboratory strain and the two control lines was also quite similar. In contrast to previous studies, we found that variation in life span among strains was due almost entirely to variation in the intercept of the Gompertz mortality trajectory. Gompertz slopes among all strains were quite similar. We suggest that the effects of laboratory culture may be responsible, in part, for the trade-offs observed between late survival and early fecundity in selection experiments designed to test the antagonistic pleiotropy model of senescence.