Abstract

An intensive study of longevity, female fecundity, and male reproductive behavior in Drosophila melanogaster was undertaken in order to establish whether late-life fitness characters in short-lived populations might be affected by the increase in deleterious alleles due to random genetic drift. We also sought to determine whether selection for late-life fertility could eliminate alleles that produce a decline in later fitness components in short-lived populations, as predicted by the mutation accumulation hypothesis for the evolution of aging. These experiments employed long-lived (O) populations, short-lived (B) populations, and hybrids made from crosses of independent lines from within the O and B populations. No detectable longevity differences were seen between hybrid B males and females and purebred B males and females. Reproduction in aged B purebred females was significantly less than in hybrid females at 3 wk of age only. A full diallel cross of the five replicate B lines showed a steady increase in hybrid male reproductive performance after the first week of adult life, relative to the parental lines. A full diallel cross of the five replicate O lines revealed no significant increase in hybrid O age-specific male reproductive success compared with the purebred O lines when assayed over the first 5 wk of adult life. The results on male reproductive behavior are consistent with the idea that relaxed age-specific selection in the B populations has been accompanied by an increase in deleterious, recessive traits that exhibit age-specific expression. Consequently, we conclude that a mutation accumulation process has been at least partly responsible for the age-specific decline in male B virility relative to that of the O populations.