Patterns of male fitness conform to predictions of evolutionary models of late-life

We studied lifetime male virility, a male fitness component, in five populations of Drosophila melanogaster. Virility was measured as the number of females, out of eight total, that a male could fertilize in 24 hours. Individual males were measured at weekly intervals until they died. Virility declined in an approximately linear fashion for the first three weeks of adult life. It then stayed low but relatively constant for another three weeks, exhibiting a clear plateau. These observations are consistent with the evolutionary theories of late-life.The results were not consistent with a simple heterogeneity theory of late-life. This is the first demonstration of a late-life plateau for a male fitness component. We also found that the virility of males that were within seven days of death was significantly lower than similarly aged males that were not about to die. This rapid deterioration of virility prior to death, or death spiral, is similar to a decline in fecundity that we had previo...