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

Abstract

We studied lifetime male virility, a male fitness component, in five populations of Drosophila melanogaster. Virility was measured as the number of females, of eight total, that a male could fertilize in 24h. Individual males were measured at weekly intervals until they died. Virility declined in an approximately linear fashion for the first 3weeks of adult life. It then stayed low but relatively constant for another 3weeks, 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 7days of death was significantly lower than that of 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 previously documented. © 2012 The Authors. Journal of Evolutionary Biology © 2012 European Society For Evolutionary Biology.