Acceleration of senescence in the collared flycatcher Ficedula albicollis by reproductive costs

Abstract

SENESCENCE is the innate deterioration of an organism that leads to a decline in its fitness components such as fecundity and survival expectations with advancing age^1,2. Williams³ proposed that the evolution of senescence could be understood in terms of age-specific pleiotropic gene action, where a mutation increases fitness early in life at the expense of reducing it later on. The basic idea, first proposed by Medawar¹, is that mutations acting early in life are more sensitive to selection than those acting later, as the early effects would be expressed in more individuals than would the late effects. A cost of reproduction, where an increase in reproductive rate reduces future survival or fecundity, could be the kind of pleiotropic gene action that generates senescence^2,3. Evidence exists for such costs in animals and plants^4–8, but their role in the evolution of senescence is so far not clear². Most empirical work has been with fruit-flies in laboratory studies, where selection experiments indicate negative genetic correlations between early and late fitness components^9–12. But it is not certain how applicable the results of such studies are to natural populations. Here we report that the clutch size of older individuals in the collared flycatcher Ficedula albicollis is affected by their reproductive effort early in life. This provides empirical support for Williams's idea that costly reproduction accelerates senescence for fertility in a vertebrate species under natural conditions.