Natural selection and the evolution of maternal age effects

Abstract

Maternal age at birth has been demonstrated to affect offspring performance in aspects associated with fitness, including juvenile survival, lifespan, and fitness. A tendency appears to exist for such maternal age effects to be deleterious (‘maternal senescence’). However, there also appears to be much variation in the degree (and even in the direction) of these effects. Why should maternal senescence evolve and where should we expect it to be strongest (or weakest)? The clearest and most general way to explore this question theoretically is to expand William Hamilton’s models of the evolution of ageing to age-specific maternal genetic effects for vital rates. This approach has been applied specifically only to juvenile survival, but it has yielded results that show: 1) that selection always favours the evolution of this manifestation of maternal senescence; 2) that the evolved rate of senescence will differ from actuarial and reproductive senescence; and 3) exactly how selection drives the age-of-onset of maternal senescence. Here I will discuss how this model of maternal genetic effects can be adapted to all other vital rates, and through these, to explain how natural selection can favour other aspects of maternal senescence, such as the Lansing Effect and reduced offspring fitness caused by advancing maternal age.