Why do organisms age? This is one of the big, unsolved questions in biology, because it is unclear how a process that decreases fitness can persist evolutionarily, and why species do not evolve to live longer. Many evolutionary theories have been suggested to explain, but it is likely that multiple factors contribute to the phenomenon. One potentially very important factor has been largely ignored: transgenerational epigenetic effects of senescence. Epigenetic effects can strongly affect the predictions of evolutionary models. One such epigenetic, trans-generational factor that affects fitness is parental age. It has been known for nearly a century that a mother's age can affect her offspring's, and even her grand- offspring's fitness. However, all studies have been done in the laboratory. Therefore, it is unknown whether the effect of parental age operates in wild populations, and how it contributes to our understanding of the evolution of longevity.
We propose to study the effects of parental and grand-parental age on their offspring's lifespan, reproductive success, physiology and genetics in a wild population of house sparrows. We have data available from a long-term study of sparrows in which we will examine these topics in detail. Only a closed population such as the one that we is uniquely suited for this study, as we can accurately estimate lifespan, fitness and parentage, which are all prerequisites for the longitudinal study of longevity on individual fitness. Also, we will use focused experiments with captive birds to cement our hypotheses, and individual-based simulation models to explore the implications of parental age effects on the evolution of longevity.
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