Trans-generational costs of reproduction and the evolution of life histories

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Why do some individuals in a population deteriorate much more rapidly with age than others? This is a question of great biological and biomedical importance, but remains a puzzle. Current theory is based on the idea that reproduction is costly: individuals that invest more in current reproduction pay a cost in terms of reduced future reproductive success and survival. There is lots of evidence to support this proposed cost of reproduction, but the underlying mechanisms remain controversial. One major theory is that reproduction entails increased levels of oxidative damage, which can have negative consequences for the functioning of cells and tissues, and thereby reduce survival. However, evidence that reproduction increases oxidative damage is equivocal: in some contexts breeding individuals show higher levels of oxidative damage, but a growing number of studies show the opposite pattern.We recently suggested that previous results can be explained if oxidative damage has negative impacts not just on mothers, but also on their developing offspring, i.e. if there are trans-generational costs of reproduction. In these circumstances mothers could gain from reducing their own levels of oxidative damage to shield their offspring from harm during sensitive developmental windows - the 'oxidative shielding' hypothesis (OSH). Trans-generational impacts of oxidative damage could have a major impact on patterns of growth, reproduction, and survival, but we currently have almost no theory to understand these impacts. Our goal is to develop this new theory of trans-generational costs of reproduction, and to carry out the first test of the OSH and our new models in a tractable wild mammal study system, the banded mongoose. It is particularly powerful to test life history theory in natural populations, where trade-offs can be measured together with their consequences for fitness. The banded mongoose is uniquely suited to our objectives because we know the full breeding history and pedigree of all animals, and we can experimentally manipulate the nutritional condition of mothers during pregnancy and follow the development and success of their offspring as they grow up and start to breed themselves.The project will advance conceptual understanding of why individuals vary so much in patterns of development and reproduction, and help to answer the question of why some individuals survive longer than others. Our theoretical framework could readily be applied to study other forms of damage that carry-over to affect offspring, such as heavy metal poisoning, or transmissible parasites and pathogens. The project fits squarely with NERC's strategy priorities to manage environmental change and understand the resilience of natural populations to environmental hazards, because both of these priorities require improved understanding of how individuals defend against environmental challenges and stressors, and how perturbations experienced by one generation reverberate through to influence the viability of future generations.