Regulatory mechanisms and cost of reproduction

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What prevents animals, including humans, from producing as many offspring of the highest quality as they like? Evolutionary biology provides the answer that there is a 'cost' to reproduction wherein the benefits of increased investment in a current reproductive bout are offset by costs in terms of current condition, future fecundity and survival. In birds, considerable evidence from studies where investment in egg production has been experimentally-manipulated supports this concept. However, one area of knowledge where we still have only a very rudimentary understanding is with regard to the causal mechanism(s) underlying costs of reproduction. Historically, it has been assumed that the cost of reproduction is energy or nutrient-dependent and that it involves a relatively simple resource-allocation mechanism where resources required for reproduction are reallocated away from other physiological functions (e.g. immune function) which in turn have negative effects. More recently it has been suggested that costs of reproduction might instead be caused by reproduction itself or the regulatory (physiological) mechanisms underlying reproduction. This project will investigate two ideas related to this: a) that anemia associated with egg production decreases the aerobic or exercise performance of females, and b) that reproduction increases susceptibility to oxidative stress ("cellular damage") and that this links sex and death. Our approach is experimental and integrates evolutionary biology, ecology and physiology. For example, we will use drugs to increase or decrease the level of anemia in laying birds and then directly test effects on flight performance, breeding success, and offspring growth. This project will provide novel, comprehensive data on causal mechanisms underlying costs of reproduction. Furthermore, although this work might seem esoteric through the application of physiological approaches our work will provide novel insight into key questions concerning effects of environmental variation (climate change) on avian populations (e.g. Mediterranean blue tit populations and Arctic-nesting eider ducks), including species of conservation and management concern (e.g. marbled murrelets).