Energetics and avian life-history trade-offs

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Species and populations of animals differ widely in growth rate, fecundity and other life-history traits. Fundamental to understanding diversity in life-history strategies is the recognition that trade-offs exist among various traits. The dominant trade-off is the "cost" of reproduction; that between current reproductive effort and future fitness. For example, when feeding dependent young, parents may offset high daytime energy expenditure by reducing, among other things, immune function and/or overnight metabolic rate. The physiological mechanisms underlying such compensatory adjustments remain largely unknown. I propose to use captive birds to identify potential metabolic and hormonal mechanisms enabling reductions in overnight metabolism. Understanding the physiological mechanisms that may constrain an individual's response to increased daytime energy expenditure is critical to predicting how populations will respond to environmental perturbations. Frequently, poor environmental conditions can result in breeding birds being unable to meet offspring food demands, with potentially negative fitness consequences. To better match their offspring to prevailing environmental conditions, parents appear able to modify offspring physiology, via signals during development (e.g., egg nutrient content or antibody levels). The second major component of my proposed research is to determine how/when such signals might increase offspring fitness. Using quail, I propose to test the effect of pre and postnatal protein limitation on the subsequent fitness of individuals when they are reared in variable environments as adults. Parallel field studies will test whether geographic variation in pathogen pressure influences the levels of prenatal antibodies females transfer to offspring, and whether levels are influenced negatively by maternal stress. If elevated maternal stress constrains prenatal antibody transmission, there may be negative implications for populations experiencing combined environmental degradation and the threat of emerging diseases.