Evolutionary endocrinology: information encoded in steroid hormone concentrations

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As evolutionary endocrinologists, we are experts in the precise measurement of hormones in biological fluids such as saliva and blood and egg yolk. These skills support student projects as diverse as hormone involvement in adolescent onset depression, testosterone variability in aging men, hormonal changes in men becoming fathers, chronic and acute responses to stress, trans-generational effects of maternal stress on development of embryos, and hormone dynamics within individuals. Understanding hormone dynamics within individuals is the focus of this proposal, with experiments that obtain up to 24 small samples from one individual and then calculate the hormonal variability that the individual experiences from day to day. In spite of our new methods that provide tight experimental controls and small measurement error, we find that repeated sampling reveals huge variability. Within one male hamster, for example, testosterone concentrations fall anywhere between a low of 20 and a high of 2000 ng/dL over 24 repeated samples. Variability is also large in men, women, and adolescent girls, whether measured for sex hormones or for stress hormones. In addition, we have preliminary evidence that our measure of variability, the dynamic index, can change at critical transitions in life, such as becoming a father, and in response to lifestyle choices, such as exercise and diet. Coding information in concentration, and in dynamic variability around that concentration, would enable one hormone to carry two independent messages. Thus, proposed research will test our hypothesis that hormone variability, or 'noise', contains a hormone 'signal'. If the hypothesis is supported, our results will transform future experimental designs, bridge missing links between hormones and behaviour, and, eventually, might lead to changes in hormone delivery that reduce health risks.