The influence of early-life stress on behaviour, physiology and fitness in the wild.

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My research tests the persistent effects of the early-life environment on individual physiology, behavior and fitness by integrating ecological and physiological methods in wild populations. Early-life conditions can have profound and lasting effects throughout an individual’s lifetime, however, the downstream influences on behaviour, physiology and fitness are not well understood. Stress and glucocorticoids have well-known and important effects on the development and function of the nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. Moreover, the HPA axis is a key physiological mechanism connecting an organism to its environment, through both acute responses and long-term adaptation, yet how stress influences fitness in wild populations is virtually unknown. Recent laboratory studies indicate that pre- or postnatal stress and/or glucocorticoid treatment have detrimental effects on the brain, behaviour and HPA axis in adult offspring. Although, if parents are adapting offspring to best match future environmental conditions, these apparent detrimental effects may, in fact, facilitate survival and reproduction in a stressful environment. To investigate the manifestation of early life stress in adulthood and the persistence across generations requires the ability to follow marked individuals within long-term populations. My students and I will work to understand the ecological and physiological long term effects of the early life environment by conducting experimental field studies in two populations. First, using a long-term marked population of Savannah sparrows (Passerculus sandwichensis) on Kent Island NB, we will investigate the effect of the early environment on physiology, song behaviour and fitness by measuring natural individual variation among chicks in their hormonal profiles (glucocorticoids, testosterone, estradiol), stress physiology, and body condition. In individuals that survive and return to breed on the island, we will measure adult stress physiology, song behaviour, survival, and reproductive output. Our second general study is a marked population of deer mice (Peromyscus maniculatus) in Algonquin Park, Ontario, where we will test hypotheses related to natal population density, maternal behaviour and downstream effects on offspring behaviour and physiology. Recent work in small mammals has demonstrated that population density is positively correlated with maternal stress hormone levels and that maternal behaviour is affected by population density. And while it is known that behavioural effects in offspring due to the maternal environment are epigenetically transmitted and F1s have an altered HPA axis in adulthood, it is not clear whether these effects persist across multiple generations and, importantly, what the consequences are for offspring fitness. In both of these populations, we will also use published genomic information for closely related conventional lab animals (zebra finch and lab mice) to develop cutting edge epigenetic tools to investigate a novel mechanism for the multigenerational transmission of signatures of the pre- and post-natal environment. Overall, these are rare opportunities to test unique predictions related to physiological and fitness consequences of early life stress. Further, because the HPA axis is a primary mediator of an organism’s response to its environment, understanding the mechanisms by which maternal stress affects HPA axis development and function is critical as more and more wild populations are being exposed to anthropogenic factors that may affect HPA function and influence fitness.