Experimental effects of early‐life corticosterone on the hypothalamic–pituitary–adrenal axis and pre‐migratory behaviour in a wild songbird

Abstract

Although laboratory studies have shown that chronic exposure to elevated glucocorticoids during development has profound effects on animals, we still have a poor understanding of the consequences of early-life stress on wild individuals. In an island population of Savannah sparrows (Passerculus sandwichensis), I examined multiple hypotheses to explain how elevated corticosterone exposure during the nestling period influenced both hypothalamic-pituitaryadrenal (HPA) axis function and the subsequent movement and survival of young after they fledged the nest. Corticosterone-treated nestlings had higher baseline corticosterone levels and lower stress reactivity than untreated individuals, and were more sensitive to inclement weather.Corticosterone-treated individuals also had higher rates of temporary emigration outside of the study site than sham or controls. My results provide support for both the ceiling hypothesis and CORT-activity hypothesis, and highlight the importance of tracking individuals across multiple life stages to understand how early life events carry-over to influence both physiology and behaviour.iii ACKNOWLEDGEMENTS

Local density regulates migratory songbird reproductive success through effects on double‐brooding and nest predation

“…The number of young fledged from a nest was recorded as the number of nestlings banded on the seventh day after hatching. In our analyses, we excluded data for females for which we lacked a complete breeding history (e.g., females for whom we were missing one or more nesting attempts or for which one or more nests was outside the standard study area) or whose nests were the subject of experimental manipulations (e.g., clutch size manipulations; Mitchell et al 2011, Pakkala et al 2015. to the penultimate egg.…”

Early-life manipulation of cortisol and its receptor alters stress axis programming and social competence

“…Although early social experience alters both stress axis programming and social competence, it is as yet unknown whether stress axis programming in early life causally determines the development of social competence, and if so, by which mechanism. Few studies have pharmacologically manipulated the stress axis prenatally or in early life to test for causal links between this axis and behaviour (neophobia [28,29]; aggression [30]; defence against an intruder [31]; migration [32]; predator avoidance [33]; exploration [34]). A well-developed social competence should be particularly important for highly social species, such as cooperative breeders, in which almost all aspects of life include social interactions [4].…”

Pre‐ and postnatal effects of experimentally manipulated maternal corticosterone on growth, stress reactivity and survival of nestling house wrens

“…This increased maternal provisioning results in nestlings achieving significantly higher size‐adjusted body mass (Bowers, Bowden, et al., ), which could, in theory, influence their stress reactivity. Experimentally increased postnatal corticosterone in nestling Savannah sparrows ( Passerculus sandwichensis ) led to lower stress reactivity than control nestlings (Pakkala, Norris, Sedinger, & Newman, ), so it seems possible that if maternal parental behaviour affects HPA axis function, females could, postnatally, influence stress reactivity of their young. Indeed, in mammals, a number of studies have shown that maternal behaviour can, to some extent, mitigate the effects of any downregulation of the HPA axis in offspring that arises from adversity experienced early in life (Fish et al., ; Weaver et al., ).…”