Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor(s)

Scott MacDougall-Shackleton

Abstract

The Developmental Stress Hypothesis proposes that the honesty of birdsong is maintained by costs incurred during development, such that song in adulthood reflects exposure to early-life stressors. The purpose of this thesis was to provide a rigorous test of the Developmental Stress Hypothesis in song sparrows (Melospiza melodia). My three objectives were to determine the long-term effects of early-life stress on: 1) physiological traits (Chapters 2, 3, and 4); 2) male song production (Chapter 5); and 3) the response of females to song (Chapter 6). Nestlings were hand-reared in captivity under one of three treatment conditions: control, food restriction, or treatment with corticosterone (CORT). Exposure to both stressors affected nestling growth, standard metabolic rates, immune function, and endocrine regulation. There were pronounced sex differences in the effects of early-life stress on physiological traits. For example, females exposed to either stressor had lower plasma estradiol levels, but CORT-treated males had higher basal testosterone levels, showing that early-life stress has opposite effects on plasma sex steroid levels in males and females. Exposure to early-life stress affected male song production. Males exposed to either stressor sang less complex song and food-restricted males sang less accurate copies of the tutor song. Neither stressor affected song stereotypy or trill performance, however, suggesting that developmental stress may not affect vocal performance in this species. Females exposed to either stressor were less selective in their behavioural response to conspecific versus heterospecific song and to high versus low complexity song. This was paralleled by differences in levels of the immediate early gene Zenk in auditory forebrain regions. Finally, male song production was significantly related to some physiological measures. Males with a stronger swelling response to phyothemagglutinin sang more complex song and produced higher quality trills. These results provide support for the Developmental Stress Hypothesis and add to a growing body of evidence showing that early-life stress programs many physiological and neural systems.


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