|Institution:||University of British Columbia|
|Full text PDF:||http://hdl.handle.net/2429/52312|
Maternal experiences can have profound effects on offspring phenotype. In oviparous animals, prolonged maternal exposure to stressors can elevate circulating cortisol and is thought to also elevate egg cortisol. Experimental increases in egg cortisol are known to affect offspring performance. In fishes, past research has focused on how chronic maternal exposure to stressors affects egg size and embryonic survival, but changes to egg hormones and progeny phenotype beyond early development are not well understood. The aim of this thesis was to test the hypothesis that maternal exposure to a stressor alters behavioural and physiological attributes of offspring, and that those alterations are mediated by increases in egg cortisol. The research focused on Pacific salmon; animals that, as adults, encounter diverse stressors during their once-in-a-lifetime migration to spawning areas. I found that experimentally elevating egg cortisol, mimicking the presumed outcome of maternal stress, modified offspring morphology, swimming performance, and behavioural responses to conspecific intruders and simulated predator attacks. However, when I chronically exposed females to a daily chase stressor during sexual maturation, egg cortisol at spawning was not affected. Despite the absence of differences in egg hormone content, maternal stressor exposure did have latent effects on offspring swimming performance and physiological stress responses. Collectively, the evidence presented in this thesis suggests that, in Pacific salmon, experimentally manipulating egg cortisol elicits changes in offspring, but maturing females may have the capacity to buffer eggs from increases in cortisol. Gametic properties other than the concentration of cortisol are likely affected by maternal stress and responsible for the observed changes to offspring performance. The multidirectional effects of maternal stress and egg cortisol treatment on offspring traits I report in this thesis support an emerging notion that the intergenerational effects of stress are highly-context dependent, as are interpretations of the adaptive versus maladaptive nature of changes to offspring. I conclude that the complexities of maternal stress and egg hormone deposition are not always captured when examining a single offspring trait at one life stage, without consideration of all components of the intergenerational process.