Date of Award

10-1-2021

Publication Type

Thesis

Degree Name

M.Sc.

Department

Biological Sciences

First Advisor

O. Love

Second Advisor

D. Higgs

Third Advisor

D. Heath

Keywords

Climate change, Environmental stressors, Maternal effects, Pacific salmon, Senescence

Rights

info:eu-repo/semantics/openAccess

Abstract

Assessing the impact of environmental challenges on maternal state and breeding success is important for predicting how migratory Pacific salmon populations will respond to an increasingly stressful world. The overall goal of my thesis was to examine fine-scale senescent changes in female Chinook salmon over time, whether these changes impacted ovulation and egg quality, and whether exposure to an environmental challenge (low water) during senescence subsequently provoked even stronger state-dependent responses to ultimately impact female longevity and egg survival. Following an experimental decrease in water availability, I quantified changes in physical, physiological, and reproductive maternal state, then linked these changes to subsequent impacts on several performance-, quality- and fitness-related traits. We found that a low water stressor did indeed exacerbate the senescence-mediated effects of reproduction, producing changes in maternal state that had downstream effects on egg quality and survival. Specifically, I found that overall senescence (particularly physical deterioration and plasma cortisol) normally begins to increase in response to entering fresh water but was delayed until after ovulation in chronically-stressed females. Our results also confirmed the role of maternal effects on egg quality, as stress-induced increases in plasma cortisol, regardless of environmental treatment, resulted in subsequent rises to egg cortisol which negatively impacted offspring survival. Low water females were found to express lower levels of a key reproductive hormone (MIS) that peaked both earlier than expected and before controls, which served to lengthen ovulation windows and potentially provide females with more opportunities to spawn, maximizing performance and fitness. Understanding the downstream effects of environmentally-induced maternal stress on reproductive decisions and fitness can provide insight as to how different individuals or even populations of salmon may respond to changing river conditions.

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