Environmental stressors experienced by wildlife can have profound impacts on behavior and physiology that may have consequences for survival. My dissertation investigates how early life stress influences physiology, behavior, and survival in lake sturgeon (Acipenser fulvescens), an ancient chondrostean fish species. Lake sturgeon are regionally threatened, and therefore exploring the mechanisms by which stressors influence fitness is important in informing conservation efforts. My dissertation examines behavioral and physiological outcomes of four potential stressors encountered by lake sturgeon larvae: high temperature, maternal-offspring environmental mismatch, captive rearing, and predator interaction. In Chapter 1, I examined effects of temperature by comparing lake sturgeon reared at 10°C (low stress) and 18°C (high stress). During the free embryo stage, individuals reared at 18C exhibited a smaller cortisol elevation in response to an acute stressor, indicating lower physiological reactivity to stress. At the larval stage, individuals reared at 18C had higher levels of swimming activity and higher survival rates when exposed to a crayfish predator. Findings suggest that physiological and behavioral phenotypes induced by early life stress may be adaptive during subsequent life stages in high-stress contexts such as exposure to predatorsIn Chapter 2, I further explored the adaptive potential of stress-related phenotypes. Since stressed females can provision eggs with elevated cortisol that potentially prepares offspring for high-stress conditions, I investigated outcomes of a match or mismatch between egg cortisol and offspring stress levels. Individuals that experienced both high egg cortisol and high stress had reduced cortisol reactivity to an acute stressor, but only in one of two families. Results suggest that family (genetic) effects may mediate the interaction of maternal and offspring stress experiences. The largest differences in swimming activity occurred between the "mismatch" treatments, indicating that the combination of egg cortisol and offspring stress is more important in determining offspring behavior than is egg cortisol or offspring stress alone. In Chapter 3, I evaluated the role of stress in conservation programs by comparing stress levels, behavior, and predation rates for hatchery-produced and wild-caught lake sturgeon larvae. Cortisol levels did not indicate that hatchery-produced individuals were more stressed, but cortisol reactivity to an acute stressor disappeared for both hatchery-produced and wild-caught larvae after 9 days in the hatchery. Predation rates increased over time for larvae from both treatments, suggesting that the hatchery environment may inhibit survival even though individuals do not exhibit high stress. Results highlight that effects of captive rearing become evident after only a short duration spent in captivity during early ontogeny. In Chapter 4, I investigated stress-related effects of encounters with aquatic insects commonly found in stream substrate during the free embryo stage. Lake sturgeon experienced stress proportional to the amount of predation risk experienced. Individuals that encountered Perlidae (obligate predators) had high mortality as well as elevated cortisol and cortisol reactivity to an acute stressor. Individuals that encountered Isonychiidae (facultative predators) had slightly elevated mortality compared to individuals that encountered no insects, and had slightly elevated cortisol levels and cortisol reactivity. Results indicate early life stress as a mechanism by which nonlethal predator interactions impact lake sturgeon, indicating the importance of community-level ecological context in predicting outcomes for species of conservation concern.
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