Effects of an endocrine disrupter on the development of behavioral differences between individuals and populations of threespined stickleback (Gasterosteus aculeatus)

This dissertation was motivated by the observation that individuals differ in behavior. With threespined stickleback (Gasterosteus aculeatus), I address two general questions. First, I ask how a pollutant might produce individual variants. Second, I ask about the consequences of behavioral syndromes, or correlations between individual differences in behaviors across contexts.; Chapters One and Two examine the influence of an endocrine disrupting chemical (EDC) on behavior. Using an EDC which mimics naturally-occurring estrogen (ethinyl estradiol), I show that exposure to an environmentally-relevant concentration of this EDC can produce changes in behaviors that are strongly tied to fitness. Chapter One describes how exposure to ethinyl estradiol reduced adult male aggressive behavior. In Chapter Two, I show that chronic exposure to ethinyl estradiol increased growth, risky behaviors and mortality in immature stickleback. These are some of the first documented cases of behavioral effects of EDCs, and suggest that some their most alarming impacts may be on heretofore-unexamined endpoints.; Chapters Three and Four address the significance of individual differences in behaviors across contexts. In Chapter 3, I ask whether the activity-aggression-boldness behavioral syndrome is a general characteristic of stickleback and test the hypothesis that behavioral syndromes can act as evolutionary constraints. According to this hypothesis, the behaviors that comprise a syndrome should be positively related to each other both within and between different populations. Neither of these predictions were supported. I found that the activity-aggression-boldness behavioral syndrome characterized one Northern Californian population (the Navarro River) but not another (Putah Creek). Moreover, the traits were actually negatively related to each other across populations.; In Chapter 4, I show that behavioral syndromes can be stable through time even though the single behaviors that comprise the syndrome are not. Promising directions for future research include examining the selective factors that favor the coupling or uncoupling of behaviors at some ages and in some populations but not others, and the proximal mechanisms which determine how easily this can occur.