Consistent individual differences in behaviour, and behavioural correlations within and across contexts, are referred to as animal personalities. These patterns of variation have been identified in many animal taxa and are likely to have important ecological and evolutionary consequences. My dissertation focuses on understanding how individual behavioral variation in free-living North american red squirrels (Tamiasciurus hudsonicus<\italic>) might be maintained in the face of natural selective pressures.I investigated the proximate sources of variation in red squirrel behavior by estimating sources of genetic, maternal and environmental variation, and the ultimate effect of behavior on reproductive success. I used a Bayesian animal model approach to estimate genetic parameters for aggression, activity and docility and found support for low heritabilities (0.08-0.12), and cohort effects (0.07-0.09), as well as low to moderate maternal effects (0.07-0.15) and permanent environmental effects (0.08-0.16). I also found evidence of a substantial positive genetic correlation (0.68) and maternal effects correlation (0.58) between activity and aggression, providing evidence of genetically based behavioral correlations in red squirrels. These results provide evidence for the presence of heritable variation in red squirrel behavior, but also emphasize the role of other sources of variation, including maternal effects, in shaping patterns of variation and covariation in behavioral traits.I then tested the hypothesis that ecological changes through time lead to fluctuating selection, which maintains variation in behavioral traits. Linear selection gradients on red squirrel dam aggression and activity significantly fluctuated in sign across years depending on the level of competition among juveniles. Selection on aggression and activity also differed among components of fitness, between the sexes and included nonlinear components between and within traits that also changed through time. These results suggest that repeatable and heritable individual differences in red squirrel behavior could be maintained by complex fluctuations in natural and sexual selection.Finally, I tested the hypotheses that mating chases provide the opportunity for both female and male red squirrels to select for context-dependent good genes and complementary genes for their offspring's recruitment. Specifically, I predicted that aggressive mates would be preferred in high-juvenile competition years, but disfavored in low competition years, and that mate choice for docility would be disassortative with low-docility squirrels preferring high-docility mates and vice-versa. I did not find support for adaptive context-dependent mate choice by females, but I did find support for male mate choice for complementary genes that was mediated through which female mating chase males attended. Male red squirrels attended mating chases disassortatively by docility, which would enhance fitness due to stabilizing selection on docility during juvenile recruitment. I also found evidence for post-copulatory selection for less aggressive males. These results highlight that even in systems with very high operational sex ratios, male choice is a factor that needs to be considered.In this dissertation I have shown that behavioral traits in red squirrels are important with strong evolutionary implications. Red squirrel behavior is heritable, subject to maternal effects and under strong selection that varies with environmental fluctuation and across components of reproductive success. This research has provided strong evidence that fluctuating selection could maintain variation in behavior. These findings provide a foundation for future work to elucidate mechanisms and continue exploring how and why behavioral variation is maintained.
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