Inter-individual differences in behavior, termed "animal personality," are often consistent over time and across contexts, and can be significantly related to fitness. Most studies of animal personality are conducted in the laboratory on captive animals or with experimental protocols on wild animals; few studies have used observational data from free-living animals to examine personality. In this dissertation, I use longitudinal data collected under naturalistic conditions to study personality in a wild population of spotted hyenas (Crocuta crocuta). This study is the first to examine the stability, the proximate causes, and the fitness implications of consistent inter-individual differences in a large, free-living carnivore. I investigated three personality traits that are particularly pertinent to survival and reproduction in spotted hyenas: boldness, aggressiveness, and sociability. Lions are a major source of mortality for hyenas, yet hyenas regularly interact with them directly due to the potential benefits of acquiring food. Because hyenas must balance the risk of injury or death with the benefits of resource acquisition, lion-hyena interactions offer a promising way to study boldness. Aggression is frequent and easily observable in hyenas; moreover, it is tightly coupled with access to food, which is a major determinant of reproductive success in this species. Finally, hyenas vary in their propensity to engage in social behavior with conspecifics, and sociability has been shown to affect fitness in species with societies that are remarkably similar in size and structure to those of spotted hyenas. I found significant differences among individual hyenas in all three traits. However, whereas both sexes exhibited consistent inter-individual differences in aggressiveness and sociability, males were less consistent than females in their boldness; this may be due to their low social status and reduced access to resources. Attributes of the individual (e.g. social rank) and situational factors (e.g. seasonal prey availability) affected all three personality traits. Heritability and maternal effects were significant, but small, for both boldness and sociability. A much larger proportion of the variation in aggressiveness could be attributed to genetic and maternal effects, supporting previous research linking hormone exposure in utero to aggressive behavior later in life. Whereas both boldness and aggressiveness were stable across age classes, sociability changed across ontogeny and the nature of this change varied with social rank; at reproductive maturity, low- but not high-ranking hyenas became more likely to greet with conspecifics. The advantages of associating with dominant hyenas, such as increased feeding tolerance, may be especially important for low-ranking individuals. Interestingly, the fitness benefits of sociability and aggression also varied with rank; high rates of aggression and sociability enhanced the reproductive success of low-ranking hyenas more than that of high-ranking hyenas. Dominant hyenas have priority of access to resources, and may not obtain additional reproductive benefits from these personality traits. However, for low-ranking hyenas, gaining feeding tolerance via sociability or increasing resource-holding potential via aggressiveness may significantly enhance reproductive success.Both boldness and sociability were linked to survival, but these traits affected longevity in different ways. Highly social hyenas lived longer than those that were less social; meanwhile, selection on boldness was stabilizing, favoring hyenas with intermediate boldness values that struck a balance between reaping the benefits of risky behavior and minimizing the risks of injury and death.
Read
