Animal personality and the social context : the role of boldness and sociability variation in schooling fish

Abstract

Throughout the animal kingdom, individuals often differ consistently from one another in how they cope with their environment. In particular, consistent behavioural variation, known as animal personality, is a substantial driver of a range of important ecological and evolutionary processes. As most animal species are social for at least part of their lives and group living is common, a crucial link between personality and the social context may be expected. In this thesis I systematically investigate this link, using three-spined stickleback fish (Gasterosteus aculeatus) as my model system. I begin by showing that fish vary consistently in their boldness and sociability, with only boldness being positively linked to food intake for fish at rest. This finding provides support for evolutionary theory that links personality variation to life-history strategies, and lays the basis for work related to the social context. I continue by investigating how the social context may modulate personality variation and show that short contact with a social group may have carry-over effects and obfuscate personality expression when individuals are alone. Next, I observed fish in different pairs over time and found that social experience from both the current as well as previous social contexts are integrated in the risk-taking and leadership decisions of individuals but also depends on their boldness type. This result provides support for the importance of social feedback in the expression of personality differences. I go on to demonstrate that, in a pair, bolder fish have lower social attraction, with positive effects on individual’s leadership but negative effects on social coordination. Finally, by detailed tracking of the collective movements and group foraging of free-swimming shoals, I reveal boldness and sociability have complementary driving effects of on social structure, collective behaviour, and group functioning. Furthermore, I show that in turn the group composition determines the performance of individual personality types, providing a potential adaptive explanation for the maintenance of personality variation. Taken together, these studies provide an integrated account of animal personality and the social context and highlight the presence of a feedback loop between them, with personality variation being a key driver of collective behaviour and group functioning but also strongly affected and potentially maintained by it.