Laterality of brain and behavior has been found to be widespread among animal species. Recently, laterality has been found to be correlated to personality. In addition, the development of both personality and laterality in fish can be influenced by environmental factors: e.g., high perceived predation leads to bolder and more lateralized individuals. Also, in fish, bolder and more lateralized individuals tend to swim in a safer and energetically more favorable position than other individuals while schooling. However, whether this correlative evidence indicates a causal relationship between laterality and personality is yet unclear. Such a causal link will have consequences for evolution, as selection on one may constrain evolution of the other.
The aim of this experiment was to manipulate rearing conditions to see to what extent both laterality and personality are affected together, which would indicate a causal relationship between the two. Three-spined stickleback larvae were therefore reared under predation cues or in the absence of it in small or large groups for 3 months in a two-by-two design, after which their behavior during schooling, social interacting, and predator inspection was recorded in standard tests. We expected that the fish reared under high predation perception and/or in large groups will show a higher tendency to school, a bolder behavior and more lateralized behavior than the control group reared under low predation pressure and small group size.