Abstract
Cerebral lateralization is an evolutionarily ancient adaptation, apparently ubiquitous among vertebrates. Despite demonstrated advantages of having a more lateralized brain, substantial variability in the strength of lateralization exists within most species. The underlying reasons for the maintenance of this variation are largely unknown. Here, we present evidence that the strength of lateralization is linked to a behavioural trait, aggressiveness, in the convict cichlid (Archocentrus nigrofasciatus), and that this relationship depends on the sex of the fish. This finding suggests that individual variation in behaviour may be linked to variation in cerebral lateralization, and must be studied with regard to the sex of the animal.