Sex differences in laterality are associated with reproduction in three-spine stickleback

Laterality, the partitioning of information processing into specific brain hemispheres, is widespread across animal taxa. Substantial unexplained variation in this trait exists, particularly between the sexes, despite multiple identified advantages of lateralisation. Here, we demonstrate a relationship between laterality (measured as directional biases), reproduction and experience of mating and parenting. Using three-spine sticklebacks Gasterosteus aculeatus, a species with uniparental male care, we showed that individuals of the caring sex (males) were more strongly lateralised than the non-caring sex (females) during reproduction, and that laterality was reduced outside the breeding season in males. Additionally, males with experience of mating and parenting were more strongly lateralised than males without this experience. Our findings suggest that fitness related behaviours that vary between the sexes, such as reproductive behaviours including courtship, spawning and parenting, are significant but previously unidentified sources of variation in laterality.