Lines of Danio rerio selected for opposite behavioural lateralization show differences in anatomical left-right asymmetries.

Previous studies suggest that laterality of the viscera, morphological asymmetries of the brain, and lateralization of cognitive functions have a common genetic origin. To test this hypothesis, we conducted an artificial selection experiment for behavioural lateralization of eye use in two strains (TL and GT) of zebrafish (Danio rerio), maintaining one selected line in each strain for five generations. In addition, we investigated, using molecular markers, whether there was any correlation among directionality in eye preference, diencephalic left-right asymmetries in the brain and positioning of the viscera. After one generation of selection, the right- and left-eye lines of both strains showed a significant difference in the behavioural trait. This difference was maintained for all the five generations even though we observed a progressive decline in the response to artificial selection in subsequent generations for both strains. Overall, anatomical evidence suggests that selection for right-eye use significantly increased the frequency of reversed asymmetry in the epithalamus while selection for left-eye use decreased it. However, the response was irregular since not all samples conformed to this pattern. The association between the direction of behavioural selection and pancreas position was less clear-cut, although the concordance between visceral and brain asymmetries exceeded 90% in both strains.