Heritability of lateralization in fish: concordance of right-left asymmetry between parents and offspring.

The poeciliid fish Girardinus falcatus shows a consistent population bias to detour a vertical-bar barrier preferentially leftwise when approaching a dummy predator to inspect it; the asymmetry seems to be due to a preferential use of the lateral field of the right eye during fixation of biologically relevant stimuli such as a predator. In order to unravel the origins of this lateral bias, we took advantage of the individual variability present in the natural population to perform artificial selection experiments. Males and females that scored similarly at the detour test were mated together and their progeny were tested in the same task. Results showed that there was a striking similarity in the strength and in the direction of the asymmetries between parents and offspring. Correlation was highly significant and the estimate of heritability was greater than 0.5. This represents the first demonstration of heritability of the direction of a behavioural asymmetry outside the primate order. The finding paves the way to the use of a novel and suitable animal model for the neuro-genetics of lateralization and to the possible identification of homologous and/or analogous genes underlying brain asymmetry among vertebrates.