Prenatal light exposure affects development of behavioural lateralization in a livebearing fish.

The existence of individual differences in handedness and other lateralized functions is an unresolved problem. Genetic factors account for only a small proportion of the variance but the contribution of environmental influences is still largely unexplored. In chicks and zebrafish the amount of environmental light reaching embryos during development greatly influences the lateralization of adults. To investigate whether a similar effect is present in livebearers, we measured behavioural lateralization in ten-day-old goldbelly topminnows born from females that have been maintained at high or low light intensities during pregnancy. Fish from high-light treatment were significantly lateralized in both visual and motor tests while fish exposed to low light intensities were not. As observed in chicks and zebrafish, the main consequence of light exposure was the alignment of the laterality of different individuals in the same direction. Lateralization is known to affect a number of fitness-related traits in topminnow and we suggest that light influence may be part of an adaptive mechanism allowing to adjust the developmental trajectories of offspring to the prevailing environmental conditions.