Sex-specific effects of maternal testosterone on lateralization in a cichlid fish

Lateralization of cerebral functions is a fundamental aspect of the organization of brain and behaviour in vertebrates. Sex differences in human lateralization have inspired researchers to postulate several hypotheses concerning the effect of prenatal testosterone on lateralization, but few experimental studies have examined these hypotheses. We investigated whether prenatal testosterone affects strength or direction of lateralization in a cichlid fish, Aequidens rivulatus. Eggs were given a control or testosterone treatment immediately after spawning, mimicking elevated maternal androgen concentrations towards the high end of the natural range. After 7 months the fish were tested in two rotational preference tests. As expected from earlier studies, control fish showed (nonsignificant) right-eye preference while viewing a predator and (significant) left-eye preference while viewing their mirror image, but no clear sex differences were apparent. A sex-specific effect of our treatment was found in the first test. Only females exposed to elevated prenatal levels of testosterone significantly shifted in direction of lateralization. In the second test no effect of the treatment was found. Our results suggest that mothers have a stronger influence on the lateralization pattern of their daughters than on their sons, but do not support any of the current hypotheses about prenatal testosterone and development of lateralization.