Social lateralization in wild Asian elephants: visual preferences of mothers and offspring

Abstract

Abstract: Theoretical and empirical evidence suggest that socio-biological factors determine the expression of behavioural lateralization across species. One would expect the same association at the intraspecific level, that is, that the differences in social strategies of the two sexes entail the sex differences in the lateralized social processing. This study aimed to test whether this hypothesis applies to the lateralized behaviour of offspring towards a mother. The preferences in the use of the lateral visual field of the left and right eye were assessed in wild Asian elephant, Elephas maximus mothers and their young sons and daughters. The spatial positioning relative to a social partner during approach was used as a behavioural indicator of visual lateralization. At the population level, elephant mothers preferred to keep the young in their left visual field during slow travelling. In contrast, young did not display a one-sided bias for the whole sample. The lateralization, however, was pronounced in a sex-specific manner—sons preferentially kept their mothers in the right visual field, while daughters preferred to keep mothers in the left visual field. Intriguingly, both sons and daughters preferentially kept the familiar older young in the left visual field. Sons, thus, showed oppositely directed lateral preferences towards mother and non-mother companion. Presumably, sons aim to approach the mother from her left side (rather than to keep her in the right visual field) and benefit from optimized maternal perception, while daughters facilitate their own perception of the mother by keeping her in the left visual field. These sex-related differences in lateralized behaviour may result from strikingly different social strategies of two sexes. Significance statement: Young mammals show robust lateralization in the form of one-sided behavioural preferences in the interactions with their mother. Previous studies suggest that the social lifestyle may serve as a driving force in the evolution of behavioural lateralization. To test this proposition, we investigated behavioural lateralization in young subjects of Asian elephants, a species in which females are more gregarious than males. The lateralized behaviour of offspring towards the mother was found to be strongly sex-specific. In contrast, interactions with older young were lateralized in a similar manner in sons and daughters. Our results suggest that the benefits of a left-sided or right-sided position relative to mother have different significance for sons and daughters because of the distinctive social strategies of two sexes.