Maternal glucocorticoids have persistent effects on offspring social phenotype irrespective of opportunity for social buffering.

Exposure to stressors and associated hormones during development can significantly affect offspring phenotype, including social and philopatric behaviour, but these effects can be mediated by the postnatal social environment ('social buffering'). While the effects of social buffering are well established for complex social behaviours-such as parental provisioning, grooming or cooperative care-the role of social buffering for simpler social interactions-such as parental tolerance of offspring-remains less understood. Here we used the facultatively social viviparous lizard, Liopholis whitii, to test the following: (i) the effects of elevated maternal glucocorticoid levels during gestation on offspring mass, growth, dispersal and social interactions after birth; and (ii) whether these effects are mediated by postnatal mother-offspring association. We conducted a factorial experiment in which pregnant lizards were given thrice-weekly doses of a glucocorticoid hormone (corticosterone) or a control during gestation. Their offspring were then raised either alone or with their mother for 3 weeks. We subsequently released mothers and offspring in large semi-natural enclosures and quantified offspring mass and social/exploratory behaviour. There were persistent negative effects of prenatal glucocorticoid exposure on offspring growth. We also observed lasting effects of prenatal glucocorticoid exposure on social behaviour: offspring from glucocorticoid-treated mothers had stronger social associations with other individuals, including with their mother and siblings, compared to offspring from control mothers. Association with their mother early in life did not mediate the effects of prenatal glucocorticoid exposure on offspring phenotype. These effects demonstrate that maternal stress can be an important mediator of variation in social behaviour in lizards, even overriding the influence of the social environment in the early postnatal period. This has potential implications for understanding how social groups form and are maintained.