Without optimum support: effect of maternal early deprivation on play in semiwild chimpanzees, Pan troglodytes

In mammals, robust connection between mothers and offspring plays pivotal roles in physiological and socioemotional development. Our study investigated the consequences of early maternal deprivation on social play behaviour in immature chimpanzees, examining expected and unexpected findings. In line with the predicted hypothesis, orphaned individuals exhibited lower frequencies of social play than mother-reared chimpanzees, supporting traditional notions of the indispensable role of maternal influence in the correct expression of social behaviours. However, the absence of discernible differences in the variability and roughness of playful patterns, tested for the first time in orphan and mother-reared chimpanzees, suggests that the presence of adult models may not be fundamental for expanding and regulating immature playful behavioural repertoire. Escalation into overt aggression did not differ between orphan and mother-reared chimpanzees, challenging the idea of the crucial role of maternal investment in developing self-restrain abilities during play. Orphans engaged in shorter sessions compared with mother-reared subjects; this strategy is naturally adopted by wild and captive chimpanzees when they need to cope with the risk of escalation during play fighting. Although maternal deprivation has been linked to anxiety-related and depressive behaviours in primates, our results reveal a degree of behavioural resilience in orphans that are still able to adhere to social rules during play, particularly when having contact with their peers. Although play behaviour development can arise from the multifaceted interconnection between early experiences, social dynamics and individual propensity to interact socially, our findings support the view, emerging from a plethora of studies on many social mammals, that play has an irreplaceable role in an individual's life history.