Date Published: March 7, 2018
Publisher: Public Library of Science
Author(s): Giada Cordoni, Ivan Norscia, Maria Bobbio, Elisabetta Palagi, Kim A. Bard.
Play behaviour reinforces social affiliation in several primate species, including humans. Via a comparative approach, we tested the hypothesis that play dynamics in a group of lowland gorillas (Gorilla gorilla gorilla) are different from those in a group of chimpanzees (Pan troglodytes) as a reflection of their difference in social affiliation and agonistic support. We selected one group of lowland gorillas and one of chimpanzees, hosted at the ZooParc de Beauval (France), managed in a similar way and living in similar enclosures. The same observers video-collected and analysed data on play behaviour in both groups, by applying identical methodological procedures. Data showed that adult play was less frequent in the group of gorillas compare to chimpanzees. Polyadic play, which involves more than two players and is characterised by the most uncertain outcome, was also less frequent in gorillas than chimpanzees. Play sessions were more unbalanced (more unidirectional patterns by one of the player towards the other) in chimpanzees than in gorillas but in the latter play escalated more frequently into serious aggression. Play asymmetry in the gorilla group increased as the number of players increased, which explains why gorillas limited their polyadic playful interactions. In conclusion, our findings on the study groups of apes can be a valuable starting point to expand the study of social play in the great apes to evaluate if inter-individual affiliative relationships really account for the differences in play distribution and dynamics.
Compared to ‘serious’ behaviors, whose functions are immediately evident (e.g., sexual behavior, aggressive behavior), play is a difficult behavior to contextualize from both a functional and an operational point of view (for an extensive definition of play see ). When we talk about play we immediately think about its long-term benefits, such as motor, cognitive and social skill improvement [2,3]. However, play has also short-term benefits that are not always obvious to the observer. It has been demonstrated that play can reduce social anxiety linked to particular contexts such as crowded condition (gorillas, ; bonobos, ), pre-feeding competition (chimpanzees, ; bonobos, ; common marmosets, ; wolves, ), intra-sexual (sifaka, ) and inter-sexual competition (brown bears, ).
Before testing the predictions relative to play dynamics in the two species, we explored if our study groups actually reflected the social characteristics already reported in literature (see the Introduction) for chimpanzees and gorillas. Specifically, we carried out an analysis by comparing the level of grooming, contact sitting and agonistic support (e.g., coalitions during aggression) between the two study groups.
The distribution of affiliation and agonistic support in the chimpanzee and gorilla groups under study confirmed that they differed in their social interaction rates. Indeed, our findings showed that chimpanzees engaged in more events of agonistic support (Fig 1a) and spent much more time in close physical contact and grooming interactions compared to the lowland gorillas (Fig 1b; Table 7).