Is it for real? Structural differences between play and real fighting in adult chimpanzees (Pan troglodytes)

In primates, as well as in other mammals, play fighting (PF) is a complex form ofplayful activity that is structurally similar to real fighting (RF) and may also be used ina competitive way. Here, we verify the structural key differences that can distinguishPF from RF in adult chimpanzees (Pan troglodytes). We collected 962 h of videorecording on 30 adult individuals belonging to four chimpanzee groups (MonaChimpanzee Sanctuary, Spain;La Vallée des SingesandZooParc de Beauval, France).We applied different indices—two of which were borrowed from the ecologicalmeasures of biodiversity—to test for structural differences between PF (345sessions) and RF (461 sessions) in the levels of behavior repetition (Repeatability ofSame Behavior Index, RSBI), distribution uniformity (Pielou Index, J), variability(Shannon Index,H′) and, symmetry (i.e., reciprocal exchange of offensive/defensivebehaviors;Asymmetry Index, AI). Moreover, we compared the session durationbetween PF and RF. We found that duration and RSBI were higher in PF than RFwhile AI was higher in RF than PF. No difference was found between J and H′.Interestingly, both females and males maintained similar ranking positions (deter-mined via Normalized David's scores) in RF and PF. Our study indicates that sessionduration, behavior repetition, and symmetry can be distinctive structural keyfeatures of PF whereas dominance role‐reversal, behavior variability, and distribu-tion uniformity were not. PF in adult chimpanzees may have elements of seriouscontexts (e.g., absence of role‐reversal as in RF) which is in line with the view thatplay is a blended, multifunctional behavior deriving from the re‐combination ofdifferent behavioral systems. Our findings highlight the need to investigate playstructure and manifestation in a nuanced way to better understand the actualmotivation that underlies what appears to be play.KEYWORDSplay fighting, real fighting, reciprocity, repetition, role reversalAm. J. Primatol. 2023;85:e23537.wileyonlinelibrary.com/journal/ajp|1of14https://doi.org/10.1002/ajp.23537This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,provided the original work is properly cited.© 2023 The Authors.American Journal of Primatologypublished by Wiley Periodicals LLC.Abbreviations:AI, Asymmetry Index; BEA, ZooParc de Beauval chimpanzee colony; BIL, Bilinga group of Mona Chimpanzee Sanctuary; D, defensive behavior; E, facial expression; H′, ShannonIndex; J, Pielou Index; MONA, Mona Chimpanzee Sanctuary colonies; MUT, Mutamba group of Mona Chimpanzee Sanctuary; N, neutral behavior; NDS, Normalized David's score; O, offensivebehavior; PF, play fighting; RF, real fighting; RSBI, Repeatability of Same Behavior Index; V, vocalization; VDS, La Vallée des Singes chimpanzee colony.