Dyadic play interactions and social relationships in three species of complex social mammals: Domestic dogs (<italic>Canis familiaris</italic>), bonobos (<italic>Pan paniscus</italic>) and chimpanzees (<italic>Pan troglodytes</italic>).

Social play is a unique category of behavior in which play partners balance competitive and cooperative tactics. Although considerable play research has been conducted, there is still much to be learned. In particular, very little information is available concerning cooperation during play. Although numerous researchers emphasize the importance of cooperative tactics like self-handicapping (when individuals make themselves more vulnerable to attacks by their opponents) and role reversal (when established dominants adopt subordinate positions) in play, very few have quantitatively evaluated their use. My research investigates the use of competitive and cooperative play tactics in three species of complex social mammals: domestic dogs, bonobos and chimpanzees. I conducted four studies---one of each individual species and one comparative study of the latter two. In the first three studies, I investigate how sex, age, size and dominance differences affect the use of competitive and cooperative tactics during dyadic play. I discuss how variation in play style might reflect existing social relationships and also provide evidence to evaluate hypotheses about the functions of play in each species. In the comparative study, I evaluate how species-typical expressions of play style might mirror differences in social systems by comparing two closely related primate species (bonobos and chimpanzees) which exhibit striking differences in social behavior and patterns of social relationships. In all three species, dyadic play ranged from symmetric play (with each partner attaining an equal proportion of dominant positions during play) to completely asymmetric play (with one partner always in the dominant position during play). In dyads of known dominance, role reversals occurred to varying degrees. Self-handicapping and role reversal were common in play, but were not required for play to occur. Although dominance relationships were more flexible in the play context, they were generally reinforced by play interactions, and, at least in dogs, evidence suggests that individual variation in play style might be influenced by one's position in the hierarchy. The egalitarian vs. despotic nature of the two ape species also seemed to influence general patterns of play interaction across dyads, but not rates of competitive vs. cooperative maneuvers during play.Ph.D.Behavioral psychologyBiological SciencesPsychobiologyPsychologyVeterinary scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125295/2/3192576.pd