Playful defensive responses in adult male rats depend on the status of the unfamiliar opponent

Abstract

Adult male rats reared as pairmates from weaning were tested in a neutral arena with both members of another pair (one at a time). The unfamiliar pairs were found to engage in play fighting, although they were more likely to escalate the encounter into serious fighting than were pairs of familiar rats. Based on their within‐home pair behavior, each pairmate was designated as a dominant or a subordinate. When the test encounters between unfamiliar males were analyzed with regard to whether the pairings consisted of two dominants, two subordinates, or a mixed pair, the pattern of play fighting was found to be attenuated. Both dominants and subordinates were more likely to initiate playful encounters, to respond defensively during these encounters, and to do so using adult‐typical tactics of defense when paired with an unfamiliar rat that was dominant in its home cage. The mechanisms by which the home status of unfamiliar male rats can be identified by another male are discussed, particularly with regard to the role that play fighting may serve for this function. It is concluded that the data support the hypothesis that play fighting can be used by adult rats for social testing, which in this case seems to involve ascertaining the opponent's fighting capability. Aggr. Behav. 25:141–152, 1999. © 1999 Wiley‐Liss, Inc.

Are 50-khz calls used as play signals in the playful interactions of rats? III. The effects of devocalization on play with unfamiliar partners as juveniles and as adults

“…The effect of this rough play is to provide a means with which to establish a dominance relationship, which, once established, leads to gentler play. However, when play fails to establish a dominance relationship, the encounter can escalate to serious fighting (Smith et al, 1999). In such a situation, the role of ultrasonic vocalizations as tactical signals to mitigate the risk of escalation from play to fighting may be more crucial.…”

“…As already noted, pairs of unfamiliar, adult male rats encountering one another in a neutral arena play more roughly with one another than with cage mates (Smith et al, 1999), and the present findings show that, in such a context, if one partner is devocalized, the encounters are more likely to escalate to serious aggression. However, this effect seems to apply only to rats encountering unfamiliar conspecifics.…”

“…First, interactions in which the initiating attack was to the nape (play) versus the rump or face (agonistic) (Blanchard et al, 1977;Pellis and Pellis, 1987) were scored for each pair. Second, the occurrence of behavioral markers that are associated with aggression, such as piloerection, lateral displays, tail wagging and biting that occurred during the trial as a whole, were scored (Smith et al, 1999). For the latter, the numerical frequency of all these markers occurring during the trial was combined into an overall index of aggressiveness.…”

Partner preferences and asymmetries in social play among domestic dog, Canis lupus familiaris, littermates

“…Similarly, young male squirrel monkeys (Biben 1998), baboons (Owens 1975), and laboratory rats (Hole 1988) preferred partners they could 'dominate' during play. It seems likely that in dogs, as in rats, male bison Bison bison, and many primates, individuals become increasingly aware of intragroup status as they mature, and play becomes more competitive (Fagen 1981;Rothstein & Griswold 1991;Smith et al 1999). Preference for partners who can be dominated could help explain why PPP scores were not reciprocal (see above).…”

“…Animals may play to learn valuable social skills (Biben 1998) or to strengthen (Bekoff 1984) or test social bonds (Zahavi 1977;Pozis-Francois et al 2004), as training for cognitive (Bekoff 1984;Spinka et al 2001) or motor development (Byers 1998), to develop the emotional flexibility needed for dealing with unexpected situations (Spinka et al 2001) or as a way to assess their own capabilities relative to conspecifics (Thompson 1998;Smith et al 1999;Palagi et al 2004). Although all of these hypotheses seem reasonable, it is extremely difficult to determine the reproductive benefits of social play.…”