The paucity of social play in juvenile Mus domesticus: what is missing from the behavioural repertoire?

First paragraph of this paper: play fighting by juvenile mammals generally involves behavioural components that can be predicted from the components involved in the fighting of adults (Meaney et al. 1985). For most species studied, this generalization is supported by findings that show the body targets attacked and defended during play fighting are the same as those attacked and defended during serious fighting (Pellis 1988). In contrast, for a variety of species of muroid rodents, including rats, Rattus norvegicus, golden hamsters, Mesocricetus auratus, Djungarian hamsters, Phodopus campbelli, fat sand jirds, Psammonys obesus, deer mice, Peromyscus maniculatus and several species of voles, Microtus spp., play fighting does not involve attack and defence of body targets typical of adult agonistic behaviour (Pellis 1988). Fighting by adult males of these species involves offensive bites mainly directed at the lower dorsum and flanks, whereas during play fighting, anterior body targets, such as the nape, mouth and cheeks, are contacted by one juvenile and defended by the recipient (Pellis 1988). These anterior body targets are the same as those contacted by the male during adult sexual encounters, especially in the earlier phases of precopulatory behaviour. Initially, the female resists such contact by evading the male or by turning to face him, thus blocking access to these targets (i.e. defence). Later, as the sexual encounter progresses, the female permits the male to lick, nuzzle or allogroom these anterior targets. The male shifts the contact to the anogenital area, which is then followed by mounting and finally by copulation (see Pellis & Pellis 1989). Based on the similarity of play targets and precopulatory targets, we suggest that play fighting in juvenile muroid rodents evolved from the precocial expression of such precopulatory behaviour.

First paragraph of this paper: play fighting by juvenile mammals generally involves behavioural components that can be predicted from the components involved in the fighting of adults (Meaney et al. 1985). For most species studied, this generalization is supported by findings that show the body targets attacked and defended during play fighting are the same as those attacked and defended during serious fighting (Pellis 1988). In contrast, for a variety of species of muroid rodents, including rats, Rattus norvegicus, golden hamsters, Mesocricetus auratus, Djungarian hamsters, Phodopus campbelli, fat sand jirds, Psammonys obesus, deer mice, Peromyscus maniculatus and several species of voles, Microtus spp., play fighting does not involve attack and defence of body targets typical of adult agonistic behaviour (Pellis 1988). Fighting by adult males of these species involves offensive bites mainly directed at the lower dorsum and flanks, whereas during play fighting, anterior body targets, such as the nape, mouth and cheeks, are contacted by one juvenile and defended by the recipient (Pellis 1988). These anterior body targets are the same as those contacted by the male during adult sexual encounters, especially in the earlier phases of precopulatory behaviour. Initially, the female resists such contact by evading the male or by turning to face him, thus blocking access to these targets (i.e. defence). Later, as the sexual encounter progresses, the female permits the male to lick, nuzzle or allogroom these anterior targets. The male shifts the contact to the anogenital area, which is then followed by mounting and finally by copulation (see Pellis & Pellis 1989). Based on the similarity of play targets and precopulatory targets, we suggest that play fighting in juvenile muroid rodents evolved from the precocial expression of such precopulatory behaviour.

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