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We videotaped behaviour in four litters of domestic dogs to explore social play and the development of relationships within litters. We collected data when the puppies were between 3 and 40 weeks of age, but collection times varied by litter. We divided data analysis into three time periods to coincide approximately with critical periods in the early social development of dogs. Early play-partner preferences were associated with preferences in later time periods, and the tendency for puppies to prefer specific partners increased over time. Play did not conform to 50-50 symmetry of roles between partners, which some researchers claim is necessary to sustain play. In the later juvenile period (time 3), dogs who engaged in high rates of offense behaviours (e.g. chasing, forcing partners down) also initiated play at higher rates, implying that winning during play may become more important as puppies mature. Self-handicapping behaviours were positively associated with play signalling, suggesting that, like play signals, self-handicapping may function to indicate playful intent. In mixed-sex dyads, males initiated play, engaged in offense behaviours, and self-handicapped more than females. Females were more likely to initiate with females across all time periods, but males were more likely to initiate with males only in time 3. We discuss results from mixed- and same-sex interactions with reference to inter- and intrasexual competition. The types of offense and self-handicapping behaviours displayed were similar across litters, suggesting that the expression of these behaviours may follow a similar ontogeny in puppies in general.

Social play involves a dynamic combination of competition and cooperation, yet few studies have systematically evaluated the cooperative side of play. We studied dyadic play in domestic dogs to investigate factors influencing variation in cooperative play strategies like self-handicapping and role reversal. Dyadic play bouts were videotaped and coded for asymmetric behaviours. We predicted that variation in play style would reflect salient aspects of the canine social system, including dominance relationships and age and size differences, but not sex differences. Our results refute the 50:50 rule proposed by some researchers, which asserts that participants must equalize their behaviour to maintain a playful atmosphere. We observed divergence from 50:50 symmetry to varying degrees across dyads. This variability was especially linked to dominance and age advantages, such that higher-ranking and/or older dogs generally showed higher proportions of attacks and pursuits and lower proportions of self-handicapping than their disadvantaged play partners. These results contradict the notion that more advantaged individuals consistently relinquish their advantage to facilitate play. Role reversals did occur, but certain social conventions apparently dictated which behaviours could be used during role reversals. For example, role reversals occurred during chases and tackles, but never during mounts, muzzle bites or muzzle licks, suggesting that these latter behaviours may be invariant indicators of formal dominance during play in domestic dogs. Play signalling was linked to self-handicapping behaviour but not to attack/pursuit behaviour, indicating that perhaps self-handicapping and play signalling work together to communicate playful intent and reinforce existing roles.

Using the Strange Situation Test originally developed for testing the mother-infant relationship in humans, we compared the attachment behaviour of extensively socialized (hand-reared) dog, Canis familiaris, and wolf, Canis lupus, puppies towards their human caregiver with that of pet dog puppies of the same age. The experiment was designed to study whether (1) dog puppies as young as 16 weeks show attachment to a human caregiver, (2) extensive socialization by human caregivers affects attachment behaviour of dog puppies and (3) evolutionary changes (in the form of species-specific differences between wolf and dog pups) affect the emergence of dog-human attachment. We found a characteristic selective responsiveness to the owner in young dogs, similar to that observed in adults. This finding supports the view that puppies show patterns of attachment towards their owners. Extensive socialization had only a minor effect on the attachment behaviour in dog puppies, as the behaviour of pet dogs and hand-reared dogs was basically similar. However, we found a significant species-specific difference between wolves and dogs: both extensively socialized and pet dog puppies were more responsive to the owner than to an unfamiliar human participant, whereas extensively socialized wolves were not. Behavioural differences could be best explained by assuming that selective processes took place in the course of domestication (genetic changes) that are related to the attachment system of the dog.