An investigation of playful behaviour in Rattus norvegicus and Mus musculus (Mammalia)

The playful behaviour of laboratory rats ( Rattus norvegicus ) was investigated in litters of five individuals with the mother present; parallel observations were made on mice ( Mus musculus ). Seven mixed litters containing four young rats and a young mouse fostered at birth were also observed.
Solitary play was recorded in both species and took a similar form but social play was only observed in rats. In rats, solitary play frequently preceeded social play.
The behavioural elements involved in the social play of Rattus norvegicus were described, and the majority of these were the playful equivalent of adult agonistic behaviour elements. These social play elements were found to be organized into definite sequences which differed from those of adult aggression. Each behavioural element was found to act as a social releaser.
Young mice did not respond playfully to social play from a rat litter mate; mice were less attractive to rats as playmates in comparison with fellow rats.     

同胞侵犯对猞猁幼仔行为的影响

研究了非自由生活的4窝11只猞猁幼仔的玩耍行为、亲和及入侵关系的变化.观察到36-57日龄幼仔的同胞打斗行为,这些打斗减少了这些幼仔之间游戏性接触的频次.这个"打斗期"与游戏行为和食性的变化同步发生.打斗后,幼仔游戏性接触的非对称性以及同胞之间的偏爱更加清楚.这些打斗导致了不同窝的幼仔之间等级结构的建立.     

Breed-typical behaviour in dogs—Historical remnants or recent constructs?

Dogs show considerable variation in morphology, genetics and behaviour caused by long periods of artificial selection. This is evident in the large number of breeds we have today. Behavioural differences among breeds have often been regarded as remnants from past selection during the breeds’ origin. However, the selection in many breeds has, during the last decades, gone through great changes, which could have influenced breed-typical behaviour. In order to investigate this, breed differences were studied using data from a standardized behavioural test from 13,097 dogs of 31 breeds from the Swedish dog population. Based on the test results, breed scores were calculated for four behavioural traits: playfulness, curiosity/fearlessness, sociability and aggressiveness. These traits have previously been found to be stable and valid, and hence regarded as personality traits in the dog. The present results suggested large differences between breeds in all of the investigated traits, even though there were within-breed variations. No relationships between breed-characteristic behaviour and function in the breeds’ origins were found. Instead, there were correlations between breed scores and current use of the breeding stocks, which suggest that selection in the recent past has affected breed-typical behaviour. The breeds’ use in dog shows, the dominating use in general, was negatively correlated with all investigated traits, both in sires and in dams. In contrast, use in Working dog trials was positively correlated with playfulness and aggressiveness in sires. Thus, these results suggest that selection for dog show use is positively correlated with social and non-social fearfulness, and negatively with playfulness, curiosity in potentially threatening situations and aggressiveness, whereas selection for Working dog use is positively correlated with playfulness and aggressiveness. Furthermore, correlation analyses show that popular breeds have higher sociability and playfulness scores than less popular breeds, suggesting that a positive attitude towards strangers is an important characteristic of a functional pet dog and desirable by dog owners. This indicates that selection towards use in dog shows may be in conflict with pet dog selection. Furthermore, these results suggest that basic dimensions of dog behaviour can be changed when selection pressure changes, and that the domestication of the dog still is in progress. A standardized behavioural test, like the one used in this study, is suggested to be highly useful as a tool in dog breeding programs.     

Play vocalizations of squirrel monkeys (Saimiri sciureus)

Vocalizations occurring during play bouts were studied in 2 pairs of young male squirrel monkeys. Two main call types, one having four variants, are described. Vocalization rate varied with the type of ongoing behavior and with play bout duration, an association considered to be indicative of motivation to play. Structural differences also varied with bout duration and longer bouts had longer and more complex calls. In addition to providing direct information about motivation, vocalizations may have a metacommunicative function in alerting adult group members (not play partners) to the presence of playful activity.     

Associations among within-litter differences in early mothering received and later emotional behaviors,mothering, and cortical tryptophan hydroxylase-2 expression in female laboratory rats

This article is part of a Special Issue “Parental Care”. The effects of differential maternal care received on offspring phenotype in rodents has been extensively studied between litters, but the consequences of differential mothering within litters on offspring neurobehavioral development have been rarely examined. We here investigated how variability in maternal care received among female rat siblings (measured four times daily on postnatal days 4, 6, 8, and 10) relates to the siblings' later emotional and maternal behaviors. As previously reported, we found that some female pups received up to three times more maternal licking bouts compared to their sisters; this difference was positively correlated with the pups' body weights. The number of maternal licking bouts that females received was negatively correlated with their later neophobic behaviors in an open field during periadolescence, but positively correlated with their anxiety-related behavior in an elevated plus maze during adulthood. Licking received was also positively correlated with females' later likelihood to retrieve pups in a maternal sensitization paradigm. In addition, females' neophobia during adolescence and anxiety-related behavior during adulthood predicted some aspects of both postpartum and sensitized maternal responsiveness. Medial prefrontal cortex expression of tryptophan hydroxylase-2 (TPH2; enzyme necessary for serotonin synthesis) was negatively associated with early maternal licking received. Interestingly, cortical TPH2 was positively associated with the maternal responsiveness of sensitized virgins but negatively associated with it in postpartum females. These results indicate that within-litter differences in maternal care received is an often neglected, but important, contributor to individual differences in offspring socioemotional behaviors as well as to the cortical serotonin neurochemistry that may influence these behaviors.     

The effects of litter-size variation on the development of play behaviour in the domestic cat: litters of one and two

In many litter-bearing species, litter-mates interact with each other in a variety of ways during early life. In the domestic cat, Felis catus, social play is a prominent form of interaction between litter-mates. The present study investigated how the lack of a litter-mate affected the development of kitten play and of the mother-kitten relationship. The subjects were 14 litters of domestic kittens living with their mothers in large indoor cages. Seven litters contained two male kittens, and the other seven contained single male kittens. Social interactions within the families were observed from day 22 to day 83 after birth. Single kittens played a more active part in maintaining close proximity to their mothers and directed more playful behaviour at them than did kittens with a sibling. Although single-kitten mothers avoided their offspring more than did mothers of litters of two, they also directed much higher levels of play behaviour at them. Despite the marked difference in the mother-kitten play relationship in the two litter types, single kittens experienced quantitatively less social play than did kittens with siblings. As the kittens grew older, single-kitten mothers showed higher levels of aggression towards their young than did mothers of litters of two.     

Play in adult bonobos (Pan paniscus): modality and potential meaning

The aim of this study was to thoroughly investigate social play and its modalities among adult bonobos. We evaluated how play intensity varies according to the sex-class combination of the playmates and we also performed an analysis on social locomotor-rotational movements (L-R play) and contact interactions (C play). Rough and gentle play sessions were performed with comparable frequencies by male-female and female-female adult dyads, with play signals unlikely when the playmates strongly differed in age and in rank position. L-R play rates did not differ according to the sex-combination of the players; in contrast, C play sessions were particularly frequent among females. Play faces (play signals) were significantly higher during C play than L-R play sessions, thus suggesting that playmates assess reciprocally yet safely their relationships by using facial displays to avoid any kind of misunderstanding. Play was positively correlated with grooming and contact sitting interactions, suggesting that it may be used as a social enhancer. Finally, we found no correlation between both play contexts (L-R and C play) and age, size and rank differences of the players. In conclusion, we suggest that bonobos with their egalitarian society, peculiar social structure, and playful tendency represent an attractive testing subject to examine empirically many emerging hypotheses on adult play behavior.     

Development of Social Behaviour in Four Litters of Dogs (Canis familiaris)

The development of social behaviour in 4 litters of dogs was observed without interfering with the puppies from birth to 8 weeks of age. Direct and continuous observation was combined with video recording. Three of the litters were observed during one session of 2 h once a week, and the fourth litter during one session of 40 min twice a week. Social interactions were divided into 1) investigation of litter mates (licking, sniffing or investigating orally), 2) social play, 3) and interactions in which agonistic elements (dominance postures, threats, bites or submission) were displayed. The different forms of social interactions appeared for the first time when the puppies were between 14 and 21 days of age. Social investigation appeared first and was followed by play and agonistic interactions. From week 5, differences between the puppies in the tendency to initiate social play and agonistic interactions emerged. Generally, within the litters individual differences were consistent over weeks 6-8 (positive correlations between weeks), whereas the tendency in the puppies during these weeks were negatively correlated with those of week 3 (play) or weeks 3 and 4 (agonistic interactions), indicating a rebound effect for both play and agonistic behaviour. No significant correlations, however, were found for social investigation. More often than expected males played or engaged in agonistic with other males, whereas these behaviours occurred less often than expected between females. Both males and females, however, preferred male partners for agonistic interactions. No sex differences were found in the direction of social investigation. Agonistic behaviour was often responded to by play and play was often responded to by agonistic behaviour, and the results indicated that before 8 weeks of age differences in social behaviour between the puppies were already established.     

Peering into the Dynamics of Social Interactions: Measuring Play Fighting in Rats

Play fighting in the rat involves attack and defense of the nape of the neck, which if contacted, is gently nuzzled with the snout. Because the movements of one animal are countered by the actions of its partner, play fighting is a complex, dynamic interaction. This dynamic complexity raises methodological problems about what to score for experimental studies. We present a scoring schema that is sensitive to the correlated nature of the actions performed. The frequency of play fighting can be measured by counting the number of playful nape attacks occurring per unit time. However, playful defense, as it can only occur in response to attack, is necessarily a contingent measure that is best measured as a percentage (#attacks defended/total # attacks X 100%). How a particular attack is defended against can involve one of several tactics, and these are contingent on defense having taken place; consequently, the type of defense is also best expressed contingently as a percentage. Two experiments illustrate how these measurements can be used to detect the effect of brain damage on play fighting even when there is no effect on overall playfulness. That is, the schema presented here is designed to detect and evaluate changes in the content of play following an experimental treatment.     

A comparison of structural and contextual features of middle school children's playful and aggressive fighting

This study compared structural and contextual features of playful [rough-and tumble play (r/t)] and aggressive fighting based on direct playground observations of two classes of 8 and two classes of 11 year old children. Most bouts of r/t and aggressive fighting were dyadic, but significantly more bouts of the former involved three or more participants than the latter. Rough-and-tumble play was found to contain more individual action patterns than aggressive fighting, but the latter was more varied in form than some earlier studies had shown. Both wrestling and chasing were seen more in r/t than aggressive fighting, but restraint in bouts of chasing was not more common in playful chasing than aggressive chasing. Positive and neutral facial expressions were more characteristic of r/t, and negative facial expressions were more characteristic of aggressive fighting. Rough-and-tumble initiations were more likely to receive an r/t response and less likely to receive an aggressive response than were aggressive initiations. Participants in r/t were more likely to have been together than to have been apart prior to the encounter, but this tendency was strongly mediated by sex. In three out of the four classes, children were more likely to have been together prior to same sex r/t interactions and to have been apart prior to mixed sex r/t interactions. Participants in r/t were not significantly more likely to have been together beforehand than participants in aggressive fighting. Finally, while most bouts of r/t led to the participants remaining together, the proportion that did so was not significantly greater than was the case for bouts of aggressive fighting. Possible reasons why r/t and aggressive fighting did or did not differ in these ways are discussed.     

Playful interactions in family groups of the common marmoset (Callithrix jacchus jacchus)

Play behaviour in six family groups of common marmosets (Callithrix jacchus jacchus) is described. Playful behaviour patterns comprised a distinct repertoire of behaviour and the patterns formed ordered sequences. The differences in the play of adults and offspring are described and analysed. Adult play was infrequent and most took the form of adult-offspring interactions; it contained fewer bouts of chasing and was less active, and adults elicited fewer bouts. No differences attributable to sex could be determined in the play of offspring and the only pattern that decreased with age was bouncing gait. Possible partner preferences were analysed, and it was found that marmoset twins showed an overall preference for playing with the twin. The vocalizations heard during bouts of play were recorded and analysed and their relationship to non-playful vocalization discussed; during bouts of play younger animals were found to vocalize to older animals. Marmoset play wrestling differed in form from aggressive wrestling, and patterns occurred during aggressive interactions which were not observed in play. The play of marmosets is discussed with regard to the socioecology of the species and compared to the play of other mammalian species.     

The ontogeny of social play in a feral troop of vervet monkeys (Cercopithecus aethiops sabaeus): The function of early play

We describe the ontogeny of social play over the first 30 weeks of age in a troop of feral vervet monkeys (Cercopithecus aethiops sabaeus) in Barbados. Play time increased rapidly for the first 10 weeks but remained relatively constant thereafter. The form of play changed with infant age; bouts became more frequent but of shorter duration. Play time, bout frequency, and bout duration at a given age differed between infants; younger infants altered their play patterns to complement those of older infants. All infants played more within their own year class than with older juveniles; play time increased with decreasing age difference between the infant and the play partner. Infants terminated a higher proportion of their play bouts the greater the age difference between themselves and their play partners. Preferred play partners are therefore individuals of similar age that will be similar in size and have matched motivation to play and form of play. Neither play time nor proportion of bouts initiated or terminated was correlated with the social rank of the play partner, which suggests that play is not directed toward individuals that may be high-value alliance partners. Maternal intervention in play occurred primarily when infants were<10 weeks old. It was not correlated with the age or social rank of the mother or with the age or social rank of her infant's play partner. Infants played more and terminated a lower proportion of their play bouts in the absence of their mothers than in their presence. Our results are consistent with the hypothesis that the primary function of early play is to enhance physical fitness and to develop coordination and other fighting skills, with minimal risk of injury.     

闽江河口湿地枯落物分解及主要影响因子

以闽江河口湿地挺水植物本地种芦苇和入侵种互花米草的花和叶枯落物为研究对象,采用分解袋法分析其分解过程及主要影响因素.结果表明:立枯分解(0～90 d)是2种湿地盐沼植物重要的分解阶段,芦苇和互花米草的花和叶质量损失率分别为(15.0±3.5)％、(13.3±1.1)％和(31.9±1.1)％、(20.8±1.4)％.倒伏分解阶段(91 ～210 d),芦苇和互花米草的花和叶质量损失率分别为(69.5±0.6)％、(71.5±2.5)％和(76.8±1.9)％、(67.5±2.1)％.在立枯分解阶段,2种挺水植物枯落物的分解速率与C/N呈正相关,与N/P呈负相关,分解过程受到P的限制程度较大.倒伏分解阶段,枯落物C/N、C/P和N/P的影响降低,而大气温湿度、土壤水分、酸碱度、盐度和沉积物特性等的影响加大.不同分解阶段枯落物分解影响因子的差异主要与其所处的微域环境和潮汐因素有关.     

Mu opioid receptors in the medial preoptic area govern social play behavior in adolescent male rats

Neural systems underlying important behaviors are usually highly conserved across species. The medial preoptic area (MPOA) has been demonstrated to play a crucial role in reward associated with affiliative, nonsexual, social communication in songbirds. However, the role of MPOA in affiliative, rewarding social behaviors (eg, social play behavior) in mammals remains largely unknown. Here we applied our insights from songbirds to rats to determine whether opioids in the MPOA govern social play behavior in rats. Using an immediate early gene (ie, Egr1, early growth response 1) expression approach, we identified increased numbers of Egr1‐labeled cells in the MPOA after social play in adolescent male rats. We also demonstrated that cells expressing mu opioid receptors (MORs, gene name Oprm1) in the MPOA displayed increased Egr1 expression when adolescent rats were engaged in social play using double immunofluorescence labeling of MOR and Egr1. Furthermore, using short hairpin RNA‐mediated gene silencing we revealed that knockdown of Oprm1 in the MPOA reduced the number of total play bouts and the frequency of pouncing. Last, RNA sequencing differential gene expression analysis identified genes involved in neuronal signaling with altered expression after Oprm1 knockdown, and identified Egr1 as potentially a key modulator for Oprm1 in the regulation of social play behavior. Altogether, these results show that the MPOA is involved in social play behavior in adolescent male rats and support the hypothesis that the MPOA is part of a conserved neural circuit across vertebrates in which opioids act to govern affiliative, intrinsically rewarded social behaviors.     

The influence of heterogeneity on the analysis of sleep-wake architecture in the single-prolonged stress rats

Objective: To observe the influence of heterogeneity on sleep-wake architecture in single-prolonged stress(SPS) animal model. Methods: SPS rats were subdivided into low responders(LR) and high responders(HR) based on their freezing responses to a novel environment. Sleeping time(ST), awakening numbers(AN), brief awakening numbers(b AN) and frequency distribution of sleep bouts were used as observing indicators, single factor variance analysis combined with Dunnett t test were used to compare the differences between control, exposure, LR and HR groups. Results: We found sleeping time was increased only in HR group. Moreover, awakening numbers and brief awakening number increased in exposure group and HR group during the light phase, but not in LR group. The number of sleep bouts for the ranges of 40-80 s increased obviously in HR group, but not in exposure and LR group. In addition, there were significant correlation between sleep-related parameters and freezing in HR group, but not in LR group. Conclusion: Heterogeneity existed in SPS model in view of different sleep-wake architectures of SPS rats. Rats in HR group exactly mimicked the freezing response and sleep disorders of PTSD. So HR rats were more appropriate to be used as PTSD-like models, especially when studying sleep disorder in PTSD.     

Play in chimpanzees of the Arnhem Zoo: Self-serving compromises

In a colony of 25 chimpanzees maintained at Arnhem (The Netherlands), play behavior was studied for four months, yielding 1,651 play bouts involving the 11 oldest immature chimpanzees on which detailed data were collected during 88 focal animal samples of 30 min each. Play frequency and object play were negatively correlated with increasing age. These findings potentially reflect changing motivations during development and increasingly perfected skills. Like-aged partners were preferred play partners and older partners initiated play more frequently, probably because younger individuals feared rough responses by older immatures and waited until the latter initiated play bouts in a self-handicapped manner. Moreover, play was frequently interrupted by short breaks. This, in conjunction with the preference for like-aged partners, may be mechanisms to achieve and maintain compromises between the play partners' different interests in social play (which e.g. depend on sex and physical development) and to minimize the risk to being cheated. Males played significantly more often than females and played more chasing games. Male-male play was over-represented whereas female-female play was underrepresented. These facts potentially foreshadow sex differences in (wild) maturing chimpanzees, where males engage in more agonistic conflicts and tend to build coalitions.     

闽江河口湿地枯落物分解及主要影响因子

以闽江河口湿地挺水植物本地种芦苇和入侵种互花米草的花和叶枯落物为研究对象,采用分解袋法分析其分解过程及主要影响因素.结果表明: 立枯分解(0～90 d)是2种湿地盐沼植物重要的分解阶段,芦苇和互花米草的花和叶质量损失率分别为(15.0±3.5)%、(13.3±1.1)%和(31.9±1.1)%、(20.8±1.4)%.倒伏分解阶段(91～210 d),芦苇和互花米草的花和叶质量损失率分别为(69.5±0.6)%、(71.5±2.5)%和(76.8±1.9)%、(67.5±2.1)%.在立枯分解阶段,2种挺水植物枯落物的分解速率与C/N呈正相关,与N/P呈负相关,分解过程受到P的限制程度较大.倒伏分解阶段,枯落物C/N、C/P和N/P的影响降低,而大气温湿度、土壤水分、酸碱度、盐度和沉积物特性等的影响加大.不同分解阶段枯落物分解影响因子的差异主要与其所处的微域环境和潮汐因素有关.     

Optimal litter size for individual growth of European rabbit pups depends on their thermal environment

In altricial mammals and birds, the presence of a large number of litter or brood mates often affects the development of individual offspring by reducing the share of resources provided by the parents. However, sibling presence can also be favourable, conferring thermoregulatory benefits when ambient temperatures are low. Consequently, shifts in the relation between costs and benefits of sibling presence can be expected as a function of the thermal environment. In a study of a European rabbit population (Oryctolagus cuniculus) living in a field enclosure, we investigated the effects of litter size and soil temperature on pup growth over 7 years. Temperatures inside the subterranean nests were positively correlated with soil temperature and with litter size. Soil temperature varied strongly across the breeding season, ranging from 3 to 21°C. Under warmer soil temperature conditions (10–15°C and >15°C), pup growth decreased with increasing litter size, where litters of two pups (smallest litter size considered) showed the highest growth rates. In contrast, under colder soil temperature conditions (<10°C), the highest growth rates were found in litters of three pups. We also asked if such temperature-dependent differences in the optimal pup growth rates might be explained by differences in maternal characteristics, which might affect lactational performance. We assessed maternal performance using females’ postpartum body mass and social rank. However, we did not find consistent differences in maternal characteristics between females giving birth to different-sized litters during different soil temperature conditions, which would have provided an alternative explanation for the observed differences in litter size-dependent pup growth. We conclude that under colder soil temperature conditions, the thermal benefits of a greater number of littermates outweigh the negative consequences of competition for milk, leading to an environment-dependent shift in the optimal litter size for individual growth in this species.     

Sex differences in play behavior in juvenile tufted capuchin monkeys (Cebus apella)

According to the motor training hypothesis, play behavior in juvenile primates improves motor skills that are required in later adult life. Sex differences in juvenile play behavior can therefore be expected when adult animals assume distinct sexually dimorphic roles. Tufted capuchin monkeys show sexually dimorphic levels of physical antagonism in both inter- and intra-group encounters. Accordingly, it can be predicted that juvenile capuchins also show sex differences in social play behavior. To test this hypothesis, the play behavior of nine juvenile and two infant capuchins was examined. As predicted, juvenile males showed significantly higher levels of social play (wrestle, chase) than juvenile females, but no differences were found in nonsocial play (arboreal, object). Levels of infant play behavior were comparable to that of juveniles. These results lend support to the motor training hypothesis and highlight the need for more detailed investigations of individual differences in play behavior. An erratum to this article can be found at