Development of partner preferences in Japanese Macaques (Macaca fuscata): Effects of gender and kinship during the second year of life

Quantitative data are presented on the effects of subject sex, partner sex,and kinship on the social interactions of 18 juveniles of the Oregon troop of Japanese macaques (Macaca fuscata).Data on these subjects as infants were also used to detail maturational changes in partner sex preferences. Nine males and nine females, whose multiparous mothers represented a cross section of dominance ranks, were observed using a focal-animal technique. Juveniles of both sexes engaged in more proximity, contact, grooming, mounting, aggression, and social play with kin than with nonkin partners. They initiated less contact with females and more contact with males during their second year. They initiated more grooming and aggression during their second year than their first year, with females displaying a strong preference for grooming females and males specifically aggressing males more during the second year. Aggression was higher between same-sexed partners than between opposite-sexed partners. Males engaged in more social interactions with males during the second year than the first year of life. Males played more than females during both years. Males played more with males during the second year than the first year, and males played with males more than did females during the second year. We conclude that sex differences in behavioral frequencies become evident during the first year of life, and sex differences in partner preferences emerge during the second year of life.     

Social behavior of infant and mother Japanese Macaques (Macaca fuscata): Effects of kinship,partner sex,and infant sex

The behavioral interactions of 22 infant and mother Japanese macaques with other group members were studied. Focal-animal observations were made from the time of each infant’s birth until 1 year of age. Infants and mothers both displayed exceedingly strong preferences for associating with matrilineal kin and, specifically, for female kin. The degree of genetic relatedness was positively correlated with levels of spatial proximity, contact, grooming, aggression, and play. Overall frequencies of interactions with nonkin were very low, and partner sex was not an important factor in interactions with nonkin. There were no significant differences between male and female infants in interactions with kin versus nonkin. There was only one significant difference between male and female infants in interactions with males versus females: female infants showed stronger preferences for initiating proximity with females over males than did male infants. Because mothers provide the focal point for infant interactions during the first year of life, we compared the behavior of infants and mothers. Mothers were the recipients of more social interactions than were infants, mothers engaged in more grooming than did infants, and infants engaged in more social play than did mothers. These findings are only partially consistent with kin-selection theory, and the inadequacies of studying matrilineal kin discrimination to test kin selection are reviewed. The near-absence of infant sex differences in associations with social partners suggests that although maternal kin other than the mother are important to infant socialization, they probably do not contribute to the development of behavioral sex differences until after the first year of life.     

Play behaviour and its effects on social development of common chimpanzees (Pan troglodytes)

The aim of the study was to monitor the social development of infant and juvenile common chimpanzees (Pan troglodytes) through their play behaviour at Taronga Zoo in Sydney in order to examine the possible effects of captivity (such as limited opportunities to play) on social development. Play behaviour was observed by focal animal sampling to determine individual differences, and their relationship to age, sex, and relatedness of the subjects. Analysis revealed marked individual variations in social, solitary, and object play behaviours indicative of a relatively well-balanced social and physical environment. Subjects showed a marked preference for play-partners of a different age compared to their own, and initiated interactions with similar frequency with members of both sexes. Many social-play dyads consisted of related individuals, and familiarity with prospective play-mates was the most decisive factor in social interactions.     

Behavioral diversity in populations of free-ranging chimpanzees in Africa: is it culture?

Behavioral differences exist among populations of wild chimpanzees (Pan troglodytes, Hominoidea) across Africa. Deciding if these are cross-cultural differences demands careful interpretation and rigorous scrutiny. Even standard patterns like social grooming may show variation in detail between neighboring populations. Some patterns of tool use, such as using hammers to crack nuts, also vary across far western Africa. At least 37 populations of free-ranging chimpanzees show tool use, and 14 show at least one habitual pattern of tool use. Regional differences exist among the three subspecies or geographical races of chimpanzees. Convincing empirical demonstration of social customs and traditions in non-human species is problematical, and even something so simple in principle as innovation is hard to show in practice. However, culture need not depend on imitation, teaching, or language, either in humans or in other species.     

Sex and group differences in feeding on animals by wild chimpanzees in the Mahale Mountains National Park,Tanzania

Sex differences in animal prey intake were revealed by fecal analysis among wild chimpanzees of the large-sized M-group (ca. 100 members) in the Mahale Mountains National Park, Tanzania: prime adult or old males feed more on vertebrates, while adult females more onCamponotus ants. By contrast, such differences were not obvious in the neighboring, small-sized K-group (ca. 20–30 members), despite the similar environment in which the two unit-groups lived. Such sex and group differences may be explained in terms of various factors, either ecological or social, or both, but social factors seem most responsible in particular for the group differences. It seems likely that increased capture rate of vertebrates per unit-group in the larger-sized M-group results in increased per capita intake of meat among prime adult or old males. Also, the more frequent interactions among prime adult or old males of M-group appear to reduce the frequency of theirCamponotus ant-fishing behavior.     

Social Play in Free-ranging Columbian Ground Squirrels,Spermophilus columbianus

Play in the Columbian ground squirrel (Spermophilus columbianus) was examined using marked individuals in a population in southwestern Alberta, Canada. The components of play varied with the age, sex and relatedness of the interactors. Only in intra-sexual play were differences apparent in littermate and non-littermate play. Male-male non-littermate play had fewer contact behaviours than littermate play, whereas female-female non-littermate play had escalations in aggressive-related behaviours. Yearling play was longer and had more aggressive-related behaviours than juvenile play. Reversals were more common in yearling bouts. The significance of those differences in social play that were related to sex, age and relatedness are discussed in light of the social organization of the Columbian ground squirrel.     

Sex Differences in Captive Olive Baboon Behavior During the First Fourteen Days of Life

I discuss newborn baboon behavioral and proximity sex differences in a population of captive olive baboons (Papio anubis) living in a social group of >500 individuals. The data are based upon 20-min focal observations of 42 mother-newborn pairs (n = 27, n = 15) for infant-days 1–7 and 36 pairs (n = 23, n = 13) for infant-days 8–14 collected late-May through late-November 2001. I examined the first two weeks of infant life via behavioral, proximity, and approach-leave/contact analyses in order to determine whether behavioral sex differences exist during the first few days of life. I examine and analyze these 2 weeks independently due to different sample sizes. I used data from the total available sample population of 57 infants (n = 36, n = 21) to discuss birth, survivorship, and infant weight. Statistically significant age and/or age-sex interactions exist for all of the behavior and proximity measures during either infant-week 1 or 2. Moreover, there is a statistically significant difference in the birth sex ratio in the sample population but no significant difference in infant mortality by sex. There are also relative and significant differences in mothers' treatment of their newborn males and females. There are also some general tendencies for female newborns on average to suckle less and to explore more per focal observation than male infants do as they age. Conversely, male newborns average slightly more time per focal observation 1 m from the mother than do female infants. However, the observed differences may be influenced by maternal behavior in that mothers have higher rates of contact with their female than their male infants.     

Ornamental colors reveal age in the king penguin

We investigated whether delayed plumage maturation occurred in king penguins (Aptenodytes patagonicus). Therefore we examined the relationships between age and sex on spectral properties and size of two colored plumage patches and a UV-reflective beak spot, using known-age cohorts. Unlike the colored patch on the breast, we found age differences in ear and beak coloration. These results suggest that head ornaments in king penguins could signal sexual maturity or social status. No sex differences were found in the intensity of colored ornaments, which can result from mutual mate choice or genetic correlation between sexes. Size of colored patches did not relate to age or sex.     

The ontogeny of sex differences in the behavior of patas monkeys

Many studies of sex differences in primates have been based on small experimental groups of peers in which only a limited range of social behavior could be expressed. In addition, the first few months of life are often the focus of such studies, with relatively little attention paid to older juveniles. In this study, 11 male and 9 female juvenile patas monkeys, living in a captive social group with all age-sex classes available, were observed between 1 and 4 years of age. A subset of seven patas monkeys was also observed between birth and 1 year of age. Here, we report the development of sex differences in independence, play, grooming, positioning behavior, and aggression over the juvenile period. Juvenile male patas monkeys played more and in longer bouts than females, but wrestling (rough-and-tumble play) was not more common among males. There were few differences in behaviors directed to male and female juveniles by other group members. Distinct differences emerged only in the behaviors of the juveniles themselves, with females being more active participants in social and aggressive interactions than males. In general, sex differences in patas monkeys show a mixture of patterns, some of which are predictive of adult sex differences and some of which appear to be specific to the particular demands of the juvenile period in this species     

Sex Differences in Object Manipulation in Wild Immature Chimpanzees (Pan troglodytes schweinfurthii) and Bonobos (Pan paniscus): Preparation for Tool Use?

Sex differences in immatures predict behavioural differences in adulthood in many mammal species. Because most studies have focused on sex differences in social interactions, little is known about possible sex differences in ‘preparation’ for adult life with regards to tool use skills. We investigated sex and age differences in object manipulation in immature apes. Chimpanzees use a variety of tools across numerous contexts, whereas bonobos use few tools and none in foraging. In both species, a female bias in adult tool use has been reported. We studied object manipulation in immature chimpanzees at Kalinzu (Uganda) and bonobos at Wamba (Democratic Republic of Congo). We tested predictions of the ‘preparation for tool use’ hypothesis. We confirmed that chimpanzees showed higher rates and more diverse types of object manipulation than bonobos. Against expectation, male chimpanzees showed higher object manipulation rates than females, whereas in bonobos no sex difference was found. However, object manipulation by male chimpanzees was play-dominated, whereas manipulation types of female chimpanzees were more diverse (e.g., bite, break, carry). Manipulation by young immatures of both species was similarly dominated by play, but only in chimpanzees did it become more diverse with age. Moreover, in chimpanzees, object types became more tool-like (i.e., sticks) with age, further suggesting preparation for tool use in adulthood. The male bias in object manipulation in immature chimpanzees, along with the late onset of tool-like object manipulation, indicates that not all (early) object manipulation (i.e., object play) in immatures prepares for subsistence tool use. Instead, given the similarity with gender differences in human children, object play may also function in motor skill practice for male-specific behaviours (e.g., dominance displays). In conclusion, even though immature behaviours almost certainly reflect preparation for adult roles, more detailed future work is needed to disentangle possible functions of object manipulation during development.     

Is Play Behavior Sexually Dimorphic in Monogamous Species?

Monogamy is a relatively rare social system in mammals, occurring only in about 3% of mammalian species. Monogamous species are characterized by the formation of pair‐bonds, biparental care, and a very low level of sexual dimorphism. Whereas in most polygynous species males engage in more rough‐and‐tumble play than females, we predicted that males and females of monogamous species would have similar, or monomorphic, play behavior. In this study, we focused on two monogamous species: coppery titi monkeys (Callicebus cupreus) and prairie voles (Microtus ochrogaster). We documented the development of play behavior in both species, and quantified different types of play behavior. We did not find any sex differences in either species in the frequencies and types of play. However, we did find sex differences in the choice of play partner in titi monkeys: female offspring spent a higher proportion of time playing with their father, while male offspring played equally with their mother and father. It is possible that rough‐and‐tumble play behavior is monomorphic in many monogamous mammals, perhaps reflecting differences from polygynous species in the effects of exposure to early androgens or in the estrogen receptor distribution. However, more subtle differences in monomorphic play behavior, such as choice of partner, may still exist.     

Inter- and intra-specific variation in the facial colours of <Emphasis Type="Italic">Perisesarma eumolpe</Emphasis> and <Emphasis Type="Italic">Perisesarma indiarum</Emphasis> (Crustacea: Brachyura: Sesarmidae)

The colour of the characteristic facial bands in the mangrove crabs Perisesarma eumolpe (De Man) and Perisesarma indiarum (Tweedie) were investigated in relation to species, sex and size. Quantitative red/blue/green (RBG) values extracted from close-up digital photographs of 27 P. indiarum and 48 P. eumolpe specimens revealed significant differences between species and sexes. Males of both species possessed facial bands characterized by a greater intensity of blue, whereas green was more pronounced in female facial bands. It is postulated that these colour differences play a role in intra-specific sexual recognition. There existed a significant positive relationship between size and the intensity of blue in the facial bands of females of both species, suggesting these traits function as an indicator of their maturity (and possibly body condition). In large males, facial band colours contrast strongly against the surrounding mudflat and may play an important role in conspecific signalling during territorial disputes or contests over access to females. Handling editor: K. Martens     

Sex Differences in the Play Behavior of Yearling Yellow-bellied Marmots

Play in yearling yellow-bellied marmots (Marmota flaviventris) was studied under non-manipulative field conditions in the Upper East River Valley of Colorado. The behavior patterns constituting play were described and illustrated and 12 specific hypotheses related to sex differences were tested. The results of these tests were used to evaluate the adaptive significance of play by comparing two major functional hypotheses: motor training and social cohesion.     

Inbreeding and incompatibility in Trichogramma nr. brassicae: evidence and implications for quality control

Inbreeding effects and incompatibility relationships were examined in strains of the egg parasitoid Trichogramma nr brassicae (Hymenoptera: Trichogrammatidae) from southeastern Australia. Crosses between strains provided weak evidence of incompatibility in a few cases. However sex ratio in crosses within strains tended to be more female-biased than in crosses between strains. Inbreeding was imposed for four generations (F>0.59) of sib mating. The fitness of inbred strains was compared to that of outbred strains generated by crossing the inbred strains. No effects of inbreeding were found for any of the four female traits examined (fecundity, body length, head width and hind tibia length), indicating that T. nr. brassicae is not subjected to inbreeding depression. Inbreeding effects were also not found for male mating success as expected for the haploid sex. There were differences among strains for all traits apart from fecundity, indicating heritable variation. Strain differences for fitness measures were uncorrelated with wasp size. The potential use of inbreeding in the quality control of Trichogramma for mass-release is discussed. Inbreeding may be a useful tool in minimising the effects of laboratory adaptation, thereby extending the useful life of a strain.     

Boys and girls on the playground: sex differences in social development are not stable across early childhood

Sex differences in human social behaviors and abilities have long been a question of public and scientific interest. Females are usually assumed to be more socially oriented and skillful than males. However, despite an extensive literature, the very existence of sex differences remains a matter of discussion while some studies found no sex differences whereas others reported differences that were either congruent or not with gender stereotypes. Moreover, the magnitude, consistency and stability across time of the differences remain an open question, especially during childhood. As play provides an excellent window into children's social development, we investigated whether and how sex differences change in social play across early childhood. Following a cross-sectional design, 164 children aged from 2 to 6 years old, divided into four age groups, were observed during outdoor free play at nursery school. We showed that sex differences are not stable over time evidencing a developmental gap between girls and boys. Social and structured forms of play emerge systematically earlier in girls than in boys leading to subsequent sex differences in favor of girls at some ages, successively in associative play at 3-4 years, cooperative play at 4-5 years, and social interactions with peers at 5-6 years. Preschool boys also display more solitary play than preschool girls, especially when young. Nevertheless, while boys catch up and girls move on towards more complex play, sex differences in social play patterns are reversed in favor of boys at the following ages, such as in associative play at 4-5 years and cooperative play at 5-6 years. This developmental perspective contributes to resolve apparent discrepancies between single-snapshot studies. A better understanding of the dynamics of sex differences in typical social development should also provide insights into atypical social developments which exhibit sex differences in prevalence, such as autism.     

Larval sex identification in the paper wasp <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Vespidae,Hymenoptera)

Identifying the sex of larvae is important in social Hymenoptera. Until now for Polistes wasps it has been necessary to genotype larvae at microsatellite loci, and assign their sex based on homozygosity at these loci. In our study on the paper wasp Polistes dominulus we have found morphological differences between larval sexes that can be used for larvae from the 3^rd instar on to easily and cheaply identify larval sex: the external gonopore and the shape and size of larval gonads. The robustness of these indicators was supported by genotype data at four microsatellite loci. Using gonopore and gonad features for sex assignment will assign diploid males as males, unlike techniques based on genetic loci or chromosomes. Received 12 July 2006; revised 4 January 2007; accepted 5 February 2007.     

Social facilitation is a better predictor of frog reproductive activity than environmental factors

Anuran breeding activity is frequently linked to environmental factors, mainly temperature and rainfall. However, a key feature of anuran reproductive behavior—gathering in choruses and producing loud advertisement calls to attract females—generates a conspicuous social cue that may also facilitate reproductive behavior. Here, I examine the relative importance of environmental and social factors in explaining the intensity of reproductive activity in the Neotropical treefrog Hypsiboas rosenbergi. I show that social cues generally play an important role, but that there are sex differences: male behavior is associated with a combination of environmental and social factors, while female behavior is associated almost exclusively with social cues. I discuss the potential benefits of using social cues in regulating breeding activity, and suggest that conservation efforts may take advantage of the apparently widespread pattern of social facilitation in anuran reproductive ecology.     

Sibships: Cooperation and competition among immature vervet monkeys

The relationships between siblings were compared with those between non-sibling peers amongst immature vervet monkeys (Cercopithecus aethiops) in three free-ranging social groups. Using the frequency and context of friendly, supportive, aggressive, and competitive interactions, sibships were found to stand out as associative units characterized by high levels of grooming and support during aggression. Competition between siblings was related to contests over access to maternal care, especially grooming, which may have been important in the establishment of relative sibling dominance. Siblings who were close in age tended to interact more frequently than those who were distant in age, but few sex differences were found. The close and supportive nature of sibling relationships appeared to affect the social structure of the groups.     

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     

Play behaviour in lowland gorillas: Age differences,sex differences,and possible functions

A study on lowland gorilla (Gorilla gorilla gorilla) play behaviour was conducted on four exhibits at three different zoological parks so that 19 gorillas were observed. Juvenile gorillas played the most, but play continued at fairly high frequencies through adolescence. Most social play occurred between dyads. Triadic groups usually chased each other. No sex differences in type of play were observed, but gender differences in partner preferences were observed. Males played with both other males and females, while females seldom played together. These data support the social skills hypothesis (Baldwin & Baldwin, 1974) of play. Data were gathered while the author was a graduate student at Tulane University and a visiting lecturer at the University of California, Riverside.