The cross-generation transmission of oxytocin in humans

Animal studies demonstrated that the neuropeptide oxytocin (OT), implicated in bond formation across mammalian species, is transmitted from mother to young through mechanisms of early social experiences; however, no research has addressed the cross-generation transmission of OT in humans. Fifty-five parents (36 mothers and 19 fathers) engaged in a 15-min interaction with their infants. Baseline plasma OT was sampled from parents and salivary OT was sampled from parents and infants before and after play and analyzed with ELISA methods. Interactions were micro-coded for parent and child's socio-affective behavior. Parent and infant's salivary OT was individually stable across assessments and showed an increase from pre- to post-interaction. Significant correlations emerged between parental and infant OT at both assessments and higher OT levels in parent and child were related to greater affect synchrony and infant social engagement. Parent-infant affect synchrony moderated the relations between parental and infant OT and the associations between OT in parent and child were stronger under conditions of high affect synchrony. Results demonstrate consistency in the neuroendocrine system supporting bond formation in humans and other mammals and underscore the role of early experience in shaping the cross-generation transmission of social affiliation in humans.     

Social learning and mother's behavior in manipulative tasks in infant marmosets

High levels of social tolerance are considered to promote social learning, as they allow direct observation of a manipulating conspecific and facilitate scrounging. Owing to tolerance toward infants, infancy is thought to be especially suited for learning socially transmitted behaviors. Despite this, few studies have investigated social learning of infants, particularly in manipulative tasks where observation might be most helpful. Here, we investigated (1) the influence of social learning on task acquisition in infant marmosets, and (2) whether the mother augments her behavior in a way that may enhance social learning by her infants. We tested infant and juvenile marmosets in four different complex foraging‐related tasks, featuring large living insects (two tasks) or artificially embedded prey (two tasks). Each individual observed the mother solving two of the tasks and served as a control in the other two tasks. Observers manipulated more and succeeded sooner than control animals, suggesting that observing the mother promoted learning either directly or by decreasing neophobia. Moreover, the data suggest that learning in 11–15 week‐old infants might be promoted actively by the mother. She solved the tasks, consumed less food, and consumed it later than when foraging with older offspring or alone. Furthermore, the results indicate the possible importance of the third and fourth month of infancy as the crucial ontogenetic period for social learning in marmosets, corroborating recent observations of free‐living common marmosets. Am. J. Primatol. 71:503–509, 2009. © 2009 Wiley‐Liss, Inc.     

Physical Environmental Effects on Infant Care and Development in Captive Callithrix jacchus

Environmental enrichment may affect infant care and development in captive primates. We investigated the effects of this factor in laboratory common marmosets (Callithrix jacchus). An enriched physical environment enhanced the social activities of the marmosets and elicited a greater repertoire of behaviors, without negatively affecting the provision of infant care. In addition, infants in enriched cages displayed certain behaviors sooner than infants in non-enriched cages did, which suggests an increased developmental rate. Infants in enriched cages also ate more solid food and engaged in solitary play and exploration more than ones in non-enriched cages did. Play and exploration probably improve spatial cognition and motor skills, which, together with a higher degree of independence, may allow infants to cope better with laboratory routines and general social interactions later in life than their counterparts reared in less complex enclosures. We conclude that laboratories can significantly increase the welfare of marmosets by providing a more complex physical environment.     

Development of infant common marmosets’ (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>) preference for their parents over adults from another group

Parent–offspring attachment is important for animals which have offspring that require parental care for their development. Infant attachment to the mother has been examined in macaques, but it remains poorly understood in common marmosets. Here, we examined the abilities of 14 common marmoset infants to show preference for their parents over adults from another group at the ages of 4, 10, and 15 weeks. Each infant was exposed to its parent and an adult from another group in an I-shaped maze. Although 4-week-old infants did not show a significant difference between approach behaviors toward their parents and other adults, 10- and 15-week-old infants approached and stayed longer near their parents than adults from another group. These results suggest selective approach behavior develops in marmosets by the age of 10 weeks.     

Neighbor effects in marmosets: social contagion of agonism and affiliation in captive Callithrix jacchus

Researchers have demonstrated the neighbor effect for affiliative and agonistic neighbor vocalizations in captive chimpanzees. We extend the investigation of the neighbor effect to New World monkeys, Callithrix jacchus. We collected data on vocalizations and behaviors of 31 focal individuals and concurrent neighbor vocalization within three behavioral categories: intragroup and intergroup aggression and intragroup affiliation. We investigated whether there was an influence of neighbor vocalizations on focal behavior within the same behavioral category. For data analysis we used approximate randomization of paired‐sample t‐tests. We found that marmosets performed intergroup aggressive behavior (bristle, anogenital present for neighbor loud shrill only) for significantly longer, and emitted significantly more intergroup agonistic vocalizations (twitter, loud shrill), at a high frequency of intergroup agonistic neighbor vocalizations (twitter, loud shrill) than at low. The marmosets were also significantly more likely to engage in bristle behavior immediately after hearing a neighbor intergroup aggressive call (twitter, loud shrill) than directly beforehand. High neighbor intragroup agonistic calls (chatter) were associated with significantly longer spent in related behavior (composite of: attack, chase, steal food). Affiliative behaviors (share food, grooming invite) were engaged in by marmosets for significantly longer at higher frequencies of affiliative neighbor chirp calls than at low. Marmosets were also significantly more likely to perform food sharing and active affiliative contact immediately after rather than before hearing a neighbor chirp call. Our findings suggest that neighbor vocalizations influence marmoset behavior through social contagion and indicate that the neighbor effect for affiliation and aggression generalizes to the marmoset. Am. J. Primatol. 72:549–558, 2010. © 2010 Wiley‐Liss, Inc.     

Manipulation of the oxytocin system alters social behavior and attraction in pair-bonding primates, Callithrix penicillata

The establishment and maintenance of stable, long-term male-female relationships, or pair-bonds, are marked by high levels of mutual attraction, selective preference for the partner, and high rates of sociosexual behavior. Central oxytocin (OT) affects social preference and partner-directed social behavior in rodents, but the role of this neuropeptide has yet to be studied in heterosexual primate relationships. The present study evaluated whether the OT system plays a role in the dynamics of social behavior and partner preference during the first 3 weeks of cohabitation in male and female marmosets, Callithrix penicillata. OT activity was stimulated by intranasal administration of OT, and inhibited by oral administration of a non-peptide OT-receptor antagonist (L-368,899; Merck). Social behavior throughout the pairing varied as a function of OT treatment. Compared to controls, marmosets initiated huddling with their social partner more often after OT treatments but reduced proximity and huddling after OT antagonist treatments. OT antagonist treatment also eliminated food sharing between partners. During the 24-h preference test, all marmosets interacted more with an opposite-sex stranger than with the partner. By the third-week preference test, marmosets interacted with the partner and stranger equally with the exception that intranasal-OT treatments facilitated initial partner-seeking behavior over initial contact with the stranger. Our findings demonstrate that pharmacological manipulations of OT activity alter partner-directed social behavior during pair interactions, suggesting that central OT may facilitate the process of pair-bond formation and social relationships in marmoset monkeys.     

Cross-generic Food Sharing in Tamarins

Adult-infant food-sharing behavior is a major component of the infant care strategies of callitrichids (marmosets and tamarins). It is particularly well-developed in cotton-top tamarins (Saguinus Oedipus) and lion tamarins (Leontopithecus spp), which show frequent adult-initiated food offering, as well as sharing of food in response to begging by infants. This report documents a case of cross-generic food sharing, in which a male golden-headed lion tamarin (Leontopithecus chrysomelas) shared food with an infant cotton-top tamarin. The lion tamarin provided more food to the infant than its mother did. This emphasizes the importance of this behavior in the reproductive strategies of the communally-rearing Callitrichidae and raises questions about mechanisms that underly it.     

The benefits of helpers: Effects of group and litter size on infant care in tamarins (Saguinus oedipus)

The Callitrichidae (marmosets and tamarins) typically give birth to twins, and infant care is shared by all group members. The potential benefits to callitrichids of having helpers were investigated in a study of 21 captive cotton-top tamarin (Saguinus oedipus) infants, living in groups with two to 12 older members. Time carried and suckled and amount of food received from other family members were recorded for each infant during the first 12 weeks of life. The results showed that infants in larger groups were carried more and received more food than those in smaller groups. Twin infants in larger families were less likely to be on the same carrier. Singleton infants were carried more than twins but did not receive more food. On average, individual caretakers in larger groups carried less and shared less food with infants than those in smaller groups. When parental contributions to care were analyzed, no effects of group size were found on mothers' contributions to carrying or food sharing, but fathers in larger groups both carried infants less and shared less food with them. There appear to be several benefits of a communal rearing system to cotton-top tamarins. 1) Infants may receive more care in larger families, thus increasing their chances of survival. 2) The burden of care is spread over several animals, reducing the costs to a given individual. 3) The parents, particularly fathers, may benefit most from reducing the costs of investing in the present litter and increasing their ability to invest in future litters.     

Hormonal regulation of agonistic and affiliative behavior in female mongolian gerbils (Meriones unguiculatus)

Ovarian steroids and oxytocin (OT) have been implicated in the regulation of social behaviors. The purpose of the present study was to examine hormonal substrates of aggression and affiliation in the female Mongolian gerbil (Meriones unguiculatus), a highly social, monogamous rodent. Sexually naive adult females were paired with sexually experienced males for 48 h and their interactions videotaped. Females were gonadally intact and tested during vaginal estrus (INT) or ovariectomized and observed after the following treatments, administered by means of sc injections: EBEB (7 days of estradiol-benzoate); EBP (2 days of EB followed by progesterone), SALEB (saline, days 1-5 then 2 days of EB), OTEB (OT for days 1-5 then 2 days of EB); OTOIL (OT for days 1-5 then 2 days of OIL); or SALOIL (saline days 1-5 then 2 days of OIL). During the first hour of pairing INT females displayed higher levels of affiliation and lower levels of sniffing and agonistic behavior than SALOIL females. All hormonal treatments reduced agonistic behaviors when compared to SALOIL, although none of the hormonal treatments restored affiliation to INT levels. During the 48-h test overt aggression varied by treatment with INT, EBEB, EBP, and OTEB females displaying lower levels than SALOIL, while all groups displayed similar levels of affiliation. The results indicate that OT and E play a significant role in regulating male-directed aggressive behavior in females and that the presence of ovarian hormones as well as OT can increase affiliation during initial contact. Over a sustained period of cohabitation social cues appear to be more important in regulating affiliation than gonadal hormones.     

Food sharing in black lion tamarins (Leontopithecus chrysopygus)

Food sharing behavior was investigated by studying 10 captive black lion tamarin (Leontopithecus chrysopygus) infants (six litters) between the ages of four and 26 weeks. The frequency of sharing by parents in response to infant begging increased steadily from the age of five to nine weeks, but then declined gradually, although infants were still receiving food even at 26 weeks. Until the age of 15 weeks, infants received more food items by transfer from other group members than they did from self-feeding. Thereafter, self-feeding predominated. Offering of food by adults without prior infant begging occurred at low frequencies (5.3% of items transferred) and ceased at 20 weeks of age. Begging success (the proportion of infant begs which resulted in food sharing) remained relatively constant, averaging 65%. In common with other lion tamarins, black lion tamarins appear to continue to share food with infants well after weaning, and until at least six months of age.     

Interactions among paternal behavior, steroid hormones, and parental experience in male marmosets (Callithrix kuhlii)

Male black tufted-ear marmosets (Callithrix kuhlii) contribute to the rearing of their offspring. Here we evaluated predictions of hypotheses suggesting that (1) T and E2 influence infant-care behavior in male marmosets, (2) levels of T and E2 are modulated by paternal experience, and (3) paternal behavior and levels of T and E2 in male marmosets covary with stress. We observed the behavior of marmosets in their family groups following the birth of infants and evaluated urinary concentrations of T, E2, and the stress hormone cortisol (CORT) among fathers before and after the birth of young. Urinary levels of T, E2, and CORT were lower among males who carried infants at high rates than males who carried at low rates, and T and CORT levels were negatively correlated with carrying rates across all males. Males had significantly lower T levels while carrying the second compared to the first litter and slightly lower rates of infant-carrying, possibly due to assistance provided by offspring of the first litter. There were increases in CORT levels of fathers after the birth of the first litter, but decreases in CORT after the birth of the second. Our results suggest a relationship in C. kuhlii between paternal behavior, hormones, and paternal experience. Rates of infant-carrying appear to be linked to hormone levels, and hormone levels in turn are affected by experience caring for young. Our data also suggest that T, E2, and CORT have synergistic influences on infant-carrying behavior or alternatively that associations between T and E2 and rates of infant-carrying are influenced by stress or other glucocorticoid-related variables. Finally, we propose a hypothesis suggesting that experience-related changes in hormones reinforce the commitment of males to successful breeding partnerships.     

Husbandry and observation methods of a breeding colony of marmosets (Callithrix jacchus) for behavioural research.

By allowing families to increase in size, co-operation between parents and adolescents in infant care was encouraged. Young adult pairs were subsequently created with these marmosets which had experience of handling infants to provide a stable basis for breeding 2nd and 3rd generation marmosets in captivity.     

Food Sharing in Pied Bare-Faced Tamarins (Saguinus bicolor bicolor): Development and Individual Differences

We investigated food sharing behavior in 5 litters of pied bare-faced tamarins (Saguinus bicolor bicolor)—8 infants, from 3 families—from 5 to 26 weeks of age. The frequency of sharing by parents in response to infant begging increased steadily from the age of 5 weeks to 16 weeks, and then declined. Offering of food by adults without prior infant begging occurred at very low frequencies throughout observations (1.5% of total items transferred). On average, infants received approximately equal amounts of food from transfers from others and by self feeding until about 20 weeks, after which self feeding began to predominate. Begging success—the proportion of infant begs which resulted in food sharing—remained relatively constant over time, at 60–70%. Overall, therefore, the frequency of food sharing seemed to be governed by changes in infant rather than adult behavior. There were individual differences between adults in their response to infant begging, but two of three fathers transferred significantly more food to infants than mothers did. The results of this study emphasize the existence of specific and individual differences in food-sharing behavior, which must be taken into account in explaining its importance in the reproductive strategies of the Callitrichidae.     

Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees

Humans excel in cooperative exchanges between unrelated individuals. Although this trait is fundamental to the success of our species, its evolution and mechanisms are poorly understood. Other social mammals also build long-term cooperative relationships between non-kin, and recent evidence shows that oxytocin, a hormone involved in parent–offspring bonding, is likely to facilitate non-kin as well as kin bonds. In a population of wild chimpanzees, we measured urinary oxytocin levels following a rare cooperative event—food sharing. Subjects showed higher urinary oxytocin levels after single food-sharing events compared with other types of social feeding, irrespective of previous social bond levels. Also, urinary oxytocin levels following food sharing were higher than following grooming, another cooperative behaviour. Therefore, food sharing in chimpanzees may play a key role in social bonding under the influence of oxytocin. We propose that food-sharing events co-opt neurobiological mechanisms evolved to support mother–infant bonding during lactation bouts, and may act as facilitators of bonding and cooperation between unrelated individuals via the oxytocinergic system across social mammals.     

Adult-infant food transfer in common marmosets: an experimental study

Infant marmosets and tamarins obtain solid food items from adults during and after the time of weaning. In addition to providing nutrients, food transfers may provide infants with the opportunity to learn about diet. The aim of this study was to investigate patterns of begging and food transfer in captive groups of common marmosets during tests with 1) palatable novel food, 2) unpalatable novel food, and 3) familiar food. Infants may gain an opportunity to learn about diet breadth by preferentially begging for novel rather than familiar items, while adults may facilitate infant learning by differing in their willingness to transfer food depending upon the food's novelty or palatability. In this study, infants exhibited more interest and begging with novel food items than with familiar ones. However, food transfers were not more likely to occur with novel foods than with familiar ones, and in fact adults were more likely to refuse infant begging attempts with novel foods. The palatability of the food also did not influence the rates of refusal and transfer: adults transferred palatable and unpalatable novel foods with similar frequencies. These results suggest that infant marmosets gain an opportunity to learn about diet breadth by begging for novel foods, but adults do not preferentially transfer novel or palatable food items.     

Does Male Care,Provided to Immature Individuals,Influence Immature Fitness in Rhesus Macaques?

Among many mammals, maternal care strongly impacts infant survival; however, less is known about whether adult males also affect infant fitness. Paternal care is expected when providing care enhances offspring survival and reproduction, which likewise increases fathers’ fitness. Males might also care for unrelated immature individuals to increase their mating probability with the immature individuals’ mothers. Studies in multimale primate groups showed that sires enhance food access for offspring and provide protection in conflicts. Furthermore, fathers’ presence during infancy has been suggested to accelerate offspring sexual maturation. However, no study has yet directly linked the degree of father-offspring bonds to offspring fitness in primates. We previously reported father-offspring affiliation in rhesus macaques, pronounced during early infancy and independent of mothers’ presence. The present study aims at investigating whether affiliation with fathers or other males affects proxies of immature fitness (body mass gain, body fat and testis size). First, we combined behavioral, genetic and morphometric data from 55 subjects of one group. Second, using demographic and genetic data, we investigated for 92 individuals of the population whether mother- and father-offspring co-residence during immaturity influenced offspring lifetime reproductive success (LRS). Our results show that focal rank and higher amounts of affiliation with high-ranking males during infancy tend to positively impact body mass gain of female, but not male focal animals. In contrast, body mass gain of male focal individuals, but not females’, appeared to be higher when affiliation of male immature individuals was evenly distributed across their adult male partners. Moreover, we found mothers’, but not fathers’, presence during immaturity to predict offspring LRS. Our results suggest that male-immature affiliation, but not father-offspring co-residence, potentially impacts proxies of immature fitness. However, future studies should investigate the underlying mechanisms of male-immature relationships and their impact on immature fitness in more detail.     

Food transfer between mother and infant chimpanzees of the Mahale Mountains National Park,Tanzania

We studied food transfer between chimpanzee mothers and infants in the Mahale Mountains National Park, Tanzania. The rate of infant solicitation for food dramatically increased in the second year of life, then gradually decreased and, in the seventh year, virtually disappeared. The pattern of the ontogeny of food sharing precisely followed that of solicitation because mothers shared food only when requested to do so by their infants. The success rate of solicitation, however, did not display extreme changes across ages. Food that was difficult to process was shared more frequently because it was more likely to be demanded by infants. We defined food retrieval as an infant’s recovery of leftovers discarded by its mother. Food types retrieved were often those that are difficult to process and were also likely to be shared by mothers. However, infants tended to solicit small, difficult food types for sharing while they often retrieved the remains of large, difficult food types. The function of food sharing and food retrieval lies in an infant’s learning food types that it cannot easily obtain or process by itself. The level of competition for food between mothers and infants remained low throughout infancy. We noted no particular characteristic about foods from which infants were displaced by mothers. As infants grew older, they increased the distance between themselves and mothers that became more aggressive.     

Infant carrying in family groups of goeldi's monkeys (Callimico goeldii)

Goeldi's monkey (Callimico goeldii) is closely related to marmosets and tamarins. Like marmosets and tamarins, C. goeldii lives in family groups, and fathers and older offspring (helpers) participate in infant carrying. In contrast to the typical twin births in marmosets and tamarins, C. goeldii has only single offspring, and paternal carrying is delayed. We studied infant carrying following 26 births in eight groups of C. goeldii, testing hypotheses proposed in the literature on infant carrying in marmosets and tamarins. The infant was carried exclusively by the mother for the first 26.3 days after birth. Afterwards other group members participated in infant carrying. Whereas the C. goeldii mother is always the main carrier, the father does not always carry more than helpers. In contrast to other callitrichids, age and sex of sibling helpers was not found to have an effect on the participation in infant carrying. The participation in infant carrying in Callimico indicated intraindividual consistency, i.e., the amount of infant carrying performed by fathers and helpers following one birth correlated significantly with the amount of infant carrying of the same individuals following the next birth. We found a significant negative correlation between parental infant carrying and group size, indicating that helpers really do help, sharing the carrying burden with their parents. This is attributed to a clear trend for a reduction in maternal carrying in the presence of helpers, whereas fathers did not benefit from helpers. We conclude that the infant-carrying pattern in C. goeldii is different from the infant-carrying pattern in marmosets and tamarins. The main differences were that the mother instead of the father is the main carrier, and that there is a clear time delay between infant birth and when the father and helpers participate in infant carrying.     

Food sharing in lion tamarins: Tests of three hypotheses

Infant marmosets and tamarins (Callitrichidae) frequently receive food from older group members. Three possible functions of food sharing in lion tamarins were examined experimentally. The first hypothesis, that food sharing ensures that infants receive sufficient food even if it is difficult for them to acquire it themselves, was tested by varying the ease with which infants could reach a food source. When access to food was restricted, infants fed themselves less, received more food from others, and had a higher success rate in begging attempts. The second hypothesis, that food sharing helps teach infants an appropriate diet, was tested by presenting fruits that were novel to infants. Although infants fed themselves less under these conditions, adults were less likely to share novel foods than familiar foods. The final experiment compared food sharing when food was abundant with behavior when food items were presented singly. Infants fed themselves less and received more food from others when food items were rare. These results suggest that food sharing in lion tamarins helps to ensure that infants receive adequate amounts of food which is difficult to locate or acquire, but that it is not involved in teaching infants which foods they should eat. © 1993 Wiley-Liss, Inc.     

Differential endocrine responses to infant odors in common marmoset (Callithrix jacchus) fathers

Olfactory cues can exert priming effects on many mammalian species. Paternally experienced marmosets, Callithrix jacchus, exposed to direct isolated olfactory contact with their own infant's scent show rapid decreases in testosterone levels within 20 min, whereas paternally inexperienced males do not. The following study tests whether there is a differential steroid response to exposure of infant scent from dependent infants (own and novel) and independent infants (own and novel). We examined the serum levels of estradiol, estrone, testosterone, dihydrotestosterone (DHT), and combined estrogens and androgens in eight male marmosets 20 min after exposure to isolated infant scent. Testosterone and androgen levels combined were significantly lower with exposure to own infant scent than a novel infant scent when the infants were at a dependent age but not at an independent age. Estrogen levels elevated significantly in response to own infant scent when the infants were at a dependent age but not at an independent age. These results suggest that marmoset fathers are more responsive to priming cues from related infants and hormonal responses from fathers are greatest when the infant is at a dependent age.