Male parenting and response to infant stimuli in the common marmoset (Callithrix jacchus)

Anxious about rejection, avoidant of neglect: Infant marmosets tune their attachment based on individual caregiver's parenting style

Children's secure attachment with their primary caregivers is crucial for physical, cognitive, and emotional maturation. Yet, the causal links between specific parenting behaviors and infant attachment patterns are not fully understood. Here we report infant attachment in New World monkeys common marmosets, characterized by shared infant care among parents and older siblings and complex vocal communications. By integrating natural variations in parenting styles and subsecond-scale microanalyses of dyadic vocal and physical interactions, we demonstrate that marmoset infants signal their needs through context-dependent call use and selective approaches toward familiar caregivers. The infant attachment behaviors are tuned to each caregiver's parenting style; infants use negative calls when carried by rejecting caregivers and selectively avoid neglectful and rejecting caregivers. Family-deprived infants fail to develop such adaptive uses of attachment behaviors. With these similarities with humans, marmosets offer a promising model for investigating the biological mechanisms of attachment security.

A calcitonin receptor-expressing subregion of the medial preoptic area is involved in alloparental tolerance in common marmosets

Like humans, common marmoset monkeys utilize family cooperation for infant care, but the neural mechanisms underlying primate parental behaviors remain largely unknown. We investigated infant care behaviors of captive marmosets in family settings and caregiver-infant dyadic situations. Marmoset caregivers exhibited individual variations in parenting styles, comprised of sensitivity and tolerance toward infants, consistently across infants, social contexts and multiple births. Seeking the neural basis of these parenting styles, we demonstrated that the calcitonin receptor-expressing neurons in the marmoset medial preoptic area (MPOA) were transcriptionally activated during infant care, as in laboratory mice. Further, site-specific neurotoxic lesions of this MPOA subregion, termed the cMPOA, significantly reduced alloparental tolerance and total infant carrying, while sparing general health and other social or nonsocial behaviors. These results suggest that the molecularly-defined neural site cMPOA is responsible for mammalian parenting, thus provide an invaluable model to study the neural basis of parenting styles in primates.

Motivational increase of androgens and behavior by infant distress calls in highly responsive common marmoset fathers, Callithrix jacchus

Common marmoset fathers are highly involved in care of their infants. However, variability exists in their response to infant behavior even in paternally experienced fathers. Using infant distress cries as a motivation test, we investigated: 1. the differences in paternally experienced fathers' motivation to search for the infant vocalization stimuli; 2. the relationship between a father's motivation to search for the source of the infant cries and testosterone levels; and 3. if there is a rapid steroidogenesis pathway leading to increased testosterone and estradiol in the peripheral circulation. Only 44% of the paternally experienced fathers showed a high frequency of searching for the source of the infant distress cries. Through the use of multisteroid analysis, we found high responsive fathers had significantly higher levels of progesterone and testosterone in response to infant distress cries compared to a control stimulus with progesterone and androstenedione correlating with testosterone, while no differences were seen in low responders. The frequency to search for the infant stimuli was positively correlated with higher testosterone compared to control vocal levels. These results suggest that searching for the source of infant cries represents a motivation behavior for fathers that is activated by testosterone and reflects rapid circulating testosterone.

Species differences in the effect of oxytocin on maternal behavior: A model incorporating the potential for allomaternal contributions

Oxytocin has historically been linked to processes involved with maternal behavior. However, the relative importance of oxytocin for maternal behavior widely varies among mammalian species, from indispensable to apparently nonessential. This review proposes a new model in which the relative importance of oxytocin for mothering across species is explained by an evolutionary pressure which we term "allomaternal potential", or the degree to which other conspecifics are capable and likely to assist with caregiving. It is notable that in animals where allomaternal potential is high (i.e., many quality helpers are available), oxytocin is decoupled from mothering. However, in animals where allomaternal potential is low (i.e., conspecifics refuse to, or do not provide, quality help), oxytocin is crucial for mothering. We posit that this relationship is a form of kin selection, whereby oxytocin is a signal that leads mothers to preferentially dispense resources to their own young when quality helpers are unlikely.

Contextual complexity of chemical signals in callitrichids

In nearly four decades our research and that of others on chemical signaling in callitrichid primates suggest a high degree of contextual complexity in both the use of signals and the response to these signals. We describe our research including observational field studies, behavioral bioassays ("playbacks"), functional imaging, and conditioning studies. Scent marking in both captivity and the wild is used for more than just territorial marking. Social contextual effects are seen in responses by subordinate females responding with ovulatory inhibition only to chemical signals from familiar dominant reproductive females. Males detect ovulation through changes in scent marks. Males responded behaviorally and hormonally to chemical signals of novel ovulating females as a function of their reproductive status (fathers, males paired with a female but not fathers, and single males). Multiple brain areas are activated in males by female chemical signals of ovulation including areas relating to memory, evaluation, and motivation. Furthermore, males can be conditioned to respond sexually to a nonsexual odor demonstrating that learning plays an important role in response to chemical signals. Male androgen and estrone levels changed significantly in response to infant chemical signals as a function of whether the males were fathers or not, whether the odors were from their own versus other infants, as well as the infant's stage of development. Chemical signals in callitrichids are providing a rich source of understanding the context and function of the chemical sensory system and its stimulation of neural, behavioral, and hormonal actions in the recipients.

Daddy, daddy cool: stallion-foal relationships in a socially-natural herd of Exmoor ponies

Different forms of direct paternal investment have been described in mammals. One such species where paternal care was noticed, but remains poorly understood, is the horse (Equus caballus), where the male keeps a long-term relationship with several females and offspring. Therefore, the aim of this study was to analyse the interactions between the harem stallion and his foals. Two herds of Exmoor ponies living under semi-feral conditions in two separate reserves within Czech Republic were studied, each during one of the two consecutive breeding seasons (in 2016 and 2017). Both herds consisted of a stallion, 14 mares and their offspring (12 and 10 foals). The behaviour of all group members was recorded focusing on the stallion-foal interactions. The results show that the stallion receives more friendly interactions, snapping and playful behaviour from foals compared with adult mares. Furthermore, the stallion is more tolerant than mares, and actively plays with his offspring. There is no statistical difference in the sex of the foals in the stallion-foal interactions; however, male foals are more active than female foals in interacting with their father. The probability of a certain behaviour occurring between adult and foals changed over time. The stallion's presence might, therefore, be crucial for the physical and psychological development of the foals, especially the colts. These results may bring new insight into the common management of domestic horses, where stallions are usually kept separately and are not allowed to form natural groups.

Individuality in the vocalizations of infant and adult coppery titi monkeys (Plecturocebus cupreus)

As social animals, many primates use acoustic communication to maintain relationships. Vocal individuality has been documented in a diverse range of primate species and call types, many of which have presumably different functions. Auditory recognition of one's neighbors may confer a selective advantage if identifying conspecifics decreases the need to participate in costly territorial behaviors. Alternatively, vocal individuality may be nonadaptive and the result of a unique combination of genetics and environment. Pair-bonded primates, in particular, often participate in coordinated vocal duets that can be heard over long distances by neighboring conspecifics. In contrast to adult calls, infant vocalizations are short-range and used for intragroup communication. Here, we provide two separate but complementary analyses of vocal individuality in distinct call types of coppery titi monkeys (Plecturocebus cupreus) to test whether individuality occurs in call types from animals of different age classes with presumably different functions. We analyzed 600 trill vocalizations from 30 infants and 169 pulse-chirp duet vocalizations from 30 adult titi monkeys. We predicted that duet contributions would exhibit a higher degree of individuality than infant trills, given their assumed function for long-distance, intergroup communication. We estimated 7 features from infant trills and 16 features from spectrograms of adult pulse-chirps, then used discriminant function analysis with leave-one-out cross-validation to classify individuals. We correctly classified infants with 48% accuracy and adults with 83% accuracy. To further investigate variance in call features, we used a multivariate variance components model to estimate variance partitioning in features across two levels: within- and between-individuals. Between-individual variance was the most important source of variance for all features in adults, and three of four features in infants. We show that pulse-chirps of adult titi monkey duets are individually distinct, and infant trills are less individually distinct, which may be due to the different functions of the vocalizations.

Towards a new taxonomy of primate vocal production learning

The extent to which vocal learning can be found in nonhuman primates is key to reconstructing the evolution of speech. Regarding the adjustment of vocal output in relation to auditory experience (vocal production learning in the narrow sense), effects on the ontogenetic trajectory of vocal development as well as adjustment to group-specific call features have been found. Yet, a comparison of the vocalizations of different primate genera revealed striking similarities in the structure of calls and repertoires in different species of the same genus, indicating that the structure of nonhuman primate vocalizations is highly conserved. Thus, modifications in relation to experience only appear to be possible within relatively tight species-specific constraints. By contrast, comprehension learning may be extremely rapid and open-ended. In conjunction, these findings corroborate the idea of an ancestral independence of vocal production and auditory comprehension learning. To overcome the futile debate about whether or not vocal production learning can be found in nonhuman primates, we suggest putting the focus on the different mechanisms that may mediate the adjustment of vocal output in response to experience; these mechanisms may include auditory facilitation and learning from success. This article is part of the theme issue 'What can animal communication teach us about human language?'

Vasopressin, but not oxytocin, modulates responses to infant stimuli in marmosets providing care to dependent infants

In family-living species, the quality and patterning of caregiving is the product of an individual's role within the family (mother, father, sibling) and parental experience, both of which interact with underlying neurobiological substrates. Among these substrates are the nonapeptides vasopressin and oxytocin, which modulate maternal, paternal, and alloparental care. We used a nonhuman primate model of the "nuclear family," the marmoset (Callithrix jacchus), to investigate relationships between caregiving experience, role within the family, and activation of either the oxytocin or vasopressin systems in shaping responsiveness to offspring. During two phases of offspring development (early infancy, juvenile), mothers, fathers, and older siblings were treated with vasopressin, oxytocin, or saline via intranasal application, and tested for responses to infant distress stimuli in a within-subjects design. Interest in infant stimuli was highest among marmosets that were caring for infants compared to those caring for juveniles, and parentally experienced marmosets were quicker to respond to infant stimuli than first-time caregivers. Moreover, marmosets treated with vasopressin showed enhanced responsiveness to infant stimuli compared to control stimuli only when caring for infants. Thus, in all classes of marmoset caregivers, vasopressin enhances responsiveness to infant-associated stimuli in caregivers during periods in which infant care is most crucial.

Music and Language in Social Interaction: Synchrony, Antiphony, and Functional Origins

Music and language are universal human abilities with many apparent similarities relating to their acoustics, structure, and frequent use in social situations. We might therefore expect them to be understood and processed similarly, and indeed an emerging body of research suggests that this is the case. But the focus has historically been on the individual, looking at the passive listener or the isolated speaker or performer, even though social interaction is the primary site of use for both domains. Nonetheless, an important goal of emerging research is to compare music and language in terms of acoustics and structure, social interaction, and functional origins to develop parallel accounts across the two domains. Indeed, a central aim of both of evolutionary musicology and language evolution research is to understand the adaptive significance or functional origin of human music and language. An influential proposal to emerge in recent years has been referred to as the social bonding hypothesis. Here, within a comparative approach to animal communication systems, I review empirical studies in support of the social bonding hypothesis in humans, non-human primates, songbirds, and various other mammals. In support of this hypothesis, I review six research fields: (i) the functional origins of music; (ii) the functional origins of language; (iii) mechanisms of social synchrony for human social bonding; (iv) language and social bonding in humans; (v) music and social bonding in humans; and (vi) pitch, tone and emotional expression in human speech and music. I conclude that the comparative study of complex vocalizations and behaviors in various extant species can provide important insights into the adaptive function(s) of these traits in these species, as well as offer evidence-based speculations for the existence of "musilanguage" in our primate ancestors, and thus inform our understanding of the biology and evolution of human music and language.

Fathering style influences health outcome in common marmoset (Callithrix jacchus) offspring

In the cooperative breeding common marmoset monkey, Callithrix jacchus, fathers share the care responsibility and energetic load with their mate from the time their infants are born. However, not all fathers show the same level of participation in direct infant care. Here we present the first results demonstrating that fathering style can improve both survival and growth trajectory of a male's offspring during the first 30 weeks of life and that these infant outcomes are consistent within a father throughout successive births. Twenty-four marmoset fathers were tested for their responsiveness to an infant distress call when their infants were approximately two weeks old. These fathers were categorized as either responsive (RS) or nonresponsive (NRS) based on their response to the calls. Survival past 1 month was then determined and bi-monthly weights of current infants through 30 weeks of age were taken. Infant survival to the first month was significantly higher with RS fathers than with NRS fathers during this critical time period. Infants from RS fathers also had a higher growth trajectory with significant differences in body weight in the 28th and 30th week after birth. Only the RS fathers showed a significant increase in serum testosterone in response to infant cries suggesting a physiological role of testosterone in the motivation to search for the infant. Furthermore, all offspring born to RS fathers from subsequent births also showed a significantly higher survival rate and higher growth trajectory than for offspring of NRS fathers. These results suggest that fathering style is a consistent trait and responsive fathers improve infant survival rate and growth during the first 30 weeks. Such fathering style traits may be passed on to the male offspring due to environmental or genetic factors.

Studying primate cognition in a social setting to improve validity and welfare: a literature review highlighting successful approaches

BACKGROUND

Studying animal cognition in a social setting is associated with practical and statistical challenges. However, conducting cognitive research without disturbing species-typical social groups can increase ecological validity, minimize distress, and improve animal welfare. Here, we review the existing literature on cognitive research run with primates in a social setting in order to determine how widespread such testing is and highlight approaches that may guide future research planning.

SURVEY METHODOLOGY

Using Google Scholar to search the terms "primate" "cognition" "experiment" and "social group," we conducted a systematic literature search covering 16 years (2000-2015 inclusive). We then conducted two supplemental searches within each journal that contained a publication meeting our criteria in the original search, using the terms "primate" and "playback" in one search and the terms "primate" "cognition" and "social group" in the second. The results were used to assess how frequently nonhuman primate cognition has been studied in a social setting (>3 individuals), to gain perspective on the species and topics that have been studied, and to extract successful approaches for social testing.

RESULTS

Our search revealed 248 unique publications in 43 journals encompassing 71 species. The absolute number of publications has increased over years, suggesting viable strategies for studying cognition in social settings. While a wide range of species were studied they were not equally represented, with 19% of the publications reporting data for chimpanzees. Field sites were the most common environment for experiments run in social groups of primates, accounting for more than half of the results. Approaches to mitigating the practical and statistical challenges were identified.

DISCUSSION

This analysis has revealed that the study of primate cognition in a social setting is increasing and taking place across a range of environments. This literature review calls attention to examples that may provide valuable models for researchers wishing to overcome potential practical and statistical challenges to studying cognition in a social setting, ultimately increasing validity and improving the welfare of the primates we study.

The effect of infant vocalization in alloparental responsiveness of common marmosets (Callithrix jacchus)

Among mammals, alloparental care can be influenced by hormones as well as by previous experience and sensory stimuli from the infants, such as sight and sound, smell, and physical contact with the infant. To determine the responsiveness of common marmoset (Callithrix jacchus) nonreproductive females and males with and without previous experience in caretaking to infant sensory cues, we exposed 12 females and 12 males to vocalization recordings for 10 min under two conditions: (1) exposure to adult conspecific vocalization recordings, and (2) exposure to infant vocalization recordings. We recorded the frequency of approach toward the sound source, the time spent near it and locomotion frequency of males and females in the cage under both conditions. Blood samples were collected after each test for cortisol measuring by EIA method. The infant vocalization affects the behavioral and hormonal responses of males and females of common marmosets. The animals approached and spent more time near the sound source and showed an increase in locomotion during infant vocalization exposure compared to the adult vocalization. However, there was no significant difference in the behavioral response of animals when previous experience and the sex were taken into account. In both sexes, cortisol levels were significantly higher following infant vocalization exposure compared to the adult vocalization. These findings suggest that the infant vocalization appears to be an effective cue that facilitates the approach of the caregiver and maintaining their responsiveness and that the cortisol seems to be important for alertness to sensory stimuli, modulating their motivation to interact with the infant.

Sampling maternal care behaviour in domestic dogs: What's the best approach?

Our understanding of the frequency and duration of maternal care behaviours in the domestic dog during the first two postnatal weeks is limited, largely due to the inconsistencies in the sampling methodologies that have been employed. In order to develop a more concise picture of maternal care behaviour during this period, and to help establish the sampling method that represents these behaviours best, we compared a variety of time sampling methods Six litters were continuously observed for a total of 96h over postnatal days 3, 6, 9 and 12 (24h per day). Frequent (dam presence, nursing duration, contact duration) and infrequent maternal behaviours (anogenital licking duration and frequency) were coded using five different time sampling methods that included: 12-h night (1800-0600h), 12-h day (0600-1800h), one hour period during the night (1800-0600h), one hour period during the day (0600-1800h) and a one hour period anytime. Each of the one hour time sampling method consisted of four randomly chosen 15-min periods. Two random sets of four 15-min period were also analysed to ensure reliability. We then determined which of the time sampling methods averaged over the three 24-h periods best represented the frequency and duration of behaviours. As might be expected, frequently occurring behaviours were adequately represented by short (oneh) sampling periods, however this was not the case with the infrequent behaviour. Thus, we argue that the time sampling methodology employed must match the behaviour of interest. This caution applies to maternal behaviour in altricial species, such as canids, as well as all systematic behavioural observations utilising time sampling methodology.

Female cats, but not males, adjust responsiveness to arousal in the voice of kittens

BACKGROUND

The infant cry is the most important communicative tool to elicit adaptive parental behaviour. Sex-specific adaptation, linked to parental investment, may have evolutionary shaped the responsiveness to changes in the voice of the infant cries. The emotional content of infant cries may trigger distinctive responsiveness either based on their general arousing properties, being part of a general affect encoding rule, or based on affective perception, linked to parental investment, differing between species. To address this question, we performed playback experiments using infant isolation calls in a species without paternal care, the domestic cat. We used kitten calls recorded in isolation contexts inducing either Low arousal (i.e., isolation only) or High arousal (i.e., additional handling), leading to respective differences in escape response of the kittens. We predicted that only females respond differently to playbacks of Low versus High arousal kitten isolation calls, based on sex-differences in parental investment.

RESULTS

Findings showed sex-specific responsiveness of adult cats listening to kitten isolation calls of different arousal conditions, with only females responding faster towards calls of the High versus the Low arousal condition. Breeding experience of females did not affect the result. Furthermore, female responsiveness correlated with acoustic parameters related to spectral characteristics of the fundamental frequency (F0): Females responded faster to kitten calls with lower F0 at call onset, lower minimum F0 and a steeper slope of the F0.

CONCLUSIONS

Our study revealed sex-specific differences in the responsiveness to kitten isolation calls of different arousal conditions independent of female breeding experience. The findings indicated that features of F0 are important to convey the arousal state of an infant. Taken together, the results suggest that differences in parental investment evolutionary shaped responsiveness (auditory sensitivity/ motivation) to infant calls in a sex-specific manner in the domestic cat.

Hormonal stimulation and paternal experience influence responsiveness to infant distress vocalizations by adult male common marmosets, Callithrix jacchus

Parental experience and hormones play a large role in the common marmoset (Callithrix jacchus) father's care of their offspring. We tested the effect of exogenous estradiol or testosterone on the responsiveness of common marmosets to respond to infant distress vocalizations and whether males who haven't become fathers yet (paired males) would have increased responsiveness to infant distress calls with either steroid or whether parental experience is the most important component for the onset of paternal care. Sixteen male marmosets (8 fathers, 8 paired males) received a vehicle, low dose or high dose of estradiol and additional 16 males were tested with testosterone at three doses for their response either to a vocal control or a recording of an infant distress call for 10min. Without steroid stimulation fathers were significantly more likely to respond to the infant distress stimulus than paired males. Low dose estradiol stimulation resulted in a significant increase in fathers' behavioral response towards the infant distress stimulus but not in paired males. Fathers also showed a significant increase in infant responsiveness from the vehicle dose to the estradiol low dose treatment, but not to the estradiol high dose treatment. Testosterone treatment did not show significant differences between infant responsiveness at either dose and between fathers and paired males. We suggest that neither steroid is involved in the onset of paternal care behaviors in the marmoset but that estradiol may be involved in facilitating paternal motivation in experienced fathers.

Oxytocin and vasopressin enhance responsiveness to infant stimuli in adult marmosets

The neuropeptides oxytocin (OT) and arginine-vasopressin (AVP) have been implicated in modulating sex-specific responses to offspring in a variety of uniparental and biparental rodent species. Despite the large body of research in rodents, the effects of these hormones in biparental primates are less understood. Marmoset monkeys (Callithrix jacchus) belong to a clade of primates with a high incidence of biparental care and also synthesize a structurally distinct variant of OT (proline instead of leucine at the 8th amino acid position; Pro(8)-OT). We examined the roles of the OT and AVP systems in the control of responses to infant stimuli in marmoset monkeys. We administered neuropeptide receptor agonists and antagonists to male and female marmosets, and then exposed them to visual and auditory infant-related and control stimuli. Intranasal Pro(8)-OT decreased latencies to respond to infant stimuli in males, and intranasal AVP decreased latencies to respond to infant stimuli in females. Our study is the first to demonstrate that Pro(8)-OT and AVP alter responsiveness to infant stimuli in a biparental New World monkey. Across species, the effects of OT and AVP on parental behavior appear to vary by species-typical caregiving responsibilities in males and females.

The marmoset as a model for the study of primate parental behavior

Parental behavior is important for the development of mammalian offspring. Research on the mechanisms underlying parental behavior, however, has been largely restricted to rodent models. As a consequence, although research on parent-infant relationships has been conducted using macaque monkeys for more than half a century, little is known about the neural mechanisms and brain regions associated with such behaviors in primates. This article reviews parental behavior and its endocrinological mechanisms in marmosets and tamarins, both cooperative breeders in the callitrichid family, and compares these findings with studies of macaque monkeys. The paper examines the similarities and differences between marmosets and humans, and suggests the possibility that marmosets can be a model for future studies of the neural underpinnings and endocrinology underlying human parental behavior.

Both parents respond equally to infant cues in the cooperatively breeding common marmoset, Callithrix jacchus

Although there has been great interest in the evolutionary approach to cooperative breeding species, few studies actually directly compare fathers and mothers on their motivation to parent offspring. We tested the responsiveness of common marmoset mothers and fathers to vocal and olfactory cues from their own and other infants using a two-chamber test apparatus designed to evaluate responses in the absence of competition from other caregivers within the family. We tested parentally experienced mothers and fathers living with young infants and former parents with no current offspring to address the following questions: (1) do mothers and fathers respond equally to sensory cues of infants; (2) do parents discriminate cues of their own offspring when the infants are highly dependent and when the infants are more independent; and (3) are parents responsive to both auditory and olfactory cues? Mothers and fathers reacted similarly in all tests. Parents responded equally to isolation calls from their own and unfamiliar dependent infants and there was minimal response to olfactory cues. Responses to infant vocal cues were significantly stronger when infants were dependent upon direct parental care. There was no difference in response between parents whose infants were no longer dependent and former parents with no current offspring. The results show that both parents are highly responsive to infant vocal cues when their own infants are dependent on parental care, supporting an effect of hormonal priming. However, parents only showed behavioural discrimination between vocalizations from their own and unfamiliar infants when their infants were mostly independent.

The evolution of speech: vision, rhythm, cooperation

A full account of human speech evolution must consider its multisensory, rhythmic, and cooperative characteristics. Humans, apes, and monkeys recognize the correspondence between vocalizations and their associated facial postures, and gain behavioral benefits from them. Some monkey vocalizations even have a speech-like acoustic rhythmicity but lack the concomitant rhythmic facial motion that speech exhibits. We review data showing that rhythmic facial expressions such as lip-smacking may have been linked to vocal output to produce an ancestral form of rhythmic audiovisual speech. Finally, we argue that human vocal cooperation (turn-taking) may have arisen through a combination of volubility and prosociality, and provide comparative evidence from one species to support this hypothesis.

Convergent evolution of vocal cooperation without convergent evolution of brain size

One pragmatic underlying successful vocal communication is the ability to take turns. Taking turns - a form of cooperation - facilitates the transmission of signals by reducing the amount of their overlap. This allows vocalizations to be better heard. Until recently, non-human primates were not thought of as particularly cooperative, especially in the vocal domain. We recently demonstrated that common marmosets (Callithrix jacchus), a small New World primate species, take turns when they exchange vocalizations with both related and unrelated conspecifics. As the common marmoset is distantly related to humans (and there is no documented evidence that Old World primates exhibit vocal turn taking), we argue that this ability arose as an instance of convergent evolution, and is part of a suite of prosocial behavioral tendencies. Such behaviors seem to be, at least in part, the outcome of the cooperative breeding strategy adopted by both humans and marmosets. Importantly, this suite of shared behaviors occurs without correspondence in encephalization. Marmoset vocal turn taking demonstrates that a large brain size and complex cognitive machinery is not needed for vocal cooperation to occur. Consistent with this idea, the temporal structure of marmoset vocal exchanges can be described in terms of coupled oscillator dynamics, similar to quantitative descriptions of human conversations. We propose a simple neural circuit mechanism that may account for these dynamics and, at its core, involves vocalization-induced reductions of arousal. Such a mechanism may underlie the evolution of vocal turn taking in both marmoset monkeys and humans.

Do newborn vocalizations affect the behavioral and hormonal responses of nonreproductive male common marmosets (Callithrix jacchus)?

Parental care in mammals is influenced by sensory stimuli from infants, such as sight and sound, and by changes in the hormone levels of caretakers. To determine the responsiveness of common marmoset (Callithrix jacchus) adult males with and without previous experience in caretaking to newborn sensory cues, we exposed twelve males to infant vocalization recordings and assessed their hormonal and behavioral responses. Males were placed in the testing cage for 10 min under two conditions: (a) control condition (exposure to adult conspecific vocalization recordings), and (b) experimental condition (exposure to infant vocalization recordings). We recorded the frequency of approach towards the sound source, the time spent near it and locomotion frequency of males in the cage under both conditions. Blood samples were collected after each test for cortisol, measured by the enzyme immunoassay method. Infant vocalization affects the behavioral and hormonal responses of non-reproductive male common marmosets. All males approached and spent more time near the sound source and showed an increase in locomotion during infant vocalization exposure compared to the control condition. Successive exposure to infant vocalization increased the responsiveness in inexperienced males. Cortisol levels were significantly higher following infant vocalization exposure compared to the control condition. These findings support the assumption that sound stimuli from the newborn are critical in initiating and maintaining caretaker responsiveness and that cortisol seems to be important for alertness to sensory stimuli, modulating their motivation to interact with infants.

Coupled oscillator dynamics of vocal turn-taking in monkeys

Cooperation is central to human communication. The foundation of cooperative verbal communication is taking turns to speak. Given the universality of turn-taking, it is natural to ask how it evolved. We used marmoset monkeys to explore whether another primate species exhibits cooperative vocal communication by taking turns. Marmosets share with humans a cooperative breeding strategy and volubility. Cooperative care behaviors are thought to scaffold prosocial cognitive processes. Moreover, marmosets and other callitrichid primates are very vocal and readily exchange vocalizations with conspecifics. By measuring the natural statistics of marmoset vocal exchanges, we observed that they take turns in extended sequences and show that this vocal turn-taking has as its foundation dynamics characteristic of coupled oscillators--one that is similar to the dynamics proposed for human conversational turn-taking. As marmoset monkeys are on a different branch of the evolutionary tree that led to humans, our data demonstrate convergent evolution of vocal cooperation. Perhaps more importantly, our data offer a plausible alternative scenario to "gestural origin" hypotheses for how human cooperative vocal communication could have evolved.

Social effects via olfactory sensory stimuli on reproductive function and dysfunction in cooperative breeding marmosets and tamarins

Most primates are social species whose reproduction is influenced by their social relationships. The cotton-top tamarin, Saguinus oedipus, and the common marmoset, Callithrix jacchus, are cooperative breeding species where the family structure alters reproductive function in many ways. While primates receive social effects on reproduction via all sensory stimuli, the marmosets and tamarins are particularly influenced by olfactory/chemosensory stimuli. The olfactory sensory processing is the "social glue" that keeps the family together. This review describes a number of studies using the marmosets and tamarins at the University of Wisconsin to demonstrate how odor cues are used for altering reproductive function and dysfunction. Several key studies will be discussed to show the role of odor signaling of the female reproductive state. The suppressive effects of odors are mediated by priming odors and can cause a suppressive influence on ovulation in young females via their mother's scents. Additionally, odor cues from the infant function as priming odors to ensure that fathers and mothers are present and receptive to their parental care duties. Neural pathways occur via the processing of priming odors that consequently stimulate alterations in the behavioral and endocrine response to the stimuli. The dynamics of the cooperative breeding system ensure that offspring have essential needs met and that they develop in a family environment. Olfactory communication plays a key role in maintenance of the social system of Callitrichid monkeys.

Alloparental responsiveness to newborns by nonreproductive, adult male, common marmosets (Callithrix jacchus)

Parental care in mammals is influenced by sensory stimuli from infants, and by changes in the hormone levels of caretakers. To determine the responsiveness to infant cues in nonreproductive adult male common marmosets (Callithrix jacchus) with and without previous experience in caretaking, we exposed 12 males to newborn marmosets and assessed their cortisol plasma levels and behavioral response. Newborn marmosets housed in transparent enclosures were placed inside the cages of the adult male subjects. Males were exposed four times to two different experimental conditions: (a) newborn enclosures remained closed during the observation period and (b) newborn enclosures were opened during the observation period to allow direct social interaction by the adult males. Blood samples from adult males were collected after each behavioral observation trial to measure the levels of cortisol. The behavioral responses of adult males exposed to the closed and open newborn enclosures showed a significant difference only with respect to the frequency of displacements, where males moved among the quadrants of their own cages with greater frequency when the newborn enclosure was sealed. Experienced males approached newborn enclosures more frequently, spent more time in close proximity, and carried and recovered newborns more quickly than inexperienced males. The successive exposure to newborns increased the responsiveness in inexperienced males. The highest levels of plasma cortisol in adult males were recorded following periods of exposure to the sealed newborn enclosures. This suggests that successive exposure to newborns and previous alloparental caregiving experience while living in family groups influences the responsiveness of male marmosets to the sensory cues of newborns.

Differential hypothalamic secretion of neurocrines in male common marmosets: parental experience effects?

Pregnancy and lactation produce a plethora of hormonal changes in females that promote maternal care of offspring. Males in the biparental marmoset species (Callithrix jacchus) demonstrate high levels of parenting behaviour and express enhanced circulating reproductive hormones. Furthermore, these hormonal changes are influenced by paternal experience. To determine whether the paternally experienced male marmoset has altered neurocrine hypothalamic release, as the maternal females does, we examined the release of several reproductive neurocrines, dopamine (DA), oxytocin (OT), vasopressin (AVP) and prolactin (PRL), in cultured explants of the hypothalamus of paternally experienced male marmosets compared to naïve, paternally inexperienced males. DA levels secreted from the isolated hypothalamus were significantly lower in the experienced males, whereas OT and PRL levels were significantly higher than levels found in inexperienced males. PRL levels decreased rapidly in the hypothalamic media, suggesting that PRL production occurs elsewhere. AVP levels did not change. Stimulation of the cultured explants with oestradiol significantly decreased DA levels in the inexperienced males but did not alter the other neurocrines, suggesting a direct effect of oestradiol on DA suppression in the hypothalamus. Although other factors such as age and rearing experience with siblings may play a role in hypothalamic neurocrine levels, these results demonstrate that paternal experience may impact upon the secretion of neurocrines in a male biparental primate.

Development of infant common marmosets' (Callithrix jacchus) 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.

Variations in male parenting behavior and physiology in the common marmoset

Infant survival and wellbeing is dependent upon good parenting skills. In some species of primates, fathers are necessary to ensure both positive developmental and social outcomes for their offspring. Common marmosets and the related cotton-top tamarin monkeys provide extensive paternal care of multiple offspring and are essential for infant survival. However, we have found significant variation in a father's motivation to respond to infant stimuli. Additionally, marmoset males who are experienced fathers are significantly more motivated to respond to infants and infant stimuli than adult males who have yet to be fathers. Expectant fathers appear to be preparing for their energetic role in infant care by responding with increases in multiple reproductive hormones and showing weight gain during their mate's pregnancy. Male marmosets have been shown to be hormonally responsive to scent signals. Males show increased testosterone shortly after smelling periovulatory scents and lower levels of testosterone following presentation of their own infant's scent. These two inverse testosterone responses combined indicate that paternal males have a flexible system of responding to socially relevant odor cues. Thus males can be ready to mate when their mate is fertile while continuing to be responsive to their infants when these two events occur simultaneously. A male's hormonal and physical responsiveness to parenting may be due to pair bonding between the male and his mate. Examining the variability between males in their behavioral, physical, and hormonal responses to their mate's pregnancy, and infant stimuli provides the means for determining the mechanisms of good parenting in fathers.

A molecular blueprint of gene expression in hippocampal subregions CA1, CA3, and DG is conserved in the brain of the common marmoset

Recent studies in rodents have shown that there are significant differences in gene expression profiles between the hippocampal subregions CA1, CA3, and DG. These differences in molecular make-up within the hippocampus most likely underlie the differences in morphology, physiology, and vulnerability to insults that exist between the subregions of the hippocampus and are as such part of the basic molecular architecture of the hippocampus. The aim of this study was to investigate at large scale whether these subregional differences in gene expression are conserved in the hippocampus of a nonhuman primate, the common marmoset. This study is very timely, given the recent development of the first marmoset-specific DNA microarray, exclusively containing sequences targeting transcripts derived from the marmoset hippocampus. Hippocampal subregions CA1, CA3, and DG were isolated by laser microdissection and RNA was isolated, amplified, and hybridized to the marmoset-specific microarray (EUMAMA) containing more than 1,500 transcripts expressed in the adult marmoset hippocampus. Large differences in expression were observed in particular between the DG region and both pyramidal subregions. Moreover, the subregion-specific patterns of gene expression showed a remarkable conservation with the rodent brain both in terms of individual genes and degree of differential expression. To our knowledge, this is the first study investigating large scale hippocampal gene expression in a nonhuman primate. The obtained expression profiles not only provide novel data on the expression of more than 1,500 transcripts per hippocampal subregion but also are of potential interest to neuroscientists interested in the role of the different subregions in learning and memory in the nonhuman primate brain.

Prolactin's mediative role in male parenting in parentally experienced marmosets (Callithrix jacchus)

Prolactin has been implicated in promoting paternal care behaviors but little evidence of causality has been found to date except for birds and fish. This study was designed to examine the possible causal relationships between prolactin and male parenting behaviors, reproductive hormones, and physical changes in cooperatively breeding common marmosets, Callithrix jacchus. Fifteen parentally experienced fathers were studied over three consecutive infant care periods during two weeks prior and three weeks following their mates' parturition under three-treatment conditions: normal control pregnancy, decreased prolactin and elevated prolactin. The treatments significantly altered the serum prolactin levels in the fathers. Using three methods of determining a father's level of parental care: infant carrying, family effort and responsiveness to infant stimulus tests, we found that only the male response to infant stimuli was altered by the hormone treatments. Lowering prolactin significantly reduced male responsiveness to infant stimuli but elevating prolactin showed the same effect. Hormonal sampling indicated that testosterone levels showed an inverse relationship to prolactin levels during a normal peripartum period and prolactin treatment reduced this relationship. Prepartum estradiol levels were significantly elevated during the lowered prolactin treatment and estradiol was significantly lowered postpartum with the elevated prolactin treatment. Father's weight decreased significantly by the third week of infant care during the normal treatment. Males in the elevated prolactin treatment lost little or no weight from prepartum while in the lowered prolactin treatment showed the most weight loss. The present findings did not distinguish a direct causal relationship of prolactin on behavior in experienced fathers but did find an interaction with other hormones and weight gain.

A combined histological and MRI brain atlas of the common marmoset monkey, Callithrix jacchus

The common marmoset, Callithrix jacchus, is of growing importance for research in neuroscience and related fields. In the present work, we describe a combined histological and magnetic resonance imaging (MRI) atlas constructed from the brains of two adult female marmosets. Histological sections were processed from Nissl staining and digitized to produce an atlas in a large format that facilitates visualization of structures with significant detail. Naming of identifiable brain structures was performed utilizing current terminology. The histological sections and a simplified schematic atlas are available online at http://udn.nichd.nih.gov/brainatlas_home.html.

Cognitive consequences of cooperative breeding in primates?

Several hypotheses propose that cooperative breeding leads to increased cognitive performance, in both nonhuman and human primates, but systematic evidence for such a relationship is missing. A causal link might exist because motivational and cognitive processes necessary for the execution and coordination of helping behaviors could also favor cognitive performance in contexts not directly related to caregiving. In callitrichids, which among primates rely most strongly on cooperative breeding, these motivational and cognitive processes include attentional biases toward monitoring others, the ability to coordinate actions spatially and temporally, increased social tolerance, increased responsiveness to others' signals, and spontaneous prosociality. These processes are likely to enhance performance particularly in socio-cognitive contexts. Therefore, cooperatively breeding primates are expected to outperform their independently breeding sister taxa in socio-cognitive tasks. We evaluate this prediction by reviewing the literature and comparing cognitive performance in callitrichids with that of their sister taxa, i.e. squirrel monkeys, which are independent breeders, and capuchin monkeys, which show an intermediate breeding system. Consistent with our prediction, this review reveals that callitrichids systematically and significantly outperform their sister taxa in the socio-cognitive, but not in the non-social domain. This comparison is complemented with more qualitative evaluations of prosociality and cognitive performance in non-primate cooperative breeders, which suggest that among mammals, cooperative breeding generally produces conditions conducive to socio-cognitive performance. In the hominid lineage, however, the adoption of extensive allomaternal care presumably resulted in more pervasive cognitive consequences, because the motivational consequences of cooperative breeding was added to an ape-level cognitive system already capable of understanding simple mental states, which enabled the emergence of shared intentionality.

Attachment and neuroendocrine profiles in infant and adult primates

Comparing adults and infants of our own species must be considered as carefully as comparisons between humans and other primates. While many of the same neuroendocrine systems are present in each, there are also important behavioral and adaptive distinctions which, if not precisely defined, may lead to erroneous conclusions about evolutionary history.