Number of adult females in a group affects infant motor development of a cooperative breeding primate (Callithrix jacchus).

Callitrichids are small Neotropical primates and, due to their cooperative breeding system, infants are of particular interest in research on social dynamics. Although a few studies have investigated the role of helpers in this type of system, there is still a lack of research in field studies seeking to determine whether there is a relationship between the number of helpers (adults) in a social group and the motor development of infants. With that in mind, four groups of wild marmosets (Callithrix jacchus) were observed and the motor behaviors of 1 to 4 month-old infants were recorded. To investigate the influence of the adult:infant ratio on motor diversity, used as an indicator of motor development, we ran a GLMM with a Gaussian distribution and found that: (i) in groups with fewer adults, 2-month-old infants show earlier motor diversity; (ii) motor diversity increases with age regardless of the ratio of adult males per infant; (iii) in groups with more adult females per infant, the motor diversity of 2-month-old infants is significantly lower compared to 3-month-old infants. Although adult callitrichid males play an important role in the care of their offspring, the presence of females appears to be a key factor in motor development at this early stage in the study groups. In a cooperative breeding system, the lack of helpers seems to drive the development of independence in infants, resulting in earlier development.

Cellular-resolution gene expression profiling in the neonatal marmoset brain reveals dynamic species- and region-specific differences.

Precise spatiotemporal control of gene expression in the developing brain is critical for neural circuit formation, and comprehensive expression mapping in the developing primate brain is crucial to understand brain function in health and disease. Here, we developed an unbiased, automated, large-scale, cellular-resolution in situ hybridization (ISH)-based gene expression profiling system (GePS) and companion analysis to reveal gene expression patterns in the neonatal New World marmoset cortex, thalamus, and striatum that are distinct from those in mice. Gene-ontology analysis of marmoset-specific genes revealed associations with catalytic activity in the visual cortex and neuropsychiatric disorders in the thalamus. Cortically expressed genes with clear area boundaries were used in a three-dimensional cortical surface mapping algorithm to delineate higher-order cortical areas not evident in two-dimensional ISH data. GePS provides a powerful platform to elucidate the molecular mechanisms underlying primate neurobiology and developmental psychiatric and neurological disorders.

The common marmoset as suitable nonhuman alternative for the analysis of primate cochlear development.

Cochlear development is a complex process with precise spatiotemporal patterns. A detailed understanding of this process is important for studies of congenital hearing loss and regenerative medicine. However, much of our understanding of cochlear development is based on rodent models. Animal models that bridge the gap between humans and rodents are needed. In this study, we investigated the development of hearing organs in a small New World monkey species, the common marmoset (Callithrix jacchus). We describe the general stages of cochlear development in comparison with those of humans and mice. Moreover, we examined more than 25 proteins involved in cochlear development and found that expression patterns were generally conserved between rodents and primates. However, several proteins involved in supporting cell processes and neuronal development exhibited interspecific expression differences. Human fetal samples for studies of primate-specific cochlear development are extremely rare, especially for late developmental stages. Our results support the use of the common marmoset as an effective alternative for analyses of primate cochlear development.

Early learning in the common marmoset (Callithrix jacchus): Behavior in the family group is related to preadolescent cognitive performance.

Early environment can have a major impact on development, with family life known to play an important role. Longitudinal studies can therefore help increase our understanding of variance in cognitive abilities in young animals, as well as over time. We followed 22 marmosets (11 male and 11 female) from infancy through to early adolescence. At 3 months old, the marmosets were trained to reliably touch a rewarded stimulus. At 5 months, behavior was observed within the natal group. At 9 months, the marmosets were given a visual discrimination task to assess learning ability. Mann-Whitney U tests found no sex or family size differences in number of errors at 3 or 9 months. While no significant relationships were found between behavior in the family and learning at 3 months, significant negative correlations were found between duration spent in locomotion and learning errors (p = .05), as well as between frequency of calm vocalizations and learning errors (p = .001) at 9 months. A U-shape curve was found between amount of social play and learning at 9 months. Positive family interactions, including moderate amounts of play, as well as calm individual behavior, may therefore be important in learning. This study sheds light on cognitive development in much younger marmosets than previously studied, and helps increase understanding of how individual differences in learning may arise.

Vocal state change through laryngeal development.

Across vertebrates, progressive changes in vocal behavior during postnatal development are typically attributed solely to developing neural circuits. How the changing body influences vocal development remains unknown. Here we show that state changes in the contact vocalizations of infant marmoset monkeys, which transition from noisy, low frequency cries to tonal, higher pitched vocalizations in adults, are caused partially by laryngeal development. Combining analyses of natural vocalizations, motorized excised larynx experiments, tensile material tests and high-speed imaging, we show that vocal state transition occurs via a sound source switch from vocal folds to apical vocal membranes, producing louder vocalizations with higher efficiency. We show with an empirically based model of descending motor control how neural circuits could interact with changing laryngeal dynamics, leading to adaptive vocal development. Our results emphasize the importance of embodied approaches to vocal development, where exploiting biomechanical consequences of changing material properties can simplify motor control, reducing the computational load on the developing brain.

Developmental and family history-based analysis of congenital fused labia phenotype in the captive common marmoset (Callithrix jacchus).

BACKGROUND: Congenital fused labia (CFL) is defined as a failure or significant delay in the opening of the juvenile sealed labia majora. This phenotype is known to be variably common in adult captive female marmosets but has never been investigated in detail before. MATERIALS AND METHODS: Here, we define, describe and quantify the variations in the degree of closure of the vulva in 122 captive marmosets (Callithrix jacchus) from 1.2 to 42 months old and include colony analysis. RESULTS: There was a negative correlation between the degree of labial fusion and animal age after prepubertal period (P < 0.05). CFL females had higher number CFL relatives (4.3 ± 0.6 vs 2.4 ± 0.5 for non-CFL, P < 0.05) and more external ancestors compared to non-CFL (P < 0.05). CONCLUSIONS: Our results therefore suggest that CFL phenotype is most likely associated with epigenetic effects induced by the captive environment and colony management strategy of extensive crossing of family lines to promote heterozygosity.

Relationship Between Immunoglobulin Deposition and Early Lesions of Progressive Glomerulonephropathy in Young Common Marmosets.

The authors previously investigated progressive glomerulonephropathy in 2- to 11-year-old common marmosets and characterized age-related changes of the renal glomeruli and development of tubulointerstitial lesions. In this study, immunoglobulin deposition and ultrastructural changes of the glomeruli were investigated in 5 young marmosets from 6 months to 3 years of age with pre-onset or early glomerulonephropathy. In all animals, the foot processes of podocytes were effaced, and IgM was deposited into the glomeruli. In glomeruli without glomerular basement membrane (GBM) alteration, IgM was the only immunoglobulin type deposited in the glomeruli. In cases with more advanced lesions of reticulation and thickening of GBM, IgA and IgG deposits were also observed. Therefore, the authors conclude that IgM may be the primary or earliest immunoglobulin deposited in this nephropathy, whereas IgA and IgG deposition may be connected to the progression of the glomerular lesions. IgM deposition and foot process effacement of podocytes occur early in the life of affected marmosets.

Developmental trajectories of macroanatomical structures in common marmoset brain.

Morphometry studies of human brain development have revealed characteristics of some growth patterns, such as gray matter (GM) and white matter (WM), but the features that make human neurodevelopment distinct from that in other species remain unclear. Studies of the common marmoset (Callithrix jacchus), a small New World primate, can provide insights into unique features such as cooperative behaviors complementary to those from comparative analyses using mouse and rhesus monkey. In the present study, we analyzed developmental patterns of GM, WM, and cortical regions with volume measurements using longitudinal sample (23 marmosets; 11 male, 12 female) between the ages of one and 30months. Regional analysis using a total of 164 magnetic resonance imaging datasets revealed that GM volume increased before puberty (5.4months), but subsequently declined until adulthood, whereas WM volume increased rapidly before stabilizing around puberty (9.9months). Cortical regions showed similar patterns of increase and decrease, patterns with global GM but differed in the timing of volume peak and degree of decline across regions. The progressive-regressive pattern detected in both global and cortical GM was well correlated to phases of synaptogenesis and synaptic pruning reported in previous marmoset studies. A rapid increase in WM in early development may represent a distinctive aspect of human neurodevelopment. These findings suggest that studies of marmoset brain development can provide valuable comparative information that will facilitate a deeper understanding of human brain growth and neurodevelopmental disorders.

Cross-species comparison of behavioral neurodevelopmental milestones in the common marmoset monkey and human child.

The common marmoset (Callithrix jacchus) is an increasingly popular non-human primate species for developing transgenic and genomic edited models of neurological disorders. These models present an opportunity to assess from birth the impact of genetic mutations and to identify candidate predictive biomarkers of early disease onset. In order to apply findings from marmosets to humans, a cross-species comparison of typical development is essential. Aiming to identify similarities, differences, and gaps in knowledge of neurodevelopment, we evaluated peer-reviewed literature focused on the first 6 months of life of marmosets and compared to humans. Five major developmental constructs, including reflexes and reactions, motor, feeding, self-help, and social, were compared. Numerous similarities were identified in the developmental sequences with differences often influenced by the purpose of the behavior, specifically for marmoset survival. The lack of detailed knowledge of marmoset development was exposed as related to the vast resources for humans.

Vocal Learning via Social Reinforcement by Infant Marmoset Monkeys.

For over half a century now, primate vocalizations have been thought to undergo little or no experience-dependent acoustic changes during development [1]. If any changes are apparent, then they are routinely (and quite reasonably) attributed to the passive consequences of growth. Indeed, previous experiments on squirrel monkeys and macaque monkeys showed that social isolation [2, 3], deafness [2], cross-fostering [4] and parental absence [5] have little or no effect on vocal development. Here, we explicitly test in marmoset monkeys-a very vocal and cooperatively breeding species [6]-whether the transformation of immature into mature contact calls by infants is influenced by contingent parental vocal feedback. Using a closed-loop design, we experimentally provided more versus less contingent vocal feedback to twin infant marmoset monkeys over their first 2 months of life, the interval during which their contact calls transform from noisy, immature calls to tonal adult-like "phee" calls [7, 8]. Infants who received more contingent feedback had a faster rate of vocal development, producing mature-sounding contact calls earlier than the other twin. The differential rate of vocal development was not linked to genetics, perinatal experience, or body growth; nor did the amount of contingency influence the overall rate of spontaneous vocal production. Thus, we provide the first experimental evidence for production-related vocal learning during the development of a nonhuman primate.

Elucidation of developmental patterns of marmoset corpus callosum through a comparative MRI in marmosets, chimpanzees, and humans.

The corpus callosum (CC) is present in all primate brains and is the major white matter tract connecting the cerebral hemispheres for integration of sensory, motor and higher-order cognitive information. The midsagittal area of the CC has frequently been used as a sensitive biomarker of brain development. Although the marmoset has been considered as an alternative non-human primate model for neuroscience research, the developmental patterns of the CC have not been explored. The present longitudinal study of magnetic resonance imaging demonstrated that marmosets show a rapid increase of CC during infancy, followed by a slow increase during the juvenile stage, as observed in chimpanzees and humans. Marmosets also show a tendency toward a greater increase in CC during late infancy and the juvenile stage, as observed in humans, but not in chimpanzees. However, several differences between marmosets and humans were identified. There was a tendency toward a greater maturation of the human CC during early infancy. Furthermore, there was a tendency toward a greater increase during late infancy and the juvenile stage in marmosets, compared to that observed in chimpanzees and humans. These differences in the developmental trajectories of the CC may be related to evolutional changes in social behavior.

The marmoset: An emerging model to unravel the evolution and development of the primate neocortex.

Throughout evolution, the neocortex has undergone a dramatic expansion providing the substrate for increasingly complex cognitive abilities, culminating with humans. The enlargement of the neocortex did not affect its' basic organization, which is remarkably conserved from rodents to primates. The mouse has thus proven an advantageous model to decipher the molecular and cellular mechanisms supporting neocortical development. However, it is of limited benefit when studying the mechanisms leading to the inclusion of higher order association areas, which form the largest fraction of the primate neocortex. In the quest for a suitable nonhuman primate model to study the developmental mechanism of neocortical patterning and expansion, researchers focussed on the Old World macaque, routinely employed in functional and behavioral studies. However, the species has many limitations making studies difficult and/or impractical. Therefore, in the past couple of decades, the New World common marmoset (Callithrix jacchus) has drawn much attention and become an accepted model. The marmoset has the advantage of a smooth neocortical sheet, enabling the direct correspondence between developing cortices and the comprehensive map established for the adult, with a significant amount of cortical maturation occurring during the postnatal period. This review presents the contributions of recent marmoset studies to our understanding of the mechanisms regulating corticogenesis in a complex species, the molecular control of neocortical patterning and the sequential maturation of visual cortical areas while commenting on the future of the species in the field. Furthermore, while these new findings are relevant to developmental biology, in order to understand how new cortical areas have emerged to expand cognitive abilities, they also represent a foundation for the better understanding of developmental cognitive disorders. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 263-272, 2017.

Prenatal androgen exposure and parental care interact to influence timing of reproductive maturation in marmosets.

The timing of reproductive maturation is susceptible to hormonal and environmental influences, and variation in this timing can be partially attributed to the prenatal and post-natal environment. We examined associations between prenatal steroid exposure and the post-natal family environment on the variability in reproductive maturation timing in young marmosets (Callithrix geoffroyi). Urine samples from pregnant females were analyzed for cortisol (CORT) and androgens (uA). Post-natal uA was measured in males to determine age (in days) of adult-like levels of androgens associated with spermatogenesis; post-natal pregnanediol glucuronide (PdG) was measured in females to determine age (in days) of first ovulation. Maternal, paternal, alloparental, and total care (carrying, grooming, and rejection/removals) of offspring were observed. Female offspring exposed to lower prenatal uA levels and higher paternal grooming and lower maternal rejection/removals showed later first ovulation, whereas female offspring exposed to higher prenatal uA showed earlier first ovulation. Male offspring showed earlier reproductive maturation as paternal grooming increased, regardless of first trimester uA exposure. Male offspring exposed to low prenatal uA levels showed earlier reproductive maturation as maternal rejections/removals increased. In offspring exposed to low prenatal CORT, high total carrying predicted earlier first ovulation in females, but later reproductive maturation in males. Total carrying duration did not affect timing of reproductive maturation in offspring exposed to high third trimester CORT levels. Our findings expand the evolutionary theory of socialization by demonstrating that the effect of post-natal family environment on timing of reproductive maturation depends on prenatal uA exposure and also influences reproductive maturation timing in male offspring.

In situ hybridization study of CYP2D mRNA in the common marmoset brain.

The common marmoset is a non-human primate that has increasingly employed in the biomedical research including the fields of neuroscience and behavioral studies. Cytochrome P450 (CYP) 2D has been speculated to be involved in psycho-neurologic actions in the human brain. In the present study, to clarify the role of CYP2D in the marmoset brain, we investigated the expression patterns of CYP2D mRNA in the brain using in situ hybridization (ISH). In addition, to identify the gene location of CYP2D19, a well-studied CYP2D isoform in the common marmoset, a fluorescence in situ hybridization (FISH) study was performed. Consistent with findings for the human brain, CYP2D mRNA was localized in the neuronal cells of different brain regions; e.g., the cerebral cortex, hippocampus, substantia nigra, and cerebellum. FISH analysis showed that the CYP2D19 gene was located on chromosome 1q, which is homologous to human chromosome 22 on which the CYP2D6 gene exists. These results suggest that CYP2D in the marmoset brain may play the same role as human CYP2D6 in terms of brain actions, and that the CYP2D19 gene is conserved in a syntenic manner. Taken together, these findings suggest that the common marmoset is a useful model for studying psychiatric disorders related to CYP2D dysfunction in the brain.

Circadian activity rhythm in pre-pubertal and pubertal marmosets (Callithrix jacchus) living in family groups.

In marmosets, a phase advance was observed in activity onset in pubertal animals living in captivity under semi-natural conditions which had stronger correlation with the times of sunrise over the course of the year than the age of the animal. In order to evaluate the effect of puberty on the circadian activity rhythm in male and female marmosets living in family groups in controlled lighting conditions, the activity of 5 dyads of twins (4 ♀/♂ and 1 ♂/♂) and their respective parents was continuously monitored by actiwatches between the 4th and 12th months of age. The families were kept under LD 12:12 h with constant humidity and temperature. The onset of puberty was identified by monitoring fecal steroids. Juveniles showed higher totals of daily activity and differences in the daily distribution of activity in relation to parents, in which the bimodal profile was characterized by higher levels in evening activity in relation to morning activity. Regarding the phase, the activity onset and offset, occurred later in relation to parents. After entering puberty, the activity onset and offset occurred later and there was an increase in total daily activity. On the other hand, when assessing the effect of sex, only females showed a delay in the activity offset and an increase in total daily activity. Therefore, the circadian activity rhythm in marmosets has peculiar characteristics in the juvenile stage in relation to the total of daily activity, the onset and offset of the active phase, and the distribution of activity during this phase. Besides, the entering puberty was associated with a phase delay and increase on total daily activity, with differences between sexes, possibly due to hormonal influences and/or social modulation on rhythm.

LANGUAGE DEVELOPMENT. The developmental dynamics of marmoset monkey vocal production.

Human vocal development occurs through two parallel interactive processes that transform infant cries into more mature vocalizations, such as cooing sounds and babbling. First, natural categories of sounds change as the vocal apparatus matures. Second, parental vocal feedback sensitizes infants to certain features of those sounds, and the sounds are modified accordingly. Paradoxically, our closest living ancestors, nonhuman primates, are thought to undergo few or no production-related acoustic changes during development, and any such changes are thought to be impervious to social feedback. Using early and dense sampling, quantitative tracking of acoustic changes, and biomechanical modeling, we showed that vocalizations in infant marmoset monkeys undergo dramatic changes that cannot be solely attributed to simple consequences of growth. Using parental interaction experiments, we found that contingent parental feedback influences the rate of vocal development. These findings overturn decades-old ideas about primate vocalizations and show that marmoset monkeys are a compelling model system for early vocal development in humans.

Vocal turn-taking in a non-human primate is learned during ontogeny.

Conversational turn-taking is an integral part of language development, as it reflects a confluence of social factors that mitigate communication. Humans coordinate the timing of speech based on the behaviour of another speaker, a behaviour that is learned during infancy. While adults in several primate species engage in vocal turn-taking, the degree to which similar learning processes underlie its development in these non-human species or are unique to language is not clear. We recorded the natural vocal interactions of common marmosets (Callithrix jacchus) occurring with both their sibling twins and parents over the first year of life and observed at least two parallels with language development. First, marmoset turn-taking is a learned vocal behaviour. Second, marmoset parents potentially played a direct role in guiding the development of turn-taking by providing feedback to their offspring when errors occurred during vocal interactions similarly to what has been observed in humans. Though species-differences are also evident, these findings suggest that similar learning mechanisms may be implemented in the ontogeny of vocal turn-taking across our Order, a finding that has important implications for our understanding of language evolution.

Development of a novel postnatal neurobehavioral scale for evaluation of common marmoset monkeys.

Common marmoset (Callithrix jacchus) monkeys when compared to rhesus macaques (Macaca mullatta) present several advantages for disease modeling, especially transgenic initiatives, as they commonly give birth to twins, which increases sample size, have accelerated development and a shorter life span that facilitates the analysis of the onset of age-related diseases. Yet, no tools are currently available to assess marmoset neurodevelopment during the initial first month of life. Here we report the creation of a novel Primate Postnatal Neurobehavioral Assessment Scale for marmoset monkeys (PPNAS-M) that was based on currently available scales for human and rhesus monkeys. Twenty-four healthy marmoset infants (12 females, 12 males) from 12 families were evaluated. The infant assessments involved 10-minute testing administered at 15 and 30 days after birth. The PPNAS-M consists of 41 noninvasive tests grouped into 5 testing categories: visual orienting, auditory and spatial orienting, motor responses, righting and body strength, and temperament tests. Testing at these two ages did not affect the overall health of the infants, suggesting that the PPNAS-M is a non-invasive testing tool. Significant maturation was demonstrated by increased scores in each of the five testing categories from postnatal day 15 to 30, with developmental patterns unique to marmosets. Principal component analysis defined 4 item groups (Orientation, State Control, Motor Maturity and Sensory Sensitivity) with 5 variables each. Orientation and State Control factors were highly similar to each other at both ages and correlated highly with previous item groupings used with rhesus macaques. Our results indicate that the PPNAS-M is a useful assessment tool for detecting neuromotor, attention, and temperament status of infant marmosets and that it is sensitive to developmental effects. Further studies to validate the PPNAS-M for the assessment of normal development versus early effects of developmental perturbations associated to prenatal exposures and transgenesis are warranted.