S-cones do not contribute to the OFF-midget pathway in the retina of the marmoset, Callithrix jacchus

It is well established that in primate retina both medium- and long-wavelength-sensitive cone types provide input to the midget-parvocellular pathway. The question, however, whether short-wavelength-sensitive (S or 'blue') cones provide input to the OFF-division of the midget-parvocellular pathway is still controversial. In the present study, we investigated the connections of nearly 400 S-cones with OFF-midget bipolar cells in central and peripheral retina of a New World monkey, the marmoset. Horizontal sections or pieces of whole retinae were double-labelled with an antiserum to S-cone opsin to identify S-cones and antibodies to the cell adhesion molecule CD15 to identify OFF-midget bipolar cells. Peanut agglutinin coupled to a fluorescent tag was used to label the cone pedicles of all cone types. Peanut agglutinin was also used to distinguish S-cones from the other cone types. The sections were analysed with deconvolution microscopy. We found that nearly all pedicles of medium- and long-wavelength-sensitive cones are located opposite distinct dendritic clusters formed by OFF-midget bipolar cells. By contrast, the S-cone pedicles are not located opposite dendritic clusters. Instead, S-cones make sparse contacts with CD15-labelled processes. Some of these processes protruded from OFF-midget bipolar clusters, whereas others could be traced to a diffuse bipolar cell type. Thus, in the marmoset retina the midget-parvocellular system does not carry a blue-OFF signal.

The neuronal representation of pitch in primate auditory cortex

Pitch perception is critical for identifying and segregating auditory objects, especially in the context of music and speech. The perception of pitch is not unique to humans and has been experimentally demonstrated in several animal species. Pitch is the subjective attribute of a sound's fundamental frequency (f(0)) that is determined by both the temporal regularity and average repetition rate of its acoustic waveform. Spectrally dissimilar sounds can have the same pitch if they share a common f(0). Even when the acoustic energy at f(0) is removed ('missing fundamental') the same pitch is still perceived. Despite its importance for hearing, how pitch is represented in the cerebral cortex is unknown. Here we show the existence of neurons in the auditory cortex of marmoset monkeys that respond to both pure tones and missing fundamental harmonic complex sounds with the same f(0), providing a neural correlate for pitch constancy. These pitch-selective neurons are located in a restricted low-frequency cortical region near the anterolateral border of the primary auditory cortex, and is consistent with the location of a pitch-selective area identified in recent imaging studies in humans.

Ductus venosus shunting in marmoset and baboon fetuses

OBJECTIVES

The increased shunting of blood through the ductus venosus (DV) during stress situations is an important mechanism that ensures fetal survival. Although primate fetuses may serve to study the function of this important venous shunt, the rate of DV shunting has not been determined in non-human primates under normal conditions.

METHODS

DV shunting was measured in 11 marmoset (eight mothers) and eight singleton baboon fetuses in mid and late gestation using Doppler ultrasound.

RESULTS

DV shunting in marmosets was 39 +/- 20% (mean +/- SD) and 28 +/- 8% in baboon fetuses. Umbilical vein (UV) blood volume rate increased significantly in baboons with gestational age (GA) (UV flow volume = -111.8 + 1.6*GA; r = 0.94, P < 0.05) and slightly in marmosets (UV flow volume = -10.37 + 0.13*GA; r = 0.42, P > 0.05). Both UV diameter (r = 0.84) and the time-averaged mean UV flow velocity in baboons depended on GA (r = 0.8, P < 0.05). Distinct pulsation was found in marmoset fetuses in the UV (pulsatility index (PI) = 1.3 +/- 0.9) and the DV (PI = 1.9 +/- 1.2) with zero blood flow velocity during atrial contraction.

CONCLUSIONS

A high level of pulsation is observed in the UV in marmoset fetuses. DV shunting in marmosets is higher than in baboon fetuses.

Sensory-motor interactions modulate a primate vocal behavior: antiphonal calling in common marmosets

A fundamental issue in neuroscience pertains to how different cortical systems interact to generate behavior. One of the most direct ways to address this issue is to investigate how sensory information is encoded and used to produce a motor response. Antiphonal calling is a natural vocal behavior that involves individuals producing their species-specific long distance vocalization in response to hearing the same call and engages both the auditory and motor systems, as well as the cognitive neural systems involved in decision making and categorization. Here we present results from a series of behavioral experiments investigating the auditory-vocal interactions during antiphonal calling in the common marmoset (Callithrix jacchus). We manipulated sensory input by placing subjects in different social contexts and found that the auditory input had a significant effect on call timing and propensity to call. Playback experiments tested the significance of the timing of vocal production in antiphonal calling and showed that a short latency between antiphonal calls was necessary to maintain reciprocal vocal interactions. Overall, this study shows that sensory-motor interactions can be experimentally induced and manipulated in a natural primate vocal behavior. Antiphonal calling represents a promising model system to examine these issues in non-human primates at both the behavioral and neural levels.

Functional organization and hemispheric comparison of primary auditory cortex in the common marmoset (Callithrix jacchus)

Hemispheric fine-grain maps of primary auditory cortex (AI) were derived from microelectrode penetrations in the temporal gyrus of the common marmoset (Callithrix jacchus) to 1) compare the functional organization of AI in the marmoset with other mammalian species and 2) compare the right and left AI maps in individual monkeys. Frequency receptive fields (FRFs) were recorded with pure tones. Five FRF parameters were analyzed: characteristic frequency, threshold, sharpness of tuning 10 dB and 40 dB above threshold, and minimum response latency. The present study confirms that the functional organization of AI is characterized by a robust tonotopic frequency gradient overlaid with spatially clustered distributions of other FRF parameters. Globally, this functional organization of AI in the common marmoset is similar to that in other mammalian species. With respect to within-subject hemispheric comparisons of the five FRF parameters, a coherent pattern of asymmetry is not evident in marmoset AI. The overall results indicate that the basic functional organization between hemispheres is similar but not identical.

Behavioral and histopathological analysis of domoic Acid administration in marmosets

PURPOSE

To induce status epilepticus (SE) followed by the subsequent onset of spontaneous recurrent seizures, thus characterizing a new model of temporal lobe epilepsy in a nonhuman primate.

METHODS

Male and female marmosets (Callithrix jacchus) (n = 18), ages between 2 and 8 years, were injected with domoic acid (0.5-4 mg/kg, i.p.) or saline, and behaviorally assessed with regard to the presence of acutely induced seizures and for < or = 6 months for spontaneous seizures. Injection of doses ranging from 3.5 to 4 mg/kg either did not induce SE or resulted in fatal SE. Even a 5-min SE duration (SE blockade resulting from diazepam injection) proved lethal to marmosets within 1 h of domoate administration, regardless of intensive care and monitoring of the animals. Animals injected with doses ranging from 0.5 to 3 mg/kg that developed only a few minor convulsive signs were allowed a 6-month survival period for the assessment of spontaneous epileptic events. At the end of the experiment, 6-month period, or acute intoxication associated with SE induction, animals were deeply anesthetized and had their brains subjected to histologic processing for Nissl and delta-FosB.

RESULTS

For the animals injected with domoate that did not develop SE (i.e., those that survived), we could not detect any behavioral signs of spontaneous epileptic seizures in the 6-month observation period, and only minor indications of neuropathologic changes (i.e., neuronal death) over Nissl-stained sections, as well as some small changes in the staining for delta-FosB in a few of the animals.

CONCLUSIONS

Systemic administration of domoic acid to marmosets is not effective for the generation of a model of chronic temporal lobe epilepsy. Administration of domoic acid at doses that do not lead to SE also did not lead to the development of temporal lobe epilepsy or clear-cut behavioral changes over a 6-month period.

Autonomic arousal in an appetitive context in primates: a behavioural and neural analysis

Central to many emotional responses is the accompanying peripheral somatic and autonomic arousal, feedback from which has been hypothesized to enhance emotional memory and to contribute to appraisal processes and decision making, and dysfunction of which may contribute to antisocial behaviour. Whilst peripheral arousal may accompany both positive and negative emotional contexts, its relationship with the former is poorly understood, as are the neural mechanisms underlying such a relationship. The purpose of the present study was to determine the autonomic correlates of anticipation, as well as consumption, of high incentive food, in the freely moving common marmoset and to investigate the contribution of the amygdala to such effects. Blood pressure (BP) and heart rate (HR) were measured remotely by a telemetric device implanted into the descending aorta and behavioural responses were monitored whilst marmosets viewed preferred or non-preferred foods and were then allowed access to eat those foods. A marked rise in blood pressure in unrestrained marmosets was observed in response both to the sight of highly preferred foods (anticipatory period) as well as during the actual consumption of those foods (consummatory period). Excitotoxic lesions of the amygdala abolished the autonomic arousal in the anticipatory period, but spared both the behavioural arousal in the anticipatory period and the autonomic arousal in the consummatory period. Together these data serve as an important step towards understanding the role of autonomic arousal in emotion and its neural underpinnings.

Opportunistic mothers: female marmosets (Callithrix kuhlii) reduce their investment in offspring when they have to, and when they can

All female primates incur energetic costs associated with producing and caring for offspring, but females belonging to the New World primate family Callitrichidae, the marmosets and tamarins, appear to face even further demands. In fact, the energetic demands of rearing callitrichid infants are thought to have led to the evolution of cooperative infant care in these species. If this explanation is true, then one might expect that natural selection should also have shaped patterns of maternal behavior to be sensitive to the costs of reproduction and equipped females to reduce their investment in offspring under certain conditions. Therefore, we examined the maternal effort and postpartum endocrine profiles of individual female marmosets (Callithrix kuhlii) across conditions that represented two hallmarks of callitrichid reproduction-conception during the early postpartum period and alloparental assistance. When females conceived during the early postpartum period and faced the upcoming demands of caring for their newly conceived litters (Study 1), they significantly reduced their caregiving effort and had significantly higher postpartum levels of estradiol relative to breeding attempts in which conception occurred later in the postpartum period. Postpartum estradiol was negatively correlated with maternal carrying effort. When experienced alloparents were present (Study 2), females again reduced their caregiving effort relative to breeding attempts in which experienced alloparents were not present. Postpartum cortisol, however, did not vary as a function of experienced alloparental assistance. The results of these studies suggest that female marmosets have been subjected to similar selection pressures as females of other primate taxa--to maximize their reproductive success by reducing their investment in offspring under the worst and best of conditions--and suggest that hormones may mediate within-female variation in maternal care. These studies also provide support for the notion that mothers are "flexible opportunists" when it comes to providing care to their young.

A novel method for activity monitoring in small non-human primates

Patterns of spontaneous activity are valuable reflections of well-being in animals and humans and, because of this, investigations have frequently incorporated some form of activity monitoring into their studies. It is widely believed that activity monitoring, alongside assessments of general behaviour, should be included in initial CNS safety pharmacology screening. As the number of marmoset studies having actimetry as their focus, or as an adjunct, is increasing, we wished to evaluate an alternative approach to those commonly used. The method is based on miniaturized accelerometer technologies, currently used for human activity monitoring.Actiwatch-Minis were used to monitor the activity of two groups of differently housed marmosets for 14 consecutive days. Group A consisted of four mixed-sex pairs of animals and group B comprised eight group-housed males. Activity profiles were generated for weekday and weekend periods. The devices captured quantifiable data which showed differences in total activity between the two differently housed groups and revealed intragroup variations in the temporal spread of activity between weekdays and weekends. The Actiwatch-Mini has been shown to generate retrospective, data-logged activity counts recorded from multiple animals in a single arena by means of non-invasive monitoring.

Sustained firing in auditory cortex evoked by preferred stimuli

It has been well documented that neurons in the auditory cortex of anaesthetized animals generally display transient responses to acoustic stimulation, and typically respond to a brief stimulus with one or fewer action potentials. The number of action potentials evoked by each stimulus usually does not increase with increasing stimulus duration. Such observations have long puzzled researchers across disciplines and raised serious questions regarding the role of the auditory cortex in encoding ongoing acoustic signals. Contrary to these long-held views, here we show that single neurons in both primary (area A1) and lateral belt areas of the auditory cortex of awake marmoset monkeys (Callithrix jacchus) are capable of firing in a sustained manner over a prolonged period of time, especially when they are driven by their preferred stimuli. In contrast, responses become more transient or phasic when auditory cortex neurons respond to non-preferred stimuli. These findings suggest that when the auditory cortex is stimulated by a sound, a particular population of neurons fire maximally throughout the duration of the sound. Responses of other, less optimally driven neurons fade away quickly after stimulus onset. This results in a selective representation of the sound across both neuronal population and time.

Establishment of graded spinal cord injury model in a nonhuman primate: the common marmoset

Most previous studies on spinal cord injury (SCI) have used rodent models. Direct extrapolation of the results obtained in rodents to clinical cases is difficult, however, because of neurofunctional and anatomic differences between rodents and primates. In the present study, the development of histopathologic changes and functional deficits were assessed quantitatively after mild, moderate, and severe spinal cord contusive injuries in common marmosets. Contusive SCI was induced by dropping one of three different weights (15, 17, or 20 g) at the C5 level from a height of 50 mm. Serial magnetic resonance images showed significant differences in the intramedullary T1 low signal and T2 high signal areas among the three groups. Quantitative histologic analyses revealed that the number of motor neurons, the myelinated areas, and the amounts of corticospinal tract fibers decreased significantly as the injury increased in severity. Motor functions were evaluated using the following tests: original behavioral scoring scale, measurements of spontaneous motor activity, bar grip test, and cage-climbing test. Significant differences in all test results were observed among the three groups. Spontaneous motor activities at 10 weeks after injury were closely correlated with the residual myelinated area at the lesion epicenter. The establishment of a reliable nonhuman primate model for SCI with objective functional evaluation methods should become an essential tool for future SCI treatment studies. Quantitative behavioral and histopathologic analyses enabled three distinct grades of injury severity (15-g, 17-g, and 20-g groups) to be characterized with heavier weights producing more serious injuries, and relatively constant behavioral and histopathologic outcomes.

Comparison between sex and age class on some physiological, thermal, and hematological indices of the cerrado's marmoset (Callithrix penicillata)*

There are few papers about physiological indices in Callithrix penicillata, an increasing primate model in biomedicine. We investigated levels of plasmatic cortisol, plasmatic glucose, free fatty acids, blood cells, tympanic temperature, rectal temperature in C. penicllata, under a fast restraint. Measures of body and weight were accomplished. Males and females were not different regarding any measurements. Body measurements indicated differences between adults and juveniles. Adults showed higher hematocrit and a tendency for higher free fatty acids than juveniles. Right tympanic temperature was higher in adults than juveniles. This result suggests a higher reaction metabolism in adults than juveniles under a restraint stress. Due to the short-time of collecting the data, plasmatic cortisol did not influence physiological parameters. Therefore, we suggest that present results could be considered referential values of C. penicillata physiology.

Colour Discrimination in the Black-Tufted-Ear Marmoset (Callithrix penicillata): Ecological Implications

The dietary diversity of marmosets is substantial, which may reflect differences in their colour vision. This study examined the colour discrimination ability of a gummivore/insectivore callitrichid, Callithrix penicillata, which inhabits the Brazilian cerrado (bush savanna). A series of ecologically relevant tasks, involving a behavioural paradigm of discrimination learning in semi-natural conditions and the usage of ecologically relevant stimuli, was executed. Three marmosets, 2 males and a female, behaved like human dichromats, showing an impaired performance when orange and green stimuli had to be discriminated. In contrast, 2 females resembled human trichromats, discriminating those kinds of pairs. Our data suggest that Callithrix penicillata presents a polymorphic trichromacy, with dichromatic males and dichromatic or trichromatic females.

Intensity of aggressive interactions modulates testosterone in male marmosets

Androgen is associated with the expression of male-typical behavior, including aggressive behavior, but high levels of androgen may be incompatible with other behavioral systems, such as paternal care. In a variety of species of birds that display paternal care, testosterone (T) levels in males are maintained at low levels, and these levels rise only in response to direct agonistic challenges. This idea has not been thoroughly studied in mammals with biparental care, and we exposed male marmosets (Callithrix kuhlii), a monogamous and biparental primate to aggressive interactions with unfamiliar intruders. Urinary levels of T and cortisol (CORT) were monitored prior to and following these interactions. Baseline T was not correlated with variation in aggression in either residents or intruders, and CORT was not affected by the encounters. However, males responded to an encounter with male intruders with changes in T that correlated with the level of aggression displayed by the resident male during the trial. Encounters with male intruders that elicited high frequencies of aggressive displays by the male resident were associated with increased T 2-6 h and 24 h following the encounter, and encounters that had few aggressive displays resulted in no change or a decrease in T concentrations. Intruders did not demonstrate a significant relationship between T and aggression. Thus, the magnitude of the hormonal response is dependent on the intensity of aggression during a male-male encounter, suggesting that elevated androgens are likely to be a consequence, rather than a cause, of aggressive interactions in marmosets.

Functional response properties of neurons in the dorsomedial visual area of New World monkeys (Callithrix jacchus)

The dorsomedial visual area (DM), a subdivision of extrastriate cortex located near the dorsal midline, is characterized by heavy myelination and a relative emphasis on peripheral vision. To date, DM remains the least understood of the three primary targets of projections from the striate cortex (V1) in New World monkeys. Here, we characterize the responses of DM neurons in anaesthetized marmosets to drifting sine wave gratings. Most (82.4%) cells showed bidirectional sensitivity, with only 6.9% being strongly direction selective. The distribution of orientation sensitivity was bimodal, with a distinct population (corresponding to over half of the sample) formed by neurons with very narrow selectivity. When compared with a sample of V1 units representing a comparable range of eccentricities, DM cells revealed a preference for much lower spatial frequencies, and higher speeds. End inhibition was extremely rare, and the responses of many cells summated over distances as large as 30 degrees. Our results suggest clear differences between DM and the two other main targets of V1 projections, the second (V2) and middle temporal (MT) areas, with cells in DM emphasizing aspects of visual information that are likely to be relevant for motor control.

Two breeding females within free-living groups may not always indicate polygyny: alternative subordinate female strategies in common marmosets (Callithrix jacchus)

The mating system of callitrichids has been reported to be monogamous, polygynous and polyandrous. In Callithrix jacchus, groups with 2 breeding females and groups with 1 breeding female have been reported. Our purpose was to evaluate the occurrence of occasional reproduction by subordinate females in free-ranging C. jacchus groups characterized as monogamous. Four groups were monitored at a field site of IBAMA-Brazil for between 20 and 72 months. We recorded the birth of 7 sets of twins to subordinate females that had never reproduced before. Sexual activities were recorded opportunistically: dominant females copulated with only the resident male, while subordinates copulated with extra-group males. We suggest these were essentially monogamous groups that occasionally had 2 reproductive females. Between-group copulations seem to be an alternative strategy used by the subordinates. Despite the costs, there would probably be benefits as a result of scanning for vacancies for reproductive positions in neighbouring groups and the establishment of ties with extra-group males that might become a reproductive partner in the future.

Seasonality of the activity pattern of Callithrix penicillata (Primates, Callitrichidae) in the cerrado (scrub savanna vegetation)

Two wild groups of Callithrix penicillata, the Black Pincelled Marmoset, were observed from January to September 1998, in two areas, one an area of dense scrub savanna vegetation (cerrado) and the other, a semidecidual woodland (cerradão), both within the boundaries of the Ecological Reserve of IBGE (Brazilian Institute of Geography and Statistics), in an environmentally protected area, the APA (Portuguese abbreviation for "environmental protected area") Gama/Cabeça-de-Veado, Brasília, DF. The behavioral data collected during the rainy (January 15 to April 15) and dry season (June 1 to September 15) were compared. Because of the proximity to the Reserve facilities, the group from the dense scrub savanna vegetation (CD) was submitted to antropic impacts different from the group in the semidecidual woodland (CE), which was using as territory an area that had been suffering from man-made fires every two years as part of a long-term experimental project on fire impacts. The behavioral data was quantified by instantaneous cross-section ("scan sampling") every ten minutes with records of locomotion, rest, foraging for insects, use of exudate, and feeding. During the whole year, the greatest percentage of time spent by CE and CD was in foraging for insects, with 44% and 39%, respectively. It was evident when comparing the data for the two seasons that, for both groups, foraging for insects was more intense during the dry season, possibly to complement the shortage of food, and locomotion increased during the rainy season. The greater the availability and distribution of fruit in the areas, the greater the locomotion of the groups to obtain these resources. None of the other behavioral patterns, including the use of exudates, presented significant differences between the two seasons. Both groups foraged more frequently during the dry season and locomoted more during the rainy one.

Proteasomal activity in brain differs between species and brain regions and changes with age

Age-related increase in protein oxidation in brain coupled to an impairment of proteasomal activity may underline neuronal loss but differences in susceptibility between species and brain regions remain unexplained. We now investigate differences in proteasomal activity, measured as chymotrypsin-, trypsin- and peptidylglutamyl-like hydrolysing activities between brain regions in rats, mice and common marmosets. In aged rats and mice, proteasomal activity was decreased in the cortex, striatum, cerebellum, globus pallidus and substantia nigra overall when compared to young animals. However, in the aged brain only chymotrypsin-like activity was decreased in the cortex and the globus pallidus while only trypsin-like activity was reduced in the cerebellum. In contrast, in the striatum, both chymotrypsin-like and trypsin-like activities were reduced and in the substantia nigra, all the three catalytic activities of proteasome were significantly impaired. Chymotrypsin-like and trypsin-like activities were significantly higher in all the brain regions of marmosets compared to those of mice and rats. Peptidylglutamyl-like activity was only significantly higher in the cerebellum and striatum of marmoset compared to rodents. The data suggest that there is higher proteasome activity in common marmoset brain compared to rat and mouse and that the basal ganglia are more prone to an age-related decrease in proteasomal activity. This may explain the involvement of altered ubiquitin-proteasome system activity in Parkinson's disease and the relationship to ageing.

Diminished maternal responsiveness during pregnancy in multiparous female common marmosets

Common marmoset monkeys (Callithrix jacchus) live in small groups in which, usually, only a single female breeds and all group members provide infant care. When two females breed concurrently, however, they may commonly kill one another's infants, especially during the peripartum period. To investigate the mechanisms underlying infanticide by breeding females, we characterized responses of multiparous females to infants and determined circulating hormone levels in adult females during early pregnancy, late pregnancy, and the early postpartum period. Additionally, we compared the responses of postpartum females to their own infants and infants of other females (unfamiliar infants). Postpartum females were highly maternal toward both their own and unfamiliar infants, and showed no differences in their behavioral or hormonal responses to the two. During both early and late pregnancy, however, these females exhibited longer latencies to initially approach unfamiliar infants and spent less time carrying unfamiliar infants. Moreover, females spent less time carrying unfamiliar infants during late pregnancy than early pregnancy. Most late pregnant females never carried infants, and those that did rejected them quickly. Prolactin concentrations were higher and progesterone concentrations lower postpartum than in early or late pregnancy, while estradiol concentrations, the estradiol-to-progesterone ratio, and cortisol levels were higher during late pregnancy. Within reproductive conditions, however, maternal behaviors were not correlated with hormone levels. These results suggest that maternal responsiveness in marmosets may be attenuated during pregnancy, especially late pregnancy, and this may contribute to infanticide by breeding females.

Resolving the organization of the New World monkey third visual complex: The dorsal extrastriate cortex of the marmoset (Callithrix jacchus)

We tested current hypotheses on the functional organization of the third visual complex, a particularly controversial region of the primate extrastriate cortex. In anatomical experiments, injections of retrograde tracers were placed in the dorsal cortex immediately rostral to the second visual area (V2) of New World monkeys (Callithrix jacchus), revealing the topography of interconnections between the "third tier" cortex and the primary visual area (V1). The data indicate the presence of a dorsomedial area (DM), which represents the entire upper and lower quadrants of the visual field, and which receives strong, topographically organized projections from the superficial layers of V1. The visuotopic organization and boundaries of DM were confirmed by electrophysiological recordings in the same animals and by architectural characteristics which were distinct from those found in ventral extrastriate cortex rostral to V2. There was no electrophysiological or histological evidence for a transitional area between V2 and DM. In particular, the central representation of the upper quadrant in DM was directly adjacent to the representation of the horizontal meridian that marks the rostral border of V2. The present results argue in favor of the hypothesis that the third visual complex in New World monkeys contains different areas in its dorsal and ventral components: area DM, near the dorsal midline, and a homolog of area 19 of other mammals, located more lateral and ventrally. The characteristics of DM suggest that it may correspond to visual area 6 (V6) of Old World monkeys.

Fecal androgen levels in common marmoset (Callithrix jacchus) males living in captive family groups

In captive common marmoset groups, the reproductive inhibition observed in subordinate female seems to be a result of olfactory, visual and behavioral cues from the dominant female. However, few studies have examined the relationship among adult males living in the same social group. These studies have shown that reproductive failure among peer males seems to be based on hormonal and behavioral mechanisms. New insights on sexual strategies in primates have been shown using fecal steroids, but so far no information is available for common marmoset males. In the present study, we evaluated the influence of light-dark cycle, age and reproductive condition on the profile of fecal androgens in males living in the same family group. Feces were collected from six fathers and six sons for androgen determination during the light phase of the 24-h cycle for eight days randomly distributed over a 4-week period. Androgen levels were determined by enzyme immunoassay technique. Adult sons showed higher androgen levels (166.97 +/- 22.95 ng/g) than fathers (80.69 +/- 44.38 ng/g) and juveniles (49.06 +/- 23.15 ng/g; P < 0.05). No diurnal variation (P > 0.05) in fecal androgen profile was observed in adults or juveniles. No indication of androgen-mediated social competition between fathers and adult sons was demonstrable. These results provide basic information on fecal androgen profile useful to investigate the socioendocrinology of free-ranging common marmoset males and verify that, in contrast to daughters, the reproductive suppression of sons is not based on physiological inhibition of their gonads.

Multibehavioral analysis of fear and anxiety before, during, and after experimentally induced predatory stress in Callithrix penicillata

A detailed behavioral analysis of nine Callithrix penicillata was conducted in the Marmoset Predator Confrontation Test (MPCT) during (a) four habituation trials with no "predator," (b) six confrontation trials with the predator (taxidermized oncilla cat, Felis tigrina), and (c) four trials with the predator removed. The marmosets habituated to the test apparatus with significant decreases in locomotion, exploration and long calls. Initial exposure to the predator elicited mainly fear-related behaviors (proximic avoidance, tsik-tsik vocalization, swaying/tongue in-out), whereas repeated confrontations attenuated these behaviors, concomitant to an increase in anxiety-associated responses (scratching/grooming/scent marking). The initial behavioral repertoire, observed before confrontations, was fully restored only upon removal of the predator. This easily discernable complex defensive behavioral repertoire is hoped to provide a comprehensive baseline for studying the biological substrates of fear/anxiety parameters in nonhuman primates.

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.

Color vision in marmosets and tamarins: behavioral evidence

Here we demonstrate differences in the relative performance of 15 callitrichids tested in a series of color visual discrimination experiments. Munsell color chips were chosen as stimuli based on their use in earlier experiments with human dichromats. We show behavioral evidence for the existence of four distinct kinds of color-vision phenotypes, each of which has slightly different color discrimination abilities. The different phenotypes may offer different advantages. The data are in accordance with the existence of a visual polymorphism in callitrichids.