Signatures of adaptive evolution in platyrrhine primate genomes.

The platyrrhine family Cebidae (capuchin and squirrel monkeys) exhibit among the largest primate encephalization quotients. Each cebid lineage is also characterized by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae such as high sensorimotor intelligence with tool use, advanced cognitive abilities, and behavioral flexibility. Here, we take a comparative genomics approach, performing genome-wide tests for positive selection across five cebid branches, to gain insight into major periods of cebid adaptive evolution. We uncover candidate targets of selection across cebid evolutionary history that may underlie the emergence of lineage-specific traits. Our analyses highlight shifting and sustained selective pressures on genes related to brain development, longevity, reproduction, and morphology, including evidence for cumulative and diversifying neurobiological adaptations across cebid evolution. In addition to generating a high-quality reference genome assembly for robust capuchins, our results lend to a better understanding of the adaptive diversification of this distinctive primate clade.

Homosexual Courtship in Young Wild Capuchin Monkeys: A Case Study.

In primates, many species exhibit same-sex sexual behaviors (SSB), defined as "genital contact or genital manipulation between same-sex individuals." Several sociosexual functions have been proposed, including proceptivity enhancement, receptivity reduction, dominance assertion, practice for heterosexual copulation, tension regulation, reconciliation, and alliance formation. Capuchin monkeys are known for their rich and flexible sexual behavioral repertoire and elaborated courtships. At present, the few reports of SSB in capuchin monkeys (genera Sapajus and Cebus) focused on mounting. Here, we describe the case observed in a population of wild yellow-breasted capuchin monkeys (Sapajus xanthosternos) in which two young males, aged 5-6 years and 19 months, performed a 15-min uninterrupted sequence of courtship behaviors and mounting. Comparing with a previously established ethogram of 20 behaviors typical for heterosexual behavior of tufted capuchins, we show that these males performed 16 of them. Thus, SSBs are already present in the repertoire of young individuals and the practice may serve to create or strengthen bonds. Although same-sex mounting and genital inspection are common in capuchins' play and other social interactions, the almost entire array of courtship behaviors has never been observed in youngsters. Additionally, this example supports the notion that primate (homo)sexual behavior is not limited to genitalia and copulation, since the observed courtship included diverse behaviors different from genital contact. Thus, we propose a broader definition of sexual behavior.

Ontogenesis of sociability of wild immature capuchin monkeys (Sapajus libidinosus): Sex more than personality explains interindividual variation.

Sociability is a fundamental trait that social animals need to survive and reproduce in societies. Sociability predicts how an individual can consistently interact with its conspecifics across time and situations. By studying capuchin monkeys (Sapajus libidinosus), a neotropical primate with complex social behavior and high cognitive capacity, our research aims to analyze the development of the social axis of personality of immature individuals, from birth to the third year of life. We studied wild monkeys belonging to a group with infants, juveniles, and adults of both sexes that inhabits northeastern Brazil. We analyzed the behavior of 12 immature capuchins (6 males and 6 females) in 94 h of videos recorded weekly from birth until 36 months, through daily focal sampling. We verified whether there was intraindividual consistency throughout development by fitting regression models for the effect of age on initiating affiliative social behaviors, controlling for monkey identity and sex. Our results indicate that the individuals of this study exhibit high variation in the initiation of behaviors at the beginning of infancy; there was low repeatability and high intra-individual variation during the first 3 years of life of these individuals, indicating that the social personality is not consolidated in this period. Immature females were more sociable than immature males. Therefore, differences in sociability in early life of bearded capuchin monkeys are best explained by sex rather than personality. We suggest that the high initial behavioral variation in the social axis of personality allows for plasticity influenced by the environment throughout development. The high sociability of females in infancy may be related to female philopatry and their high sociability in adulthood.

Diet, activity patterns, and home range use in forest and cultivated areas for one wild group of endangered crested capuchin monkeys (Sapajus robustus) in Reserva Natural Vale, Espírito Santo, Brazil.

Robust capuchin monkeys (Sapajus spp.) are distributed widely in the Neotropics and may be able to survive in modified landscapes because of their omnivorous, opportunistic diet. The poorly known and endangered crested capuchin monkey (Sapajus robustus) is endemic to the Atlantic Forest in Bahia, Minas Gerais and Espírito Santo states, Brazil. We collected data on diet and home range for a crested capuchin group with access to forest and cultivated areas. We hypothesized that with access to cultivated exotic fruit, capuchins would use cultivated areas more for feeding during the season of fruit scarcity in the surrounding forest and have a small home range size because of higher fruit availability. Both the forest and the cultivated areas peaked in fruit availability in the wet season, with a low proportion of trees producing fruit in the dry season; cultivated areas had a higher proportion of trees in fruit compared to the forest throughout the study. While monkeys consumed exotic fruits like jackfruit and oil palm, we recorded more samples of them eating forest fruits than exotic fruits in all but 1 month, and they consumed a more diverse array of forest fruits (56 species) but only six exotic species. Home range size was relatively small compared with other studies: 120.5 ha across the year (wet season 102 ha, dry season 111.5 ha). Natural and human-intensified fruit sources in a protected area without hunting may have allowed monkeys to maintain a smaller home range size. The group composition changed during the study; this also likely influenced home range use. Studies focused on robust capuchin groups that utilize agricultural or cultivated foods may underestimate home range needs for groups without access to human-intensified food sources. Studying crested capuchin ecology in additional locations will be important for establishing a sound species conservation program.

Anticipating future actions: Motor planning improves with age in wild bearded capuchin monkeys (Sapajus libidinosus).

Self-directed object manipulation tasks illuminate development of motor planning. Grasping strategies that lead to good object control to perform the following action(s) reveal second-order motor planning. Motor planning for efficient grips develops slowly in children. Age-related differences in other primates have been poorly investigated. Here, we investigated anticipatory motor planning of infant, juvenile and adult wild capuchin monkeys grasping a horizontally positioned stick baited to the left or right side (a version of the elevated spoon task). We recorded the grasps capuchins used to bring the baited end of the stick to the mouth. The percentage of efficient radial grips positively correlated with age and adults used efficient grips significantly more frequently than infants. Adult wild capuchins' use of radial grips was higher than that reported for adult captive capuchins in similar tasks, suggesting that experience throughout life may influence motor anticipation. Self-directed object manipulation tasks will be useful to compare this aspect of cognition across primates. A video abstract of this article can be viewed at https://youtu.be/a1Zbr_AQkb8.

The role of hunting on Sapajus xanthosternos' landscape of fear in the Atlantic Forest, Brazil.

Habitats with spatial variation in food availability, predation risk, and hunting pressure allow us to study how animals resolve the trade-off between food searching and predator avoidance. We investigated the influence of food availability, predation risk, and the perceived predation risk on habitat use by a primate living under high hunting pressure, the yellow-breasted capuchin monkeys, Sapajus xanthosternos, at Una Biological Reserve (ReBio Una). We hypothesized that the hunting pressure occurring in the capuchins' home range would favor predator avoidance to the detriment of searching for food. We characterized a set of covariates related to resource availability (fruit and invertebrate biomasses, feeding on dispersed and clumped food items, sleeping sites), perceived predation risk (alarm calls given to terrestrial and aerial predators, silent group movement, and vigilance behavior), and actual predation risk (evidence of hunting) and estimated their effects on how one group of capuchin monkeys uses its habitat. The group divides its time among three major forest types within their home range: agroforest, mature, and secondary. Our results suggest that the actual and perceived risk of hunting by humans, as well as the perceived predation risk by both terrestrial and aerial predators, were significant determinants of capuchin monkeys' space use. Yellow-breasted capuchin monkeys' space use was negatively related to the risk of hunting by humans (actual evidence and silent behavior), the perceived risk of predation by both aerial and terrestrial predators, and the presence of sleeping sites. Capuchin monkeys' use of space was not related to the biomass of fruits in the habitat, and the biomass of invertebrates had a very low positive effect. We confirmed our prediction that in a habitat with high hunting pressure, the risk of predation, both perceived and actual, had a more significant impact on how yellow-breasted capuchins used space than did food availability.

Optional tool use: The case of wild bearded capuchins (Sapajus libidinosus) cracking cashew nuts by biting or by using percussors.

Tool use in humans can be optional, that is, the same person can use different tools or no tool to achieve a given goal. Strategies to reach the same goal may differ across individuals and cultures and at the intra-individual level. This is the first experimental study at the intra-individual level on the optional use of a tool in wild nonhuman primates. We investigated optional tool use by wild bearded capuchins (Sapajus libidinosus) of Fazenda Boa Vista (FBV; Piauí, Brazil). These monkeys habitually succeed in cracking open the mesocarp of dry cashew nuts (Anacardium spp.) by pounding them with stones and/or by biting. We assessed whether availability of a stone and resistance of the nut affected capuchins' choice to pound or to bite the nuts and their rates of success. Sixteen capuchins (1-16 years) received small and large dry cashew nuts by an anvil together with a stone (Stone condition) or without a stone (No-Stone condition). In the Stone conditions, subjects used it to crack the nut in 89.1% (large nuts) and 90.1% (small nut) of the trials. Nut size significantly affected the number of strikes used to open it. Availability of the stone significantly increased the average percent of success. In the No-Stone conditions, monkeys searched for and used other percussors to crack the nuts in 54% of trials. In all conditions, age affects percentage of success and number of strikes to reach success. We argue that exclusive use of stones in other sites may be due to the higher abundance of stones at these sites compared with FBV. Since capuchins opened cashews with a tool 1-2 years earlier than they succeed at cracking more resistant palm nuts, we suggest that success at opening cashew nuts with percussors may support the monkeys' persistent efforts to crack palm nuts.

Isotopic and elemental corroborates for wild bearded capuchin (Sapajus libidinosus) omnivorous dietary adaptation at Fazenda Boa Vista, Brazil.

RATIONALE: This study analyzes variability in the diets of wild bearded capuchin monkeys, Sapajus libidinosus, by analyzing stable carbon (δ13 C) and nitrogen (δ15 N) isotope ratios and elemental concentrations (%C and %N) of fecal samples and food items. Developing isotopic and elemental correlates for diets of habituated subjects is a necessary step towards applying similar methods to interpret diets of unhabituated or cryptic subjects. METHODS: Fecal samples from wild capuchins and their foods were collected at Fazenda Boa Vista, Brazil. Fecal samples from laboratory-housed Sapajus spp. and their foods were analyzed to establish diet-feces offsets for δ13 C, δ15 N, %C, and %N. Samples were dried, powdered, and measured for isotopic and elemental values. A Bayesian mixing model commutes isotopic and elemental data from wild capuchins into likely proportions of different food categories. RESULTS: The captive study shows small diet-feces spaces for Sapajus spp. of -0.8 ± 0.7‰ for δ13 C, -0.2 ± 0.4‰ for δ15 N, -6.1 ± 1.7% for %C, and -1.0 ± 0.6% for %N. The wild study shows omnivorous diets based on C3 , C4 , and CAM plants, and fauna. Subject diets are highly varied within and between days. Fecal data show age-related differences in diet and crop-raiding. There is no consistent isotopic or elemental difference between mothers and infants. CONCLUSIONS: Fecal stable isotope and elemental evidence employed in a Bayesian mixing model reflects the highly varied diets of capuchin monkeys in an isotopically heterogeneous environment. The isotopic and elemental variability reported here will aid similar diet reconstructions among unhabituated subjects in the future, but precludes tracking weaning isotopically among capuchins in this environment.

A longitudinal assessment of behavioral development in wild capuchins: Personality is not established in the first 3 years.

Animal personality is defined as consistent individual differences across time and situations, but little is known about how or when those differences are established during development. Likewise, several studies described the personality structure of adult capuchin monkeys, without assessing the ontogeny of these personality traits. We analyzed the behavioral repertoire of 12 wild infants (9 males, 3 females) yellow-breasted capuchin monkeys (Sapajus xanthosternos), in Una Biological Reserve (Bahia, Brazil). Each infant was observed and filmed weekly from birth until 36 months, through daily focal sampling. We analyzed the behavior of each individual in 10 developmental points. By means of component reduction (principal component analysis), we obtained four behavioral traits: Sociability, Anxiety, Openness, and Activity. We investigated whether there were developmental effects on those traits by fitting regression models for the effect of time on behavioral traits, controlling for monkey identity, sex, and cohort. Sociability (decreasing) and Anxiety (increasing) changed significantly along development. By means of repeatability analysis, we did not find intra-individual consistency across time in those traits, so we cannot discriminate stable personality traits in early ontogeny. Our results show that the personality structure of capuchin monkeys is not established during early development, in agreement with the literature on human personality.

Adult and juvenile bearded capuchin monkeys handle stone hammers differently during nut-cracking.

Wild bearded capuchin monkeys (Sapajus libidinosus) habitually use stone hammers to crack open palm nuts and seeds on anvils. This activity requires strength, balance, and precise movement of a large stone with respect to the item placed on an anvil. We explored how well young monkeys cope with these challenges by examining their behavior and the behavior of adults while they cracked palm nuts using a stone. Using video records, we compared actions of six juvenile (2-5 years) and six adult (7+ years) wild monkeys during their first 20 strikes with one unfamiliar ellipsoid, quartzite stone (540 g), and the outcomes of these strikes. Compared with adults, juveniles cracked fewer nuts, performed a more diverse set of exploratory actions, and less frequently placed one or both hands on top of the stone on the downward motion. Adults and juveniles displayed similar low frequencies of striking with a slanted trajectory, missing the nut, and losing control over the nut or stone after striking. These findings indicate that young monkeys control the trajectory of a stone adequately but that is not sufficient to crack nuts as effectively as adults do. Compared with juveniles, adults more quickly perceive how to grip the stone efficiently, and they are able to adjust their grip dynamically during the strike. Young monkeys develop expertise in the latter aspects of cracking nuts over the course of several years of regular practice, indicating that perceptual learning about these aspects of percussion occurs slowly. Juvenile and adult humans learning to use stones to crack nuts also master these features of cracking nuts very slowly.

Synchronized practice helps bearded capuchin monkeys learn to extend attention while learning a tradition.

Culture extends biology in that the setting of development shapes the traditions that individuals learn, and over time, traditions evolve as occasional variations are learned by others. In humans, interactions with others impact the development of cognitive processes, such as sustained attention, that shape how individuals learn as well as what they learn. Thus, learning itself is impacted by culture. Here, we explore how social partners might shape the development of psychological processes impacting learning a tradition. We studied bearded capuchin monkeys learning a traditional tool-using skill, cracking nuts using stone hammers. Young monkeys practice components of cracking nuts with stones for years before achieving proficiency. We examined the time course of young monkeys' activity with nuts before, during, and following others' cracking nuts. Results demonstrate that the onset of others' cracking nuts immediately prompts young monkeys to start handling and percussing nuts, and they continue these activities while others are cracking. When others stop cracking nuts, young monkeys sustain the uncommon actions of percussing and striking nuts for shorter periods than the more common actions of handling nuts. We conclude that nut-cracking by adults can promote the development of sustained attention for the critical but less common actions that young monkeys must practice to learn this traditional skill. This work suggests that in nonhuman species, as in humans, socially specified settings of development impact learning processes as well as learning outcomes. Nonhumans, like humans, may be culturally variable learners.

Face-to-face interactions between mothers and female infants in wild bearded capuchin monkeys (Sapajus libidinosus).

Once considered uniquely human, mother-infant face-to-face interactions (FF) were observed in a few captive primates. In these studies, FF were correlated to physical contact suggesting a mechanism mediating proximity between mother and infant, as is the case for humans. We investigated this hypothesis in wild capuchin monkeys (Sapajus libidinosus) during the first year of life of eight female infants. Data were weekly focal-day videos of infants from which we recorded FF with mothers. We expected FF would increase with infants' age (as time in contact with mothers decreased) and would more likely occur in the absence of physical contact between the dyad. There was no effect of age in the proportion of interaction time spent in FF, nor in types of FF. A quarter of FF episodes occurred in the absence of physical contact between the dyad, and in most of them physical contact was resumed following the FF. Contrary to predictions, the stability in the first year, mainly when mothers-female infants were in contact, indicates that FF act primarily promoting opportunities for affective communication and intuitive care. However, we found some supportive evidence for the hypothesis that FF regulate proximity between mother and infant, mainly in resume physical contact.

Manual skills for processing plant underground storage organs by wild bearded capuchins.

OBJECTIVES: Wild Sapajus libidinosus exploit underground storage organs (USOs) that require extraction and extensive processing before consumption. Since capuchin monkeys are small-sized extractive foragers that cannot perform forceful precision grips, we expected that: (a) they would use other body parts together with their hands, (b) older (and larger) capuchins would be more efficient than younger (and smaller) ones, and (c) capuchins would invest greater effort/time to exploit USOs than other foods. MATERIALS AND METHODS: We recorded 178 episodes of USO processing performed by 20 individuals. The behavior was videotaped and scored frame-by-frame. RESULTS: We identified six sequential stages of processing: Excavation, extraction, soil removal, transport, peeling, and fragmenting the inner tissues. Capuchins made frequent use of forceful hand postures and manipulation in which the hands were strongly supported by other body parts, principally the mouth. Older capuchins were more efficient than younger individuals in pulling the USOs out of the ground. Finally, exploiting USOs was time-consuming, lasting more than 4 min per item, on average. DISCUSSION: Despite having smaller body-mass and greater manual constraints than catarrhine extractive foragers, capuchins, even smaller individuals, mastered USO processing thanks to their behavioral flexibility and persistence. Our findings reveal that precision grips are not essential for forceful actions during complex food processing and that, unlike catarrhines, capuchins, especially adults, rarely use thumb opposition during forceful grasping of food. In contrast, extended sustained attention and varied manual behavior appear to be convergent features of platyrrhine and catarrhine extractive foragers.

Positional behavior and substrate use in wild adult bearded capuchin monkeys (Sapajus libidinosus).

Natural selection for positional behavior (posture and locomotion) has at least partially driven the evolution of anatomical form and function in the order Primates. Examination of bipedal behaviors associated with daily activity patterns, foraging, and terrestrial habitat use in nonhuman primates, particularly those that adopt bipedal postures and use bipedal locomotion, allows us to refine hypotheses concerning the evolution of bipedalism in humans. This study describes the positional behavior of wild bearded capuchins (Sapajus libidinosus), a species that is known for its use of terrestrial substrates and its habitual use of stones as tools. Here, we test the association of terrestrial substrate use with bipedal posture and locomotion, and the influence of sex (which co-varies with body mass in adults of this species) on positional behavior and substrate use. Behavior and location of 16 wild adult bearded capuchins from two groups were sampled systematically at 15 s intervals for 2 min periods for 1 year (10,244 samples). Despite their different body masses, adult males (average 3.5 kg) and females (average 2.1 kg) in this study did not differ substantially in their positional behaviors, postures, or use of substrates for particular activities. The monkeys used terrestrial substrates in 27% of samples. Bipedal postures and behaviors, while not a prominent feature of their behavior, occurred in different forms on the two substrates. The monkeys crouched bipedally in trees, but did not use other bipedal postures in trees. While on terrestrial substrates, they also crouched bipedally but occasionally stood upright and moved bipedally with orthograde posture. Bearded capuchin monkeys' behavior supports the suggestion from anatomical analysis that S. libidinosus is morphologically better adapted than its congeners to adopt orthograde postures.

How bearded capuchin monkeys (Sapajus libidinosus) prepare to use a stone to crack nuts.

Bearded capuchin monkeys crack nuts with naturally varying stone hammers, suggesting they may tune their grips and muscular forces to each stone. If so, they might use discrete actions on a stone before lifting and striking, and they would likely use these actions more frequently when the stone is larger and/or less familiar and/or when first initiating striking. We examined the behavior of (a) four monkeys (all proficient at cracking nuts) with two larger (1 kg) and two smaller (0.5 kg) stones, (b) 12 monkeys with one 1 kg stone, and (c) one monkey during its first 100 strikes with an initially unfamiliar 1 kg stone. Bearded capuchin monkeys used three discrete actions on the stone before striking, all more often with the larger stones than the smaller stones. We infer that the first discrete action (Spin) aided the monkey in determining where to grip the stone, the second (Flip) allowed it to position the stone on the anvil ergonomically before lifting it, and the third (Preparatory Lift) readied the monkey for the strenuous lifting action. The monkey that provided 100 strikes with one initially unfamiliar stone performed fewer Spins in later strikes but performed Flip and Preparatory Lift at consistent rates. The monkeys gripped the stone with both hands along the sides to lift it, but usually moved one or both hands to the top of the stone at the zenith of the lift for the downward strike. The findings highlight two new aspects of the capuchins' nut-cracking: (a) Anticipatory actions with the stone before striking, especially when the stone is larger or unfamiliar, and when initiating striking and (b) shifting grips on the stone during a strike. We invite researchers to investigate if other taxa use anticipatory actions and shift their grips during percussive activity.

Unique perceptuomotor control of stone hammers in wild monkeys.

We analysed the patterns of coordination of striking movement and perceptuomotor control of stone hammers in wild bearded capuchin monkeys, Sapajus libidinosus as they cracked open palm nut using hammers of different mass, a habitual behaviour in our study population. We aimed to determine why these monkeys cannot produce conchoidally fractured flakes as do contemporary human knappers or as did prehistoric hominin knappers. We found that the monkeys altered their patterns of coordination of movement to accommodate changes in hammer mass. By altering their patterns of coordination, the monkeys kept the strike's amplitude and the hammer's velocity at impact constant with respect to hammer mass. In doing so, the hammer's kinetic energy at impact-which determines the propagation of a fracture/crack in a nut-varied across hammers of different mass. The monkeys did not control the hammer's kinetic energy at impact, the key parameter a perceiver-actor should control while knapping stones. These findings support the hypothesis that the perceptuomotor control of stone hammers in wild bearded capuchin monkeys is inadequate to produce conchoidally fractured flakes by knapping stones, as do humans.

Foraging and inter-individual distances of bearded capuchin monkeys.

Extractive foraging is a skill young capuchin monkeys learn over time. A key unknown is whether unskilled individuals occupy spatial positions that increase their opportunities to learn. We observed the spatial positions of individuals in a group of capuchin monkeys in Northeastern Brazil. To improve our understanding of the relationship between learning by young capuchin monkeys and inter-individual distance, we investigated the associations between the proximity of individuals and their age, activity, and proficiency at extractive foraging. To do this, we used one form of extractive foraging, opening palm nuts, as an index of proficiency at all types of extractive foraging. Our results indicate that, in the subset of the data where dyads consisted of one proficient individual and a partner with any level of proficiency, the distance between individuals was predicted by their foraging activity (i.e., extractive foraging, other foraging, or not foraging). In those dyads, the proficiency of the partner did not significantly improve prediction of inter-individual distances, indicating that spatial proximity of proficient individuals to others does not function primarily to increase opportunities for unskilled individuals to observe extractive foraging. Dyads in which both individuals were engaged in similar foraging activities (e.g., both "extractive foraging") exhibited the shortest inter-individual distances. Proximity between individuals engaged in similar foraging activities may result from the spatial distribution of resources or from social learning mechanisms, such as local or stimulus enhancement.

Age-related variation in the mechanical properties of foods processed by Sapajus libidinosus.

OBJECTIVES: The diet of tufted capuchins (Sapajus) is characterized by annual or seasonal incorporation of mechanically protected foods. Reliance on these foods raises questions about the dietary strategies of young individuals that lack strength and experience to access these resources. Previous research has demonstrated differences between the feeding competencies of adult and juvenile tufted capuchins. Here we test the hypothesis that, compared to adults, juveniles will process foods with lower toughness and elastic moduli. MATERIALS AND METHODS: We present data on variation in the toughness and elastic modulus of food tissues processed by Sapajus libidinosus during the dry season at Fazenda Boa Vista, Brazil. Food mechanical property data were collected using a portable universal mechanical tester. RESULTS: Results show that food tissues processed by the capuchins showed significant differences in toughness and stiffness. However, we found no relationship between an individual's age and mean or maximum food toughness or elastic modulus, indicating both juvenile and adult S. libidinosus are able to process foods of comparable properties. DISCUSSION: Although it has been suggested that juveniles avoid mechanically protected foods, age-related differences in feeding competence are not solely due to variation in food toughness or stiffness. Other factors related to food type (e.g., learning complex behavioral sequences, achieving manual dexterity, obtaining physical strength to lift stone tools, or recognizing subtle cues about food state) combined with food mechanical properties better explain variation in juvenile feeding competency.

Factors affecting cashew processing by wild bearded capuchin monkeys (Sapajus libidinosus, Kerr 1792).

Cashew nuts are very nutritious but so well defended by caustic chemicals that very few species eat them. We investigated how wild bearded capuchin monkeys (Sapajus libidinosus) living at Fazenda Boa Vista (FBV; Piauí, Brazil) process cashew nuts (Anacardium spp.) to avoid the caustic chemicals contained in the seed mesocarp. We recorded the behavior of 23 individuals toward fresh (N = 1282) and dry (N = 477) cashew nuts. Adult capuchins used different sets of behaviors to process nuts: rubbing for fresh nuts and tool use for dry nuts. Moreover, adults succeed to open dry nuts both by using teeth and tools. Age and body mass significantly affected success. Signs of discomfort (e.g., chemical burns, drooling) were rare. Young capuchins do not frequently closely observe adults processing cashew nuts, nor eat bits of nut processed by others. Thus, observing the behavior of skillful group members does not seem important for learning how to process cashew nuts, although being together with group members eating cashews is likely to facilitate interest toward nuts and their inclusion into the diet. These findings differ from those obtained when capuchins crack palm nuts, where observations of others cracking nuts and encounters with the artifacts of cracking produced by others are common and support young individuals' persistent practice at cracking. Cashew nut processing by capuchins in FBV appears to differ from that observed in a conspecific population living 320 km apart, where capuchins use tools to open both fresh and dry nuts. Moreover, in the latter population, chemical burns due to cashew caustic compounds appear to be common. The sources of these differences across populations deserve investigation, especially given that social influences on young monkeys learning to open cashew nuts at FBV seem to be nonspecific. Am. J. Primatol. 78:799-815, 2016. © 2016 Wiley Periodicals, Inc.

Body mass in wild bearded capuchins, (Sapajus libidinosus): Ontogeny and sexual dimorphism.

Body mass is fundamental for understanding growth, health, and aspects of life history but records of body mass are rarely available for wild primates. We documented the body mass of all individuals in a group of wild bearded capuchin monkeys (Sapajus libidinosus) at annual intervals for seven consecutive years. Sexual dimorphism in body mass was more pronounced than reported in the literature for adults in this genus: females in our sample were relatively light (average 2.1 kg), while males had average body mass (3.5 kg). Three other notable differences between males and females were evident. First, males grew more rapidly and for a longer period than females. We estimate that males attained full body mass at 9.8 years of age and females at 7.5 years. Second, males showed greater inter-individual variability than females in growth rates and adult mass. Third, males gained about 20% above their baseline body mass upon becoming alpha, and lost that amount when they lost that status, but body mass in females was unrelated to social status. We also report preliminary data on mass and age of natal males at dispersal and mass and age at first reproduction for one female. The pattern of sexual dimorphism in ontogeny and inter-individual variability in body mass in bearded capuchins suggests different competitive risks in the two sexes commensurate with a mating system characterized by female choice of mates in multi-male, multi-female groups. Am. J. Primatol. 78:473-484, 2016. © 2015 Wiley Periodicals, Inc.