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Pronounced temporal and spatial variation in the availability of food resources can produce energetic deficits in organisms. Fruit-dependent Bornean orangutans face extreme variation in fruit availability and experience negative energy and protein balance during episodes of fruit scarcity. We evaluate the possibility that orangutans of different sexes and ages catabolize muscle tissue when the availability of fruit is low. We assess variation in muscle mass by examining the relationship between urinary creatinine and specific gravity and use the residuals as a non-invasive measure of estimated lean body mass (ELBM). Despite orangutans having a suite of adaptations to buffer them from fruit scarcity and associated caloric deficits, ELBM was lower during low fruit periods in all age-sex classes. As predicted, adult male orangutans had higher ELBM than adult females and immatures. Contrary to expectation, flanged and unflanged males did not differ significantly in ELBM. These findings highlight the precarity of orangutan health in the face of rapid environmental change and add to a growing body of evidence that orangutans are characterized by unique metabolic traits shaped by their unpredictable forest environment.

Objectives: Although fermented food use is ubiquitous in humans, the ecological and evolutionary factors contributing to its emergence are unclear. Here we investigated the ecological contexts surrounding the consumption of fruits in the late stages of fermentation by wild primates to provide insight into its adaptive function. We hypothesized that climate, socioecological traits, and habitat patch size would influence the occurrence of this behavior due to effects on the environmental prevalence of late-stage fermented foods, the ability of primates to detect them, and potential nutritional benefits. Materials and methods: We compiled data from field studies lasting at least 9 months to describe the contexts in which primates were observed consuming fruits in the late stages of fermentation. Using generalized linear mixed-effects models, we assessed the effects of 18 predictor variables on the occurrence of fermented food use in primates. Results: Late-stage fermented foods were consumed by a wide taxonomic breadth of primates. However, they generally made up 0.01%–3% of the annual diet and were limited to a subset of fruit species, many of which are reported to have mechanical and chemical defenses against herbivores when not fermented. Additionally, latestage fermented food consumption was best predicted by climate and habitat patch size. It was more likely to occur in larger habitat patches with lower annual mean rainfall and higher annual mean maximum temperatures. Discussion: We posit that primates capitalize on the natural fermentation of some fruits as part of a nutritional strategy to maximize periods of fruit exploitation and/or access a wider range of plant species. We speculate that these factors contributed to the evolutionary emergence of the human propensity for fermented foods. Canadian Institute for Advanced Research/[]/CIFAR/Canadá UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biología

Vertebrate predation and consumption by wild Bornean orangutans (Pongo pygmaeus spp.) is rare. In contrast to recorded observations of slow loris consumption by Sumatran orangutans (Pongo abelii), no cases of this have been previously published for Bornean orangutans in the wild. In 2017, we observed the capture and consumption of a slow loris (Nycticebus borneanus) by an adult unflanged male Bornean orangutan at Tuanan Orangutan Research Station, which is located in the Kapuas region of Central Kalimantan. The unflanged male was together with an adult female and her 3.5-year-old offspring throughout the event. However, despite the mother and her offspring watching the male closely and occasionally begging while he consumed the loris, he resisted all food-taking attempts. This study reports, to the best of our knowledge, the first documented case of slow loris predation and consumption by a Bornean orangutan, and thus provides an important data point for understanding primate predation on other primate species.

The use of urine test strips (e.g., Roche Chemstrip®) has become the standard for quickly assessing the physiological condition and/or health of wild primates. These strips have been used to detect ketosis as a marker of fat catabolism in several primate taxa in their natural environments in response to changing food availability. However, the use of urine strips to determine ketosis has only been validated in human studies, and thus it remains unclear whether these strips accurately detect and quantify ketone bodies in nonhuman primates. We examined variations in ketone body concentrations in urine samples collected from wild Bornean orangutans at the Tuanan Orangutan Research Station. We assessed the accuracy of qualitative results from Chemstrip test strips in the field (i.e., negative, small, moderate, and large) using an enzyme-linked assay in the laboratory to determine the concentrations of acetoacetate of the same urine samples. Urine samples that tested positive for ketones in the field had significantly higher levels of ketones in the enzymatic assay compared to those that tested negative. There was significant variation in acetoacetate concentrations among the 4 Chemstrip values; however, post hoc tests revealed no significant differences between negative and small samples. We conclude that urinary test strips provide a useful tool for determining ketotic state in wild orangutans, but caution should be taken when interpreting results from samples showing only small levels of ketones on these strips.

OBJECTIVES Here, we examine (1) if the sex-related differences in iron (Fe) and copper (Cu) isotope ratios, represented as δ56 Fe and δ65 Cu values, respectively observed in humans exist in bulk occipital bone and incisors of male and female non-human primates, and (2) if the variation of Fe and Cu isotope ratios, known to vary in human blood as a factor of age are similar in non-human primate bone. MATERIALS AND METHODS Isotope ratios were measured from the skeletal elements of 20 rhesus macaques (Macaca mulatta) with known life history traits. The metals were purified by column chromatography and their isotope ratios measured by MC-ICP-MS. Data were analyzed using generalized additive models (GAM). RESULTS When accounting for age and sex independently, we found a significant relationship between δ65 Cu values and occipital bone, but not in incisors. There were no significant relationships observed between δ56 Fe values, occipital bone, or incisors. Similarly, there were no significant relationships observed between δ56 Fe values, δ65 Cu values, and age. DISCUSSION We suggest that Cu and Fe isotope ratios have the potential to be useful supplementary tools in future research in biological anthropology, but additional studies are needed to further verify the relationship between sex, age, δ65 Cu, and δ56 Fe values in primates.

Abstract Sexual coercion, in the form of forced copulations, is relatively frequently observed in orangutans and generally attributed to their semi-solitary lifestyle. High ecological costs of association for females may be responsible for this lifestyle and may have prevented the evolution of morphological fertility indicators (e.g., sexual swellings), which would attract (male) associates. Therefore, sexual conflict may arise not only about mating per se but also about associations, because males may benefit from associations with females to monitor their reproductive state and attempt to monopolize their sexual activities. Here, we evaluate association patterns and costs for females when associating with both males and females of two different orangutan species at two study sites: Suaq, Sumatra (Pongo abelii), and Tuanan, Borneo (Pongo pygmaeus wurmbii). Female association frequency with both males and females was higher in the Sumatran population, living in more productive habitat. Accordingly, we found that the cost of association, in terms of reduced feeding to moving ratio and increased time being active, is higher in the less sociable Bornean population. Males generally initiated and maintained such costly associations with females, and prolonged associations with males led to increased female fecal cortisol metabolite (FCM) levels at Tuanan, the Bornean population. We conclude that male-maintained associations are an expression of sexual conflict in orangutans, at least at Tuanan. For females, this cost of association may be responsible for the lack of sexual signaling, while needing to confuse paternity. Significance statement Socioecological theory predicts a trade-off between the benefits of sociality and the ecological costs of increased feeding competition. Orangutans’ semi-solitary lifestyle has been attributed to the combination of high association costs and low predation risk. Previous work revealed a positive correlation between association frequencies and habitat productivity, but did not measure the costs of association. In this comparative study, we show that females likely incur costs from involuntary, male-maintained associations, especially when they last for several days and particularly in the population characterized by lower association frequencies. Association maintenance therefore qualifies as another expression of sexual conflict in orangutans, and especially prolonged, male-maintained associations may qualify as an indirect form of sexual coercion.

Abstract Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these differences develop in immatures. We analyzed 11 years of feeding data on ten adult female, seven flanged male, and 14 immature Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan in Central Kalimantan, Indonesia. We found that the diets of the adult females were significantly broader and required more processing steps before ingestion than the diets of flanged males. We also found evidence for a similar difference in overall diet repertoire sizes. For the immatures, we found that whereas females reached 100% of their mothers’ diet spectrum size by the age of weaning, males reached only around 80%. From the age of 4 years on (i.e., years before being weaned) females had significantly broader daily diets than males. We found no difference in daily or overall diet processing intensity of immature males and females but found preliminary evidence that immature males included fewer items of their mother’s diet in their own diets that were processing-intensive. Overall, our results suggest that by eating a broader variety and more complex to process food items, female orangutans go to greater lengths to achieve a balanced diet than males do. These behavioral differences are not just apparent in adult foraging behavior but also reflected in immature development from an early age on. Significance Statement In many species, males and females have different nutritional needs and are thus expected to show sex-specific foraging behavior. Sex differences in several aspects of foraging behavior have been found in various species, but it remains largely unclear when and how those develop during ontogeny, which is especially relevant for long-lived altricial species that learn foraging skills over many years. In our study, we analyzed a cross-sectional and longitudinal data set containing more than 750,000 feeding events of adult and immature Bornean orangutans (Pongo pygmaeus wurmbii). We found that adult females had significantly broader and more complex diets than males. We also found that these differences started to develop during infancy, suggesting that immature orangutans prepare for their sex-specific foraging niches long before those become physiologically relevant while they are still in constant association with their mothers and before being frequently exposed to other role models.

Summary To sustain life, humans and other terrestrial animals must maintain a tight balance of water gain and water loss each day. 1 , 2 , 3 However, the evolution of human water balance physiology is poorly understood due to the absence of comparative measures from other hominoids. While humans drink daily to maintain water balance, rainforest-living great apes typically obtain adequate water from their food and can go days or weeks without drinking 4 , 5 , 6 . Here, we compare isotope-depletion measures of water turnover (L/d) in zoo- and rainforest-sanctuary-housed apes (chimpanzees, bonobos, gorillas, and orangutans) with 5 diverse human populations, including a hunter-gatherer community in a semi-arid savannah. Across the entire sample, water turnover was strongly related to total energy expenditure (TEE, kcal/d), physical activity, climate (ambient temperature and humidity), and fat free mass. In analyses controlling for those factors, water turnover was 30% to 50% lower in humans than in other apes despite humans’ greater sweating capacity. Water turnover in zoo and sanctuary apes was similar to estimated turnover in wild populations, as was the ratio of water intake to dietary energy intake (∼2.8 mL/kcal). However, zoo and sanctuary apes ingested a greater ratio of water to dry matter of food, which might contribute to digestive problems in captivity. Compared to apes, humans appear to target a lower ratio of water/energy intake (∼1.5 mL/kcal). Water stress due to changes in climate, diet, and behavior apparently led to previously unknown water conservation adaptations in hominin physiology.

Indonesia’s peatlands experience frequent and intense wildfires, producing hazardous smoke with consequences for human health, yet there is a lack of research into adverse effects on wildlife. We evaluated the effects of smoke on the activity and energy balance of Bornean orangutans (Pongo pygmaeus wurmbii) in a peat swamp forest at the Tuanan Research Station, Central Kalimantan. We collected behavioural data and urine samples from four adult flanged males before, during, and after wildfires between March 2015 and January 2016. During fires, particulate matter (PM10) concentrations were hazardous. Orangutans increased rest time during and after the smoke period, and decreased travel time and distance and increased fat catabolism post-smoke. The increase in post-smoke ketones was not related to changes in caloric intake and was likely due to an increase in energy expenditure, possibly related to immune response. Results show that wildfire smoke negatively affects orangutan condition, and sustained research is needed to assess the magnitude of the threat to the long-term viability of this Critically Endangered species.

Past attempts to establish a relationship between mandibular morphology and different dietary categories (e.g., frugivore, folivore, insectivore) have had mixed results, possibly because descriptive dietary categories are too broad and obscure variation within primate diets. Another potential reason is that not all aspects of skeletal architecture, especially trabecular anisotropy, have factored into functional assessments of dietary inputs into jaw form. Recent emphasis on quantifying food mechanical properties (FMPs) has provided an alternative to reliance on dietary categories. We used data on FMPs to test for correlations among dietary toughness and Young's modulus and the trabecular structure of the mandibular condyle, which is loaded during feeding and should reflect differences in masticatory stresses associated with different dietary FMPs. Adult primate mandibles from 11 species were imaged using high-resolution X-ray computed tomography, and trabecular structure was analyzed with BoneJ and Quant3D to assess common three-dimensional trabecular parameters. Results of phylogenetic generalized least squares analysis suggested a positive correlation between the degree of anisotropy (DA) and toughness, and weaker correlations between FMPs and various other trabecular variables. Because the DA contributes to the mechanical properties of bone, these results suggest a functional relationship between dietary toughness and trabecular anisotropy in the mandibular condyle. Such a perspective underscores the need to consider all aspects of skeletal morphology in evaluating the links between diet and jaw biomechanics. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Primates develop slowly relative to their body size, a pattern posited to result from ecological risk aversion. Little is known, however, about how energy balance contributes to allostatic load in juveniles. Using data collected over 8 consecutive months, we examined variation in energy balance (as measured by urinary C-peptide) and how energy balance, life history status, and social competition related to allostatic load (as measured by deviation from baseline fecal glucocorticoid metabolites, dfGCs) in 41 wild juvenile blue monkeys from 3 social groups. Juvenile energy balance was higher among females, older juveniles, when ripe fruit was more available, and when rainfall was lower. Energy balance, but not life history or competitive environments, predicted dfGC concentrations, such that juveniles generally had lower mean dfGCs when they had higher energy balance. An additional exploratory analysis of how dfGCs relate to social strategies revealed that subjects had lower dfGCs when they groomed less, and played more. Time spent grooming interacted with energy balance in predicting dfGC concentrations, so that individuals that groomed more actually had higher dfGCs when they had higher energy balance. Together these results reveal that energetic deficiencies are a true ecological risk factor in blue monkeys, and suggest that navigating the social environment via overt affiliative behavior is potentially both a stress-relieving and stress-inducing endeavor during development.

Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus. We found a complex relationship among food mechanical properties, body mass, and feeding time, with a potential interaction between median toughness and body mass. The relationship between mean toughness and feeding time is straightforward: feeding time increases as toughness increases. However, when considering median toughness, the relationship with feeding time may depend upon body mass, such that smaller primates increase their feeding time in response to an increase in median dietary toughness, whereas larger primates may feed for shorter periods of time as toughness increases. Our results emphasize the need for additional studies quantifying the mechanical and chemical properties of primate diets so that they may be meaningfully compared to research on feeding behavior and jaw morphology.

Orangutans have one of the slowest-paced life histories of all mammals. Whereas life-history theory suggests that the time to reach adulthood is constrained by the time needed to reach adult body size, the needing-to-learn hypothesis instead suggests that it is limited by the time needed to acquire adult-level skills. To test between these two hypotheses, we compared the development of foraging skills and growth trajectories of immature wild orangutans in two populations: at Tuanan (We found that adult-like diet repertoires are attained around the age of weaning and that female immatures increase their repertoire size faster than their male peers. Adult-level feeding rates of easy techniques are reached just after weaning, but several years later for more difficult techniques, albeit always before adulthood (i.e. age at first reproduction). Independent immatures had faster feeding rates for easy to process items than their mothers, with male immatures achieving faster feeding rates earlier in development relative to females. Sumatran immatures reach adult-level feeding rates 2-3 years later than their Bornean peers, in line with their higher dietary complexity and later weaning. The range-use competence of independently ranging and weaned immatures is similar to that of adult females. Body size measurements showed, immatures grow until female age of first reproduction.In conclusion, unlike in humans, orangutan foraging skills are in place prior to reproduction. Growth trajectories suggest that energetic constraints, rather than skills, best explain the length of immaturity. However, skill competence for dietary independence is reached later where the adult niche is more complex, which is consistent with the relatively later weaning age with increasing brain size found generally in primates, and apes in particular.

The timing and frequency of flowering and fruiting events are key tropical forest characteristics that have substantial influence on fauna. Although our understanding of geographic variation in habitat-wide timing and frequency of flowering and fruiting is advancing, corresponding information for individual tree species is limited. Thus, we compared climate and reproductive phenology of 16 tree species over 70 mo at two Bornean tropical peat-swamp forest sites. We found significant inter-site correlations in rainfall and temperature, and only small absolute temperature differences. In both sites, most species exhibited within-site synchrony in flowering and fruiting onset. Broad-scale flowering and fruiting onset frequency classifications showed high congruence between sites. Significant correlations in flowering and fruiting onset timing between sites were found for only 19 and 17 percent of the species, respectively. This remained the case when applying 1- and 2-month lag periods for both sites, with neither site consistently lagging behind. Significant differences in the exact frequency of new flowering and fruiting events were detected for 44 and 58 percent of species, respectively, and no significant relationships between the onset timing synchrony and exact frequency of new reproductive events were found for either flowers or fruit. We conclude that inter-site climatic and ecological similarities do not necessarily lead to high inter-site synchrony in either onset timing or exact frequency of tree reproductive events. Potential reasons for this are discussed, as are the implications for understanding tropical forest ecology and improving forest restoration project seed collections.

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. Am J Phys Anthropol, 2015. © 2015 Wiley Periodicals, Inc.

The uneven representation of frugivorous mammals and birds across tropical regions - high in the New World, low in Madagascar and intermediate in Africa and Asia - represents a long-standing enigma in ecology. Several hypotheses have been proposed to explain these differences but the ultimate drivers remain unclear. Here, we tested the hypothesis that fruits in Madagascar contain insufficient nitrogen to meet primate metabolic requirements, thus constraining the evolution of frugivory. We performed a global analysis of nitrogen in fruits consumed by primates, as collated from 79 studies. Our results showed that average frugivory among lemur communities was lower compared to New World and Asian-African primate communities. Fruits in Madagascar contain lower average nitrogen than those in the New World and Old World. Nitrogen content in the overall diets of primate species did not differ significantly between major taxonomic radiations. There is no relationship between fruit protein and the degree of frugivory among primates either globally or within regions, with the exception of Madagascar. This suggests that low protein availability in fruits influences current lemur communities to select for protein from other sources, whereas in the New World and Old World other factors are more significant in shaping primate communities. Fil: Donati, Giuseppe. Oxford Brookes University; Reino Unido Fil: Santini, Luca. Radboud Universiteit Nijmegen; Países Bajos Fil: Eppley, Timothy M.. Oxford Brookes University; Reino Unido. Zoological Society Of San Diego; Estados Unidos. Universitat Hamburg; Alemania Fil: Arrigo-Nelson, Summer J.. University of Pennsylvania; Estados Unidos Fil: Balestri, Michela. Oxford Brookes University; Reino Unido Fil: Boinski, Sue. University of Florida; Estados Unidos Fil: Bollen, An. No especifica; Fil: Bridgeman, Leandra L.. Washington University in St. Louis; Estados Unidos Fil: Campera, Marco. Oxford Brookes University; Reino Unido Fil: Carrai, Valentina. Università degli Studi di Pisa; Italia Fil: Chalise, Mukesh K.. Tribhuvan University; Nepal Fil: Derby Lewis, Abigail. Field Museum Of Natural History; Estados Unidos Fil: Hohmann, Gottfried. Institut Max Planck for Evolutionary Anthropology; Alemania Fil: Kinnaird, Margaret F.. Mpala Research Centre; Kenia Fil: Koenig, Andreas. Stony Brook University; Estados Unidos Fil: Kowalewski, Miguel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina Fil: Lahann, Petra. Universitat Hamburg; Alemania Fil: McLennan, Matthew R.. Oxford Brookes University; Reino Unido Fil: Nekaris, Anna K. I.. Oxford Brookes University; Reino Unido Fil: Nijman, Vincent. Oxford Brookes University; Reino Unido Fil: Norscia, Ivan. Università degli Studi di Pisa; Italia Fil: Ostner, Julia. German Primate Center; Alemania Fil: Polowinsky, Sandra Y.. Bristol Zoological Society Ltd; Reino Unido Fil: Schülke, Oliver. German Primate Center; Alemania Fil: Schwitzer, Christoph. Bristol Zoological Society Ltd; Reino Unido Fil: Stevenson, Pablo R.. Universidad de Los Andes; Colombia Fil: Talebi, Mauricio G.. Universidade Federal de Sao Paulo; Brasil Fil: Tan, Chia. San Diego Zoo Institute For Conservation Research; Estados Unidos Fil: Tomaschewski, Irene. Universitat Hamburg; Alemania Fil: Vogel, Erin R.. Rutgers University; Estados Unidos Fil: Wright, Patricia C.. Stony Brook University; Estados Unidos Fil: Ganzhorn, Jörg U.. Universitat Hamburg; Alemania

Bornean orangutan mandibular morphology has been functionally linked to the exploitation of hard and tough foods, based on evidence that Pongo pygmaeus wurmbii spends a greater percentage of time feeding on bark, seeds and vegetation compared with Pongo abelii (Sumatran orangutans) and the assumption that these tissues are more challenging to process than fruit pulp. We measured and compared toughness ( R ) and Young's modulus ( E ) of ripe and unripe foods exploited by P. abelii and P. p. wurmbii . Additionally, we recorded and compared the percentage of time these orangutans fed on plants/plant parts of varying degrees of R and E . Compared with P. abelii , P. p. wurmbii consumed significantly tougher and more displacement limited ( R/E ) 0.5 fruit parts, leaves and inner bark, and spent a significantly greater percentage of time feeding on immature leaves, unripe fruit and other vegetation. Modulus did not vary as expected between species, likely because we failed to capture the high-end range of modulus values for tissues consumed by P. p. wurmbii . Notably, P. p. wurmbii spent ∼40% of its feeding time on the toughest foods consumed (between 1000 and 4000 J m −2 ). Thus, the hypothesis that mandibular robusticity in P. p. wurmbii is functionally linked to feeding on tough foods is supported and is likely related to countering relatively larger external forces and/or repetitive loads required to process the toughest tissues. The importance of elastic modulus on morphological divergence awaits future studies capturing the full range of this material property for P. p. wurmbii . Finally, phenophase and fruit availability influence orangutan species differences in food material properties and percentage of time spent feeding on various foods, emphasizing the importance of incorporating these variables in future studies of feeding ecology and craniodental morphology in extant taxa.

Past attempts to establish a relationship between mandibular morphology and different dietary categories (e.g., frugivore, folivore, insectivore) have had mixed results, possibly because descriptive dietary categories are too broad and obscure variation within primate diets. Another potential reason is that not all aspects of skeletal architecture, especially trabecular anisotropy, have factored into functional assessments of dietary inputs into jaw form. Recent emphasis on quantifying food mechanical properties (FMPs) has provided an alternative to reliance on dietary categories. We used data on FMPs to test for correlations among dietary toughness and Young's modulus and the trabecular structure of the mandibular condyle, which is loaded during feeding and should reflect differences in masticatory stresses associated with different dietary FMPs. Adult primate mandibles from 11 species were imaged using high-resolution X-ray computed tomography, and trabecular structure was analyzed with BoneJ and Quant3D to assess common three-dimensional trabecular parameters. Results of phylogenetic generalized least squares analysis suggested a positive correlation between the degree of anisotropy (DA) and toughness, and weaker correlations between FMPs and various other trabecular variables. Because the DA contributes to the mechanical properties of bone, these results suggest a functional relationship between dietary toughness and trabecular anisotropy in the mandibular condyle. Such a perspective underscores the need to consider all aspects of skeletal morphology in evaluating the links between diet and jaw biomechanics. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

The robust masticatory system of mountain gorillas is thought to have evolved for the comminution of tough vegetation, yet, compared to other primates, the toughness of the mountain gorilla diet is unremarkable. This may be a result of low plant toughness in the mountain gorilla environment or of mountain gorillas feeding selectively on low-toughness foods. The goal of this paper is to determine how the toughness of the mountain gorilla diet varies across their habitat, which spans a large altitudinal range, and whether there is a relationship between toughness and food selection by mountain gorillas. We collected data on the following variables to determine whether, and if so how, they change with altitude: leaf toughness of two plant species consumed by mountain gorillas, at every 100 m increase in altitude (2,600-3,700 m); toughness of consumed foods comprising over 85% of the gorilla diet across five vegetation zones; and toughness of unconsumed/infrequently consumed plant parts of those foods. Although leaf toughness increased with altitude, the toughness of the gorilla diet remained similar. There was a negative relationship between toughness and consumption frequency, and toughness was a better predictor of consumption frequency than plant frequency, biomass, and density. Consumed plant parts were less tough than unconsumed/infrequently consumed parts and toughness of the latter increased with altitude. Although it is unclear whether gorillas select food based on toughness or use toughness as a sensory cue to impart other plant properties (e.g., macronutrients, chemicals), our results that gorillas maintain a consistent low-toughness dietary profile across altitude, despite toughness increasing with altitude, suggest that the robust gorilla masticatory apparatus evolved for repetitive mastication of foods that are not high in toughness.

The spatial and temporal variation in food abundance has strong effects on wildlife feeding and nutrition. This variation is exemplified by the peatland forests of Central Kalimantan, which are characterized by unpredictable fruiting fluctuations, relatively low levels of fruit availability, and low fruit periods (

Female Bornean orangutans (Pongo pygmaeus wurmbii) are mainly solitary and philopatric, leading to adult female relatives sharing adjacent and overlapping home ranges. Females tend to be intolerant of unrelated females, with whom they also may have overlapping home ranges. However, fights that lead to injuries are extremely rare and lethal aggression had never been observed. Here, we report the first case of lethal female-female aggression during over 26,000 h of focal data collected on adult females at Tuanan, Central Kalimantan: A young female, who had recently lost her infant, attacked an old resident female. The interaction’s unique feature was that the attacking female was supported by an unflanged male, who had been in consort with her during the week preceding the attack and was responsible for the lethal injuries to the victim. The victim received protection from a flanged male who was probably attracted to the noise generated by the fight. We conclude that even in a species in which coercion is frequently observed in male-female interactions, female leverage over males can coax males into providing services, such as coalitionary support.

The theme of this special issue of the International Journal of Primatology centers onrecent advances in primate feeding ecology methods. These articles represent lecturesand the essence of demonstrations given during a two-day National Science Foun-dation-sponsored workshop hosted by the Center for Advanced Studies of HominidPaleobiology and the Department of Anthropology at the George Washington Uni-versity. In organizing this workshop and special issue, our aim was to bring togethernot only researchers using novel methods, but also those employing familiar methodsin new ways to address a broad array of topics in primate feeding ecology. Thisworkshop was modeled after a three-day workshop held in 1982 by the PrimateSociety of Great Britain and the Anatomical Society of Great Brittan and Ireland,which resulted in the classic volume Food Acquisition and Processing in Primates(Chivers et al. 1984). The series of articles presented here echo the breadth ofresearch topics explored in that volume and describe new and exciting methods thatinform our understanding of primate adaptations related to diet.Historically, primarily observational studies have dominated the field of primatefeeding ecology. These long-term studies have laid the foundation for testing ecolog-ical and behavioral hypotheses regarding primate feeding. However, even when long-term observational data are available, answering questions concerning primate diet

Protein is a limiting resource that is essential to the growth, maintenance and reproduction of tropical frugivores, yet few studies have examined how wild animals maintain protein balance. During chronic periods of fruit scarcity, Bornean orangutans ( Pongo pygmaeus ) often catabolize their own fat reserves despite unusually low metabolic requirements. Such energy deficits suggest a marginal existence, and raise the possibility that orangutans also endure periods of negative protein balance. To test this hypothesis, we conducted the first study of protein cycling in a wild primate. Our five year analysis of urinary metabolites revealed evidence of protein recycling when fruit was scarce. During these periods, orangutans consumed more leaves and bark, proteinaceous but tough foods that yielded a mean daily intake of 1.4 g protein kg −1 metabolic mass. Such an amount is inadequate for humans and one-tenth the intake of mountain gorillas, but sufficient to avert, perhaps narrowly, a severe protein deficit. Our findings highlight the functional and adaptive value of traits that maximize protein assimilation during periods of ecological exigency.

The vital role of body protein as an energy reserve has received little focus in studies of wild primates. Owing to the relatively low protein content of fruit, some frugivorous primates could face a protein deficit if body protein is catabolized for energy during periods of low fruit availability. Such an imbalance can be detected if fatty acids, amino acids, and nitrogen (N) catabolites are reincorporated or recycled back to tissues. Here we describe a method to quantify protein recycling by measuring standardized urea concentration and N isotope signatures from urine samples collected from wild Bornean orangutans (Pongo pygmaeus wurmbii). Our overall goal was to explore if concentrations of urea and δ15N values could be used as indicators of the amount of protein consumed and the degree of protein recycling, respectively, in wild, free-ranging primates. We examine the relationships between urea concentration, δ15N values, protein intake, and fruit availability. Urea concentration increased with fruit availability, reflecting a slight increase in protein consumption when fruit was abundant. However, we found no relationship between δ15N values and fruit availability, suggesting that orangutans avert a negative protein balance during periods of low fruit availability. These noninvasive methods complement recent advances in primate energy balance research and will contribute to our understanding of adaptations of primates during periods of fruit shortage.

The mechanical properties of plant foods play an important role in the feeding process, being one of many criteria for food acceptance or rejection by primates. One of the simplest justifications for this statement is the general finding that primates tend to avoid foods with high fiber. Although fiber is largely tasteless, odorless, and colorless, it imparts texture, a sensation in the mouth related to the physical properties of foods. All primates encounter such mechanical resistance when they bite into plant food, and studies on humans show that an incisal bite facilitates quick oral assessment of a property called toughness. Thus, it is feasible that primates make similar assessments of quality in this manner. Here, we review methods of measuring the toughness of primate foods, which can be used either for making general surveys of the properties of foods available to primates or for establishing the mechanisms that protect these foods from the evolved form of the dentition.

Aim We sought to quantify geographical variation in the stable isotope values of mouse lemurs (Microcebus) and to determine whether this variation reflects trophic differences among populations or baseline isotopic differences among habitats. If the latter pattern is demonstrated, then Microcebus can become a proxy for tracking baseline habitat isotopic variability. Establishing such a baseline is crucial for identifying niche partitioning in modern and ancient communities. Location We studied five species of Microcebus from eight distinct habitats across Madagascar. Methods We compared isotopic variation in C3 plants and Microcebus fur within and among localities. We predicted that carbon and nitrogen isotope values of Microcebus should: (1) vary as a function of abiotic variables such as rainfall and temperature, and (2) covary with isotopic values in plants. We checked for trophic differences among Microcebus populations by comparing the average difference between mouse lemur and plant isotope values for each locality. We then used multiple regression models to explain spatial isotope variation in mouse lemurs, testing a suite of explanatory abiotic variables. Results We found substantial isotopic variation geographically. Ranges for mean isotope values were similar for both Microcebus and plants across localities (carbon 3.5–4.0&; nitrogen 10.5–11.0&). Mean mouse lemur and plant isotope values were lowest in cool, moist localities and highest in hot, dry localities. Rainfall explained 58% of the variation in Microcebus carbon isotope values, and mean plant nitrogen isotope values explained 99.7% of the variation in Microcebus nitrogen isotope values. Average differences between mouse lemur and plant isotope values (carbon 5.0& ;n itrogen 5.9 &) were similar across localities. Main conclusions Isotopic data suggest that trophic differences among Microcebus populations were small. Carbon isotope values in mouse lemurs were negatively correlated with rainfall. Nitrogen isotope values inMicrocebus and plants covaried. Such findings suggest that nitrogen isotope values for Microcebus are a particularly good proxy for tracking baseline isotopic differences among habitats. Our results will facilitate future comparative research on modern mouse lemur communities, and ecological interpretations of extinct Holocene communities.

Food abundance and distribution have played a central role in the conceptual theory of primate socioecology. This theory predicts that agonistic (contest) competition should occur when food is distributed in discrete, defensible patches; in contrast, when food sources are distributed uniformly or randomly, nonagonistic (scramble) competition is expected. Primatologists usually measure resource density and patchiness from a botanical perspective, without an explicit link to the biology of the animal being studied. Such an approach may be irrelevant to how the animals view the dispersion of resources. For studies related to feeding competition, we suggest the use of a method that provides a consumer-based index of food distribution. We then describe such an approach and apply it to understand agonistic behavior in white-faced capuchins (Cebus capucinus), at Lomas Barbudal. Instead of choosing sample plots at random, we use each actual feeding tree of a group as the center of a sample plot and we use the monkey species’ average group spread as the sampling area. This focal tree method allows us to evaluate the resource availability both within and outside of the feeding tree during a particular feeding bout. To summarize the spatial distribution of food at the level of a foraging group, we define and use an extension of Lloyd’s Dispersion Index, Lloyd’s Extended Index (LEI), designed to allow the inclusion of resources of diverse sizes and species in a single measure. We evaluate if LEI can be used to predict the frequency of aggression, if changing the area of the plot alters these results, and if calculating LEI based on fruit abundance or fruit biomass better predicts the frequency of aggression in this population of capuchins. In support of socioecological predictions, our results show that the frequency of agonism in a focal tree declines as LEI increases. This relationship is significant when LEI is calculated using a 20-m plot size and weighting tree size by fruit counts, but not when using larger plot sizes, unweighted tree counts, or weighting by fruit biomass. Our approach demonstrates the importance of carefully considering plot size and different measures of food availability when testing socioecological models relating resource distribution and quality to aggression in nonhuman primates.

Periodic episodes of food scarcity may highlight the adaptive value of certain anatomical traits, particularly those that facilitate the acquisition and digestion of exigent fallback foods. To better understand the selective pressures that favored the distinctive dental and locomotor morphologies of gibbons and orangutans, we examined the foraging and ranging behavior of sympatric Hylobates albibarbis and Pongo pygmaeus wurmbii during an episode of low fruit availability at Tuanan, Kalimantan Tengah, Indonesia. We found that Hylobates ranged 0.5 km day(-1) or 33% farther than did Pongo, but the overall daily ranging of both species did not vary as fruit availability decreased by as much as 50%. Among gibbons, we observed dietary switching to fallback foods; in particular, there was a progressively greater reliance on figs, liana products, and unripe fruit. Orangutans relied heavily on unripe fruit and fracture-resistant bark and pith tissues. Despite these divergent fallback patterns, the stiffness of fruit mesocarp consumed by Hylobates and Pongo did not differ. We discuss canine and molar functional morphology with respect to dietary mechanics. Next, to contextualize these results, we discuss our findings with respect to forest structure. The rain forests of Southeast Asia have been described as having open, discontinuous canopies. Such a structure may inform our understanding of the ranging behavior and distinctive locomotion of apes in the region, namely richochetal brachiation and quadrumanous clambering. Our approach of integrating behavioral ecology with physical measures of food may be a powerful tool for understanding the functional adaptations of primates.

This paper models the coalition formation process among primates as a sequential game. The population consists of individuals having distinct social ranks which is determined by the individual’s resource holding potential. Each member of the population is interested in gaining access to a food resource, either individually or via a coalition. At any given stage of the game, a player can either propose a specific coalition or he can be proposed to in order to join one. Hence, the strategy of a player consists of a sequence of decisions regarding who to propose to for the formation of a coalition and which proposals to accept or reject. We derive the preferences of the players over the various coalition structures under the assumption that the probability of a coalition to obtain the resource is given by a logistic distribution as a function of relative strengths of the players. We show that, given the primates’ strategic behavior, a variety of different coalition structures can emerge in equilibrium.

Feeding systems and behaviors must evolve to satisfy the metabolic needs of organisms. This includes modifications to feeding systems as body size and metabolic needs change. Using our own data and data from the literature, we examine how size-related changes in metabolic needs are met by size-related changes in daily feeding time, chew cycle duration, volume of food processed per chew, and daily food volume intake in primates. Increases in chew cycle duration with body mass in haplorhine primates are described by a simple power function (cycle time α body mass 0.181 ). Daily feeding time increases with body mass when analyzed using raw data from the “tips” of the primate phylogenetic tree, but not when using phylogenetically independent contrasts. Whether or not daily feeding time remains constant or increases with body mass, isometry of ingested bite size and the slow rate of increase in chew cycle time with body size combine to allow daily ingested food volume to scale faster than predicted by metabolic rate. This positive allometry of daily ingested food volume may compensate for negative allometry of nutrient concentration in primate foods. Food material properties such as toughness and hardness have little impact on scaling of chew cycle durations, sequence durations, or numbers of chews in a sequence. Size-related changes in food processing abilities appear to accommodate size-related changes in food material properties, and primates may alter ingested bite sizes in order to minimize the impacts of food material properties on temporal variables such as chew cycle duration and chew sequence duration.

Numerous comparative studies have sought to demonstrate a functional link between feeding behavior, diet, and mandibular form in primates. In lieu of data on the material properties of foods ingested and masticated, many investigators have relied on qualitative dietary classifications such as "folivore" or "frugivore." Here we provide the first analysis of the relationship between jaw form, dietary profiles, and food material properties in large-bodied hominoids. We employed ratios of area moments of inertia and condylar area to estimate moments imposed on the mandible in order to evaluate and compare the relative ability to counter mandibular loads among central Bornean orangutans (Pongo pygmaeus wurmbii), Virunga mountain gorillas (Gorilla beringei beringei), and east African chimpanzees (Pan troglodytes schweinfurthii). We used data on elastic modulus (E) of fruit, fracture toughness (R) of fruit, leaves, and non-fruit, non-leaf vegetation, and derived fragmentation indices ( R/E and ER), as proxies for bite force. We generated bending and twisting moments (forcexmoment arm) for various mandibular loading behaviors using food material properties to estimate minimally required bite forces. Based on E and R of foods ingested and masticated, we hypothesized improved resistance to mandibular loads in Pongo p. wurmbii compared to the African apes, and in G. b. beringei compared to Pan t. schweinfurthii. Results reveal that our predictions are borne out only when bite forces are estimated from maximum R of non-fruit, non-leaf vegetation. For all other tissues and material properties results were contrary to our predictions. Importantly, as food material properties change, the moments imposed on the mandible change; this, in turn, alters the entire ratio of relative load resistance to moment. The net effect is that species appear over- or under-designed for the moments imposed on the mandible. Our hypothesis, therefore, is supported only if we accept that maximum R of these vegetative tissues represents the relevant mechanical property influencing the magnitude of neuromuscular activity, food fragmentation, and mandibular morphology. A general implication is that reliable estimates of average and maximum bite forces from food material properties require that the full range of tissues masticated be tested. Synthesizing data on ingestive and masticatory behaviors, the number of chewing cycles associated with a given food, and food mechanical properties, should inform the broader question of which foods and feeding behaviors are most influential on the mandibular loading environment.

The diet of early human ancestors has received renewed theoretical interest since the discovery of elevated δ13C values in the enamel of Australopithecus africanus and Paranthropus robustus. As a result, the hominin diet is hypothesized to have included C4 grass or the tissues of animals which themselves consumed C4 grass. On mechanical grounds, such a diet is incompatible with the dental morphology and dental microwear of early hominins. Most inferences, particularly for Paranthropus, favor a diet of hard or mechanically resistant foods. This discrepancy has invigorated the longstanding hypothesis that hominins consumed plant underground storage organs (USOs). Plant USOs are attractive candidate foods because many bulbous grasses and cormous sedges use C4 photosynthesis. Yet mechanical data for USOs—or any putative hominin food—are scarcely known. To fill this empirical void we measured the mechanical properties of USOs from 98 plant species from across sub-Saharan Africa. We found that rhizomes were the most resistant to deformation and fracture, followed by tubers, corms, and bulbs. An important result of this study is that corms exhibited low toughness values (mean = 265.0 J m−2) and relatively high Young’s modulus values (mean = 4.9 MPa). This combination of properties fits many descriptions of the hominin diet as consisting of hard-brittle objects. When compared to corms, bulbs are tougher (mean = 325.0 J m−2) and less stiff (mean = 2.5 MPa). Again, this combination of traits resembles dietary inferences, especially for Australopithecus, which is predicted to have consumed soft-tough foods. Lastly, we observed the roasting behavior of Hadza hunter-gatherers and measured the effects of roasting on the toughness on undomesticated tubers. Our results support assumptions that roasting lessens the work of mastication, and, by inference, the cost of digestion. Together these findings provide the first mechanical basis for discussing the adaptive advantages of roasting tubers and the plausibility of USOs in the diet of early hominins.

The divergent molar characteristics of Pan troglodytes and Pongo pygmaeus provide an instructive paradigm for examining the adaptive form-function relationship between molar enamel thickness and food hardness. Although both species exhibit a categorical preference for ripe fruit over other food objects, the thick enamel and crenulated occlusal surface of Pongo molar teeth predict a diet that is more resistant to deformation (hard) and fracture (tough) than the diet of Pan. We confirm these predictions with behavioral observations of Pan troglodytes schweinfurthii and Pongo pygmaeus wurmbii in the wild and describe the mechanical properties of foods utilized during periods when preferred foods are scarce. Such fallback foods may have exerted a selective pressure on tooth evolution, particularly molar enamel thinness, which is interpreted as a functional adaptation to seasonal folivory and a derived character trait within the hominoid clade. The thick enamel and crenulated occlusal surface of Pongo molars is interpreted as a functional adaptation to the routine consumption of relatively tough and hard foods. We discuss the implications of these interpretations for inferring the diet of hominin species, which possessed varying degrees of thick molar enamel. These data, which are among the first reported for hominoid primates, fill an important empirical void for evaluating the mechanical plausibility of putative hominin food objects.

Food abundance and distribution have played a central role in the conceptual theory of primate socioecology [Janson, Behaviour 105:53–76, 1988; Isbell, Behavioral Ecology 2:143–155, 1991; Sterck et al., Behavioral Ecology and Sociobiology 41:291–309, 1997; van Schaik, In: Standen V, Foley RA, editors, Comparative Socioecology. Oxford: Blackwell. p 195–218, 1989]. This theory predicts that agonistic (“contest”) competition should occur when food is distributed in discrete, defensible patches; in contrast, when food sources are distributed uniformly or randomly, non-agonistic (“scramble”) competition is expected. Primatologists usually measure resource density and patchiness from a botanical perspective, ignoring the biology of the animal being studied. Such an approach may be irrelevant in terms of how animals view the dispersion of resources. Using a novel focal-tree method that measures resource availability on a scale that is both spatially and temporally relevant to the animal under investigation, we take a cost-benefit approach to predict the frequency of food-related agonism in white-faced capuchin monkeys (Cebus capucinus) from 11 ecological and social variables. We retained four variables in the regression model: two representing the opportunity for aggression (i.e., feeding bout length and the number of feeding adult females), and two representing opportunity costs (i.e., fruit abundance and the number of potential feeding sites in the focal tree). The results of this study indicate that the amount of food-related aggression in white-faced capuchins can be predicted by variables representing the costs and benefits of contesting a food resource. Am. J. Primatol. 69:533–550, 2007. © 2006 Wiley-Liss, Inc.

The reduction of occlusal dimensions in early Homo is often proposed to be a functional adaptation to diet. With their smaller occlusal surfaces, species of early Homo are suggested to have reduced food-processing abilities, particularly for foods with high material properties (e.g., increased toughness). Here, we employ chewing efficiency as a measure of masticatory performance to test the relationships between masticatory function and food properties. We predicted that humans are more efficient when processing foods of lower toughness and Young's modulus values, and that subjects with larger occlusal surfaces will be less efficient when processing foods with higher toughness and Young's modulus, as the greater area spreads out the overall bite force applied to food particles. Chewing efficiency was measured in 26 adults using high-speed motion capture and surface electromyography. The dentition of each subject was cast and the occlusal surface was quantified using dental topographic analysis. Toughness and displacement-limited index were negatively correlated with chewing efficiency, but Young's modulus was not. Increased occlusal two-dimensional area and surface area were positively correlated with chewing efficiency for all foods. Thus, larger occlusal surface areas were more efficient when processing foods of greater toughness. These results suggest that the reduction in occlusal area in early Homo was associated with a reduction in chewing efficiency, particularly for foods with greater toughness. Further, the larger occlusal surfaces of earlier hominins such as Australopithecus would have likely increased chewing efficiency and increased the probability of fracture when processing tough foods.

Bottom-up regulatory factors have been proposed to exert a strong influence on mammalian population density. Studies relating habitat quality to population density have typically made comparisons among distant species or communities without considering variation in food quality among localities. We compared dietary nutritional quality of two Bornean orangutan populations with differing population densities in peatland habitats, Tuanan and Sabangau, separated by 63 km. We hypothesized that because Tuanan is alluvial, the plant species included in the orangutan diet would be of higher nutritional quality compared to Sabangau, resulting in higher daily caloric intake in Tuanan. We also predicted that forest productivity would be greater in Tuanan compared to Sabangau. In support of these hypotheses, the overall quality of the diet and the quality of matched dietary items were higher in Tuanan, resulting in higher daily caloric intake compared to Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is almost two times greater in Tuanan compared to Sabangau, in agreement with a potentially important influence of diet quality on primate population density. published

New World monkeys exhibit a color vision polymorphism. It results from allelic variation of the single-locus middle-to-long wavelength opsin gene on the X chromosome. Females that are heterozygous for the gene possess trichromatic vision. All other individuals possess dichromatic vision. The prevailing hypothesis for the maintenance of the color vision polymorphism is through a consistent fitness advantage to heterozygous trichromatic females. Such females are predicted to be more efficient than dichromats when detecting and selecting fruit. Recent experiments with captive callitrichid primates provided support for this hypothesis by demonstrating that color vision phenotype affects behavioral responses to contrived food targets. Yet, the assumptions that trichromatic females acquire more calories from fruit, or that number of offspring is linked to caloric intake, remain untested. Here, we assess if, in the wild, heterozygous trichromatic individuals in a group of white-faced capuchins (Cebus capucinus) enjoy an energetic advantage over dichromats when foraging on fruit. Contrary to the assumptions of previous theoretical and experimental studies, our analysis of C. capucinus foraging behavior shows that trichromats do not differ from dichromats in their fruit or energy acquisition rates. For white-faced capuchins, the advantage of trichromatic vision may be related to the detection of predators, animal prey, or fruit under mesopic conditions. This result demonstrates the importance of using a fitness currency that is relevant to individual animals to test evolutionary hypotheses. Copyright 2007, Oxford University Press.

In this work we report the first published observational evidence of rescue behavior during an intergroup interaction in white-faced capuchin monkeys (Cebus capucinus). The study groups (groups AA and RR) inhabit the forest of Lomas Barbudal Biological Reserve in Guanacaste, Costa Rica, and have been under investigation since 1990 and 1997, respectively. Here we report a single interaction in which a victim mother-infant pair was rescued from potential injury or death by the intervention of an adult male from their social group during an intergroup encounter. We discuss several hypotheses that may be relevant in explaining this unique observation.

Colour vision varies within the family Atelidae (Primates, Platyrrhini), which consists of four genera with the following cladistic relationship: { Alouatta [ Ateles ( Lagothrix and Brachyteles )]}. Spider monkeys ( Ateles ) and woolly monkeys ( Lagothrix ) are characteristic of platyrrhine monkeys in possessing a colour vision polymorphism. The polymorphism results from allelic variation of the single-locus middle-to-long wavelength (M/L) cone opsin gene on the X-chromosome. The presence in the population of alleles coding for different M/L photopigments results in a variety of colour vision phenotypes. Such a polymorphism is absent in howling monkeys ( Alouatta ), which, alone among platyrrhines, acquired uniform trichromatic vision similar to that of Old World monkeys, apes, and humans through opsin gene duplication. Dietary and morphological similarities between howling monkeys and muriquis ( Brachyteles ) raise the possibility that the two genera share a similar form of colour vision, uniform trichromacy. Yet parsimony predicts that the colour vision of Brachyteles will resemble the polymorphism present in Lagothrix and Ateles . Here we test this assumption. We obtained DNA from the blood or faeces of 18 muriquis and sequenced exons 3 and 5 of the M/L opsin gene. Our results affirm the existence of a single M/L cone opsin gene in the genus Brachyteles . We detected three alleles with predicted λ max values of 530, 550, and 562 nm. Two females were heterozygous and are thus predicted to have different types of M/L cone pigment. We discuss the implication of this result towards understanding the evolutionary ecology of trichromatic vision.

The effect of aggressive competition over food resources on energy intake rate is analyzed for individuals of three groups of 25–35 white-faced capuchin monkeys, Cebus capucinus, living in and near Lomas Barbudal Biological Reserve, Costa Rica. An individual’s energy intake rate on a given food species was affected by its rank and the number of agonistic interactions within the feeding tree. Dominant group members had higher energy intake rates relative to subordinate group members whether or not there was agonism within the feeding tree. Low- and mid-ranked individuals had lower energy intake rates in trees with higher amounts of aggression, while energy intake rate of high-ranked individuals was not affected by the amount of aggression in the feeding tree. Energy intake was not influenced by the sex of the individual when rank was held constant statistically. Energy intake was positively correlated with total crown energy (measured in kilojoules) within the feeding tree for two of three study groups. This difference may be explained by the quality of each group’s territory. Finally, high-ranked individuals are responsible for the majority of agonism within feeding trees and target middle- and low-ranked individuals equally. These findings fit the predictions of current socioecological models for within-group contest competition over food resources. The results of this study suggest that within-group competition affects energy intake rate in white-faced capuchin monkeys.

Perhaps the most common form of cooperation among primates is the formation of coalitions. Competition among males within a group concerns a constant quantity of the limiting resource (fertilizations). Contest competition over fertilizations is known to produce payoffs that are distributed according to the priority-of-access model, and hence show an exponential decline in payoff with rank. We develop a model for rank-changing, within-group coalitions among primate males. For these coalitions to occur, they must be both profitable (i.e. improve fitness) for all coalition members and feasible (i.e. be able to beat the targets). We assume that the value of the coalition is the sum of the payoffs of the partners in their original ranks. We distinguish three basic coalition configurations, depending on the dominance ranks of the coalition partners relative to their target. We predict five basic coalition types. First, all-up, rank-changing coalitions targeting individuals ranking above all coalition partners; these are expected to involve coalition partners ranking just below their target, concern top rank, and be small, just two or three animals. Second, bridging, rank-changing coalitions, where higher-rankers support lower-rankers to rise to a rank below themselves; these are expected to be most common where a high-ranking male in a despotic system can support a low-ranking relative. Third, bridging non-rank-changing coalitions; these are expected to be common whenever high-ranking males have low-ranking close relatives. Fourth, non-rank-changing coalitions by high-rankers against lower-ranking targets; these are expected to serve to counteract or prevent the first type. Fifth, non-rank-changing, leveling coalitions, in which all partners rank below their target and which flatten the payoff distribution; these are expected to be large and mainly involve lower-ranking males. Bridging, rank-changing coalitions are expected in situations where contest is strong, all-up rank-changing coalitions where contest is intermediate, and leveling coalitions where contest is weak. We review the empirical patterns found among primates. The strong predictions of the model are confirmed by observational data on male-male coalitions in primates.

Capuchins exhibit considerable cross-site variation in domains such as foraging strategy, vocal communication and social interaction. We report interactions between white-faced capuchins (Cebus capucinus) and other species. We present comparative data for 11 groups from 3 sites in Costa Rica that are ecologically similar and geographically close, thus reducing the likelihood that differences are due solely to genetic or ecological differences. Our aim is to document both the range of variation and common elements across sites and situations. We also consider factors that contribute to the variation or consistency or both, including social learning, local ecology, and temperament. We consider 4 categories of allospecifics: (1) vertebrate prey, (2) potential predators, (3) feeding competitors, and (4) neutral species. Although we cannot rule out local differences in ecology, our data suggest that social learning may account for at least some cross-site differences in behavior toward allospecifics. Our strongest finding is that boldness, aggression and pugnacity are displayed consistently across sites, groups and circumstances, even in interactions with neutral species, which reflects a critical aspect of species-specific temperament in Cebus capucinus that has been evolutionarily developed and reinforced through highly opportunistic foraging, strong predator defense, and active hunting. We suggest directions for future research, particularly in regard to primate temperament as an evolved trait with consequences for fitness.

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.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 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.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.