American Journal of Primatology最新文献

Answers to the question of what characteristics allow animals to thrive in human-dominated environments remain elusive. Consistent interindividual differences or personalities can potentially explain the functional significance of habitat-specific traits that enable animals to coexist with humans. Rhesus macaques (Macaca mulatta) are the most successful nonhuman primates in the Anthropocene, living in diverse climatic and environmental conditions. Studying the personalities of synanthropic rhesus macaques, that is, those that thrive in anthropogenic habitats, can provide insights into the biological traits facilitating their success. We planned a multi-method “bottom-up” approach of behavioral observations and novelty experiments, standardized for assessing captive nonhuman primates, to evaluate the personalities of adult rhesus macaques (N = 52). Novelty experiments encountered significant challenges, limiting their effectiveness. So, we continued with behavioral observations in the form of focal sampling, that revealed two repeatable traits, subjectively labeled as social tension and meekness. We found an association of sex with social tension, where males exhibited higher social tension than females. In an additional analysis, we found that individuals that obtained food through contact provisioning had higher scores for the meekness trait than individuals that obtained food through noncontact provisioning. We discuss how the observed personality traits may offer adaptive advantages in human-dominated environments, where despotic rhesus macaques face both benefits and costs (including social) of living in an anthropogenic setting. We also emphasize that protocols designed for captive conditions may not be directly applicable to free-living animals. The study underscores the need to reconsider behavioral experiments to obtain comparable measures between captive and non-captive populations. This would enhance the ecological validity of personality assessments. Nevertheless, empirically identifying traits using observations in synanthropic species can provide valuable insights into the mechanisms that enable certain animals to thrive amidst a rapid expansion of anthropogenic activities.

Temperature has a known potential to influence glucocorticoid concentrations obtained from fecal samples in nonhuman primates. Studies reliant on hair cortisol estimates obtained using samples from outdoor subjects, however, may not control for temperature. This omission is despite the general utility of hair as a sample matrix with relatively longer periods of accrual time. We examined these dynamics in rhesus macaques (Macaca mulatta); importantly, this population of rhesus macaques exhibits covariation between season and breeding behavior. Thus, we also examined temperature relative to contributions of social behavior associated with breeding seasons, which may coincide with climatic shifts. We utilized 1921 hair samples from 580 subjects across six large outdoor-housed mixed-sex groups at the California National Primate Research Center to quantify the capacity for warmer or cooler outdoor temperatures to influence hair cortisol concentrations. We found that colder maximum temperature estimates over the days preceding hair sampling were associated with elevated hair cortisol concentrations, relative to warmer periods. Temperature contributed similarly in a model with a reduced data set (1418 samples) which included breeding-associated social behaviors. Consortship behavior was associated with hair cortisol without temperature, but was not associated with temperature included. Aggression was associated with cortisol, with or without the inclusion of temperature. Outdoor temperature is an important confound or covariate to account for statistically or via careful study design. Inclusion is especially important among research projects reliant on hair cortisol from outdoor-housed primates and spanning multiple seasons.

Innovation is a key component of behavioral flexibility. When individuals are presented with novel problems, their ability to behave flexibly often relies upon their exploratory tendencies, motivational states and intrinsic traits. Studies of repeated innovation pose additional benefits to understand mechanisms of behavioral flexibility, including measuring persistence, exploration and inhibitory control when learned solutions are blocked. The multi-access box (MAB) paradigm tests repeated innovation without prior training and minimal habituation. We tested fifty adult captive female rhesus macaques (Macaca mulatta) with a MAB to evaluate the role of individual traits on repeated innovation and explore the relationship between inhibitory responses and innovation. We found that exploratory diversity positively predicted repeated innovation, as has been reported for previous studies. We also found that traits such as age and personality influenced innovation, where younger individuals and those that scored high on nervousness had higher innovation scores. However, we did not find any relationship between inhibitory responses and innovation. Our study provides the first assessment of repeated innovation in rhesus macaques using a MAB design and highlights the importance of individual traits for repeated innovation in this species.

Wild primates face a wide range of anthropogenic influences globally that impact their health, fitness, and survival. One area of potential impact that has been particularly understudied is the supplementation of wild primate diets with human foods. Although the consumption of human foods represents a substantial dietary change for wild primates, knowledge of how it impacts their physiology and behavior is limited. Here we explore how human food supplementation impacts wild primates by comparing the gut microbiomes of free-ranging brown howler monkeys (Alouatta guariba) in periurban Brazil that do or do not have access to human foods. We found that howler monkeys consuming human foods had reduced gut microbial diversity and reduced relative abundances of fiber degrading microbial taxa, which has been associated with negative health consequences in other animals, including humans. However, the effect size of these differences was relatively small and varied over time. Additionally, the composition of the gut microbiome varied significantly across months, regardless of the access to human foods. We suggest that the biology of this howler monkey population is minimally impacted by human foods. Further empirical research will help clarify the relationship between human food supplementation and health across primate populations, facilitating conservation applications.

Arboreal habitats are three-dimensionally complex and are composed of substrates that differ in size, compliance, and continuity. In response, arboreal vertebrates have evolved morphological and behavioral traits allowing them to successfully move through these environments. Prehensile tails constitute one of such adaptations, yet remain poorly studied. Variation in prehensile tail use between species might result in anatomical variations, as has been shown in primates but remains undocumented in most species. The present study, therefore, sought to describe prehensile tail use and substrate type utilization between two primates, the Guianan red howler (Alouatta macconnelli) and Brown capuchin (Sapajus apella) and one carnivoran, the Kinkajou (Potos flavus). To do so, we used 1431 photographs obtained from camera traps placed in the canopy in French Guyana. The results showed that P. flavus exhibits a greater diversity of overall positional and prehensile tail-associated behaviors compared to S. apella and A. macconnelli. Moreover, P. flavus used its tail for both stability and mass-bearing purposes during locomotor and postural behaviors, while A. macconnelli and S. apella used their tails mainly for mass bearing and stability, respectively, and this was only during postural behaviors. P. flavus mostly used large substrates but A. macconnelli used more small substrates. S. apella showed a preference for both medium and large substrates. Multivariate analyses showed that the three species were well discriminated regarding positional behaviors, with P. flavus exhibiting several postural and especially locomotor behaviors not shared by the two primate species, as well as a combination of behaviors shared with either of the two aforementioned species. A. macconnelli was mainly characterized by suspensory posture and vertical displacements, whereas S. apella mainly used above-branch postures using its tail to anchor itself.