Social hair pulling in captive rhesus macaques (Macaca mulatta)

Effects of Seasonality and Pregnancy on Hair Loss and Regrowth in Rhesus Macaques

Several studies have examined the etiology of alopecia, or hair loss, in rhesus macaques. While outcomes differ across studies, some commonalities have emerged. Females, particularly pregnant females, show more alopecia than males, and alopecia follows a seasonal pattern. Much research has explored causes of hair loss; however, alopecia can result from lack of hair growth in addition to hair loss. To better understand how sex, reproductive state, and season affect alopecia, we followed 241 rhesus macaques (Macaca mulatta) in outdoor breeding groups over one year, recording both alopecia severity and presence of hair regrowth. We found that both alopecia and hair regrowth followed a seasonal pattern; alopecia was highest in spring and lowest in late summer, while regrowth started in spring and peaked in late summer. Reproductive state also correlated with both alopecia and hair growth. Females in their third trimester had the highest average level of alopecia and the lowest amount of hair regrowth. Regrowth resumed postpartum, regardless of whether females were rearing an infant. Results indicate that the seasonal pattern of alopecia is due in part to the seasonal limitations on hair regrowth, and that breeding, which also occurs seasonally in rhesus macaques, may further suppress hair regrowth.

A markerless platform for ambulatory systems neuroscience

Motor systems neuroscience seeks to understand how the brain controls movement. To minimize confounding variables, large-animal studies typically constrain body movement from areas not under observation, ensuring consistent, repeatable behaviors. Such studies have fueled decades of research, but they may be artificially limiting the richness of neural data observed, preventing generalization to more natural movements and settings. Neuroscience studies of unconstrained movement would capture a greater range of behavior and a more complete view of neuronal activity, but instrumenting an experimental rig suitable for large animals presents substantial engineering challenges. Here, we present a markerless, full-body motion tracking and synchronized wireless neural electrophysiology platform for large, ambulatory animals. Composed of four depth (RGB-D) cameras that provide a 360° view of a 4.5-square-meters enclosed area, this system is designed to record a diverse range of neuroethologically relevant behaviors. This platform also allows for the simultaneous acquisition of hundreds of wireless neural recording channels in multiple brain regions. As behavioral and neuronal data are generated at rates below 200 megabytes per second, a single desktop can facilitate hours of continuous recording. This setup is designed for systems neuroscience and neuroengineering research, where synchronized kinematic behavior and neural data are the foundation for investigation. By enabling the study of previously unexplored movement tasks, this system can generate insights into the functioning of the mammalian motor system and provide a platform to develop brain-machine interfaces for unconstrained applications.

Increased produce enrichment reduces trauma in socially-housed captive rhesus macaques (Macaca mulatta)

Due to primate adaptations for sociality, captive rhesus macaques have optimal welfare and utility as a biomedical model when they can be maintained in outdoor social groups. As a despotic species; however, aggression can result in costly injuries and may result in temporary or permanent removal of specific individuals from social housing. Enrichment items, such as toys, climbing structures, and foraging material, are employed to keep captive animals occupied. We hypothesized that produce enrichment that requires more processing to extract may reduce socially-derived injuries by keeping animals occupied. We tested the effects of additional weekly produce (corn-in-husk, whole melon, or whole squash) on trauma incidence in an outdoor social group of rhesus macaques across two distinct seasons (mating and birthing seasons) at the California National Primate Research Center. Aggression and status behavioral data, food resource use and proximity, and trauma incidence were collected over two 16-week periods, with eight control and treatment conditions alternating biweekly. Mixed-effects regression modeling was used to determine the best predictors of trauma risk and severe aggression at the group level and at an individual level. We found that food resource use was an important predictor of trauma risk at both group and individual levels; greater use of food resources reduced trauma risk. Produce enrichment did not; however, reduce severe aggression. We suggest that other captive social groups of rhesus macaques with high levels of trauma may benefit from supplemental produce enrichment that increases animal engagement with food resources.

Social hair plucking is a grooming convention in a group of captive bonobos (Pan paniscus)

Hair plucking is observed in many captive primate species and is often characterized as an abnormal behavior. However, this behavior may be both self-directed and social and may have different etiologies. Early research in captive macaques (Macaca mulatta) described the aggressive nature of social hair plucking while more recent observations did not find an association with aggression or grooming, but the behavior was initiated most frequently by individuals with more secure dominance rank. Here, we investigate patterns of social hair plucking in a group of captive bonobos at the Columbus Zoo. We tested the hypothesis that social plucking reflects the dominance hierarchy by examining the association between social plucking and grooming, dominance, and kinship. We collected 128 h of grooming data on 16 captive bonobos using all-occurrence sampling. We ran three Mantel tests between a directed grooming matrix and (1) a plucking matrix, (2) a matrix reflecting dominance, and (3) matrix of relatedness. Grooming and hair plucking were significantly correlated (r = 0.25, p < 0.01), however, there was no association between plucking and dominance (r = - 0.04, p = 0.67), or plucking and relatedness (r = 0.07, p = 0.24). These results support the hypothesis that social plucking in bonobos is a grooming convention and is unrelated to dominance.

Alopecia in rhesus macaques (Macaca mulatta): Association with pregnancy and chronic stress

BACKGROUND

Alopecia in captive non-human primates is often presented as a welfare issue. However, it is a complex condition with a number of possible causes. The purpose of this study was to assess the impact of pregnancy and hair cortisol concentrations on alopecia in rhesus macaques.

METHODS

Subjects were 113 socially housed adult female rhesus macaques (27 pregnant, 35 nursing infants, 51 controls). During routine physicals, photographs were taken for alopecia assessment and hair samples were collected for cortisol assay.

RESULTS

Alopecia was more prevalent in pregnant than in control females, but there was no association between alopecia and hair cortisol. However, there was a significant effect of pregnancy on hair cortisol. Nursing females had higher hair cortisol levels than pregnant females, which had higher levels than control females.

CONCLUSIONS

Although alopecia does not appear to be associated with hair cortisol, both alopecia and hair cortisol were associated with pregnancy.

Prevalence and characteristics of hair plucking in captive bonobos (Pan paniscus) in North American zoos

When primates exhibit hair loss and are observed to engage in self or social hair plucking (a rapid jerking away of the hair shaft and follicle by the hand or mouth, often accompanied by inspection, and consumption) the altered appearance, and behavior patterns are thought to reflect individual physiological, and psychological well-being. Hair loss and hair plucking occur in many captive primate species, including all of the great apes. We present the first survey of this behavior among captive bonobos (N = 88; 50 females and 38 males) in seven zoos in the United States. We found that 43% of the population engaged in this behavior pattern and discounting youngsters (who are not observed to hair pluck until the age of five), 58% of individuals hair plucked. Of the individuals who hair plucked, 97% engaged in social plucking, whereas 46% engaged in self-directed plucking. We regressed the occurrence of hair plucking with multiple predictor variables using binary logistic regression and multimodel inference to determine which predictors best explained the prevalence of self-directed and social plucking. We also analyzed publicly available data on hair plucking in captive chimpanzees. We found that the occurrence of another abnormal behavior, age, origin, and pelage condition best explained self-directed plucking in bonobos. Social plucking was explained by age, origin, pelage, and sex. Our analysis of chimpanzee hair plucking revealed that plucking is strongly influenced by rearing and sex. This study demonstrates that hair plucking is more prevalent in captive bonobos compared to captive chimpanzees and gorillas, however, the covariates associated with hair plucking for each species are different. Our data suggest a potential link between self-directed plucking and well-being. However, the higher prevalence and etiology of social hair plucking is more difficult to explain.