Analysis of hair cortisol levels in captive chimpanzees: Effect of various methods on cortisol stability and variability

Hair cortisol has been reported to be a useful measure of long-term hypothalamic-pituitary-adrenal (HPA) axis activation in several species. It serves as a practical tool for long-term stress assessment, but it is important to understand the methodological factors that can affects hair cortisol assays to avoid methodological artifacts. To that end, we tested several procedures for measuring cortisol levels in hair collected from captive chimpanzees. The results showed that reproducibility was high, and we found no differences in cortisol levels among the various storage, drying, and sampling methods. However, the fineness of homogenized hair, sample weight, and extraction time affected absolute hair cortisol concentration. Although hair cortisol levels were stable over time, factors that may influence measurement results should be kept constant throughout a study.We modified and validated a methodology involving enzyme immunoassays to reliably measure the hair cortisol levels of captive chimpanzees.The results revealed that the fineness of homogenized hair, sample weight, and extraction time caused variations in absolute hair cortisol concentrations in chimpanzees. In contrast, storage, drying, and sampling from similar body parts did not affect the results

Environmental Influences on Sleep Behavior in Captive Male Chimpanzees (Pan troglodytes)

Little is known as to the influence of captivity and stressful events on sleep patterns in primates. We investigated the sleep patterns of 19 male chimpanzees living under similar conditions at the Chimpanzee Sanctuary Uto (CSU) in Kumamoto, Japan, using a behavioral sleep index. We conducted nighttime observations of all subjects during a stable period and then observed three subjects after relocation to an unfamiliar facility at CSU. We estimated length of sleep and nonsleep periods over 13-h video recordings using instantaneous sampling at 1-min intervals to record sleep, which we defined operationally as an inactive posture with the body lying down with the head on the floor or on nesting materials. The 19 subjects slept for a mean ± SEM of 11.3 ± 0.26 h during the stable period, and sleep patterns varied significantly among the subjects. The three relocated subjects all showed temporarily decreased sleep duration in the post-move period but subsequently recovered to the levels observed during the stable period when habituated to the new living quarters. These results suggest that a stressful event may induce temporary sleep shortage lasting for >1 wk in captive chimpanzees. Sleep patterns may serve as a useful behavioral index of the stress response, as it is less confounded by other behaviors and the actions of human caretakers than other indices

Social relationship and hair cortisol level in captive male chimpanzees (Pan troglodytes)

Understanding how social relationships affect long-term stress is important because stress has a profound impact on the welfare of animals and social relationships often exert a strong influence on their stress responses. The purpose of this study was to investigate the relationship between social behaviors and long-term stress levels as assessed by hair cortisol (HC) concentration. The subjects were 11 chimpanzees living in an all-male group (divided into two sub-groups) in Kumamoto Sanctuary, Kyoto University, Japan. Behavioral data were collected between December 2014 and March 2015. The total observation time was 129 h. Hair samples were collected in late March and early April 2015, and cortisol was extracted from the hair and measured with enzyme immunoassay. The hair growth rate was estimated to be 1.33 ± 0.06 cm/month. The results revealed that there was a positive correlation between the rate of receiving aggression and HC levels. We also found a significant negative correlation between the balance between giving and receiving grooming (grooming balance index: GBI), which was calculated by subtracting the rate with which grooming is given from that with which it is received, and the rate of receiving aggression and between the GBI and HC levels. Thus, individuals receiving higher levels of aggression also tended to give grooming for relatively long periods compared to the time they were being groomed. In contrast, the rate of initiating aggression did not have a relationship with either HC levels or any measure of social grooming. We did not find social buffering effects, as there was no correlation between mutual social grooming and HC levels. These results show that not only aggressive interactions but also overall social situations in which animals do not have balanced relationships with others might result in the long-term elevation of cortisol levels in captive male chimpanzees

Spontaneous Object Sharing in Captive Chimpanzees (Pan troglodytes)

Episodes of object transfer were observed among 3 adult and 2 juvenile unrelated females chimpanzees, kept in adjacent cages with bars between them. Only the adult females had small objects available in their cage only juveniles were observed to request them. Although the possessors could easily prevent transfers, 15 episodes of active sharing were recorded, including spontaneous unsolicited donations, sharing preceded by requests, as well as transfers under obnoxious solicitation

Spontaneous Object Sharing in Captive Chimpanzees (Pan troglodytes)

Episodes of object transfer were observed among 3 adult and 2 juvenile unrelated females chimpanzees, kept in adjacent cages with bars between them. Only the adult females had small objects available in their cage only juveniles were observed to request them. Although the possessors could easily prevent transfers, 15 episodes of active sharing were recorded, including spontaneous unsolicited donations, sharing preceded by requests, as well as transfers under obnoxious solicitation

Effects of Relocation and Individual and Environmental Factors on the Long-Term Stress Levels in Captive Chimpanzees (Pan troglodytes): Monitoring Hair Cortisol and Behaviors

Understanding the factors associated with the long-term stress levels of captive animals is important from the view of animal welfare. In this study, we investigated the effects of relocation in addition to individual and environmental factors related to social management on long-term stress level in group-living captive chimpanzees by examining behaviors and hair cortisol (HC). Specifically, we conducted two studies. The first compared changes in HC levels before and after the relocation of 8 chimpanzees (Study 1) and the second examined the relationship between individual and environmental factors and individual HC levels in 58 chimpanzees living in Kumamoto Sanctuary (KS), Kyoto University (Study 2). We hypothesized that relocation, social situation, sex, and early rearing conditions, would affect the HC levels of captive chimpanzees. We cut arm hair from chimpanzees and extracted and assayed cortisol with an enzyme immunoassay. Aggressive behaviors were recorded ad libitum by keepers using a daily behavior monitoring sheet developed for this study. The results of Study 1 indicate that HC levels increased during the first year after relocation to the new environment and then decreased during the second year. We observed individual differences in reactions to relocation and hypothesized that social factors may mediate these changes. In Study 2, we found that the standardized rate of receiving aggression, rearing history, sex, and group formation had a significant influence on mean HC levels. Relocation status was not a significant factor, but mean HC level was positively correlated with the rate of receiving aggression. Mean HC levels were higher in males than in females, and the association between aggressive interactions and HC levels differed by sex. These results suggest that, although relocation can affect long-term stress level, individuals’ experiences of aggression and sex may be more important contributors to long-term stress than relocation alone

Changes in aggressive behaviors by an alpha male and HC levels of two males after relocation.

<p>Bar plots indicate the number of aggressive encounters initiated by an alpha male toward group members. Line charts indicate changes in HC concentration in this male and one other after relocation. The alpha male (Loi) moved to another institution in the 20^th month.</p

Profile of chimpanzees in Study 1.

<p>Profile of chimpanzees in Study 1.</p

Parameter estimates from the models used to explain variation in the average HC levels of KS chimpanzees in 2013.

<p>Parameter estimates from the models used to explain variation in the average HC levels of KS chimpanzees in 2013.</p

AIC tables of the models to explain variation in the average HC levels of KS chimpanzees in 2013.

<p>AIC tables of the models to explain variation in the average HC levels of KS chimpanzees in 2013.</p