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

Abstract

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.

Aggression and social support predict long‐term cortisol levels in captive tufted capuchin monkeys (Cebus [Sapajus] apella)

“…Dominance rank, aggression received, and rank certainty have all been independently associated with cortisol levels in various primate species. However, these variables are also often correlated with one another (Abbott et al, ; Feng et al, ; Janson, ; Yamanashi et al, ). One aim of this study was to determine which of these factors best predicted long‐term cortisol levels in capuchin monkeys.…”

“…Strong, enduring affiliative relationships have been associated with increased longevity, decreased disease transmission, and increased infant survival (Balasubramaniam, Beisner, Vandeleest, Atwill, & McCowan, ; Silk, Alberts, & Altmann, ; Silk et al, ; ). In contrast, social stressors such as aggression have been associated with immune suppression, cardiovascular decline, and reproductive suppression (Padgett & Glaser, ; Sapolsky, ; Walker, ; Yamanashi et al, ; Yamanashi, Teramoto, Morimura, Nogami, & Hirata, ).…”

“…Likewise, monkeys with insecure rank positions may experience regular stressors in the form of rank challenges (Vandeleest et al, ). While dominance rank and rank uncertainty have been identified as predictors of basal cortisol levels in primates in independent analyses (Abbott et al, ; Engh et al, ; Sapolsky, ; ; ; Sapolsky, Alberts, & Altmann, ), these measures are often confounded with the amount of aggression received, with low‐ranking monkeys or monkeys in unstable rank positions receiving higher levels of aggression (Feng et al, ; Sapolsky, ; Yamanashi et al, ). As high levels of received aggression have also been associated with high chronic cortisol (Feng et al, ; Yamanashi et al, ; Yamanashi et al, ), the individual contributions of aggression received, dominance rank, and rank uncertainty remain unclear.…”

“…Affiliative behavior in primates is often measured through dyadic interactions such as grooming, contact, and proximity. Increases in the amount of grooming given (Shutt, MacLarnon, Heistermann, & Semple, ; Wooddell et al, ), higher equitability in grooming relationships (Yamanashi et al, ), concentration of grooming relationships (Sonnweber et al, ), and increased initiation of affiliative behaviors such as contact and play (Wooddell et al, ) have all been associated with low cortisol levels in various primate species. These affiliative interactions often involve physical contact (Dunbar, ).…”

“…However, it has been proposed that, in primates, the physiological benefits of affiliative interactions may be due, not to physical contact alone, but to the psychological effects of the social support that these affiliative interactions reflect (Cheney & Seyfarth, ). Animals who have stronger social relationships or who have more central positions in the social group may be better buffered against stress due to the presence of these supportive relationships (Brent, Semple, Dubuc, Heistermann, & MacLarnon, ; Cheney & Seyfarth, ; Dunbar, ; Soares et al, ; Yamanashi et al, ). If this is the case, position in the social group would be a better predictor of long‐term cortisol levels than the general rate of affiliative interaction.…”