Single Aggressive Interactions Increase Urinary Glucocorticoid Levels in Wild Male Chimpanzees

Abstract

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.

Urinary Cortisol, Aggression, Dominance and Competition in Wild, West African Male Chimpanzees

“…Thus, higher urinary cortisol levels of males during social instability might be due to the exposure to psychosocial rather than energetic stressors. These results are in line with findings of a recent study conducted in the same chimpanzee groups and study period (Samuni et al, 2019), as well as with another study in male chimpanzees (Wittig et al, 2015), that both found support for an association between urinary glucocorticoid levels and exposure to psychosocial more than energetic stressors. Overall, our results indicate that all males, independent of dominance status, were affected by social instability and therefore support previous empirical work (Sapolsky, 1992(Sapolsky, , 2005, by showing that social uncertainty is a potent psychosocial stressor.…”

Urinary Cortisol, Aggression, Dominance and Competition in Wild, West African Male Chimpanzees

“…Thus, higher urinary cortisol levels of males during social instability might be due to the exposure to psychosocial rather than energetic stressors. These results are in line with findings of a recent study conducted in the same chimpanzee groups and study period (Samuni et al, 2019), as well as with another study in male chimpanzees (Wittig et al, 2015), that both found support for an association between urinary glucocorticoid levels and exposure to psychosocial more than energetic stressors. Overall, our results indicate that all males, independent of dominance status, were affected by social instability and therefore support previous empirical work (Sapolsky, 1992(Sapolsky, , 2005, by showing that social uncertainty is a potent psychosocial stressor.…”

Correlates of hormonal modulation in mantled howler monkey males,Alouatta palliata

“…Involvement in agonistic interactions was related to variation in GC and T concentrations. These results are in line with studies demonstrating that intrasexual competition represents a strong challenge for primate males and is linked to hormonal mechanisms (e.g., Bergman et al, 2005;Crist obal-Azkarate et al, 2006;Jaeggi et al, 2018;Muller & Wrangham, 2004a;Wittig et al, 2015). The positive relationship between rates of agonism and GC also supports previous findings from this population (Dias et al, 2017;G omez-Espinosa et al, 2014).…”

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

“…We found that the rate of receiving aggression positively correlated with HC levels, while that of initiating aggression negatively correlated with HC levels in male chimpanzees. Although a previous study reported that single aggressive interactions in both directions (initiating or receiving) can increase urinary glucocorticoid levels (Wittig et al 2015), our study showed different effects of initiating and receiving aggressive interactions on HC levels in captive chimpanzees (Yamanashi et al 2016a). Compared with urinary glucocorticoid levels (Bahr et al 2000), HC levels can reflect long-term accumulation of cortisol over several months (Davenport et al 2006;Russell et al 2012).…”

Urinary Cortisol, Aggression, Dominance and Competition in Wild, West African Male Chimpanzees

“…Thus, higher urinary cortisol levels of males during social instability might be due to the exposure to psychosocial rather than energetic stressors. These results are in line with findings of a recent study conducted in the same chimpanzee groups and study period (Samuni et al, 2019), as well as with another study in male chimpanzees (Wittig et al, 2015), that both found support for an association between urinary glucocorticoid levels and exposure to psychosocial more than energetic stressors. Overall, our results indicate that all males, independent of dominance status, were affected by social instability and therefore support previous empirical work (Sapolsky, 1992(Sapolsky, , 2005, by showing that social uncertainty is a potent psychosocial stressor.…”

Correlates of hormonal modulation in mantled howler monkey males,Alouatta palliata

“…Involvement in agonistic interactions was related to variation in GC and T concentrations. These results are in line with studies demonstrating that intrasexual competition represents a strong challenge for primate males and is linked to hormonal mechanisms (e.g., Bergman et al, 2005;Crist obal-Azkarate et al, 2006;Jaeggi et al, 2018;Muller & Wrangham, 2004a;Wittig et al, 2015). The positive relationship between rates of agonism and GC also supports previous findings from this population (Dias et al, 2017;G omez-Espinosa et al, 2014).…”

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

“…We found that the rate of receiving aggression positively correlated with HC levels, while that of initiating aggression negatively correlated with HC levels in male chimpanzees. Although a previous study reported that single aggressive interactions in both directions (initiating or receiving) can increase urinary glucocorticoid levels (Wittig et al 2015), our study showed different effects of initiating and receiving aggressive interactions on HC levels in captive chimpanzees (Yamanashi et al 2016a). Compared with urinary glucocorticoid levels (Bahr et al 2000), HC levels can reflect long-term accumulation of cortisol over several months (Davenport et al 2006;Russell et al 2012).…”

Urinary Cortisol, Aggression, Dominance and Competition in Wild, West African Male Chimpanzees

“…Thus, higher urinary cortisol levels of males during social instability might be due to the exposure to psychosocial rather than energetic stressors. These results are in line with findings of a recent study conducted in the same chimpanzee groups and study period (Samuni et al, 2019), as well as with another study in male chimpanzees (Wittig et al, 2015), that both found support for an association between urinary glucocorticoid levels and exposure to psychosocial more than energetic stressors. Overall, our results indicate that all males, independent of dominance status, were affected by social instability and therefore support previous empirical work (Sapolsky, 1992(Sapolsky, , 2005, by showing that social uncertainty is a potent psychosocial stressor.…”

Correlates of hormonal modulation in mantled howler monkey males,Alouatta palliata

“…Involvement in agonistic interactions was related to variation in GC and T concentrations. These results are in line with studies demonstrating that intrasexual competition represents a strong challenge for primate males and is linked to hormonal mechanisms (e.g., Bergman et al, 2005;Crist obal-Azkarate et al, 2006;Jaeggi et al, 2018;Muller & Wrangham, 2004a;Wittig et al, 2015). The positive relationship between rates of agonism and GC also supports previous findings from this population (Dias et al, 2017;G omez-Espinosa et al, 2014).…”

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

“…We found that the rate of receiving aggression positively correlated with HC levels, while that of initiating aggression negatively correlated with HC levels in male chimpanzees. Although a previous study reported that single aggressive interactions in both directions (initiating or receiving) can increase urinary glucocorticoid levels (Wittig et al 2015), our study showed different effects of initiating and receiving aggressive interactions on HC levels in captive chimpanzees (Yamanashi et al 2016a). Compared with urinary glucocorticoid levels (Bahr et al 2000), HC levels can reflect long-term accumulation of cortisol over several months (Davenport et al 2006;Russell et al 2012).…”