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Published on: January 18, 2013
Self-injurious behavior in male rhesus macaques does not reflect externally directed aggression
Corrine Lutz1, Lucinda Marinus, William Chase
1New England Regional Primate Research Center, Harvard Medical School, One Pine Hill Drive, P O Box 9102, Southborough, MA 01772-9102, USA. Corrine_Lutz@hms.harvard.edu
Abstract:
Self-injurious behaviors (SIB), such as self-biting and self-wounding, have been observed in a small percentage of captive nonhuman primates. Because rhesus monkeys that exhibit SIB also tend to be more aggressive, it was hypothesized that SIB is related to externally directed aggression and is associated with contexts in which physical contact between participants is prevented. The purpose of this study was to test the hypothesized relationship between SIB and outward aggression. Subjects were first presented with videotapes of conspecifics, scenery and a blank screen, and their behavior was recorded. Levels of salivary cortisol, an indicator of stress, were also measured before and after presentation of the videos. Although aggression increased when subjects viewed tapes containing conspecifics, neither cortisol levels nor self-biting behavior varied as a function of tape content. The subjects were then placed in two additional test situations: an empty room and the same room containing an unfamiliar conspecific. Aggression was significantly higher in the stranger condition compared to the empty room condition. The two situations yielded parallel increases in cortisol, suggesting that being alone was just as stressful as being paired with an unfamiliar conspecific. Self-biting rates were also similar in these two conditions. Thus, contrary to our prediction, increases in aggression did not correlate with increases in SIB. These results suggest that under similarly stressful conditions, SIB and externally directed aggression are unrelated.
Insights
Self-injurious behaviors (SIB) in rhesus monkeys are not linked to outward aggression, even under stressful conditions. This study found no correlation between increased aggression and SIB in captive primates.
Area of Science:
- Primate behavior
- Animal welfare
- Neuroscience
Background:
- Self-injurious behaviors (SIB), including self-biting and self-wounding, occur in a subset of captive nonhuman primates.
- Previous observations suggest a link between SIB and increased aggression in rhesus monkeys.
- It was hypothesized that SIB is related to externally directed aggression, particularly in situations limiting physical contact.
Purpose of the Study:
- To investigate the relationship between self-injurious behaviors (SIB) and outward aggression in captive rhesus monkeys.
- To determine if increased aggression correlates with SIB under varying social and environmental conditions.
Main Methods:
- Rhesus monkeys were exposed to video stimuli (conspecifics, scenery, blank screen) while behavior and salivary cortisol levels were recorded.
- Subjects were then placed in an empty room versus a room with an unfamiliar conspecific to assess aggression and stress responses.
- Salivary cortisol was measured as a physiological indicator of stress.
Main Results:
- Aggression levels increased when subjects viewed conspecific videos, but SIB and cortisol did not change.
- Aggression was significantly higher when housed with an unfamiliar conspecific compared to being housed alone.
- Cortisol levels and self-biting rates were similar in both the alone and stranger conditions, indicating comparable stress levels.
- Contrary to the hypothesis, increased aggression did not correlate with increased SIB.
Conclusions:
- Self-injurious behaviors (SIB) and externally directed aggression appear to be unrelated in rhesus monkeys under similarly stressful conditions.
- The findings challenge the proposed link between SIB and outward aggression in this species.
- Further research is needed to understand the underlying mechanisms of SIB in captive primates.
