Measuring Stress in Captive Bonobos: A Look to the Past and Future to Improve Methods
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Understanding stress in primates has wide ranging implications. It impacts how we understand human stress from an evolutionary perspective and how captive and laboratory primates are kept to best impact their health and well-being. Stress studies in non-human primates often focus on measuring cortisol. Cortisol can be measured in blood, urine, feces, saliva, or hair in primates. Quantification of cortisol is typically achieved by enzyme or radio immunoassay, high performance liquid chromatography, or mass spectroscopy. Once cortisol is quantified, it is traditionally related to stress in primates by determining associations to variables classically seen as potential stressors, such as dominance rank, aggression received, food availability, or moving facilities for captive primates. It is vitally important that researchers engaging in non-human primate cortisol research properly select the sample type and quantification method best suited to answer their particular research questions. It is also important that the quantification of cortisol and the subsequent reporting of methods and results obtained is done correctly and transparently so that other researchers are able to interpret and build upon previous results. In this dissertation, the past instances of non-human primate cortisol analyses are reviewed with a particular focus on urinary analyses. A critical view is taken of past methods and means of reporting results, and suggestions for better practices are made. Researchers should be reporting ranges of raw values measured for cortisol in order to help establish expected values in specific species, as well as explicit justifications for protocol modifications if any are made. A new method for assessment of urinary cortisol in bonobos (Pan paniscus) is validated and reported. A longitudinal study of captive bonobos at the Columbus Zoo and Aquarium contributed 154 urine samples for analyses over three field seasons (2012, 2013, and 2014). A commercially available cortisol EIA kit (Arbor Assays, Ann Arbor, MI) was determined to be appropriate for use in bonobos and subsequently used to test 154 urine samples. A diurnal cortisol rhythm was detected in bonobos for the first time. Individual differences were identified in AM and PM samples and will be the foundation for future behavioral association investigations.