Maggioncalda, A. N., Czekala, N. M., & Sapolsky, R. M. (2002). Male orangutan subadulthood: a new twist on the relationship between chronic stress and developmental arrest. American Journal of Physical Anthropology, 118(1), 25-32.
Kingsley’s (1982) study asserted that a significant and noteworthy arrest of the development of secondary sexual traits is observed in some male orangutans not only in captivity but also in the wild (Maggioncalda et al., 2002). The study by Maggioncalda et al. sought to test the hypothesis that chronic stress especially in growing male orangutans that results from their aggressive, belligerent, and antagonistic mature counterparts affects the endocrinological axes that are crucial in the onset and development of secondary sexual characteristics. The hypothesis was put forward by several researchers based on their empirical studies and findings. Contrary to the hypothesis, the study found that there was no tangible evidence that unending stress is responsible for the arrest of the onset and development of sexual characteristics in adolescent orangutans. The study that involved 23 orangutans for a period of 3 years with urine as the major sample from which hormonal assays were performed concluded that arrested adolescence was in fact and adaptive mechanism to avoid stress rather than the result (Maggioncalda et al., 2002). Arresting adolescence ensures that male orangutans escape stress, hostility, and grievance while still being able to reproduce.
The use of urine samples to assess stress hormone levels, the three-year period of the study and inclusion of juvenile, arrested adolescents, developing adolescents and matured orangutans are the key strengths of the study (Maggioncalda et al. 2002). First, early morning urine has been shown to not only contain a significant amount of stress hormones which consist of majorly cortisol and prolactin but also sex hormones in males especially testosterone. Also, the process of collecting urine as the preferred sample does not cause any stress or discomfort to subjects which could alter the findings as compared to the collection of blood. Secondly, the three-year period of the study ensures that consistency and plausibility of the study is enhanced while maintaining the reproducibility of the findings. Lastly, the incorporation of both arrested and developing adolescents provides a control study where the results from hormonal assays can be compared to those from matured and juvenile orangutans. This gives the study a basis to compare and contrast its findings before drawing conclusions.
However, the use of different subspecies of orangutans and the confinement of the subjects in different geographical areas under different conditions are the two major weaknesses of the study. The study involved 23 orangutans of which seven of them were from the Bornean subspecies, eight from the Sumatran subspecies and the rest were hybrids (Maggioncalda et al. 2002). The fact that the subjects were from different subspecies means that the inferential aspect of the study can be challenged. This is because the biological and hormonal response of the subjects to stress, the environment and pressure could differ according to their subspecies. The difference in their facial morphologies and hair could also mean a difference in their biological responses to different stimuli. The environment has been shown to cause stress on animals and human beings and this can affect the levels of stress hormones in their systems. The keeping of the orangutans in different locations under different conditions thus could influence and cause biasness in the results of the study.
Kingsley (1982) informed the basis for the study by Maggioncalda et al by suggesting that the even though adolescence arrest amongst orangutans is common in the wild, it also occurs in captivity. The fact that adolescence arrest could occur in any environment and situation according to Kingsley’s study challenged Maggioncalda et al. (2002) to test the hypothesis that chronic stress was the greatest cause of subadulthood amongst orangutans. The establishment of an existing relationship between unremitting stress and adolescence arrest by Kingsley (1982) also formed the fundamental variables that the researchers focused on in order to test the hypothesis. With the intention of furthering knowledge and understanding of how chronic stress and adolescence arrest in orangutans relate, a future study on why the Bornean subspecies deal with stress differently from the other subspecies should be conducted. According to a 2012 research, Bornean subspecies show an instantaneous response to stress with very little signs of chronic stress (Amrein et al. 2014). Their interaction with eco-tourists led to acute increase of stress hormones especially cortisol which later fell back to the baseline. However, other subspecies of orangutans show permanent modifications in stress response.
New Release; Chronic Stress Can Also Lead to Low Cortisol Levels
Although stress hormones especially cortisol has traditionally been known to increase during stress, a recent study that was carried out on fifty nine horses in Rennes France has revealed otherwise (Pawluski, 2017). The study involved forty four geldings and fifteen mares all from dissimilar riding centers. They were subjected to stressful conditions for several weeks that if made recurrent would create chronic stress. Cortisol levels were then measured using blood samples and also stool samples amongst the horses that were subjected to stress and compared to other horses that had not been exposed to the unfavorable conditions. Contrary to the norm, Pawluski (2017) denotes that the levels in horses that showed signs of compromised wellbeing due to being exposed to stressors were lower than in the other horses. The conclusions were in line with earlier observations that had revealed a drop in cortisol in horses that showed depressive-like characteristics (Pawluski, 2017). This study seeks to question the suitability of Cortisol as the definitive indicator of stress. Furthermore, it seeks to trigger conversations around the criteria used to decide that acute stress has persisted enough to be termed chronic.
References
Amrein, M., Heistermann, M., & Weingrill, T. (2014). The effect of fission–fusion zoo housing on hormonal and behavioral indicators of stress in Bornean orangutans (Pongo pygmaeus). International Journal of Primatology, 35(2), 509-528.
Kingsley, S. (1982). Causes of non-breeding and the development of the secondary sexual characteristics in the male orang-utan: a hormonal study. The Orang-Utan, Its Biology and Conservation. The Hague: W. Junk, 215-229.
Maggioncalda, A. N., Czekala, N. M., & Sapolsky, R. M. (2002). Male orangutan subadulthood: a new twist on the relationship between chronic stress and developmental arrest. American Journal of Physical Anthropology, 118(1), 25-32.
Pawluski, J., Jego, P., Henry, S., Bruchet, A., Palme, R., Coste, C., & Hausberger, M. (2017). Low plasma cortisol and fecal cortisol metabolite measures as indicators of compromised welfare in domestic horses (Equus caballus). PloS one, 12(9), e0182257.
