A Comparative Analysis of Fecal Cortisol Concentrations Between Four Populations of Woolly Monkeys (Lagothrix lagotricha) Living Under Different Environmental Conditions
Over 16,000 woolly monkeys, Lagothrix lagotricha, were imported into the United States beginning in the 1960s. They have an extremely high mortality rate in captivity and it is estimated that there are less than 25 remaining in zoos and in private ownership in the United States today. Studies have indicated that woolly monkeys in captivity have a very high incidence of hypertension and related disorders.1-3
It is unknown whether woolly monkeys develop hypertension under natural conditions or if it is in some way related to captivity. One possible explanation for the high incidence of hypertension is that this species may be in some way hypersensitive to physiological and/or psychological stressors affiliated with a captive environment resulting in chronic stress response activity and an associated hypertensive state. If abnormally high stress associated with captivity is a primary factor in the development of hypertension in this species, then measurable indices of stress response activity would be expected to be significantly higher in captive populations, especially in traditional zoological settings, than they would in wild populations.
The primary purpose of this pilot study is to investigate whether differences exist in fecal cortisol levels from woolly monkeys living under different environmental conditions and to evaluate fecal cortisol as a potential hormonal indicator of chronic stress response activity in this species. Fecal cortisol analysis is a very new area of research, especially in nonhuman primates. In the future, fecal cortisol analysis may prove to be a safe and noninvasive method for measuring cortisol levels and assessing stress in animals.
Mean fecal cortisol concentrations were determined from four populations of woolly monkeys living under different conditions to discern if significant differences exist between them. The four populations consist of one from a zoo setting (the Louisville Zoo), one from a less conventional captive environment (the Monkey Sanctuary), a population of orphans who have daily human contact but live freely at the Caparu Biological Station in the Colombian Amazon Rainforest and a wild population living in the vicinity of the field station. The Caparu Biological Station is located deep in the Amazon Rainforest far away from any human populations so it is expected that these monkeys will not have any additional stress brought about by proximity to human populations such as hunting or habitat loss, which is the case elsewhere.
Fecal cortisol concentrations were determined using a cortisol enzyme immunoassay (EIA) at the Assay Services Laboratory of the Wisconsin Regional Primate Research Center. Prior to assaying the samples, two woolly monkey samples were separated through high performance liquid chromatography (HPLC): a thoroughly mixed pool of wild woolly monkey feces (wfp) and a sample from a captive male 3-yr-old. UV detection indicated that both cortisol and cortisone were identified in the feces of the woolly monkey. HPLC elutes were fractionated into 0.025 or 1 ml aliquots. The aliquots were then assayed for cortisol by enzyme immunoassay (EIA) using the technique described by Ziegler et al. with minor modifications.5 Results indicated that both cortisol and cortisone were present in the feces of the woolly monkey and that the cortisol EIA antibody cross reacted with both steroids (100% with cortisol and 60% with cortisone) giving a complete profile of cortisol metabolites. Assayed fractions indicated that over 80% of cortisol activity occurred at the retention times of cortisol and cortisone.
The enzyme immunoassay was used to determine cortisol concentrations in fecal samples collected from individuals from all four populations. Fecal samples were either collected in ethanol and later frozen or first frozen and later placed in ethanol prior to processing. The alcohol was evaporated off and samples were lyophilized to complete dryness. Prior to assaying, a portion of each sample was weighed, extracted with water/ethanol and put through solvolysis to remove all conjugates following previously reported methods.4
Mean cortisol levels were calculated for individual animals for which there were multiple samples. Mean population cortisol levels were then calculated. Statistical analysis using the Kruskal-Wallis test showed significant differences in mean population cortisol levels between all population comparisons except between the wild and orphan populations (p<0.01). The cortisol mean from the Louisville Zoo was higher than the mean from the Monkey Sanctuary and both captive population cortisol means were significantly higher than wild and orphan means.
Further research will continue to investigate the possibility that woolly monkeys living in traditional captive settings are subjected to greater stress than woolly monkeys living in more stimulating captive habitats or in natural environments to which they are evolutionarily adapted and whether fecal cortisol measurements can accurately be used for assessing stress response activity in this species. This research project has many potential implications in terms of ecosystem health, animal welfare and captive breeding programs. If zoological parks or other institutions decide that woolly monkeys should be kept in an enriched or otherwise improved captive environment, then fecal cortisol measurement may prove useful in the future as a simple and noninvasive method for continually assessing the risk of hypertensive disease. This method would allow for the early identification of inadequate captive habitat and living conditions so that efforts could be made to improve them prior to the onset of disease.
This study also has the potential for identifying fecal cortisol in the future as an easily measured, early, sensitive indicator of environmental changes in habitats in which woolly monkeys occur. Future study in this area will involve field investigations in which woolly monkey fecal cortisol concentrations are compared at different levels of environmental perturbation, ranging from areas with little or no human population pressures to areas where human population pressures are great. The purpose of this will be to investigate the suitability of the fecal cortisol parameter as an indicator of habitat health in neotropical rainforests.
The authors wish to thank Drs. Tom and Sara Defler of the Caparu Biological Station; Dr. Roy Burns, Silvia Logsdon and the Louisville Zoo; Dr. Jordi Casamitjana and the Monkey Sanctuary, and Dr. Robert Yaffee of New York University for all of their essential contributions to this project. We also wish to acknowledge the helpful input of Dr. Brent White, Daniel Wittwer, Nicholas Wolfinger and Frank LoPresti. We are grateful to the Geraldine R. Dodge Foundation and the National Institute of Health for providing the funding which made this research possible.
1. Giddens WE, Jr., Combs CA, Smith OA, Klein EC. 1987. Spontaneous hypertension and its sequelae in woolly monkeys (Lagothrix lagotricha). Lab Anim Sci. 37(6): 750–756.
2. Müller M, Heldstab A, Luginbühl H. 1989. The woolly monkey (Lagothrix lagotricha): a possible model for human hypertension research. Schweiz Arch Tierheilk. 131: 569–576.
3. Wagner RA, Klein EC, Coombs CA. 1985. Clinical observations of hypertension in woolly monkeys. Proc Amer Assoc Zoo Vet. 43–44.
4. Ziegler TE, Scheffler G, Abbott DH. 1996. Metabolism of reproductive steroids during the ovarian cycle in two species of callitrichids, Saguinus oedipus and Callithrix jacchus, and estimation of the ovulatory period from fecal steroids. Biol of Reprod. 54: 91–99.
5. Ziegler TE, Scheffler G, Snowdon CT. 1995. The relationship of cortisol levels to social environment and reproductive functioning in female cotton-top tamarins, Saguinus oedipus. Hormones and Behavior. 29: 407–424.