Introduction / Background
Endocrine system function is vital for a variety of life processes. This case focuses on the role of hormones in the maturation process of animals. The case was adapted from results summarized in Maggioncalda and Sapolsky’s (2002) article in Scientific American and presents evidence for why an unusual adaptation for reproduction in subordinate male primates may have evolved as a means of reducing stress.
The case serves several purposes: as an introduction to hypothalamic-pituitary-endocrine gland physiology; an introduction to stress physiology; an examination of the link between hormones, development, and behavior; and evaluation of data to formulate new hypotheses. The case was designed for an upper division comparative anatomy and physiology class taken by junior and senior biology majors. It could also be used in an animal behavior course in a similar unit on hormonal control of behavior, or in an advanced physiology course that focuses more intensively on endocrinology.
Objectives
Upon completing this case study, students should be able to:
- Understand the normal homeostatic regulation of peripheral endocrine glands, such as the adrenal and gonadal glands by the hypothalamus and pituitary.
- Describe how one life process such as growth and maturation is regulated by a variety of synergizing hypothalamic and pituitary hormones.
- Describe the action of stress hormones on normal physiology; understand the “fight or flight” response; appreciate the effect of stress hormones on growth and development.
- Understand the effect of hormones on behavior.
- Evaluate data to determine whether it supports hypotheses; generate new hypotheses based on results presented.
Classroom Management
This interrupted case can be used during one classroom meeting after students have been introduced to the fundamentals of endocrine physiology, or its three sections can be discussed at greater length over parts of two or more classroom periods depending on the level of detail on fundamentals of endocrine physiology desired.
I assign Part I (review of hypothalamic and pituitary function) as individual homework and then have students discuss their answers in small groups of three to four during the next class meeting before going on to Parts II and III. This pre-class preparation for the case study facilitates a more focused and richer discussion of Part I, uses up less class time, and leads naturally to consideration of the data presented in Part II. The reporter in each small group presents answers to the questions in Part I for the whole class to hear; if there are discrepancies between the groups’ answers, they can be addressed during the large group debriefing. Allow at least 20 minutes for this part of the case, including time for the debriefing on small group discussion.
Analysis of the data in Part II is relatively easy for intermediate and advanced level students, and this section requires the least time of the three sections. The data analysis should contradict small group answers to the final question in Part I (“What sort of data might support the researcher’s hypothesis?”), so that students must then propose alternative hypotheses for the hormone profiles reported in the graphs; this is good practice using the scientific method. Again, small group discussion and reporting back to the entire class usually takes about 15–20 minutes, depending on the level of the analytical approach.
Further consideration of the new data presented in Part III forces students to integrate the more complex control of reproduction by many hypothalamic-pituitary hormones to understand how a developmentally arrested male can still be reproductively competent. Students come to appreciate that subtle differences in the amount of testosterone secreted by arrested males (enough to mature sperm, not enough to promote development of secondary sex structures) accounts for the development of two sexually competent male reproductive strategies. Students may spend significant time discussing how two such divergent strategies evolved in male orangutans in response to stress, and may need significant prompting to understand that the low stress, arrested male has as much of an evolutionary advantage as the high stress, fully mature adult. For the physiology students, I would emphasize the understanding of hormonal control of sexual competence (sperm production) in males; for the animal behavior students, I might emphasize the understanding of the evolution of alternative reproductive strategies. Allow at least 20 minutes for this part, including the wrap-up summary of “what did we learn from this case.”
Blocks of Analysis
Having students diagram hypothalamic-pituitary-endocrine gland relationships is essential to understanding the control of hormone levels by negative feedback. In addition, students should realize that there are multiple hormonal controllers of any one life process such as growth, and they should add all of the relevant hormones to their simple Hypo-Pit-Gland diagram. A good review of endocrine hormones with some interactive diagrams is available at: http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/index.html
Sapolsky (2000) provides an excellent and short summary of the impact of acute and chronic stress on the body. It is a good introduction to the subject of stress physiology and an excellent resource for this case study to supplement the text for the course (whether physiology or animal behavior). The chronic stress expected in this case is that imposed by adult males’ aggression toward developing juvenile males. As Sapolsky summarizes, the consequences of this are inhibition of the immune system, interference with normal growth (leading to dwarfism), inhibition of sexual maturation or reproductive cycles, hypertension and atherosclerosis, muscle wasting, ulcers and poor digestion/nutrition, and even neuronal dysfunction and atrophy. Thus, the case sets the students up to think that stress explains the arrested development in juvenile male orangutans.
Analysis of preliminary data on cortisol and prolactin levels in all stages of adult male development (juvenile to adult) reveals that arrested male orangutans are not, in fact, exhibiting stress; the revelation of these data forces students to think of alternative hypotheses to explain the arrested development, and their creative minds come up with some very interesting ones. Most students think that arrested males are nutritionally deprived because they are somehow excluded from feeding at prime sites. In fact orangutans are not very social, and males are often solitary. In Part III, students learn that arrested males are sexually competent and that there are two viable reproductive strategies. Now that stress is removed as an explanation for arrested development, students should be encouraged to explore the evolutionary basis for two reproductive strategies, such as exhibited in orangutans.
Detailed case analysis with answers to the study questions is provided in a separate, password-protected Answer Key.
Answer Key
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References
- Bowen, R. Pathophysiology of the Endocrine System. http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/index.html. Accessed June, 2008.
- Cavigelli, S.A., and M.E. Pereira. (2000). Mating season aggression and fecal testosterone levels in male ring-tailed lemurs (Lemur catta). Hormones and Behavior 37: 246–255.
- Maggioncalda, A.N., and R.M. Sapolsky. (2002). Disturbing behaviors of the orangutan. Scientific American 286(6): 60–65.
- Maggioncalda, A.N., N.M. Czekala, and R.M. Sapolsky. (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.
- Maggioncalda, A.N., N.M. Czekala, and R.M. Sapolsky. (1999). Growth hormone and thyroid stimulating hormone concentrations in captive male orangutans: Implications for understanding developmental arrest. American Journal of Primatology 50: 67–76.
- Maggioncalda, A.N., N.M. Czekala, and R.M. Sapolsky. (1999). Reproductive hormone profiles in captive male orangutans: Implications for understanding developmental arrest. American Journal of Physical Anthropology 109: 19–32.
- Sapolsky, R.M. (2000). Stress hormones: Good and bad. Neurobiology of Disease 7: 540–542.
Date Posted: January 13, 2009.
Originally published at http://www.sciencecases.org/orangutans/orangutans_notes.asp
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