As the phone rang, I knew who it was before I picked it up. Just yesterday the latest copy of the American Journal of Primatology had landed on my desk, and Anne’s article on growth hormone levels in captive male orangutans had caught my eye.
“Lisa, I’ve finished the study of arrested development in juvenile orangutans and am sending you some of the additional data we’ve collected. It was quite a puzzle to put together. We ended up analyzing almost every pituitary and gonadal hormone to understand the complete picture of development. I think we understand the basis for arrested development, but it has a subtle twist that no one recognized until they observed sexual activity in the arrested individuals.”
“Give me the short version Anne. How does it work,” I prodded her.
“OK, here it is in a nutshell. Growth hormone levels of developing males are three times higher than in juveniles, arrested males, and full adults, who were all similar to one another. Developing males also had far higher levels of testosterone and LH (luteinzing hormone) than arrested males, as expected, BUT the levels of these hormones in arrested males were similar to mature adults. AND arrested males had higher levels of FSH (follicle stimulating hormone), comparable to that in developing males and mature adults. Finally, and most surprisingly, arrested males had mature and functional sperm in their testes, and the testes were the same size as developing males. Futhermore, a new study on sexual activity of adolescent males in the wild has shown that these arrested males are in fact reproductively active, will force copulations with females when the dominant territorial male is absent, and sire a significant proportion of the infants.”
“So, apparently arrested males are neither stressed nor reproductively suppressed. What is going on? And why?” I wondered aloud.
Questions
- Based on the additional data provided by Anne’s research, explain how males that appear physically arrested in development might have mature, functional sperm. What is the significance of their hormone profile (growth hormone, testosterone, LH, FSH, prolactin)?
- The seemingly arrested development of some adolescent males constitutes an alternative reproductive strategy. How do you think such a strategy might have evolved—in a way that makes sense for males to remain juvenile looking, but reproductively capable?
- How do the two reproductive strategies fit with the stress hormone results?
Originally published at http://www.sciencecases.org/orangutans/case3.asp
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