BLOOMINGTON, Ind. -- A field study of the relationship between testosterone and natural selection in an American songbird, the dark-eyed junco, has defied some expectations and confirmed others.
Scientists from Indiana University Bloomington, the University of Virginia, Indiana University-Purdue University Indianapolis, and the University of Southern Mississippi report in the June issue of The American Naturalist (now online) that extreme testosterone production -- high or low -- puts male dark-eyed junco at a disadvantage in both survival and reproduction outside their semi-monogamous breeding pairs. The results are based on a wild population of juncos studied near the University of Virginia's Mountain Lake Biological Station.
"Our goal in this study was to characterize natural variation in testosterone production in the wild and to learn how that relates to natural variation in survival and reproductive success," said Joel McGlothlin, a Virginia postdoctoral fellow who conducted the project as an IU Bloomington Ph.D. student. "We learned there are far more complex things going on here than we expected."
Past studies of juncos (and other animals) have shown that testosterone presents something of a trade-off, by exerting opposing effects on survival and reproduction in wild populations. High testosterone is often associated with aggression in male animals and sometimes with suppressed immunity. These effects can harm a male's chances of survival but also yield more opportunities for him to mate. Low testosterone production is presumed to have the opposite effect -- increased survival and fewer mating opportunities.
But that isn't what members of IU Bloomington Distinguished Professor of Biology Ellen Ketterson's research group saw.
Instead, they saw "stabilizing selection" on testosterone production when looking at both survival and reproduction. The male juncos that were most likely to survive produced i
|Contact: David Bricker|