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Testosterone turns male juncos into blustery hunks -- and bad dads
Date:10/15/2007

out there to fertilize, so every male can't be successful getting extra-pair fertilizations," McGlothlin said. "High-quality males -- those who have more energy to invest -- ought to spend more of it on trying to attract mates. These males may be less likely to survive, but they are more likely to be successful at getting extra-pair fertilizations. The low-quality males don't have as much energy to invest, so they play it safe."

Ketterson, McGlothlin and Jawor studied a natural population of Carolina dark-eyed juncos (Junco hyemalis carolinensis). The birds' behavior is well known -- thanks to the work of IU Bloomington biologist (emeritus) Val Nolan, who is married to Ketterson. Male birds were observed extensively in and around nests, and were at times captured and catalogued. During the male birds' brief captivity, the scientists measured circulating testosterone levels, then injected the birds with gonadotropin-releasing hormone (GnRH) to determine the degree to which each male could produce testosterone in response.

Males that were capable of producing more testosterone in response to the injections not only demonstrated more aggressive behavior, but were also observed to spend less time parenting.

"The next essential step is to relate variation in testosterone to actual measures of fitness, namely lifespan and offspring actually produced," Ketterson said. "Is it true that individuals who resolve the trade-off in different ways have equal fitness" Can a good parent be just as successful in an evolutionary sense as a good mater""


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Contact: David Bricker
brickerd@indiana.edu
812-856-9035
Indiana University
Source:Eurekalert

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