Study shows costs and benefits of testosterone in birds

May 13, 2010

Do nice guys finish last, or will the meek inherit the earth? A new study published in The American Naturalist suggests that, at least for birds, the right answer is somewhere in between.

Individual male birds can differ dramatically in their behavior, and this difference is often due in part to how much testosterone they produce. In many species, some males produce high testosterone and are more aggressive, while others produce lower levels and are more parental.

Testosterone and the behaviors it mediates may predict how well a male succeeds. For example, an aggressive male may be more likely to obtain high-quality territories that attract females. At the same time, might pose a survival risk, because aggressive males might be more likely to engage in costly fights. These considerations suggest that hormones like testosterone might be under strong in the wild.

To test this idea, a team of researchers from Indiana University studied a common , the dark-eyed junco in the Appalachian Mountains of Virginia. They tested how much testosterone a male could produce by using an injection of a hormone produced in the brain that causes the bird to increase its testosterone levels temporarily, mimicking what they do naturally when fighting with other males. The researchers then followed the birds, measuring their survival and success at reproduction, both in their own nest and those of their neighbors.

They found strong relationships between testosterone and both reproduction and survival, demonstrating that natural selection is currently acting on testosterone production in this population of juncos. The exact pattern of selection they found was surprising, however. "The males that did the best at both survival and reproduction had testosterone production very close to average," said Joel McGlothlin, the lead author of the study who is now a postdoctoral fellow at the University of Virginia. "It was bad to produce either really high or really low levels of testosterone." High-testosterone males did have one universal advantage—they were more likely to be the genetic father of the offspring raised in their nests.

These results indicate that the trade-offs that testosterone regulates are quite complex. "It's not as simple as saying testosterone is good for reproduction and bad for survival," McGlothlin said. " seems to underlie this delicate balance between competing traits and behaviors, and the right balance might be different for different males."

Explore further: Male monkey filmed caring for dying mate (w/ Video)

Related Stories

Men's testosterone levels predict competitiveness

Dec 04, 2006

After a man loses a challenge, whether or not he is willing to get back into the game depends on changes in his testosterone levels, according to new research at The University of Texas at Austin.

Testosterone key to disease transmission

Aug 08, 2008

High levels of testosterone may be a key factor in spreading disease among mice, according to biologists. The findings could help explain why males in a population are often more likely to get infected, and ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Plants with dormant seeds give rise to more species

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.