belgareth
06-04-2008, 05:02 AM
Marked-up
birds become sexier, exude testosterone
By SETH BORENSTEIN, AP Science Writer1 hour, 24 minutes ago
A
little strategically placed makeup quickly turns the wimpiest of male barn swallows into chick magnets, amping up
their testosterone and even trimming their weight, new research shows.
It's a "clothes make the man" lesson that —
with some caveats — also applies to human males, researchers say.
Using a $5.99 marker, scientists darkened the
rust-colored breast feathers of male New Jersey barn swallows, turning lighter birds to the level of those naturally
darkest.
They had already found, in a test three years ago, that the marked-up males were more attractive to
females and mated more often.
This time they found out that the more attractive appearance, at least in the bird
world, triggered changes to the animals' body chemistry, increasing testosterone.
"Other females might be looking
at them as being a little more sexy, and the birds might be feeling better about themselves in response to that,"
said study co-author Kevin McGraw, an evolutionary biology professor at Arizona State University.
McGraw said the
findings are surprising, in part because the hormonal changes occurred after only one week.
The study was published
in Tuesday's edition of the journal Current Biology.
In the 30 male barn swallows who were darkened, testosterone
was up 36 percent after one week, during a time of year when levels of that hormone would normally drop.
At the
same time, testosterone levels in the 33 birds that didn't get the coloring treatment fell by half, said lead
author Rebecca Safran, an evolutionary biology professor at the University of Colorado in Boulder.
"It's the
`clothes make the man'" idea, Safran said. "It's like you walk down the street and you're driving a Rolls Royce
and people notice. And your physiology accommodates this."
Before you feel superior to these birds, Safran
cautioned, people's mating systems are more similar to birds' than we might like to admit.
Barn swallows are
"socially monogamous and genetically promiscuous, same as humans," she said. "There are some interesting parallels,
but we do need to be careful about making them."
In people, hormonal changes have been observed after changes in
behavior. A 1998 study found that loyal male fans of sports teams experienced a 20 percent rise in testosterone when
their teams won.
The researchers aren't certain how the testosterone boost happens. It could be that because of
the darkened color, the birds mate more often and that changes their testosterone levels.
It could also be that
because of the darkened color, other males think the pecking order has changed and that boosts the darker swallows'
hormone levels. Or it could be both. The authors said figuring out which theory is right is the next step.
The
birds' weight loss is more easily explained, Safran said. The more macho swallows could be spending more time
mating than eating or working off the calories, she said.
Most of the time it's the hormones that change the
behavior or appearance, but this work shows "it can go more than one way," said study co-author James Adelman, a
Princeton University researcher.
"It certainly is a very new and interesting finding," said Cornell University
psychology and neurobiology professor Elizabeth Adkins-Regan, who had no role in the study.
___
On the Net:
Current Biology: http://www.current-biology.com/
birds become sexier, exude testosterone
By SETH BORENSTEIN, AP Science Writer1 hour, 24 minutes ago
A
little strategically placed makeup quickly turns the wimpiest of male barn swallows into chick magnets, amping up
their testosterone and even trimming their weight, new research shows.
It's a "clothes make the man" lesson that —
with some caveats — also applies to human males, researchers say.
Using a $5.99 marker, scientists darkened the
rust-colored breast feathers of male New Jersey barn swallows, turning lighter birds to the level of those naturally
darkest.
They had already found, in a test three years ago, that the marked-up males were more attractive to
females and mated more often.
This time they found out that the more attractive appearance, at least in the bird
world, triggered changes to the animals' body chemistry, increasing testosterone.
"Other females might be looking
at them as being a little more sexy, and the birds might be feeling better about themselves in response to that,"
said study co-author Kevin McGraw, an evolutionary biology professor at Arizona State University.
McGraw said the
findings are surprising, in part because the hormonal changes occurred after only one week.
The study was published
in Tuesday's edition of the journal Current Biology.
In the 30 male barn swallows who were darkened, testosterone
was up 36 percent after one week, during a time of year when levels of that hormone would normally drop.
At the
same time, testosterone levels in the 33 birds that didn't get the coloring treatment fell by half, said lead
author Rebecca Safran, an evolutionary biology professor at the University of Colorado in Boulder.
"It's the
`clothes make the man'" idea, Safran said. "It's like you walk down the street and you're driving a Rolls Royce
and people notice. And your physiology accommodates this."
Before you feel superior to these birds, Safran
cautioned, people's mating systems are more similar to birds' than we might like to admit.
Barn swallows are
"socially monogamous and genetically promiscuous, same as humans," she said. "There are some interesting parallels,
but we do need to be careful about making them."
In people, hormonal changes have been observed after changes in
behavior. A 1998 study found that loyal male fans of sports teams experienced a 20 percent rise in testosterone when
their teams won.
The researchers aren't certain how the testosterone boost happens. It could be that because of
the darkened color, the birds mate more often and that changes their testosterone levels.
It could also be that
because of the darkened color, other males think the pecking order has changed and that boosts the darker swallows'
hormone levels. Or it could be both. The authors said figuring out which theory is right is the next step.
The
birds' weight loss is more easily explained, Safran said. The more macho swallows could be spending more time
mating than eating or working off the calories, she said.
Most of the time it's the hormones that change the
behavior or appearance, but this work shows "it can go more than one way," said study co-author James Adelman, a
Princeton University researcher.
"It certainly is a very new and interesting finding," said Cornell University
psychology and neurobiology professor Elizabeth Adkins-Regan, who had no role in the study.
___
On the Net:
Current Biology: http://www.current-biology.com/